Electrical Cable Test 

Results and Analysis 

During Fire Exposure 

(ELECTRA-FIRE) 

A Consolidation of Three Major 

Fire-Induced Circuit and Cable 

Failure Experiments Performed 

Between 2001 and 2011

Final Report

Office of Nuclear Regulatory Research

NUREG-2128
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Electrical Cable Test 

Results and Analysis 

During Fire Exposure 

(ELECTRA-FIRE)

A Consolidation of Three Major 

Fire-Induced Circuit and Cable 

Failure Experiments Performed 

Between 2001 and 2011

Final Report

Manuscript Completed: February 2013

Date Published: September 2013

Prepared by: 

G. Taylor1, N. Melly1, H. Woods1, and T. Pennywell1

T. Olivier2 and C. Lopez2

1

NRC, Office of Nuclear Regulatory Research

2

Sandia National Laboratories

Office of Nuclear Regulatory Research

NUREG-2128
 

 
 

iii 

ABSTRACT 

Over the past 10 years, there have been three major test programs exploring realistic electrical 

functionality of electrical cables under fire conditions. The three programs were: 

- The Electric Power Research Institute (EPRI) and the Nuclear Energy Institute (NEI), 

2002 

o Research and test efforts undertaken jointly by EPRI and NEI to investigate, 

characterize, and quantify fire-induced circuit failures. 

- NRC Cable Response to Live Fire (CAROLFIRE), 2008 

o CAROLFIRE was started at the end of the NEI/EPRI test program. It provides an 

experimental basis for resolving five of the six items identified as “Bin 2” circuit 

configurations in Regulatory Issue Summary (RIS) 2004-003, “Risk-Informed 

Approach for Post-Fire Safe-Shutdown Circuit Inspections.” 

o Improved fire modeling tools for the prediction of cable damage under fire 

conditions. 

- NRC Direct Current Electrical Shorting in Response to Exposure Fire (DESIREE-FIRE), 

2012 

o Provides fire-induced cable failures modes and effects data for dc-powered 

control circuits. 

Corresponding EPRI and U.S. Nuclear Regulatory Commission (NRC) technical reports 

document the test results; however, only the EPRI tests provided an evaluation of various 

parameters affecting the likelihood of cable failure modes. However, these evaluations were 

based on a limited set of test data (18 tests). Since then, NRC-sponsored testing has added 

several hundred data points on the electrical failure characteristics of electrical cable exposure 

to intense thermal conditions. Evaluating these and other parameters using all available test 

data would improve understanding of the effects of various parameters on cable failure modes. 

During an electrical expert Phenomena Identification and Ranking Table (PIRT) meeting in 

2011, it became apparent that having individual experts independently analyze the three data 

sets to derive conclusions to support the PIRT was inefficient and impractical. Thus, the NRC, 

with support from EPRI and Sandia National Laboratories (SNL), began a project to analyze and 

catalogue the whole experimental data set to allow the PIRT panel members to make 

responsible technical decisions. This report documents the background work that was done to 

analyze the data sets and provides the results in tabular and graphical formats. The authors did 

not attempt to remove outliers or perform other probabilistic methods to arrive at the conclusions 

in this report. The objective of this report is to present the data in a factual and coherent format 

to allow the PIRT panel members to make their best informed decisions. 
 
 

v 

TABLE OF CONTENTS 

Section Page

ABSTRACT .............................................................................................................................. iii 

TABLE OF CONTENTS ................................................................................................................ v 

LIST OF FIGURES ...................................................................................................................... vii 

LIST OF TABLES ......................................................................................................................... xi 

EXECUTIVE SUMMARY ............................................................................................................ xv 

ACKNOWLEDGEMENTS ........................................................................................................... xix 

ACRONYMS AND ABBREVIATIONS ......................................................................................... xxi 

1. INTRODUCTION ................................................................................................ 1-1 

1.1 Background ........................................................................................................ 1-1 

1.2 Objective ............................................................................................................ 1-3 

1.3 The Approach ..................................................................................................... 1-3 

1.4 Report Organization ........................................................................................... 1-8 

2. INTRA-CABLE – ALTERNATING CURRENT CIRCUITS .................................. 2-1 

2.1 AC Data Analysis Approach ............................................................................... 2-1 

2.2 Conductor Count ................................................................................................ 2-5 

2.3 Thermal Exposure Conditions ............................................................................ 2-6 

2.4 Cable Orientation ............................................................................................... 2-9 

2.5 Raceway Routing ............................................................................................. 2-11 

2.6 Raceway Fill ..................................................................................................... 2-13 

2.7 Insulation Type ................................................................................................. 2-15 

2.8 Insulation Material ............................................................................................ 2-17 

2.9 Insulation-Jacket Type Combinations............................................................... 2-19 

2.10 CPT Size .......................................................................................................... 2-21 

2.11 Circuit Grounding ............................................................................................. 2-23 

2.12 Wiring Configuration ......................................................................................... 2-25 

2.13 Conductor Size ................................................................................................. 2-26 

2.14 Water Based Fire Suppression Effects on AC Circuit Failures ......................... 2-28 

2.15 AC Circuit Concurrence of Hot Short-Induced Spurious Operations ................ 2-31 

3. INTER-CABLE – ALTERNATING CURRENT CIRCUITS .................................. 3-1 

4. INTRA-CABLE – DIRECT CURRENT CIRCUITS .............................................. 4-1 

4.1 DC Data Analysis Approach ............................................................................... 4-1 

4.2 Conductor Count .............................................................................................. 4-13 

4.3 Thermal Exposure Conditions .......................................................................... 4-14 

4.4 Raceway Routing ............................................................................................. 4-16 

4.5 Cable Orientation ............................................................................................. 4-18 

4.6 Raceway Fill ..................................................................................................... 4-18 

4.7 Insulation Type ................................................................................................. 4-23 

4.8 Insulation Material ............................................................................................ 4-24 

4.9 Insulation-Jacket Type Combinations............................................................... 4-26 

4.10 Wiring Configuration ......................................................................................... 4-28 

4.11 Conductor Size ................................................................................................. 4-30 

4.12 Circuit Type ...................................................................................................... 4-32 
 

vi 

Section Page 

4.13 Fuse Size ......................................................................................................... 4-34 

4.14 Cable Shielding ................................................................................................ 4-35 

4.15 DC Concurrence of Hot Short-Induced Spurious Operations ........................... 4-37 

5. INTER-CABLE DIRECT CURRENT CIRCUITS ................................................. 5-1 

5.1 Traditional Inter-Cable Failure Analysis for DESIREE-FIRE Results ................. 5-1 

5.2 Penlight Tests – Ground Fault Equivalent Hot Short .......................................... 5-5 

5.3 Intermediate-Scale Tests – Ground Fault Equivalent Hot Short ......................... 5-6 

6. SUMMARY OF FINDINGS ................................................................................. 6-1 

6.1 Alternating Current Test Results (NEI/EPRI, CAROLFIRE, DESIREE-FIRE) .... 6-1 

6.2 Direct Current Test Results (DESIREE-FIRE) .................................................... 6-3 

6.3 Ground Equivalent Hot Shorts ............................................................................ 6-3 

7. CONCLUSIONS AND FUTURE RESEARCH RECOMMENDATIONS .............. 7-1 

8. REFERENCES ................................................................................................... 8-1 

APPENDIX A: Penlight Ground Fault Equivalent Inter-Cable Failure Mode Evaluation ........... A-1 

APPENDIX B: Supplemental Information for the CAROLFIRE Reports, Including Additional 

Data Retrieval .................................................................................................... B-1 

 
 

vii 

LIST OF FIGURES 

Figure Page 

1-1 Examples global approach failure mode column plot ............................................... 1-6 

1-2 Box and whisker plot example .................................................................................. 1-6 

2-1 CAROLFIRE AC MOV circuit ................................................................................... 2-3 

2-2 Conductor count column plot, global approach, AC tests ........................................ 2-5 

2-3 Conductor count box plot, duration, AC tests ........................................................... 2-6 

2-4 Intermediate-scale cable raceway location .............................................................. 2-7 

2-5 Thermal exposure conditions column plot, global approach, AC tests ..................... 2-8 

2-6 Thermal exposure conditions box plot, duration, AC tests ....................................... 2-9 

2-7 Cable orientation column plot, global approach, AC tests ...................................... 2-10 

2-8 Cable orientation box plot, duration, AC tests ........................................................ 2-11 

2-9 Raceway routing column plot, global approach, AC tests ...................................... 2-12 

2-10 Raceway routing box plot, duration, AC tests ........................................................ 2-13 

2-11 Cable bundle arrangements (3-, 4-, 6-, & 12-cable bundles) ................................. 2-13 

2-12 Cable tray fill intermediate ...................................................................................... 2-13 

2-13 Single layer cable fill ............................................................................................... 2-14 

2-14 Raceway fill column plot, global approach, AC tests .............................................. 2-14 

2-15 Raceway fill box plot, duration, AC tests ................................................................ 2-15 

2-16 Insulation type column plot, global approach, AC tests .......................................... 2-16 

2-17 Insulation type box plot, duration, AC tests ............................................................ 2-17 

2-18 Insulation material column plot, global approach, AC tests .................................... 2-18 

2-19 Insulation material box plot, duration, AC tests ...................................................... 2-19 

2-20 Insulation-jacket type column plot, global approach, AC tests ............................... 2-20 

2-21 Insulation-jacket type box plot, duration, AC tests ................................................. 2-21 

2-22 CPT size column plot, global approach, AC tests .................................................. 2-22 

2-23 CPT size box plot, duration, AC tests ..................................................................... 2-23 

2-24 Circuit grounding column plot, global approach, AC tests ...................................... 2-24 

2-25 Circuit grounding box plot, duration, AC tests ........................................................ 2-24 

2-26 Wiring configuration column plot, global approach, AC tests ................................. 2-25 

2-27 Wiring configuration box plot, duration, AC tests ................................................... 2-26 

2-28 Conductor size column plot, global approach, AC tests ........................................ 2-27 

2-29 Conductor size box plot, duration, AC tests ........................................................... 2-28 

2-30 NEI/EPRI test 3 voltage plot - water spray ............................................................. 2-29 

2-31 NEI/EPRI test 10 voltage response following water spray ..................................... 2-30 

2-32 (a) CAROLFIRE and (b) DESIREE-FIRE intermediate-scale exposure 

location designation .......................................................................................... 2-32 

2-33 Concurrent hot shorts - Location A - 4 cables ........................................................ 2-33 

2-34 Concurrent hot shorts - Location A - 2 cables ........................................................ 2-34 

2-35 Concurrent hot shorts - upper hot gas layer - 4 cables .......................................... 2-35 

3-1 NEI/EPRI inter-cable test tray fill .............................................................................. 3-1 

3-2 CAROLFIRE inter-cable test tray fill ......................................................................... 3-2 

3-3 NEI/EPRI cable configuration ................................................................................... 3-3 

 
 

viii 

Figure Page 

4-1 Line drawing of the DC-SIM panel layout for a 1-inch coil circuit ............................. 4-2 

4-2 Line drawing for the DC large coil circuit .................................................................. 4-4 

4-3 Line drawing for DC MOV circuit .............................................................................. 4-6 

4-4 Line drawing for DC SOV circuit ............................................................................... 4-7 

4-5 Line drawing for DC SWGR 1 circuit ........................................................................ 4-9 

4-6 Line drawing for DC SWGR 2 circuit ...................................................................... 4-10 

4-7 Conductor count column plot, global approach, DC tests ...................................... 4-13 

4-8 Conductor count box plot, duration, DC tests ......................................................... 4-14 

4-9 Thermal exposure conditions column plot, global approach, DC tests .................. 4-15 

4-10 Thermal exposure conditions box plot, duration, DC tests ..................................... 4-16 

4-11 Raceway routing column plot, global approach, DC tests ...................................... 4-17 

4-12 Raceway routing box plot, duration, DC tests ........................................................ 4-17 

4-13 Circuit cable orientation within the cable trays for single fill ................................... 4-18 

4-14 Circuit cable orientation for filled trays ................................................................... 4-19 

4-15 Circuit cable orientation for partitioned trays .......................................................... 4-20 

4-16 Circuit cable orientation for specialized trays ......................................................... 4-21 

4-17 Raceway fill column plot, global approach, DC tests ............................................. 4-21 

4-18 Raceway fill box plot, duration, DC tests ................................................................ 4-22 

4-19 Insulation type column plot, global approach, DC tests ......................................... 4-23 

4-20 Insulation type box plot, duration, DC tests ............................................................ 4-24 

4-21 Insulation material column plot, global approach, DC tests ................................... 4-25 

4-22 Insulation material box plot, duration, DC tests ...................................................... 4-26 

4-23 Insulation-jacket type column plot, global approach, DC tests ............................... 4-27 

4-24 Insulation-jacket type box plot, duration, DC tests ................................................. 4-28 

4-25 Wiring configuration column plot, global approach, DC tests ................................. 4-29 

4-26 Wiring configuration box plot, duration, DC tests ................................................... 4-30 

4-27 Conductor size column plot, global approach, DC tests ......................................... 4-31 

4-28 Conductor size box plot, duration, DC tests ........................................................... 4-31 

4-29 Circuit type column plot, global approach, DC tests ............................................... 4-32 

4-30 Circuit type box plot, duration, DC tests ................................................................. 4-33 

4-31 Fuse size column plot, global approach, DC tests ................................................. 4-34 

4-32 Fuse size box plot, duration, DC tests .................................................................... 4-35 

4-33 Cable shielding column plot, global approach, DC tests ........................................ 4-36 

4-34 Cable shielding box plot, duration, DC tests .......................................................... 4-37 

4-35 Time plot of concurrent hot shorts for DESIREE-FIRE 

intermediate-scale test 5 .................................................................................. 4-39 

4-36 Plot of intermediate-scale test 5 for MOV and SOV cable locations ...................... 4-39 

4-37 Concurrent hot shorts - test 6 ................................................................................. 4-40 

4-38 Plot of intermediate-scale test 6 for 1-inch valve and switchgear cable 

locations ........................................................................................................... 4-41 

4-39 Concurrent hot shorts - test 8 ................................................................................. 4-42 

4-40 Concurrent hot shorts - test 9 ................................................................................. 4-43 

4-41 Time plot of concurrent spurious operations for DESIREE-FIRE among all test 

circuits in Location A ........................................................................................ 4-44 

4-42 Time plot of concurrent spurious operations for DESIREE-FIRE among all test 

circuits in Location D ........................................................................................ 4-46 

 
 

ix 

Figure Page 

4-43 Time plot of concurrent spurious operations for DESIREE-FIRE among 

 all Penlight test with exposure temperatures in the range of 325-375C......... 4-47 

4-44 Time plot of concurrent spurious operations for DESIREE-FIRE among 

all Penlight test with exposure temperatures in the range of 400-480C.......... 4-48 

4-45 Time plot of concurrent spurious operations for DESIREE-FIRE among 

all Penlight test with exposure temperatures in the range of 500-525C.......... 4-50 

5-1 DESIREE-FIRE inter-cable configuration ................................................................. 5-1 

5-2 DESIREE-FIRE inter-cable test results penlight test 47 ........................................... 5-2 

5-3 DC MOV schematic showing current summation used in identifying 

inter-cable shorting behavior .............................................................................. 5-4 

5-4 Penlight cable tray typical loading, showing two electrically instrumented 

cables and a thermal response (temperature recording) cable located in 

the center. .......................................................................................................... 5-5 

5-5 Intermediate-scale test preliminary 1 cable loading configuration ............................ 5-7 

5-6 Intermediate-scale test preliminary 2 cable loading configuration ............................ 5-8 

5-7 Intermediate-scale test preliminary 2 – inter-cable shorting between 

SOV-2 and MOV-2 ............................................................................................. 5-9 

5-8 Intermediate-scale test 1 cable loading configuration ............................................ 5-10 

5-9 Outstanding current hot shorting for intermediate-scale test 1 between 

1-inch valve, large coil, and MOV-1 circuits ..................................................... 5-11 

5-10 Intermediate-scale test 2 cable loading .................................................................. 5-12 

5-11 Outstanding current shorting in intermediate-scale test 2, between 

SOV-2 and MOV-2 ........................................................................................... 5-13 

5-12 Intermediate-scale test 3 cable loading .................................................................. 5-14 

5-13 Outstanding current shorting in intermediate-scale test 3,between 

SOV-2 and SWGR-T ........................................................................................ 5-15 

5-14 Outstanding current shorting in intermediate-scale test 3, between 

1 inch valve and SWGR-T ................................................................................ 5-15 

5-15 Intermediate-scale test 4 cable loading .................................................................. 5-16 

5-16 Intermediate-scale test 5 cable loading .................................................................. 5-17 

5-17 Outstanding current shorting in intermediate-scale test 5, between 

SOV-1 and SWGR-T ........................................................................................ 5-18 

5-18 Intermediate-scale test 6 cable loading .................................................................. 5-19 

5-19 Intermediate-scale test 7 cable loading .................................................................. 5-20 

5-20 Intermediate-scale test 8 cable loading .................................................................. 5-21 

5-21 Outstanding current shorting in intermediate-scale test 8, between 

MOV-1 and Lg Coil ........................................................................................... 5-22 

5-22 Intermediate-scale test 9 cable loading .................................................................. 5-23 

5-23 Intermediate-scale test 10 cable loading ................................................................ 5-24 

5-24 Intermediate-scale test 11 cable loading ................................................................ 5-25 

5-25 Intermediate-scale test 11 current summation ....................................................... 5-26 

5-26 Intermediate-scale test 12 cable loading ................................................................ 5-27 

5-27 Intermediate-scale test 12 current summation plot ................................................ 5-28 

5-28 Ground fault detection voltage response for second large coil SO ........................ 5-30 

5-29 Intermediate-scale test contingency A cable loading configuration ........................ 5-30 
 
 

xi 

LIST OF TABLES 

Table Page

1-1 Example of failure mode table .................................................................................. 1-5 

2-1 AC threshold values used for MOV hot short & spurious operation 

determinations .................................................................................................... 2-1 

2-2 CAROLFIRE AC MOV circuit path configuration ...................................................... 2-3 

2-3 Conductor count, global approach, AC tests ............................................................ 2-5 

2-4 Conductor count, duration data, AC tests ................................................................ 2-6 

2-5 Thermal exposure conditions, global approach, AC tests ........................................ 2-7 

2-6 Thermal exposure conditions, duration data, AC tests ............................................. 2-8 

2-7 Cable orientation, global approach, AC tests ........................................................... 2-9 

2-8 Cable orientation, duration data, AC tests .............................................................. 2-10 

2-9 Raceway routing, global approach, AC tests ......................................................... 2-11 

2-10 Raceway routing, duration data, AC tests .............................................................. 2-12 

2-11 Raceway fill, global approach, AC tests ................................................................. 2-14 

2-12 Raceway fill, duration data, AC tests ...................................................................... 2-15 

2-13 Breakdown of insulation material by type, AC tests ............................................... 2-16 

2-14 Insulation type, global approach, AC tests ............................................................. 2-16 

2-15 Insulation type, duration data, AC tests .................................................................. 2-16 

2-16 Insulation material, global approach, AC tests ....................................................... 2-17 

2-17 Insulation material, hot short only, duration data, AC tests .................................... 2-18 

2-18 Insulation material spurious operation only, duration data, AC tests ..................... 2-19 

2-19 Insulation-jacket type, global approach, AC tests .................................................. 2-20 

2-20 Insulation-jacket type, duration data, AC tests ....................................................... 2-20 

2-21 Test project CPT size ............................................................................................. 2-21 

2-22 CPT size, global approach, AC tests ...................................................................... 2-22 

2-23 CPT size, duration data, AC tests .......................................................................... 2-22 

2-24 Circuit grounding, global approach, AC tests ......................................................... 2-23 

2-25 Circuit grounding, duration data, AC tests .............................................................. 2-24 

2-26 Wiring configurations .............................................................................................. 2-25 

2-27 Wiring configuration, global approach, AC tests .................................................... 2-25 

2-28 Wiring configuration, duration data, AC tests ......................................................... 2-26 

2-29 Conductor size, global approach, AC tests ............................................................ 2-27 

2-30 Conductor size, duration data, AC tests ................................................................. 2-27 

2-31 Concurrent spurious operation durations – test location A (concurrence time 

shown in seconds) .................................................................................................. 2-34 

2-32 Concurrent spurious operations – upper hot gas layer .......................................... 2-36 

3-1 NEI/EPRI inter-cable failure characteristics ............................................................. 3-3 

3-2 CAROLFIRE AC inter-cable failure characteristics .................................................. 3-4 

4-1 Analysis logic for 1-in valve penlight tests ................................................................ 4-3 

4-2 Analysis logic for 1-in valve intermediate-scale tests ............................................... 4-3 

4-3 Analysis logic for large coil penlight and intermediate-scale tests ........................... 4-5 

4-4 Analysis logic for MOV Penlight and intermediate-scale tests ................................. 4-6 

4-5 Analysis logic for SOV Penlight and intermediate-scale tests .................................. 4-8 

 
 

xii 

Table Page 

4-6 Analysis logic for SWGR Penlight tests and intermediate-scale ............................ 4-11 

4-7 Analysis logic for SWGR Intermediate Scale Tests 1, 3, 5, 6, 7, 8, 9, 10, 

Cont 1, and Cont 2 ........................................................................................... 4-12 

4-8 Conductor count, global approach, DC tests .......................................................... 4-13 

4-9 Conductor count, duration data, DC tests .............................................................. 4-14 

4-10 Thermal exposure conditions, global approach, DC tests ...................................... 4-15 

4-11 Thermal exposure conditions, duration data, DC tests .......................................... 4-16 

4-12 Raceway routing, global approach, DC tests ......................................................... 4-16 

4-13 Raceway routing, duration data, DC tests .............................................................. 4-17 

4-14 Raceway fill, global approach, DC tests ................................................................. 4-21 

4-15 Raceway fill, duration data, DC tests ..................................................................... 4-22 

4-16 Breakdown of insulation material by type, DC tests ............................................... 4-23 

4-17 Insulation type, global approach, DC tests ............................................................. 4-23 

4-18 Insulation type, duration data, DC tests ................................................................. 4-24 

4-19 Insulation material, global approach, DC tests ....................................................... 4-25 

4-20 Insulation material, duration data, DC tests ........................................................... 4-25 

4-21 Insulation-jacket type, global approach, DC tests .................................................. 4-26 

4-22 Insulation-jacket type, duration data, DC tests ....................................................... 4-27 

4-23 DC test data wiring configurations .......................................................................... 4-28 

4-24 Wiring configuration, global approach, DC tests .................................................... 4-29 

4-25 Wiring configuration, duration data, DC tests ......................................................... 4-29 

4-26 Conductor size, global approach, DC tests ............................................................ 4-30 

4-27 Conductor size, duration data, DC tests ................................................................. 4-31 

4-28 Circuit type, global approach, DC Tests ................................................................. 4-32 

4-29 Circuit type hot short only, duration data, DC tests ................................................ 4-33 

4-30 Circuit type spurious operation only, duration data - DC tests ............................... 4-33 

4-31 Fuse size, global approach, DC tests ..................................................................... 4-34 

4-32 Fuse size, duration data, DC tests ......................................................................... 4-35 

4-33 Cable shielding, global approach, DC tests ........................................................... 4-36 

4-34 Cable shielding, duration data, DC tests ................................................................ 4-36 

4-35 Listing of concurrent spurious operations during intermediate-scale 

DC testing ......................................................................................................... 4-38 

4-36 Test data for Location A of DESIREE-FIRE for cases where concurrent 

spurious operations occurred ........................................................................... 4-44 

4-37 Test data for Location B of DESIREE-FIRE for cases where concurrent 

spurious operations occurred ........................................................................... 4-45 

4-38 Test data for Location D of DESIREE-FIRE for cases where concurrent 

spurious operations occurred ........................................................................... 4-46 

4-39 Test data for DESIREE-FIRE cases where concurrent spurious operations 

occurred during Penlight exposures in the range of 325 - 375C ..................... 4-47 

4-40 Test data for DESIREE-FIRE cases where concurrent spurious operations 

occurred during Penlight exposures in the range of 400 - 480C ..................... 4-49 

4-41 Test data for DESIREE-FIRE cases where concurrent spurious operations 

occurred during Penlight exposures in the range of 500-525C ....................... 4-50 

4-42 Test data for DESIREE-FIRE cases where concurrent spurious operations 

occurred during Penlight exposures among tests not binned together 

in the analysis presented previously................................................................. 4-52 

 
 

xiii 

Table Page 

5-1 Results of inter-cable shorting during Penlight DESIREE-Fire tests ........................ 5-6 

5-2 Intermediate-scale preliminary test #1 ..................................................................... 5-7 

5-3 Intermediate-scale preliminary test #2 ..................................................................... 5-8 

5-4 Intermediate-Scale test #1 ..................................................................................... 5-10 

5-5 Intermediate-scale test #2 ...................................................................................... 5-12 

5-6 Intermediate-scale test #3 ...................................................................................... 5-14 

5-7 Intermediate-scale test #4 ...................................................................................... 5-16 

5-8 Intermediate-scale test #5 ...................................................................................... 5-17 

5-9 Intermediate-scale test #6 ...................................................................................... 5-19 

5-10 Intermediate-scale test #7 ...................................................................................... 5-20 

5-11 Intermediate-scale test #8 ...................................................................................... 5-21 

5-12 Intermediate-scale test #9 ...................................................................................... 5-23 

5-13 Intermediate-scale test #10 .................................................................................... 5-24 

5-14 Intermediate-scale test #11 .................................................................................... 5-26 

5-15 Intermediate-scale test #12 .................................................................................... 5-29 

5-16 Intermediate-scale contingency test #A ................................................................. 5-31 

5-17 Intermediate-scale contingency test #B ................................................................. 5-31 

5-18 Summary of initial failure mode for inter-cable test circuits .................................... 5-32 
 
 

xv 

EXECUTIVE SUMMARY 

Background 

NRC regulatory requirements, guidance, and staff technical positions regarding post-fire safeshutdown are contained in various NRC documents. One objective of the fire protection 

requirements and guidance is to provide reasonable assurance that fire-induced failure of 

associated circuits that could prevent the operation, or cause maloperation, of equipment 

necessary to achieve and maintain post-fire safe-shutdown will not occur. In the late 1990s the 

NRC began to receive a series of licensee event reports (LERs) identifying plant-specific 

problems related to potential fire-induced electrical circuit failures that could prevent operation 

or cause maloperation of equipment necessary to achieve and maintain hot shutdown. The 

NRC documented its concerns in Information Notice (IN) 99-17, “Problems Associated with 

Post-Fire Safe-Shutdown Circuit Analysis.” 

The NRC determined that the issue should be treated generically and contracted with 

Brookhaven National Laboratory (BNL) to develop a post-fire safe-shutdown analysis letter 

report (ML023430533). In 2001, the industry (under the direction of the Nuclear Energy Institute 

(NEI) and the Electric Power Research Institute (EPRI)) performed a series of cable functionality 

fire tests to be used to develop the guidance later included in NEI 00-01, “Guidance for PostFire Safe-Shutdown Analysis” (ML023010376). These NEI/EPRI tests are the first set of test 

data used in the analysis for this report. An expert panel reviewed the results of the NEI testing 

and documented their insights on fire-induced failures of electrical cables in EPRI Technical 

Report 1006961, “Spurious Operation of Electrical Circuits Due to Cable Fires: Results of an 

Expert Elicitation,” dated May 2002. 

In February 2003, the NRC facilitated a public workshop primarily driven by the new NEI/EPRI 

report to exchange information for identifying circuit configurations fitting into the following three 

bins (ML03062006): 

Bin 1 – the most risk-significant associated circuit configurations 

Bin 2 – other associated circuit configurations that require further research 

Bin 3 – low-risk-significant associated circuit configurations 

The outcome of the facilitated workshop was the issuance of Regulatory Issue Summary 2004-

03, “Risk-Informed Approach for Post-Fire Safe-Shutdown Associated Circuit Inspections” 

(ML040620400). Of interest to the research community were “Bin 2” items that required 

additional data as a basis for either including or excluding these configurations from the 

inspection procedures. The basis for the Bin 2 items was subsequently provided by an NRCsponsored testing program conducted by Sandia National Laboratories, referred to as the 

“Cable Response to Live Fire (CAROLFIRE)” project. This project provides the second major 

testing data set to be used in this report. The results of the CAROLFIRE project were published 

in 2008 and documented in NUREG/CR-6931, Volumes 1 - 3. 

Concurrent with the CAROLFIRE testing, a nuclear utility conducted its own fire-induced circuit 

failure testing on an armored cable that is used extensively in its plants. The results of this 

testing, although proprietary, established that control circuits under direct current (DC) power 

may fail differently than those tested previously in the CAROLFIRE and NEI/EPRI tests, which 

were powered solely by alternating current (AC) configurations. As a result of these different 
 

xvi 

failure characteristics and the large number of risk-significant control circuits powered using DC, 

the NRC sponsored a confirmatory testing project to evaluate the likelihood and the failure 

characteristics of DC-powered control circuits. These test results are documented in 

NUREG/CR-7100, “Direct Current Electrical Shorting In Response to Exposure Fire (DESIREEFIRE),” published in 2012 and is the third major set of experimental data that was used in this 

report. 

The three major test projects conducted over a ten year period provide a substantial amount of 

information to base technical recommendations on the functionality of electrical cables under 

thermal fire conditions. In 2011, during an electrical expert Phenomena Identification and 

Ranking Table (PIRT) meeting, it was determined that the current format of data presented in 

the test report could not support the PIRT objectives without a large amount of redundant effort. 

To make the PIRT effort more efficient, the NRC undertook an initiative to collect and analyze 

past cable fire testing data for insights on various parameter effects. 

This report documents the analysis of the test data from three major fire test programs which 

evaluated cable electrical performance under thermal (fire exposure) conditions. This report 

supports the PIRT by providing an analysis of test data in an objective and factual manner to 

support the panel’s discussion of parameters affecting the failure modes of electrical cables 

under fire-induced damaging conditions. The contents of this report were discussed during the 

electrical expert PIRT panel meetings. 

Data Analysis Overview 

The general purpose of the analysis is to evaluate the entire data set to identify parameters that 

may influence fire-induced failure modes. The analysis conducted in this report attempts to 

present the experimental data in a factual and clear format to allow for the identification of any 

influencing factors. The majority of the data is used to evaluate influencing parameters for intracable faults (i.e., fire-induced cable damage that results in the failure of conductors within a 

cable). A small fraction of the data has applicable information regarding inter-cable (cable-tocable) interactions; however, the minimal data set limits the effectiveness of using a systematic 

approach to evaluate the test results for inter-cable interactions. Important parameters of the 

inter-cable data are simply presented instead. 

This report documents the intra-cable results using a substantial number of tables and graphical 

techniques. Graphical tools help to gain insights on the data set related to testing assumptions, 

relationship identification, and outlier detection. The use of graphical tools relies on column 

plots to present the failure mode likelihood data (i.e., fuse clears, hot shorts, spurious 

operations) and box plots to present the hot short duration data. Presenting the consolidated 

test information in tabular and graphical forms aided in the determination of any trends in the 

data. General conclusions are made, and any potential causes are identified. 

 
 

xvii 

Conclusions 

The data consolidation and analysis documented in this report identify several important fireinduced circuit phenomena. The systematic review of the AC and DC data has identified 

raceway fill, thermal exposure conditions, fuse size, circuit type, cable construction, and 

raceway routing as parameters that can influence the likelihood of experiencing a specific intracable failure mode and/or influence the length of intra-cable fire-induced hot short duration. 

This analysis has also identified areas in the data set where additional information would be 

beneficial to better understand how variations in parameters affect the circuit response under 

fire conditions. 

Information pertaining to fire-induced inter-cable (cable-to-cable) failure data is sparse; 

however, the available data is presented for both AC and DC circuits. The results show that 

while the likelihood of experiencing these failures is lower than it is for intra-cable, there are 

cases where inter-cable hot shorts were experienced. Most of this data comes from the 

CAROLFIRE and NEI/EPRI test data sets. 

The DESIREE-FIRE test data has revealed a newly observed failure mode in which multiple 

shorts to ground (from ungrounded systems) cause spurious operation in a circuit. This failure 

mode has been identified as “ground fault equivalent hot short,” and is the only inter-cable 

failure mode observed in the DESIREE-FIRE testing program. The only cable-to-cable shorts 

observed in the DC testing occurred through the ground plane. This unique failure mode may 

require some industry attention for circuits routed in dedicated conduits. Depending on the 

physical configurations in the plants, there may be some scenarios where safety significant 

electrical cables routed in dedicated conduits may be damaged by a fire, and, depending on the 

types of cables in the area, the ground fault equivalent hot short may be capable of causing hot 

short-induced spurious operations for a specific circuit. 
 
 

xix 

ACKNOWLEDGEMENTS 

The authors would like to offer their thanks and appreciation to the many individuals who 

provided support and comments during the development of this report. First we acknowledge 

the contributions of the NRC-RES/EPRI electrical expert Phenomena Identification and Ranking 

Table (PIRT) panel members. Their contributions and review resulted in a higher quality 

product that will help its readers to make informed decisions, both now and in the future. The 

electrical PIRT panel members include: 

 Harold Barrett

 Robert Daley

 Steven Nowlen

 Gabriel Taylor

 David Crane

 Daniel Funk

 Thomas Gorman

 Andy Ratchford

Rick Wachowiak of EPRI also made numerous contributions that improved this report and 

provided an added level of insight, and also facilitated this work via the NRC-RES/EPRI 

Memorandum of Understanding (MOU) Addendum to Fire Risk. Working with EPRI under the 

MOU collaborative research agreement has allowed for the use of the EPRI fire-induced test 

data set, which has greatly supplemented the amount of data related to fire-induced cable 

failure phenomena. 

The authors would also like to thank the individuals at Sandia National Laboratories (SNL) who 

performed and documented the testing and answered numerous questions during the analysis 

of the data and the development of this report. 

The authors would like to thank Mark Henry Salley for supporting the development of this report 

and providing the resources needed to complete this effort. The authors are also grateful for the 

individuals at the NRC who worked on this report, and would like to extend their gratitude 

specifically to Mollie Semmes. 

Finally, we would like to thank the internal and external stakeholders who took the time to 

provide comments and suggestions on the draft of this report when it was published in the 

Federal Register (77FR37717) on June 22, 2012: 

 Thomas Gorman, PPL Susquehanna, LLC 

 Michael D. Jesse, Exelon Generation Company, LLC 

 Manomohan Subudhi, Brookhaven National Laboratory 
 
 

xxi 

ACRONYMS AND ABBREVIATIONS 

AC alternating current 

ADAMS Agencywide Document and Access Management System 

AT active target 

AWG American Wire Gauge 

BNL Brookhaven National Laboratories 

/C conductor 

CAROLFIRE Cable Response to Live Fire 

CPT control power transformer 

CSPE chlorosulfonated polyethylene 

DAQ Data Acquisition System 

DC direct current 

DESIREE-FIRE Direct Current Electrical Shorting in Response to Exposure Fire 

EPR ethylene propylene rubber 

EPRI Electric Power Research Institute 

FR-Kerite flame-retardant keriteTM 

HGL hot gas layer 

HS hot short 

IN Information Notice 

IR insulation resistance 

IRMS insulation resistance measurement system 

IT intermediate-scale test 

LER Licensee Event Report 

MOV motor-operated valve 

NEC National Electric Code 

NEI Nuclear Energy Institute 

NFPA National Fire Protection Association 

NPP nuclear power plant 

NRC Nuclear Regulatory Commission 

NRR Office of Nuclear Reactor Regulation 

PE polyethylene 

PIRT Phenomena Identification and Ranking Table 

PRA probabilistic risk assessment 

PT passive target 

PVC polyvinyl chloride 

RES Office of Nuclear Regulatory Research 
 

xxii 

SO spurious operation 

SCDU surrogate circuit diagnostic unit 

SNL Sandia National Laboratories 

SOV solenoid-operated valve 

SR silicone rubber 

SR-V silicone rubber vitalink 

SWGR switchgear 

TEF TefzelTM 

TP thermoplastic 

TS thermoset 

VA volt-amp 

XLPE cross-linked polyethylene 

XLPO cross-linked polyolefin 
 

1-1 

1. INTRODUCTION 

1.1 Background 

In 1997, U.S. Nuclear Regulatory Commission (NRC) staff began to notice that an increasing 

number of licensee event reports (LERs) were identifying plant-specific problems related to 

potential fire-induced electrical circuit failures. These problems were documented in Information 

Notice (IN) 99-17, “Problems Associated with Post-Fire Safe-Shutdown Circuit Analysis.” The 

NRC determined that this issue should be treated generically and began working with 

stakeholders to understand the issue. 

The NRC contracted with Brookhaven National Laboratories (BNL) to develop a post-fire safeshutdown analysis letter report (Agencywide Document Access and Management System 

(ADAMS) Accession No. ML023430533). Meanwhile, the nuclear industry, working with the 

Electric Power Research Institute (EPRI) under the direction of the Nuclear Energy Institute 

(NEI), performed a series of cable functionality fire tests to better understand the failure modes 

of cables and circuits under fire conditions. Following the completion of the NEI testing, the 

NRC hosted a facilitated public workshop1

 in Rockville, MD to discuss and gather stakeholder 

input on a proposed risk-informed post-fire safe-shutdown circuit analysis inspection. The 

workshop grouped circuit issues into three bins. Bin 1 contained the most risk-significant 

associated circuit configurations, Bin 2 included configurations that required additional research 

before a risk-significance determination could be made, and Bin 3 contained low-risk-significant 

associated circuits of concern. Bin 2 items included: 

A. Inter-cable shorting for thermoset cables 

B. Inter-cable shorting between thermoplastic and thermoset cables 

C. Configurations requiring three or more cable failures 

D. Multiple spurious operations in control circuits with properly sized control power 

transformers (CPTs) 

E. Fire-induced hot shorts that must last more than 20 minutes to impair a plant’s ability to 

achieve hot shutdown 

F. Cold shutdown circuits 

To provide the needed information to disposition the Bin 2 items into either of the other two bins, 

following the NEI/EPRI testing, the NRC sponsored a testing project at Sandia National 

Laboratories (SNL). The SNL project was entitled “Cable Response to Live Fire 

(CAROLFIRE),” and it provided enough data on five of the six Bin 2 circuit configurations that a 

determination of risk-significance could be made. Test data was not required to resolve RIS 

2004-03, Bin 2, Item F. CAROLFIRE also provided data that resulted in the development of a 

better predictive model for cable thermal response in deterministic fire models. 

Around the same time that the CAROLFIRE testing was being conducted, Duke Energy 

Corporation, a U.S. nuclear utility, performed its own fire-induced circuit failure testing on a 

unique armor-type cable used extensively in its plants. Although the test results from this 

program are proprietary, the NRC was able to witness these tests and gain the unique insights 

of the testing. 

 

1

 The facilitated public workshop was an open forum meeting between the NRC staff and its stakeholders where the 

discussion was facilitated by an independent third party. 
 

1-2 

The results of the Duke testing indicated that risk-significant circuits operating on direct current 

(DC) may experience unique failure modes when compared to alternating current (AC) circuits 

(ML052900252, ML071200168). The NRC and the industry also experienced difficulties in 

developing methods and conditional probabilities for DC circuits based solely on the results of 

AC testing. To evaluate these concerns, the NRC sponsored a confirmatory testing project with 

SNL to evaluate the spurious operation likelihood associated with ungrounded DC control 

circuits exposed to fire conditions. This project was titled “Direct Current Electrical Shorting In 

Response to Exposure Fire (DESIREE-FIRE).” The DC testing identified three unique failure 

characteristics of DC control circuits. First, the physical cable failures were more energetic than 

they were in the AC tests, with sparks and electrical arching readily visible to the test engineer. 

Second, open circuits were noted to occur as the first failure mode. Third, fuse sizing played a 

role in the duration of the hot short failures. In some cases the hot short durations lasted for 

longer than 20 minutes. 

It is important to note that one additional testing program was completed to specifically evaluate 

the thermal failure temperature threshold of a unique cable insulation material manufactured by 

Kerite. This unique insulation material, “FR-Kerite” has shown poor insulation resistance 

characteristics at elevated temperature in past testing. As such, the NRC guidance indicated 

using a generic thermoplastic failure threshold when analyzing the FR-Kerite performance, 

instead of the higher temperature failure threshold for thermoset materials. Chemically, 

FR-Kerite is a thermoset material. However it also exhibits thermoplastic properties such as 

self-healing. Under its collaborative research agreement with EPRI, the NRC was able to obtain 

samples of 1970’s vintage FR-Kerite cables. Because of its unique construction, having 

insulation thicknesses much greater than typical electrical cables found in U.S nuclear power 

plants, the results from this fourth testing project have not been included in this report or 

analysis. Rather, limited data on FR-Kerite cables obtained from the DESIREE-FIRE project 

were evaluated here. The results and conclusions from the FR-Kerite test program can be 

found in a separate report, NUREG/CR-7102, “Kerite Analysis in Thermal Environment of FIRE 

(KATE-Fire): Test Results.” 

Following the completion of this testing, the NRC (in collaboration with EPRI) convened a panel 

of electrical experts with a background in nuclear and fire protection engineering to evaluate the 

various parameters that affect fire-induced cable failures. This electrical expert Phenomena 

Identification and Ranking Table (PIRT) panel experienced difficulties in making informed 

decisions due to the massive amount of test data on which to base its decisions. As a result, 

the NRC began an effort among its staff and the staff at SNL to systematically evaluate and 

present the experimental data in a clearer format to assist the PIRT panel in making informed 

decisions. This report documents that effort. 

 
 

1-3 

1.2 Objective 

There have been numerous testing projects aimed at evaluating the fault modes of electrical 

cables and circuits exposed to fire conditions. Only one of these projects thoroughly evaluated 

specific aspects of a small number of the test results. The objective of this report is to provide a 

simplistic presentation of all of the available test data, using various circuit parameters to 

identify any correlations among fault modes and any correlations among hot short duration. The 

core set of parameters selected by the PIRT panel for comparison of the intra-cable results 

includes: 

 Conductor Count

 Thermal Exposure Conditions

 Cable Orientation (AC only)

 Raceway Routing

 Raceway Fill

 Insulation Type

 Insulation Material 

 Insulation-Jacket Type

 CPT Size (AC only)

 Circuit Grounding (AC only)

 Wiring Configuration

 Conductor Size

 Circuit Type (DC only)

 Fuse Size (DC only)

 Cable Shielding (DC only)

In addition to these parameters, the report documents a review of the data for inter-cable 

failures, effects of suppression on circuit response, multiple circuit concurrent hot shorting 

events, and a phenomenon observed in the DC testing, identified as the “ground fault equivalent 

hot short.” 

Conducting the evaluation in this systematic manner allows for a better understanding of the 

data and identification of the areas in which additional data may be needed, and also supports 

the electrical expert PIRT work. The focus of this report is to document the data analysis that 

was conducted to support the PIRT panel. Brookhaven National Laboratory will document the 

results of a PRA expert elicitation quantification of fire-induced spurious operation likelihood and 

duration in Volume 2 of NUREG/CR-7150. Limited statistical methods and no probabilistic risk 

assessment methods were employed in the evaluation, just factual inference of the data. 

1.3 The Approach 

The data used in developing this report was obtained from the NEI/EPRI cable testing report [4], 

along with the NRC-sponsored CAROLFIRE (NUREG/CR-6931)[1-3] and DESIREE-FIRE 

(NUREG/CR-7100) testing project [5]. It is assumed that the reader is familiar with those 

reports, and only brief descriptions of the testing will be provided in this report. A reader 

unfamiliar with this testing is urged to review the test reports to better understand the testing 

methods and results. 

A database was generated from the information provided in the reports and associated 

electronic data files. The database included all pertinent information regarding the circuit 

configuration and failure modes/characteristics. The cable failure data were obtained from the 

actual data files and cross-referenced with the results documented in the associated reports. 

This provided an increased level of quality assurance to ensure that the electronic files and data 

report information were consistent, thereby minimizing the likelihood of information transfer 

errors. Once the database was populated with information found to be important for this project, 

it was sorted by parameters of interest so that specific information could be collected, reviewed, 

and reported. 
 

1-4 

Staff members from the NRC’s Office of Nuclear Regulatory Research (RES) were responsible 

for analyzing the AC test data from NEI/EPRI and CAROLFIRE testing, while staff from SNL 

processed and reviewed the DC test data. The intent was to have two groups complete the 

work in parallel to reduce time and increase efficiency. Throughout the process, NRC-RES and 

SNL staff coordinated with each other to ensure a high level of consistency and quality among 

the split effort. To ensure the quality of the developed database, NRC-RES staff other than 

those performing the original data analysis effort performed spot check of the database with the 

actual data files and corresponding reports. No errors were found in the cases examined. 

The analysis focuses on presenting the test data in a manner that will assist the electrical expert 

PIRT panel members in making informed decisions regarding the ranking of various circuit 

parameters and key phenomena. This information was determined by identifying the number of 

specific failure modes (fuse clear, hot shorts, and spurious operations), given a particular circuit 

or cable parameter. For this analysis, the following definitions developed by the PIRT panel 

were used to classify fire-induced circuit failures: 

Hot Short: Individual conductors of the same or different cables that come in contact with 

each other and that may result in an impressed voltage or current on the circuit 

being analyzed. (Regulatory Guide 1.189) 

For the purposes of the PIRT, only a hot short that is of sufficient quality to actuate the end 

device is of interest. 

Spurious Operation2,3: 

A circuit failure mode wherein an operational mode of the circuit is initiated (in full 

or in part) due to failure(s) in one or more of the circuit’s components (including 

cables). For example, such modes include a pump (starting or stopping) or a 

valve spuriously repositioning. 

Duration: The time (reported in seconds) that a particular hot short or spurious operation 

persisted. In cases where sequential hot shorts or spurious operations occurred 

one after another, the durations of all occurrences were summed to obtain a total 

duration, which was then reported (i.e., the reported total duration was not 

necessarily continuous). 

1.3.1 Presentation of failure mode data 

There are three primary circuit failure modes of interest to the electrical expert PIRT panel: fuse 

clear failures, hot shorts, and hot short-induced spurious operation. These failure modes are 

provided in this report, using what is referred to as the “global approach,” which evaluates 

failure modes in a binary fashion. This binary approach defines the first failure mode as being 

either a fuse clear or a hot short. For a given cable/circuit combination, either a fuse clears or a 

hot short occurs. To facilitate a better understanding of the fraction of hot shorts that are 

spurious operations, the spurious operation data are also reported separately, but it must be 

understood that the hot short data includes spurious operations by definition. Therefore, 

 

2

 Definition of “Spurious Operation” was quoted from NUREG/CR-7150, Volume 1, “Joint Assessment of 

Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE).” This definition differs from 

Regulatory Guide 1.189, and NEI-00-01, Rev. 2. 

3

 “Spurious Operation” and “Spurious Actuation” are used synonymously throughout this report. 
 

1-5 

for the global approach in reporting failure mode data, the number of hot shorts is always by 

definition larger than or equal to the number of spurious operations. 

In general, fire-induced circuit testing has shown that a damaged cable will eventually short to a 

common ground and cause the protective fuses to clear. In this report, in must be clear that the 

fuse clear category only counts fuse clear failures from the first failure mode. For example, if a 

circuit experienced a spurious operation at 100 seconds and then experienced a fuse clear at 

130 seconds, this report would count the hot short and spurious operation, but not the fuse 

clear. Specifics on how the failure modes are counted and reported are presented in Section 

2.1 for AC circuits and in Section 4.1 for DC circuits. 

Another aspect of this analytical approach, relative to the spurious operation count, is best 

shown with another example. Start with a circuit that experiences a hot short on a conductor 

that is not associated with a device that can cause a spurious operation (e.g., indicating lamp – 

a passive target). Sometime in the future, another hot short occurs, this time on a conductor 

that can cause a spurious operation. In this case, the hot short and the spurious operation 

would be included in the count (i.e., # hot shorts = 1, # spurious operations = 1). Note that the 

hot short count is not two, even though two hot shorts have occurred in an individual circuit (i.e., 

one hot short for the passive target and one hot short for the active target). The analysis was 

done in this manner to ensure that if a spurious operation occurred, it would be counted and 

reported. In reality, when circuits fail from fire-induced exposures, it is common for a single 

circuit to experience multiple hot shorts. 

An example of how the global approach failure mode information is presented in this report is 

shown in Table 1-1 and Figure 1-1. Table 1-1 documents the number and types of failure 

modes for each scenario, while Figure 1-1 shows this information graphically in a column chart. 

In this example, there are three different scenarios (A-C), and the columns identify the number 

of individual failure modes associated with the specific scenario. The first failure mode is a 

“fuse clear” failure. This refers to failures in which the circuit failed in such a way as to cause 

the protective fuse to clear, meaning that no hot shorts occurred. The next failure mode 

represents the number of spurious operations. This information identifies the number of circuits 

that experienced hot short-induced spurious operations. The next column, “Hot Shorts,” 

represents the number of circuits that experienced a hot short. If we take Scenario A as an 

example, six spurious operations and 13 hot shorts occurred. However, of those 13 hot shorts, 

six were spurious operations (by definition); thus, seven of the hot shorts in Scenario A were 

associated with conductors that, when energized, would not result in a spurious operation (e.g., 

indicating lamps, spare conductors, etc). The column plots also have the associated 

percentages at the top of each column. 

Table 1-1. Example of failure mode table

Scenario A Scenario B Scenario C

Fuse Clear 5 20 10

Hot Short 13 5 17

Spurious Operation 6 5 15

HS/SO Possible 18 25 27
 

1-6 

Figure 1-1. Examples global approach failure mode column plot 

1.3.2 Failure mode duration presentation of data 

To provide a realistic and simple graphical representation of the duration data set, this report 

provides hot short and spurious operation duration box plots, also known as box and whisker 

plots. An example of a box and whisker plot is provided in Figure 1-2. The example data set 

used to prepare this example plot is a continuous set of integers ranging from 21 to 80. 

q1 35.75 

min 21 

median 50.5 

max 80 

q3 65.25 

Figure 1-2. Box and whisker plot example 

The duration of hot shorts and spurious operations were evaluated on a conductor by conductor 

basis. In this way, the duration of each hot short was tabulated by evaluating each conductor 

voltage and current profile for each test and summing the duration of the hot short(s) for each 

conductor. The conductor durations were then used to produce the box plots. Since spurious 

operations are a form of hot short, this report presents hot short duration box plots that 

represent both hot short and spurious operation durations, while the spurious operation duration 

Scenario A Scenario B Scenario C

Count

0

10

20

30

40

Fuse Clear

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

28%

72%

33%

80%

20%

20%

37%

63%

55%

0

10

20

30

40

50

60

70

80

90

Data Set

q1

min

median

max

q3

maximum

lower

quartile

upper

quartile

25th

percentile

50th percentile

75th

percentile
 

1-7 

box plots only account for conductors that are associated with an end device which actually 

spurious operated. 

Box plots show a measure of central location (median), two measures of dispersion (the 

interquartile range, defined as the difference between the first and third quartiles), the skew, and 

potential outliers. Box plots do this by using the minimum and maximum values, along with the 

first, second, and third quartiles of the data set. Quartiles are related to percentiles in that the 

first quartile (designated q1) is the 25th percentile. The second quartile (q2) is the 50th

percentile, and is also referred to as the median. The third quartile (q3) is the 75th percentile of 

the data. It should be noted that no distributions are assumed in presenting data using box 

plots. 

The box plots identify the minimum and maximum values in the data set. Lines from these two 

points are referred to as the whiskers, and connect to the boxes’ limits. The boxes’ lower and 

upper limits indicate the first and third quartiles, respectively. The median is located within the 

box and is a reference point for identifying any skewness in the data set. As a general rule, any 

whisker which is three times longer than the length of the box most likely indicates an outlier. 

As you will see in the test result sections below, the duration data has several long duration 

outliers that make it difficult to interpret any variations of the core data. Rather than remove 

these long duration data points, the authors have reduced the plot ranges (y-axis) to provide a 

better representation of the data variations, with the maximum values designated at the top of 

the plot. Tables are included with these box plots to provide all of the information numerically, in 

tabular form. 

There are numerous methods for calculating quartiles. For simplicity, the authors chose to use 

the built-in “quartile” function of Microsoft Excel. Excel uses the following equations to calculate 

quartiles: 

ݕ ൌ ሺ1െ݃ሻ ∗ ݔሺ݆൅1ሻ ൅ ݃ ∗ ݔሺ݆ ൅ 2ሻ (Equation 1-1) 

ሺ݊െ1ሻ ∗݌ൌ݆൅݃ (Equation 1-2) 

Where 

 n = number of values 

 y = observation number (when values are arranged in ascending order) 

 p = percentile 

 j = integer 

 g = decimal 

 x() = specific value in ascending list 

These equations can be simplified into the following form for the first, second, and third 

quartiles: 

 1st quartile (q1): 1⁄4*(n+3)th observation 

 2nd quartile (median): 1⁄2*(n+1) th observation 

 3rd quartile (q3): 1⁄4*(3*n+1)th observation. 

 
 

1-8 

1.4 Report Organization 

Section 2 presents the AC data taken from the NEI/EPRI, CAROLFIRE, and DESIREE-FIRE 

testing projects, evaluating the various intra-cable failure parameters where data was available. 

A summary of the systematic parameter evaluation is presented in the latter portion of Section 

2, along with evaluations of the effects of suppression and hot short concurrence. 

Section 3 provides a review of inter-cable failures observed during testing and the authors’ 

identification of any influencing parameters. This discussion identifies what was done in the 

EPRI and NRC testing programs to provide tests that could be used to evaluate the likelihood of 

inter-cable fire-induced hot shorts of AC circuits. 

Section 4 presents the DC data taken from the DESIREE-FIRE testing project, evaluating the 

various intra-cable failure parameters. This analysis complements the information from Section 

2 on the AC data, but also evaluates several additional parameters. This section also includes 

a summary of the systematic evaluation of the DC data, along with a review of concurrent hot 

shorts that occurred in the intermediate-scale testing of DC circuits. 

Section 5 provides a summary of test data related to inter-cable interactions for AC circuits, 

similar to what was done in Section 3. The larger portion of Section 5 involves the evaluation of 

what is being called “ground equivalent hot shorts,” where multiple cables experience hot 

shorts. 

Section 6 provides a summary of findings for the entire report. 

Section 7 contains the report conclusions. 

Section 8 provides references. 

Appendix A contains data on the penlight ground fault equivalent inter-cable failure mode 

evaluation. 

Appendix B contains supplemental information for the CAROLFIRE reports, including additional 

data retrieval. 
 

2-1 

2. INTRA-CABLE – ALTERNATING CURRENT CIRCUITS 

2.1 AC Data Analysis Approach 

An alternating current (AC) motor-operated valve (MOV) circuit was the primary circuit used in 

the NEI/EPRI and Cable Response to Live Fire (CAROLFIRE) testing projects to evaluate the 

likelihood of spurious operations. A small set of tests in the Direct Current Electrical Shorting in 

Response to Exposure Fire (DESIREE-FIRE) project also used the AC MOV circuitry. The AC 

MOV circuit typically had passive targets representing indicating lamps, two active targets 

(forward and reverse motor starter contactor), spare conductors, one to two energized (source) 

conductors, and at least one common return. 

The definition of a hot short is important to this work. As stated previously, only a hot short that 

is of sufficient quality to actuate the end device is of interest. Thus, low-quality hot shorts that 

would not cause the circuit to respond would not be of interest. Therefore, threshold values are 

defined as identifying the energy levels (voltage or current) that would be required to cause the 

active and passive targets to change state. This information is presented in Table 2-1, 

identifying the failure threshold values for the AC MOV circuit. Active targets are considered to 

be those cable conductors which are connected to one of the two MOV contactors. If these 

active target conductors become energized during fire-induced cable failure with sufficient 

voltage and current, the contactors will pull in, and, in real plant systems, the motor will become 

energized to move in either the open or close direction, depending upon which contactor 

becomes energized. For the AC test data, a hot short on a passive target or on a spare 

conductor was counted when that electrical conductor achieved a voltage level of 80V. The 

choice of 80V is based on the authors’ judgment and discussion with the Phenomena 

Identification and Ranking Table (PIRT) panel. For an indication lamp, 80V is sufficient to 

illuminate the lamp, and for an ungrounded spare the 80V threshold was thought to be sufficient 

to eliminate the likelihood that the measurement would derive from induced voltages on the 

spare conductor. 

Table 2-1. AC threshold values used for MOV hot short & spurious operation 

determinations 

 NEI/EPRI CAROLFIRE DESIREE-FIRE 

Active Targets Pick-up Voltage 80V 72V 80V 

Drop-out Voltage 60V 65V 60V 

Passive Targets Voltage 80V 80V 80V 

Spare Voltage 100V 100V 100V 

For continuous hot shorts, the duration time was calculated from the start of a hot short to the 

end, which was typically a fuse clear. In several cases, a circuit will experience several 

successive hot shorts on the same conductor. In these cases, the duration is based on the sum 

of the individual durations. For example, assume that conductor number three of circuit A 

experienced three hot shorts lasting 10, 15, and 5 seconds respectively; the duration reported 

would be 30 seconds, based on the authors’ judgment and discussions among the PIRT panel. 

This is considered to be a conservative approach, but also realistic for components, such as a 

motor-operated valve, that would not return to their original state following the clearing of the hot 

short/spurious operation, requiring a finite stroke time to open or close. 
 

2-2 

Once all of the information from the tests was entered into the spreadsheet, the data was 

reviewed for circuit configurations that fell outside of the majority of the test data. These outlier 

circuit configurations were removed from further use in the study. For instance, in CAROLFIRE, 

there were several tests that were designed to evaluate the likelihood of inter-cable shorting. 

Since this analysis is only concerned with intra-cable interactions, the inter-cable data was 

removed from this analysis, but is used in Section 3 to evaluate inter-cable hot shorting. In 

some of the CAROLFIRE and several of the NEI/EPRI tests, the cables did not fail. In the 

cases where the cables are not driven to thermal failure, there is no information on the failure 

modes to be learned. Thus, the test circuits that did not fail were removed from further use in 

this study. 

The final type of data points that were removed from the spreadsheet were instances where the 

circuit was instrumented in such a way that it was impossible for the electrical protective device 

(fuse) to clear or configure, so that the only method that would allow a fuse clear would be a 

short to an external ground. The majority of these cases are from the DESIREE-FIRE testing, 

where a flame-retardant KeriteTM (FR-Kerite) cable was tested using AC diagnostics to evaluate 

the thermal failure temperature. Here, only source conductors and active target conductors 

were included in the test cables. As such, there were no common return paths within the cable 

that would cause a fuse clear, which could only occur when an energized conductor came in 

contact with a ground plane at low resistance. Although configurations in the plants may exist 

when there is no common power source return in a cable with sources and targets, the authors 

believed that this data would skew the results, especially for hot short likelihood and duration. 

As such, these data points were removed, and were not used in this study. 

The last point to make clear is the manner in which the data is presented in the report. 

Specifically, there are several ways to present the fault mode data in terms of counting hot 

shorts. The discussion that follows provides clarification on the methods that were used in this 

report. 

Figure 2-1 is a schematic of the surrogate circuit diagnostic unit (SCDU) used in CAROLFIRE to 

represent an AC MOV motor starter circuit. Similar circuits were used in the NEI/EPRI and 

DESIREE-FIRE testing projects. In Figure 2-1, there are two energized source conductors, 

shown as circuit paths 1 and 2. A resistor used to represent an indication lamp is considered to 

be a passive target (PT), and is connected to circuit path 4. Circuit paths 5 and 6 are connected 

to the forward and reverse motor starter contactors, “K1” and “K2.” These two paths are 

considered active targets (AT). Circuit path 7 is connected to the common power supply return, 

and circuit path 8 is considered to be an ungrounded spare conductor. 
 

2-3 

Figure 2-1. CAROLFIRE AC MOV circuit 

Table 2-2 provides information pertaining to the circuit path configuration for the CAROLFIRE 

AC MOV SCDU. As shown, paths 5 and 6 can experience both hot shorts and spurious 

operations. Circuit Paths 4 and 8 can experience a hot short only. 

Table 2-2. CAROLFIRE AC MOV circuit path configuration 

Source Hot Short Spurious Operation

Power Supply 

Common Return 

Circuit Path 1 X 

Circuit Path 2 X 

Circuit Path 4 X 

Circuit Path 5 X X 

Circuit Path 6 X X 

Circuit Path 7 X 

Circuit Path 8 X 

Using the global approach, there can only be one of two outcomes: (1) the cable experiences 

hot short(s), or (2) the cable experiences a ground fault (clearing of the circuit fuse). Note that 

spurious operations are a subset of hot shorts. The global approach does not provide an 

indication on the number of hot shorts that occur within a multi-conductor cable; either it occurs, 

or it doesn’t. This method does not make any distinction between the numbers of hot shorts. 

From these examples, it is important to note that there will always be at least as many hot 

shorts as spurious operations. This is because every spurious operation is classified as a hot 

short, but not every hot short is classified as a spurious operation. 

 
 

2-4 

For example, let’s assume that the AC MOV circuit shown in Figure 2-1 is used in a test, and 

that the following failure modes occurred in this case: 

 @ 954 seconds – circuit path 4 experienced a hot short 

 @ 1005 seconds – circuit path 6 experienced a hot short 

 @ 1013 seconds – circuit path 6 experienced a hot short 

 @ 1020 seconds – the circuit fuse cleared 

In this example, using the global approach to counting hot shorts and spurious operations, there 

was one hot short, one spurious operation, and no fuse clears. In reality there were three hot 

shorts, two spurious operations, and one fuse clear. Again, the global approach looks at the 

circuit failure modes in a binary fashion. This point is important for understanding the 

information that follows in this section and in Section 4. 

With regard to calculating duration of the hot shorts and hot short induced spurious operations, 

more information is required to calculate the duration using the method outlined above. Using 

the previous example, the duration of the hot short and spurious operation is presented using 

the following information: 

 circuit path 4, hot shorts as follows; 

o 954 seconds – hot short starts 

o 1020 seconds - hot short ends 

 circuit path 6 experienced a hot short induced spurious operation as follows; 

o 1005 seconds - spurious operation begins 

o 1010 seconds - spurious operation ends 

o 1013 seconds - spurious operation begins 

o 1020 seconds - spurious operation ends 

For circuit path 4, since only one fire-induced hot short occurred, the duration is calculated as 

the hot short end time (1020s) minus the hot short start time (954s) resulting a hot short 

duration of 66 seconds. For circuit path 6, multiple hot short-induced spurious operations occur 

on the same end device. Here the duration is calculated for each individual spurious operation 

and all of the individual durations are summed together to arrive at a total duration for circuit 

path 6. This is shown in Equation 2-1. 

Circuit Path 6 duration: (1010 s – 1005 s) + (1020 s – 1013 s) = 12 seconds Equation 2-1 

The last point to make regarding the analysis of the AC test data is that some of CAROLFIRE 

and DESIREE-FIRE tests also employed SNL’s patented Insulation Resistance Measurement 

System (IRMS), which was operated using AC power. This system provides measurements of 

a monitored electrical cable’s insulation resistance as a function of time during fire-induced 

cable failure. The IRMS can provide detailed information as to how the individual conductors 

are failing; however, it does not represent any type of electrical circuit used in a nuclear power 

plant. Several concepts regarding the use of the IRMS data to evaluate failure modes were 

discussed during the electrical expert PIRT meetings, but none were technically accurate 

enough to be used to supplement the data analysis documented here. 

The remainder of this section presents the AC test data evaluated by the various parameters 

outlined earlier. Each parameter discusses how the data was binned and then presents the 

failure mode likelihood, followed by information on the hot short duration. 
 

2-5 

2.2 Conductor Count 

The effects of the conductor count on failure modes are evaluated here. The test data included 

multi-conductor cables with 3, 5, 6, 7, 8, and 9 conductors. The PIRT members suggested that 

the conductor count bins be labeled “1/C,” “2-6/C,” “7-9/C,” “10-15/C,” and “Greater than 15/C.” 

Table 2-3 provides the failure mode likelihood data, separated into conductor count ranges. 

There is no data publically available for 1/C cables, or for cables with conductor counts greater 

than 10/C. 

Table 2-3. Conductor count, global approach, AC tests 

Global Approach 1/C 2-6/C 7-9/C 10-15/C >15/C 

Fuse Clear - 4 41 - - 

Hot Short - 2 65 - - 

Spurious Operation - 2 56 - - 

HS/SO Possible - 6 106 - - 

Figure 2-2 presents the information from the above tables in column format. These figures 

show that a large portion of data has been collected in the 7-9 conductor range, making it 

difficult to assess the influence that conductor count has on hot short and spurious operation 

likelihood. 

Figure 2-2. Conductor count column plot, global approach, AC tests 

Table 2-4 presents data related to the durations of hot shorts and spurious operations, divided 

into the same conductor count ranges used above. Figure 2-3 presents this data visually, in a 

box plot. Again, the sparse data limits the amount of information that can be obtained relating to 

the influence of conductor count on hot short and spurious operation likelihood. 

 

1/C 2-6/C 7-9/C 10-15/C >15/C

Count

0

20

40

60

80

100

120

140

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

53%

61%

39%

100%

67%

33%33%
 

2-6 

Table 2-4. Conductor count, duration data, AC tests 

 Hot Short Spurious Operation 

 1/C 2-6/C 7-9/C 10-15/C >15/C 1/C 2-6/C 7-9/C 10-15/C >15/C 

q1 - 3 8 - - - 4 10 - - 

min - 1 1 - - - 1 1 - - 

median - 6 27 - - - 8 33 - - 

max - 15 1345 - - - 15 456 - - 

q3 - 10 79 - - - 11 81 - - 

mean - 7 69 - - - 8 61 - - 

Figure 2-3. Conductor count box plot, duration, AC tests 

2.3 Thermal Exposure Conditions 

The test data used to evaluate the thermal exposure parameter is separated into four general 

exposure conditions, radiant, flame, plume, and hot gas layer (HGL). Figure 2-4 shows the 

intermediate-scale testing rig used in the CAROLFIRE and DESIREE-FIRE testing projects. It 

is important to note that the locations were identified differently in the two testing projects, and 

that the lower exterior HGL locations in the CAROLFIRE project (i.e., B and D) were not used in 

the DESIREE-FIRE testing project. Care was taken during the analysis to ensure that the 

naming conventions did not cause the different exposure locations to be combined within the 

same bin. 

Flame exposures were considered to be any electrically monitored cable in location A. In 

addition, if location A was filled with cables to provide a fuel source during an experiment, the 

locations directly above location A (C for CAROLFIRE and B for DESIREE-FIRE) would also be 

considered flame exposure locations. Plume exposure locations were considered to be 

locations C and F in CAROLFIRE and locations B and D in DESIREE-FIRE unless designated 

as flame locations, as discussed previously. HGLs were considered to be those locations 

outside of the flame and plume locations. Therefore, HGL exposure bins included locations B, 

D, E, and G for CAROLFIRE, and locations C and E for DESIREE-FIRE. In addition, the 

penlight exposure provided a radiated thermal exposure to the cables, and all of the Penlight 

0

25

50

75

100

1/C 2‐6/C 7‐9/C 10‐15/C >15/C 1/C 2‐6/C 7‐9/C 10‐15/C >15/C

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 456s
 

2-7 

data is separated into an individual bin labeled “radiant.” The exposure conditions classification 

used in the EPRI test report were adopted as reported. 

CAROLFIRE DESIREE-FIRE 

Figure 2-4. Intermediate-scale cable raceway location 

Table 2-5 and Figure 2-5 present the ground fault, hot short, and spurious operation data. This 

data shows some deviations between thermal exposure conditions with regard to ground faults, 

hot shorts, or spurious operations. Here the flame region has a lower likelihood of experiencing 

a fuse clear fault and a higher likelihood of experiencing hot shorts and spurious operations. 

The limited number of AC circuit radiant energy tests (five in total) are all from the AC tests 

conducted during the DESIREE-FIRE project. Three of these cable samples were of the FRKerite variety, and the remaining two samples were cross-linked polyethylene (XLPE)-insulated. 

Table 2-5. Thermal exposure conditions, global approach, AC tests 

Global Approach Flame Plume HGL Radiant 

Fuse Clear 7 15 19 4 

Hot Short 18 22 26 1 

Spurious Operation 17 17 23 1 

HS/SO Possible 25 37 45 5 
 

2-8 

Figure 2-5. Thermal exposure conditions column plot, global approach, AC tests 

Table 2-6 and Figure 2-6 present the duration data, separated by thermal exposure conditions 

of flame, plume, and HGL exposures. The box and whisker plot shows that there may be a 

correlation between hot short/spurious operation duration and thermal exposure conditions. For 

flame exposures, the durations are very short, lasting between 1 and 32 seconds. The plume 

thermal exposure conditions have durations with a slightly longer and wider range of 6 to 120 

seconds4

. The hot gas layer thermal exposures have the largest range of duration, running from 

1 to 456 seconds. 

This observation is consistent with the physical response of the cables to these exposure 

conditions. In a flame impingement exposure, there is a very intense thermal insult on the 

cables and the insulation degrades rapidly, thus progressing from the onset of electrical failure 

to final circuit failures (fuse clear) in a short time frame. As the exposure conditions become 

less intense (i.e., plume then HGL exposures), the degradation of the conductor insulation is 

slower and the failures do not cascade to full failure as rapidly. 

Table 2-6. Thermal exposure conditions, duration data, AC tests 

 

 Hot Short Spurious Operation 

 Flame Plume HGL Radiant Flame Plume HGL Radiant 

q1 2.3 17.5 20.7 0.6 4.2 24 28.9 0.6 

min 0.2 5.8 0.4 0.6 0.2 6 0.8 0.6 

median 7.3 45.6 78.8 0.6 8 47.4 78.8 0.6 

max 31.6 1345 456 0.6 31.6 126 456 0.6 

q3 20 72 169.7 0.6 24.6 60 120.7 0.6 

mean 11.1 80.6 106.6 0.6 12.7 51.1 103.4 0.6 

 

4

 Note that one duration for the hot short plume data set was 1345 seconds. This data point has been removed from the 

generalized discussion, but is important when considering maximum test data durations. 

Flame Plume HGL Radiant

Count

0

10

20

30

40

50

60

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

46%

59%

41%

100%

72%

68%

28%

100%

51%

58%

42%

100%

20%

20%

80%
 

2-9 

Figure 2-6. Thermal exposure conditions box plot, duration, AC tests 

2.4 Cable Orientation 

Available test data consists of cable arrangement in the vertical and horizontal orientations. 

However, only one test project (NEI/EPRI) included testing cables in the vertical orientation, and 

the majority of the test data is for cables oriented horizontally. As such, there is too little 

information on fire-induced cable failures in the vertical orientation to allow for comparisons. 

Table 2-7 and Figure 2-7 present the data, which is separated by cable orientation. 

Table 2-7. Cable orientation, global approach, AC tests 

Global Approach Horizontal Vertical Total 

Fuse Clear 42 3 45 

Hot Short 65 2 67 

Spurious Operation 56 2 58 

HS/SO Possible 107 5 112 

 

0

50

100

150

200

Flame Plume HGL Radiant Flame Plume HGL Radiant

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 456s 456s
 

2-10 

Figure 2-7. Cable orientation column plot, global approach, AC tests 

Table 2-8 and Figure 2-8 present the duration information based on cable orientation binning. 

Again, the minimal amount of data in the vertical position inhibits an evaluation of how cable 

orientation affects hot short duration. 

Table 2-8. Cable orientation, duration data, AC tests 

Hot Short Spurious Operation 

 Horizontal Vertical Horizontal Vertical 

q1 7 11 10 12 

min 1 6 1 6 

median 27 15 32 18 

max 1345 120 456 120 

q3 77 44 79 69 

mean 69 39 60 48 

 

Horizontal Vertical

Count

0

20

40

60

80

100

120

140

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

39%

61%

52%

60%

40%

40%
 

2-11 

Figure 2-8. Cable orientation box plot, duration, AC tests 

2.5 Raceway Routing 

Open ladder-back cable trays, rigid steel conduits, and air drop configurations were all used 

during testing. However, the use of cable trays was predominant, and the lack of sufficient data 

in the air drop and conduit configurations makes it difficult to determine the effects of raceway 

routing type on fire-induced circuit failures. In addition, no data is available for cable trays with 

solid bottom covers or vented covers. Table 2-9 and Figure 2-9 present the test data separated 

by raceway routing configurations and air, conduit, and tray configurations. 

Table 2-9. Raceway routing, global approach, AC tests 

Global Approach Air Conduit Tray 

Fuse Clear 0 2 43 

Hot Short 2 2 63 

Spurious Operation 2 2 54 

HS/SO Possible 2 4 106 

0

50

100

150

Horizontal Vertical Horizontal Vertical

Hot Short SpuriuosOperation

Seconds

q1

min

median

max

q3

1345s 456s
 

2-12 

Figure 2-9. Raceway routing column plot, global approach, AC tests 

Table 2-10 and Figure 2-10 present the duration data separated by raceway routing 

configurations. This information indicates that air drop tests last longer than configurations 

using conduit or cable tray raceways. This observation is likely the result of the ground plane’s 

influence on the circuit’s ability to clear fuses. In an air drop test configuration, there is typically 

only one conductor that can cause a circuit to experience a fuse clear. This is a common power 

supply return (the neutral from the power supply), and it is typically grounded. For a circuit to 

clear its protective fusing, a source conductor is required to come in contact with a common 

ground. In conduit and cable tray configurations, a more substantial ground plane exists for 

source conductors to contact during cable failure. Thus, the lack of ground plane is likely the 

cause of the longer durations in the air drop configurations. The effects of gravity, cable type, 

and cable clamps/ties may also affect the failure modes among horizontal and vertical 

configurations. Although this hypothesis seems reasonable, it should be stated that the air drop 

and conduit data are scarce and additional data points may help reinforce this hypothesis. 

Table 2-10. Raceway routing, duration data, AC tests 

Hot Short Spurious Operation 

 Air Conduit Tray Air Conduit Tray 

q1 79 18 7 179 46 9 

min 28 3 1 34 23 1 

median 247 48 24 261 75 30 

max 320 126 1345 296 126 456 

q3 295 86 65 295 100 62 

mean 195 56 62 213 75 53 

Air Conduit Tray

Count

0

20

40

60

80

100

120

140

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

0%

100%

100%

50%

50%

50%

41%

59%

51%
 

2-13 

Figure 2-10. Raceway routing box plot, duration, AC tests 

2.6 Raceway Fill 

Numerous cable raceway fill configurations were used during testing. To sort the data, three 

configuration groups were selected based on the testing configurations, namely bundles, 

intermediate fill, and single cable fill. Figure 2-11, Figure 2-12, and Figure 2-13 provide 

illustrations of the bundles, intermediate and single cable fill, respectively. Note that no tests 

involved cable trays or conduits filled to their maximum loading per the national electric code 

(NEC – NFPA 70). Even though the NEI/EPRI test configurations used a 7/c cable surrounded 

by three single conductors, that configuration has not been considered a bundle in this work, as 

it was loaded into cable trays with numerous other fill cables, as shown in Figure 2-12 and 

Figure 2-13. 

 

Figure 2-11. Cable bundle arrangements (3-, 4-, 6-, & 12-cable bundles) 

Figure 2-12. Cable tray fill intermediate 

0

50

100

150

200

250

300

350

AIR CONDUIT TRAY AIR CONDUIT TRAY

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 456s
 

2-14 

Figure 2-13. Single layer cable fill 

Table 2-11 and Figure 2-14 present the failure mode data binned by raceway fill. One 

observation from this data is that the bundle data deviate from the intermediate and single cable 

arrangement in both ground faults and hot short/spurious operation occurrences. The data 

shows that the occurrence of a ground fault is roughly twice as likely (~52-53%) for the 

intermediate and single cable configurations as it is for a bundle configuration (~26%). The 

lower likelihood of a ground fault has a dependent effect on the occurrence of a hot short or 

spurious operation in the bundle configurations versus the other two configurations. One 

possibility is that the bundle configurations typically involve electrical cables at the top of the 

cable bundle and are shielded from the cable tray by fill cables that are not monitored for 

electrical response. Thus, for grounded circuits, which make up the majority of the test data, 

there is a barrier between the electrically monitored cable and the cable tray/conduit, thus 

reducing the ground plane influence and decreasing the likelihood of a ground fault. Again, the 

ground plane may influence failure mode likelihoods. 

Table 2-11. Raceway fill, global approach, AC tests 

Global Approach Bundle Intermediate Single 

Fuse Clear 13 16 16 

Hot Short 37 14 15 

Spurious Operation 35 11 11 

HS/SO Possible 50 30 31 

Figure 2-14. Raceway fill column plot, global approach, AC tests 

 

Bundle Intermediate Single

Count

0

20

40

60

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

74%

70%

26%

53%

47%

37%

52%

48%

35%
 

2-15 

Table 2-12 and Figure 2-15 present the hot short and spurious operation duration data 

separated by raceway fill categories (bundle, intermediate, and single). From this data, there is 

some indication that the intermediate fill duration data differs from that of the other two 

configurations; however, the reasoning behind this observation is unclear. One possibility is 

that the fill cables act as a heat sink and/or shield for the target cables from the thermal 

exposure, thus lowering the thermal exposure condition for the electrically monitored cables. 

Table 2-12. Raceway fill, duration data, AC tests 

 Hot Short Spurious Operation 

 Bundle Intermediate Single Bundle Intermediate Single 

q1 7 18 11 8 24 7 

min 1 1 1 1 1 1 

median 25 54 21 30 57 21 

max 453 1345 198 296 456 198 

q3 62 120 63 62 111 75 

mean 56 126 43 51 95 51 

Figure 2-15. Raceway fill box plot, duration, AC tests 

2.7 Insulation Type 

The insulation type parameter separates insulation materials into two polymer types, thermoset 

(TS) and thermoplastic (TP). Table 2-13 provides a breakdown of how insulation materials were 

classified by insulation type. Section 2.8 of this report provides a comparison of failure 

characteristics based on insulation materials. Table 2-14 and Figure 2-16 present the test data 

separated by cable conductor insulation type, TS and TP. A comparison of the failure modes 

between the TS and TP data sets indicate that there is no substantial difference in fuse clear, 

hot short, or spurious operations. 

 

0

100

200

300

Bundle Intermediate Single Bundle Intermediate Single

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3
 

2-16 

Table 2-13. Breakdown of insulation material by type, AC tests 

Thermoset Materials (TS) Thermoplastic Materials (TP) 

EPR – ethylene propylene rubber PE – polyethylene 

FR-Kerite – Flame Retardant KeriteTM PVC – polyvinyl chloride 

SR – Silicone Rubber TEF – Tefzel 

SR-V – Silicone Rubber VitalinkTM 

XLPE – cross-linked polyethylene 

XLPO – cross-linked polyolefin 

Table 2-14. Insulation type, global approach, AC tests 

Global Approach TP TS 

Fuse Clear 17 28 

Hot Short 22 45 

Spurious Operation 20 38 

HS/SO Possible 39 73 

Figure 2-16. Insulation type column plot, global approach, AC tests 

Table 2-15 and Figure 2-17 present the duration data for test configurations segregated by 

cable conductor insulation type. Although the mean duration times are slightly higher for TP 

materials (73-80 seconds) than for TS materials (53-61 seconds), the inter-quartile range for the 

data presented in the box and whisker plot in Figure 2-17 shows no trend between TS and TP 

insulation types. 

Table 2-15. Insulation type, duration data, AC tests 

 Hot Short Spurious Operation 

 TP TS TP TS 

q1 5 11 6 15 

min 1 1 1 1 

median 23 28 24 39 

max 456 1345 456 231 

q3 100 72 64 81 

mean 80 61 73 53 

TP TS

Count

0

20

40

60

80

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

44%

56% 51%

38%

62%

52%
 

2-17 

Figure 2-17. Insulation type box plot, duration, AC tests 

2.8 Insulation Material 

In the previous section, the data was segregated by insulation type. In this section, the data 

expanded to insulation type classifications to show how insulation materials differ. Table 2-16 

and Figure 2-18 present the ground fault, hot short, and spurious operation data segregated by 

cable conductor insulation material. 

Table 2-16. Insulation material, global approach, AC tests 

 TS TP 

 EPR XLPE SR FR-Kerite PE PVC TEF 

Fuse Clear 11 11 3 2 9 4 4 

Hot Short 23 19 1 1 9 9 4 

Spurious Operation 16 19 1 1 7 9 4 

HS/SO Possible 34 30 4 3 18 13 8 

 

0

50

100

150

TP TS TP TS

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

456s 1345s 456s 231s
 

2-18 

Figure 2-18. Insulation material column plot, global approach, AC tests 

As shown in the figures above, there is minimal data for silicone rubber (SR) and FR-Kerite. 

Thus, interpreting the results is difficult, and it will not be attempted here. Figure 2-18 indicates 

that the ethylene propylene rubber (EPR) material differs from the others in that there is a 

relatively larger gap between hot shorts and spurious operations (about 20%). The other 

materials show a nearly unified correlation between hot short and spurious operations based on 

the global analysis approach. Over 50% of the EPR data comes from the NEI/EPRI test set, 

and that test set-up may influence these results. However, the direct reasoning behind this 

difference is unclear to the authors. A comparison of the remaining cable conductor insulation 

materials shows similar results related to ground fault, hot short, and spurious operation 

likelihoods. 

Table 2-17, Table 2-18, and Figure 2-19 present the duration data segregated by cable 

insulation material. Note that SR and FR-Kerite have been removed due to a lack of data. One 

interesting aspect of this duration data is the small inter-quartile range for polyvinyl chloride 

(PVC)-insulated conductors versus the other two TP cable types, polyethylene (PE) and 

TefzelTM (TEF). Both PE and TEF insulation materials show the longest average durations, 

which was reflected in the previous section. However, PVC insulation materials have a very 

short duration. 

Table 2-17. Insulation material hot short only, duration data, AC tests 

 TS TP 

 EPR XLPE PE PVC TEF 

q1 12 11 18 1 33 

min 1 1 1 1 8 

median 60 30 55 4 168 

max 324 1345 453 32 456 

q3 90 49 233 10 203 

mean 64 65 117 8 158 

 

EPR XLPE SR FR-Kerite PE PVC TEF

Count

0

10

20

30

40

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

100%

100%

100%

100%

68%

47%

32%

37%

63%

63%

75%

25%

25%

67%

33%33%

50%

39%

50%

31%

69%

69%

50%

50%50%
 

2-19 

Table 2-18. Insulation material spurious operation only, duration data, AC tests 

 TS TP 

 EPR XLPE PE PVC TEF 

q1 12 19 27 1 33 

min 2 1 3 1 10 

median 62 38 55 6 126 

max 198 231 296 32 456 

q3 100 54 114 14 264 

mean 63 50 95 10 172 

Figure 2-19. Insulation material box plot, duration, AC tests 

2.9 Insulation-Jacket Type Combinations 

The previous two sections evaluated the effects of conductor insulation type and materials. The 

next logical parameter to evaluate would be cable jacket materials and polymer types. Although 

this was done initially, a review by the electrical expert PIRT panel found that the analysis was 

less than useful, and it was suggested that the synergistic effects of cable jacket type and cable 

insulation type should be evaluated instead. 

This section provides that evaluation by looking at the insulation/jacket polymer type 

combinations available from the test data. This evaluation creates three bins, which include 

cables with (1) TP insulation and TP jacket, (2) TS insulation and TS jacket, and (3) TS 

insulation and TP jacket (mixed cable type). Table 2-19 and Figure 2-20 present the failure 

mode likelihood information, while Table 2-20 and Figure 2-21 reference the duration data for 

these configurations. The likelihood information provides little value in identifying any influence 

by insulation/jacket types on a particular failure mode. The duration evaluation indicates that 

the TS-TS cables have longer durations in general than the TP-TP and TS-TP configurations, 

based on the mean and the inter-quartile range. 

0

100

200

300

400

EPR XLPE PE PVC TEF EPR XLPE PE PVC TEF

TS TP TS TP

Hot Short SpuriousOperation

Secnods

q1

min

median

max

q3

1345 453s

s

456s 456s
 

2-20 

Table 2-19. Insulation-jacket type, global approach, AC tests 

Global Approach TP-TP TS-TS TS-TP 

Fuse Clear 17 20 8 

Hot Short 22 36 9 

Spurious Operation 20 29 9 

HS/SO Possible 39 56 17 

Figure 2-20. Insulation-jacket type column plot, global approach, AC tests 

Table 2-20. Insulation-jacket type, duration data, AC tests 

Hot Short Spurious Operation 

 TP-TP TS-TS TS-TP TP-TP TS-TS TS-TP 

q1 5 12 7.6 6 16.7 14.45 

min 0.2 0.4 0.2 0.2 0.6 0.8 

median 23.3 43.2 24 24 47.6 27.1 

max 456 1345 62.4 456 231 62.4 

q3 96.6 94.6 32.9 64.2 96.3 43.05 

mean 79.8 76.1 23.1 73.4 61.9 28.8 

TP-TP TS-TS TS-TP

Count

0

10

20

30

40

50

60

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

44%

56%

51%

36%

64%

52%

100%

100%

47%

53%

53%
 

2-21 

Figure 2-21. Insulation-jacket type box plot, duration, AC tests 

2.10 CPT Size 

Several differently sized control power transformers (CPTs) were used in the testing to evaluate 

the effects of CPT size on fire-induced circuit response. Table 2-21 provides information on the 

size of CPTs used during the various testing projects. At the time of this writing, the authors 

were not able to determine the size of the CPTs used in the NEI/EPRI testing project; thus, this 

data has been separated into its own bin for this review. 

Table 2-21. Test project CPT size 

 75VA 100VA 150VA 200VA Unknown Size No CPT

NEI/EPRI X X 

CAROLFIRE X X X X 

DESIREE-FIRE X X X X 

Table 2-22 and Figure 2-22 provide the circuit fault modes based on variously sized CPTs used 

during testing. The limited number of tests (two in total) using the 75VA CPT, and the fact that 

one test cleared the fuse while the other resulted in a spurious operation; provide little 

information on this configuration’s effect on failure mode. The 100VA and 150VA data are very 

similar to the ~32-33% ground fault mode likelihood and the ~65-67% hot short/spurious 

operation likelihood. The 200VA CPT and no CPT data are also similar to the ground fault 

likelihood of ~40-41% and the spurious operation likelihood of ~50-53%. 

The NEI/EPRI data doesn’t conform to the fault mode characteristics of the SNL data, as it 

shows a much higher likelihood of ground faults (~59%), a lower likelihood of hot shorts (~41%), 

and a much lower likelihood of spurious operations (~18%). Although there are many aspects 

within the NEI/EPRI testing that could lead to these results, the authors are unable to pinpoint 

the exact cause of the differences between the NEI/EPRI test data and the other data. 

 

0

100

200

TP‐TP TS‐TS TS‐TP TP‐TP TS‐TS TS‐TP

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

456s 1345s 456s 231s
 

2-22 

Table 2-22. CPT size, global approach, AC tests 

Global Approach 75VA 100VA 150VA 200VA Unknown Size (EPRI) None 

Fuse Clear 1 5 10 7 10 12 

Hot Short 1 10 21 10 7 18 

Spurious Operation 1 10 20 9 3 15 

HS/SO Possible 2 15 31 17 17 30 

Figure 2-22. CPT size column plot, global approach, AC tests 

Table 2-23 and Figure 2-23 present the duration data segregated by CPT size. The data shows 

that the hot short and spurious operation duration for cases where no CPT is used is on 

average longer than when a CPT is used. In general, there is not much difference between the 

CPT size and the duration of the hot short or the spurious operation. 

Table 2-23. CPT size, duration data, AC tests 

 Hot Short 

 75VA 100VA 150VA 200VA EPRI None 

q1 21 4 5 7 12 18 

min 9 1 1 1 6 1 

median 32 38 24 10 21 57 

max 52 453 320 238 198 1345 

q3 42 65 54 41 57 120 

mean 31 67 53 47 50 108 

Spurious Operation 

75VA 100VA 150VA 200VA EPRI None 

q1 37 5 9 7 24 22 

min 32 1 1 1 18 6 

median 42 38 30 10 54 60 

max 52 97 296 231 198 456 

q3 47 62 61 42 120 114 

mean 42 37 56 46 83 83 

75VA 100VA 150VA 200VA Unknown Size None

Count

0

10

20

30

40

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

65%

100%

100%

100%

50%

50%

50%

33%

67%67%

32%

68%

41%

59%

53%

59%

41%

18%

40%

60%

50%
 

2-23 

Figure 2-23. CPT size box plot, duration, AC tests 

2.11 Circuit Grounding 

This section explores how circuit grounding affects fire-induced AC circuit response by 

examining the effects of having a grounded versus an ungrounded AC power supply on the fault 

mode likelihood during fire exposures. For grounded AC circuits that are powered from a CPT, 

the neutral on the secondary side of the CPT would be connected to the ground. For a 

grounded AC circuit not using a CPT, but connected directly to outlet power, the neutral would 

be grounded. The circuit ground connection for the experiments is the same ground plane 

associated with the cable raceway, cable trays, and conduits. Ungrounded AC circuits tested in 

the NRC tests are identical to the grounded circuits with the one exception of the common 

return of the power supply not being connected to ground. No data from circuits powered by a 

DC power supply has been included in this section. 

Table 2-24 and Figure 2-24 provide the ground fault, spurious operation, and hot short fault 

mode information. The data indicates that circuits that are ungrounded have a higher likelihood 

of experiencing a hot short (~85%) than a circuit that is grounded (~58%). Looking at the data 

in the fuse clearing aspects, a grounded circuit has a higher chance of clearing a fuse (~42%) 

than an ungrounded circuit (~15%). For the grounded configurations, 3% of the fuse clears are 

attributed to seven test points that used armored cable. DC testing by NEI/EPRI, Duke Energy 

Corporation, and the U.S. Nuclear Regulatory Commission (NRC) has shown that when an 

armored cable is used in a grounded circuit, the likelihood of experiencing a fuse clear failure is 

approximately 1. 

Table 2-24. Circuit grounding, global approach, AC tests 

Global Approach Un-Grounded Grounded 

Fuse Clear 2 41 

Hot Short 11 56 

Spurious Operation 11 47 

HS/SO Possible 13 97 

0

100

200

300

75VA

100VA150VA200VA

EPRI

None

75VA

100VA150VA200VA

EPRI

None

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

453s 320s 1345s 456s
 

2-24 

Figure 2-24. Circuit grounding column plot, global approach, AC tests 

Table 2-25 and Figure 2-25 present the duration data segregated by circuit grounding 

(grounded versus ungrounded). The data indicates that the grounded circuits have a slightly 

higher average duration time, but the ranges of durations shown in Figure 2-25 indicates few 

differences. 

Table 2-25. Circuit grounding, duration data, AC tests 

Hot Short Spurious Operation 

 Grounded Ungrounded Grounded Ungrounded 

q1 8 7 10 16 

min 1 1 1 1 

median 24 29 31 33 

max 1345 224 456 121 

q3 84 62 84 71 

Mean 74 44 63 45 

Figure 2-25. Circuit grounding box plot, duration, AC tests 

Not Gnd Gnd

Count

0

20

40

60

80

100

120

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

15%

85%

85%

42%

58%

48%

100%

0

40

80

120

160

Gnd UnGnd Gnd UnGnd

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 224s 456s
 

2-25 

2.12 Wiring Configuration 

Wiring configuration refers to the number of sources, targets, and neutrals/grounds located 

within a cable of interest. This parameter evaluation does not evaluate circuit-to-conductor 

connection patterns within a cable. EPRI conducted an evaluation of conductor connection 

patterns and determined that the “source-centered” configuration resulted in the highest 

likelihood of a circuit experiencing a hot short. The NRC-sponsored CAROLFIRE and 

DESIREE-FIRE projects typically connected circuits in the source-centered configuration. Thus, 

there is little to no new data to provide an evaluation of conductor connection patterns. 

Table 2-26 provides a breakdown of the three wiring configurations and the number of source, 

target, and common return conductors in each configuration. A vast majority of the tests used a 

common configuration with two (2) energized source conductors, four (4) target conductors 

(passive targets, active targets, and spares), and one (1) common power supply return 

conductor (either a ground or a neutral, depending on circuit grounding configuration). 

Table 2-27 and Figure 2-26 present the spurious operation likelihood information by wiring 

configuration. 

Table 2-26. Wiring configurations 

 # Sources # Targets # Returns 

Configuration 1 2 4 1 

Configuration 2 2 3 1 

Configuration 3 2 2 1 

Table 2-27. Wiring configuration, global approach, AC tests 

Global Approach Config. 1 Config. 2 Config. 3 

Fuse Clear 41 1 3 

Hot Short 65 1 1 

Spurious Operation 56 1 1 

HS/SO Possible 106 2 4 

Figure 2-26. Wiring configuration column plot, global approach, AC tests 

Config. 1 Config. 2 Config. 3

Count

0

20

40

60

80

100

120

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

39%

61%

53%

50%

50%

50%

100%

75%

25%25%

100%
 

2-26 

The duration data is difficult to interpret for this parameter due to the lack of data for 

configurations 2 and 3. Table 2-28 and Figure 2-27 present the duration data based on wiring 

configuration. 

Table 2-28. Wiring configuration, duration data, AC tests 

Hot Short Spurious Operation 

 Config. 1 Config. 2 Config. 3 Config. 1 Config. 2 Config. 3 

q1 7 8 1 10 15 1 

min 1 6 1 1 15 1 

median 27 10 1 33 15 1 

max 1345 15 1 456 15 1 

q3 79 12 1 81 15 1 

mean 69 10 1 61 15 1 

Figure 2-27. Wiring configuration box plot, duration, AC tests 

2.13 Conductor Size 

Control cables used in nuclear power plants (NPPs) are typically constructed with # 12 or # 14 

American wire gauge (AWG) conductors. From the test data, only one AC MOV test used a 

cable conductor size outside of this range, and it was a 3/C # 8 AWG cable using a modified 

MOV circuit. To evaluate this parameter, the conductor size data was segregated into three 

bins, <12 AWG, 12 AWG, and 14 AWG. All of the 14 AWG data came from the NEI/EPRI 

testing project. The 12 AWG bin contains test data from all three test projects, and the single 

<12 AWG data point came from the CAROLFIRE project. 

Table 2-29 and Figure 2-28 present the test data segregated by conductor size in tabular and 

graphical format. From this data, there is no direct indication that conductor size has any effect 

on the hot short likelihood. However, a comparison of the spurious operation likelihood between 

12 AWG and 14 AWG (NEI/EPRI tests) indicates that there is a lower likelihood for 14 AWG 

conductor cables to experience a spurious operation. Although this is what the data shows, the 

0

20

40

60

80

100

Config. 1 Config. 2 Config. 3 Config. 1 Config. 2 Config. 3

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 456s
 

2-27 

authors believe that some other parameter is influencing this outcome, possibly the EPRI CPT 

circuit data, which showed low spurious operation probability. 

Table 2-29. Conductor size, global approach, AC tests 

Global Approach <12 AWG 12 AWG 14 AWG 

Fuse Clear 1 30 14 

Hot Short 0 47 20 

Spurious Operation 0 43 15 

HS/SO Possible 1 77 34 

Figure 2-28. Conductor size column plot, global approach, AC tests 

Table 2-30 and Figure 2-29 present the duration data based on the conductor size bins. The 

data indicates that the smaller 14 AWG conductor cables have a longer duration (60 second 

median) than 12 AWG conductor-sized cables (24-27 second median). 

Table 2-30. Conductor size, duration data, AC tests 

Hot Short Spurious Operation 

 <12 AWG 12 AWG 14 AWG <12 AWG 12 AWG 14 AWG 

q1 - 7 15 - 8 18 

min - 1 1 - 1 6 

median - 24 60 - 27 60 

max - 453 1345 - 296 456 

q3 - 55 120 - 56 120 

mean - 52 115 - 49 94 

<12 AWG 12 AWG 14 AWG

Count

0

20

40

60

80

100

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

0%

0%

100%

39%

61%

56%

100%

100%

41%

59%

44%
 

2-28 

Figure 2-29. Conductor size box plot, duration, AC tests 

2.14 Water Based Fire Suppression Effects on AC Circuit Failures 

The effect of water spray on thermally fragile cables was only explored in a minimal set of tests. 

During the NEI/EPRI tests, a single sprinkler head was located in the ceiling corner of the fire 

test enclosure above the cable tray bend in the general fire location. The sprinkler was 

manually activated, and it was not used in every test. There were also a few tests in which 

manual water suppression was applied using a garden hose. In CAROLFIRE, a single open 

head sprinkler was installed near the ceiling center of the intermediate-scale test structure, on a 

pendant about 150 mm (6 in.) long. The water flow was manually initiated using a small electric 

pump and only initiated in those tests where one or more of the cables had not experienced 

electrical failure (silicone rubber). No water suppression was used in the DESIREE-FIRE 

testing. 

Water spray was observed to cause spurious operations in only one NEI/EPRI test, Test 3. In 

this case, a spurious operation did coincide with water spray, and persisted for approximately 24 

seconds before a fuse clear occurred. This test cable was located at the center of the top layer 

of a two-layer cable fill test. Figure 2-30 provides a voltage plot of test circuit 3 for NEI/EPRI 

Test #3, showing the spurious operation on the target conductor, Wire #4 but only hot shorts on 

non-spurious operation target Wire #5 and Wire #7. 

0

40

80

120

160

200

<12 AWG 12 AWG 14 AWG <12 AWG 12 AWG 14 AWG

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

453s 1345s 296s 456s
 

2-29 

Figure 2-30. NEI/EPRI test 3 voltage plot - water spray 

In Test 10 of the EPRI program, water spray was applied during an ongoing spurious operation. 

The application of water terminated the spurious operation (cleared for 42 seconds), followed by 

a brief operation of a target conductor (6 seconds), followed by a fuse clear failure. These 

electrical interactions are shown in Figure 2-31. In two other tests, water spray showed 

marginal effects on the cable electrical response. In one case, an induced voltage had built 

upon the spare conductor. When water spray was initiated, the induced voltage was rapidly 

lost. In the other case, very minimal current spikes (~0.05 amps) were observed in the 1/C 

cables, coincident with water application. The reader is encouraged to refer to the EPRI test 

report for more information. 

Time (s)

4500 4520 4540 4560 4580 4600 4620 4640 4660

Voltage (V)

-20

0

20

40

60

80

100

120

140

7/C Wire #1 

7/C Wire #2 

7/C Wire #4 

7/C Wire #5 

7/C Wire #7 

Application of Water
 

2-30 

Figure 2-31. NEI/EPRI test 10 voltage response following water spray 

The CAROLFIRE intermediate-scale tests used the water sprinkler in five tests (IT5, IT6, IT9, 

IT10, IT13). In all of these tests, the only cable types operating at the time of manual sprinkler 

activation were the Silicone Rubber or Vita-Link cables. In one instance, the sprinkler activation 

caused an SR cable to fail in a manner that resulted in a spurious operation. All other cables 

exposed to the water spray were connected to the insulation resistance measurement system. 

Of those seven cables, six resulted in a short circuit of less than 1,000 ohms5

. A single cable 

experienced a short circuit of less than 1,000 ohms, followed momentarily by some insulation 

resistance recovery above 1,000 ohms. 

Another complicating matter for evaluating water spray effects on cable response is that water 

suppression was applied near the end of the testing, and many of the circuits had already 

experienced fuse clear circuit failures. Although there is data available on the effects of water 

spray on thermally fragile cables, an understanding of the cables’ response to water at earlier 

stages of cable damage is unavailable at this time. 

 

 

5

 1,000 ohms was used as the insulation resistance threshold for failure of a cable. Insulation resistance measurements under 

1,000 ohms indicate that insulation is not capable of performing its design function. 

Time (s)

4400 4600 4800 5000 5200 5400 5600 5800

Voltage (V)

0

20

40

60

80

100

120

140

1/C Wire #1 

1/C Wire #2 

1/C Wire #3 

Water Applied
 

2-31 

2.15 AC Circuit Concurrence of Hot Short-Induced Spurious 

Operations 

Concurrence of hot short-induced spurious operations, as discussed in this report, occurs when 

more than one circuit (or cable) experiences individual spurious operations at the same time 

(i.e., concurrence). The AC test circuit configurations eliminated the possibility of a single cable 

causing multiple concurrent hot short-induced spurious operations. Thus, when reviewing the 

test results, two cables must experience a hot short-induced spurious operation at the same 

time to be considered concurrent. 

In all of the AC testing to date, the concurrence of spurious operations or hot shorts has not 

been observed within any individual test. In some cases, the concurrence between two circuits 

was missed by only a few seconds, but, given the strict definition of concurrent hot shortinduced spurious operations, this phenomenon was not observed in any AC circuit testing. 

There are several reasons that this phenomenon was not observed in testing. First, only a 

limited number of cables/circuits can be instrumented electrically during each test. The 

NRC/SNL small-scale radiant testing was limited to two electrically instrumented cables per test, 

while the larger scale testing (both industry- and NRC-sponsored) was limited to four surrogate 

AC MOV circuits for the AC testing. Secondly, the exposure conditions for the majority of the 

test were fairly intense, as the tests were designed to cause failure within 10-30 minutes for a 

risk-significant scenario. These intense exposures resulted in the cables quickly cascading 

through failure modes, as well as shorter spurious operation durations. Thirdly, a variety of 

cable types were tested (especially in the NRC/SNL testing), and each cable type has a unique 

thermal failure threshold; thus, even with fairly uniform exposure conditions for multiple cables, 

the failure times may never align in the testing because of differing cable thermal failure 

thresholds. Lastly, the larger scale testing allowed for a variety of thermal exposure conditions 

due to the locations of the cables relative to the heat source and their locations within a tray 

loaded with cables. For instance, a cable located on the bottom row of cables in an open 

ladder-back cable tray in a fire plume will be exposed to more intense thermal conditions than a 

cable in the same cable tray, but insulated from the fire conditions by other cables. 

During a PIRT panel meeting, it was suggested that the NRC/SNL tests could be combined 

based on exposure location in the intermediate-scale test apparatus to evaluate their likelihood 

of concurrence. As the thermal exposures were kept fairly constant among the NRC/SNL 

intermediate-scale tests (~200kW), this concept was explored. 

To complete this comparison, the intermediate-scale test data from CAROLFIRE and the 

intermediate-scale AC test data from DESIREE-FIRE were combined and separated by 

location. As shown in Figure 2-32, the locations were labeled differently between projects, so 

care was taken to ensure that labeling differences did not lead to binning errors. Symmetrical 

cable locations were grouped together as one location because of identical exposure conditions. 

For example, in the CAROLFIRE configuration in Figure 2-32(a), locations E and G were 

grouped together, as well as locations C and E of the DESIREE-FIRE configuration in Figure 2-

32(b). However, locations C and F of CAROLFIRE and locations B and D of DESIREE-FIRE 

were not grouped together because the plume transition zone near the top location (F in 

CAROLFIRE, D in DESIREE-FIRE) likely has different exposure conditions than the location 

directly below. Trays grouped by location would be exposed to the same fire conditions, heat 

release rate, and location relative to the wall. The data from all AC NRC tests was then 

analyzed to find times when multiple hot short-induced spurious operations occurred in the 
 

2-32 

same physical location at the same time (i.e., concurrence). The data was also processed to 

account for the electrical and mechanical interlocks that would typically be used in NPP 

applications, but were not used during testing. For instance, the MOV starters have two active 

targets that, if energized by a fire-induced hot short, would be classified as hot-short induced 

spurious operations by the testing protocol. In reality, however, only one MOV contactor can be 

energized at a time. Thus, the data was post-processed to represent circuit response in NPP 

applications where the interlocks would be used. 

(a) (b) 

Figure 2-32. (a) CAROLFIRE and (b) DESIREE-FIRE intermediate-scale exposure location 

designation 

Analyzing the data in this manner confirms that concurrent hot short-induced spurious 

operations were observed in CAROLFIRE/DESIREE-FIRE location A and CAROLFIRE location 

G/E (DESIREE-FIRE location C/E), “upper hot gas layer,” when the individual test data was 

grouped together. Conductors C5 and C6 are the active targets in the AC MOV circuits, which 

represent spurious operations/hot short targets. The draft version of this report contained 

concurrence of conductors C4 and C8, which are the passive targets and represent only hot 

short targets. A public comment noted that the inclusion of the hot short data made the results 

difficult to interpret and provided little value in evaluating multiple spurious operations. As such, 

the data for conductors C4 and C8 has been removed from the plots. 

At location A, two sets of concurrence were identified, as shown in Figure 2-33 and Figure 2-34. 

The blue diamonds in these figures indicate the start of a hot short-induced spurious operation, 

the red squares indicate the end, and the line between them represents the duration. A 

concurrence occurs when hot shorts within different cables have overlapping times. The 

information on the horizontal axis indicates: 

 test series (C = CAROLFIRE), 

 testing scale (IT = Intermediate, P = Penlight), 

 test number, 

 circuit number (CK#), and 

 the conductor that experienced the hot short (C#). 
 

2-33 

Figure 2-33. Concurrent hot shorts - Location A - 4 cables 

Figure 2-33 shows the first set of concurrences to be identified, which included four cables, 

none of which were the same cable type (XLPO/XLPO6

, EPR/CPE, TEF/TEF, and XLPE/PVC). 

The data set representing location A consisted of 25 test cables, which resulted in 17 spurious 

operations. Of the 17 operations involving the four cables, there were 10 instances where two 

cables experienced hot short-induced spurious operations concurrently. Five of these 10 

instances involved three cables. Concurrences that only involve spurious operation targets are 

identified in Table 2-31, along with the durations of these concurrences. In this table, the test 

circuits are identified on the vertical and horizontal axes, and any concurrences are identified by 

a number that represents the duration (in seconds) of the concurrence. This table also presents 

the start and stop times for the individual circuit spurious operations at the bottom of the table. 

In Table 2-31, for example, a value of 2.6 in the top row indicates that test “C-IT-6-CK4-C5” and 

test “C-IT-7-CK2-C5” experienced a concurrent spurious operation for 2.6 seconds. This value 

can be confirmed by looking at the individual circuit spurious operation start and stop times: “CIT-6-CK4-C5” experienced a spurious operation starting at 268.8 seconds and ending at 272.8 

seconds, while “C-IT-7-CK2-C5” experienced a spurious operation starting at 250.4 seconds 

and ending at 271.4 seconds. Thus, from 268.8 to 271.4 seconds, both circuits experienced 

spurious operations. It should also be pointed out that the table is presented such that the 

values to the right of the diagonal shaded boxes mirror the values to the left of the diagonal 

shaded boxes. The last column in the table presents the number of cables involved in 

concurrent operations. For instance, the top row indicates that three cables were involved in 

concurrent spurious operations (SOs). These three cables were identified as “C-IT-6-CK4-C5,” 

“C-IT-7-CK2-C5,” and “C-IT-11-CK4-C6.” 

 

 

6

 A typical convention for identifying a cable’s insulation and jacket materials is to write the insulation material first, followed by the 

jacket material. For example, XLPE/PVC is a cross-link polyethylene (XLPE) insulated cable with a polyvinyl chloride (PVC) jacket. 

220.0

230.0

240.0

250.0

260.0

270.0

280.0

Time (s)

start

stop
 

2-34 

Table 2-31. Concurrent spurious operation durations – test Location A 

(concurrence time shown in seconds) 

Test ID

Test ID

C-IT-6-CK4-C5c-IT-6-CK4-C6C-IT-7-CK2-C5C-IT-7-CK2-C6C-IT-10-CK3-C5C-IT-11-CK4-C5C-IT-11-CK4-C6C-IT-11-CK4-C5C-IT-11-CK4-C6# of concurrent cable SOs

C-IT-6-CK4-C5 - 2.6 - - - - - 4 3

C-IT-6-CK4-C6 - 4.8 - - - - - 4.8 3

C-IT-7-CK2-C5 2.6 4.8 - - 2.8 1 2.8 10.8 3

C-IT-7-CK2-C6 - - - 7.8 7.8 - - - 3

C-IT-10-CK3-C5 - - - 7.8 - - - - 2

C-IT-11-CK4-C5 - - 2.8 7.8 - - - - 2

C-IT-11-CK4-C6 - - 1 - - - - - 2

C-IT-11-CK4-C5 - - 2.8 - - - - - 2

C-IT-11-CK4-C6 4 4.8 10.8 - - - - - 3

Start Time 268.8 264.0 250.4 227.2 225.0 242.6 253.2 254.2 260.6

Stop Time 272.8 268.8 271.4 250.4 235.0 253.2 254.2 257.0 276.0

Duration 4.0 4.8 21.0 23.2 10.0 10.6 1.0 2.8 15.4

Figure 2-34 presents the second set of concurrences that occurred in location A. Here, again, 

different cable types were involved (XLPE/PVC and PE/PVC). There is only one instance in 

which multiple spurious operations occurred concurrently. Here circuit three of Test 7 

experiences a spurious operation at the same time as circuit two of Test 8. 

Figure 2-34. Concurrent hot shorts - Location A - 2 cables 

375

380

385

390

395

400

405

410

415

C‐IT‐7‐CK3 c5 C‐IT‐8‐CK2 c5

Time (s)

start

stop
 

2-35 

The other instance in which concurrent hot shorting was identified in this analysis was in the 

upper hot gas layer exposure locations (CAROLFIRE location G/E, DESIREE-FIRE location 

C/E). In these locations the data represents 20 test cables. Of these 20 cases, 12 spurious 

operations occurred, with 14 instances of concurrence. The only set of concurrences included 

four cables, of which three were of the same construction (PE/PVC) and the other was 

PVC/PVC. All were of the thermoplastic polymer variety. Figure 2-35 presents a plot of the hot 

short-induced spurious operation durations, and Table 2-32 provides a listing of the circuits 

involved in spurious operation concurrences and associated durations. The durations of these 

concurrences are longer than those in Location A, likely due to the difference in thermal 

exposure conditions. 

Figure 2-35. Concurrent hot shorts - upper hot gas layer - 4 cables 

 

625

675

725

775

825

875

925

975

1025

1075

1125

C‐IT‐11‐CK2 c5

C‐IT‐12‐CK2 c6

C‐IT‐9‐CK4 c5

C‐IT‐9‐CK4 c6

C‐IT‐10‐CK1 c5

C‐IT‐10‐CK1 c6

C‐IT‐10‐CK1 c6

C‐IT‐10‐CK1 c6

Time (s)

stop

start

(0.8s)
 

2-36 

Table 2-32. Concurrent spurious operations – upper hot gas layer Test ID C-IT-11-CK2-C5 C-IT-9-CK4-C5 C-IT-12-CK2-C6 C-IT9-CK4-C6 C-IT10-CK1-C6 C-IT-10-CK1-C6 C-IT-10-CK1-C5 C-IT-10-CK1-C6 # of concurrent cable SO’s

Test ID

C-IT-11-CK2-C5 38.2 97.4 47.4 0.8 31 10.8 - 4

C-IT-9-CK4-C5 38.2 25.8 - - - - - 3

C-IT-12-CK2-C6 97.4 25.8 47.4 0.8 53 81.4 46.4 4

C-IT-9-CK4-C6 47.4 - 47.4 20.4 6.8 - - 4

C-IT-10-CK1-C6 0.8 - 0.8 20.4 - - - 4

C-IT-10-CK1-C5 31 - 53 6.8 - - - 4

C-IT-10-CK1-C6 10.8 - 81.4 - - - - 3

C-IT-10-CK1-C6 - - 46.4 - - - - 2

Start Time (s) 658.0 776.2 788.6 814.4 841.4 855.0 875.2 910.2

Stop Time (s) 886.0 814.4 1084.8 861.8 842.2 908.0 956.6 956.6

Duration (s) 228.0 38.2 296.2 47.4 0.8 62.0 81.4 46.4

The rest of the locations showed no instances of concurrence. Four tests were run using 

CAROLFIRE location B/D, ten tests were run using CAROLFIRE location C (DESIREE-FIRE 

location B), and fourteen tests were run using CAROLFIRE location F (DESIREE-FIRE location 

D). None of these tests produced any instances of hot short concurrences. Section 4.15 

provides the concurrent hot shorting for the dc circuits tested in the DESIREE-FIRE project. 
 

3-1 

3. INTER-CABLE – ALTERNATING CURRENT CIRCUITS 

The evaluation of circuit failure results becomes increasingly complex when more than one 

cable is involved in the electrical failure. Cable-to-cable interactions are referred to as “intercable,” and, for an inter-cable hot short to occur, a source conductor in one cable must come 

into electrical contact with a target conductor in a different cable. 

The number of recorded cable-to-cable interactions from the AC tests is significantly lower than 

the number of intra-cable interactions (within a cable). Thus, testing to date has provided only a 

small pool of data from which to draw conclusions about the effects of parameters on the 

likelihood and duration of these inter-cable interactions. Even with these limitations, there are 

some conclusions that can be drawn from the data. These conclusions are presented below 

and may provide some insight into the influencing factors of inter-cable electrical interactions. 

This section will not systematically evaluate parameter effects on the fire-induced circuit failure 

response, as was done in the previous section for the intra-cable evaluation. 

All of the major testing projects (Electric Power Research Institute/Nuclear Energy Institute 

(NEI/EPRI), Cable Response to Live Fire (CAROLFIRE), and Direct Current Electrical Shorting 

In Response to Exposure Fire (DESIREE-FIRE)) provide at least two test configurations to 

evaluate the occurrence of inter-cable failures. In most cases, the voltage and current 

measurements from the simulated circuit could be evaluated to determine whether any intercable interactions occurred. In addition, separate circuit configurations were used in all test 

programs to specifically focus on understanding, and, in some cases, stacking the odds to 

trigger inter-cable interaction. The following provides a description of how the tests were 

conducted and what results were achieved. 

Figure 3-1 provides an illustration of how the cables were oriented within a cable tray for the 

inter-cable tests during the NEI/EPRI program. Cables 1-3 were monitored for electrical 

response, with cables 1 and 3 containing both energized source conductors and target 

conductors, while cable 2 only contained target conductors. The target conductors were 

connected to burden resistors to simulate a load. The black cables in Figure 3-1 represent fill 

cables that were not monitored for electrical response, but were used as a buffer between the 

electrically monitored cables and the metallic cable tray. These fill cables likely reduced the 

likelihood of an energized source coming in contact with the ground plane and causing a fuse 

clear failure. 

Figure 3-1. NEI/EPRI inter-cable test tray fill 

Two NEI/EPRI tests used this configuration, and both tests showed similar results. The voltage 

and current readings indicate that the cables failed internally prior to any external interactions 

between cables. Since this configuration didn’t represent system circuits used in plants, it is 
 

3-2 

difficult to determine whether or not inter-cable interactions would have caused hot shorts of 

sufficient quality to result in a component repositioning in an actual plant system. 

The CAROLFIRE inter-cable test set-up was slightly different in that all of the conductors in two 

multi-conductor cables were energized as sources and a third multi-conductor cable had all of 

its conductors connected to a motor starter contactor, a target. Thus, the CAROLFIRE circuit 

could detect inter-cable interactions, but was unable to recognize when conductors internal to 

the multi-conductor cables had failed. The CAROLFIRE inter-cable test set-up is shown in 

Figure 3-2. 

Figure 3-2. CAROLFIRE inter-cable test tray fill 

Twelve inter-cable circuit trials were used in a total of four intermediate-scale fire tests during 

CAROLFIRE. Three of these circuits were left ungrounded, resulting in no possibility for the 

circuit fuse to clear. Because of this configuration, hot shorts/spurious operations were 

inevitable, and, in all three instances, prolonged spurious operations did occur. Of the 

remaining nine test circuits, seven experienced fuse clear faults. The remaining two circuits, 

both from test IT-3, experienced some inter-cable induced voltages, although this was not 

sufficient to cause a spurious operation. The CAROLFIRE inter-cable failure data does not 

provide a strong basis for understanding the inter-cable shorting phenomenon. In actual fires 

involving energized control cables for safety significant systems, there is a competing factor 

between the conductors internal to the failing cable and any inter-cable interactions. It is 

unfortunate that the CAROLFIRE results could not provide more insights into this competitive 

factor. 

As discussed above, all three testing programs used surrogate motor-operated valve (MOV) 

circuits to monitor cable electrical response during a fire test. A review of this data can provide 

information on how the cable fails internally versus failing externally. However, before looking at 

this data, it is important to understand some of the differences between the NEI/EPRI and U.S. 

Nuclear Regulatory Commission/Sandia National Laboratories (NRC/SNL) test arrangements. 

First, the industry tests used a configuration in which a 7/C cable was surrounded by three 

individual 1/C insulated conductors (without jacketing), zip-tied to the 7/C cable. This 

configuration is shown in Figure 3-3. The 7/C cable contained source, target, spare, and neutral 

conductors, while the exterior single conductors were either an energized source or an active 

target. All energized conductors were powered by the same source (wall power or control 

power transformer (CPT)). It should be noted that this configuration is not commonly found in 

U.S. nuclear power plants (NPPs). If single conductor cables are used, they will typically have a 

protective jacket over the single conductor insulation. The NEI/EPRI testing simply used an 

unjacketed insulated conductor that was stripped from a multi-conductor cable. That said, the 

results are still valuable and may be considered more conservative in that this configuration may 
 

3-3 

increase the likelihood of inter-cable interactions because of the lack of jacket and the use of 

cable ties to keep the single conductors in close proximity to the 7/C cable. 

Figure 3-3. NEI/EPRI cable configuration 

The NEI/EPRI test results indicate that of the 17 test circuit device spurious operations that 

experienced inter-cable spurious operation(s), seven were between the 1/C cables. In four 

cases, the 7/C cable acted as a source to a 1/C cable target, and, in six cases, a 1/C cable 

energized a target conductor in a 7/C cable. Table 3-1 presents the results of the NEI/EPRI 

inter-cable results. 

Table 3-1. NEI/EPRI inter-cable failure characteristics 

Test ID Source Cable 

(#/C, wire, insulation)

Target Cable 

(#/C, wire, insulation) Duration (seconds) 

Test 3, Circuit 1, Device 3 1/C – S1 (TS) 1/C – S3 (TS) 6 

Test 4, Circuit 2, Device 3 1/C – S2 (TP) 1/C – S3 (TP) 66 

Test 4, Circuit 3, Device 3 1/C – S2 (TP) 1/C – S3 (TP) 342 

Test 4, Circuit 4, Device 1 1/C – S1&S2 (TP) 7/C – W5 (TP) 54 

Test 4, Circuit 4, Device 2 1/C – S1&S2 (TP) 7/C – W4 (TP) 12 

Test 4, Circuit 4, Device 3 7/C – W2 (TP) & 

1/C – S2 (TP) 1/C – S3 (TP) 318 

Test 6, Circuit 1, Device 1 1/C – S2 (TP) 7/C – W5 (TP) 192 

Test 6, Circuit 1, Device 2 1/C – S2 (TP) 7/C – W4 (TP) 282 

Test 6, Circuit 1, Device 3 1/C – S2 (TP) 1/C – S3 (TP) 492 

Test 6, Circuit 2, Device 3 7/C – W2 (TP) 1/C – S3 (TP) 606 

Test 8, Circuit 1, Device 3 1/C – S2 (TS) 1/C – S3 (TS) 18 

Test 9, Circuit 4, Device 3 1/C – S2 (TS) 1/C – S3 (TS) 6 

Test 10, Circuit 2, Device 3 1/C – S1 (TS) & 

7/C – W2 (TS) 1/C – S3 (TS) 804 

Test 10, Circuit 4, Device 3 1/C – S2 (TS) 1/C – S3 (TS) 486 

Test 12, Circuit 3, Device 3 7/C – W1 (TS) 1/C – S3 (TS) 12 

Test 17, Circuit 1, Device 1 1/C – S2 (TP) 7/C W5 (TP) 66 

Test 17, Circuit 1, Device 2 1/C – S2 (TP) 7/C W4 (TP) 66 

In the CAROLFIRE testing, multi-conductor cables were connected to individual surrogate 

circuit diagnostic units (SCDUs) and arranged in 3- or 6-cable triangular bundles. The results 

from the CAROLFIRE SCDU testing where inter-cable interactions were observed are shown in 
 

3-4 

Table 3-2. CAROLFIRE did not use NEI configuration. All inter-cable interactions were from 

adjacent cables. 

Table 3-2. CAROLFIRE AC inter-cable failure characteristics 

Test ID 

Source Cable 

(Circuit, Insulation)

Target Cable 

(Circuit, Insulation)

Duration 

(seconds) 

Test IP 4, Circuit 1* Circuit 2, TP 7/C – W6, TP 1 

Test IP 4, Circuit 3* Circuit 2, TP 7/C – W5 & W6, TP 1 

Test IP 4, Circuit 4 Circuit 2, TP 7/C – W6, TP 1 

Test 1, Circuit 4* Circuit 1, TS 7/C – W4 (HS), TS 1 

Test 7, Circuit 2* Circuit 3, TS 7/C – W4 (HS), TS 1 

Test 8, Circuit 2* Circuit 3, TS 7/C – W4 (HS), TP 44 

 * Indicates inter-cable interactions occurring after the circuit fuse cleared. 

In the CAROLFIRE project, the insulation resistance measurement system (IRMS) was used 

during Penlight radiant exposure tests and during the intermediate-scale testing. The IRMS can 

detect the onset of inter-cable shorting behavior, can measure the relative timing of inter-cable 

shorting versus both intra-cable shorting and shorts to the external ground, and can measure 

the duration of inter-cable shorts (i.e., how long an inter-cable conductor-to-conductor short 

remains independent of the external ground) [NUREG/CR-6931, V1]. 

The CAROLFIRE tests did detect some cases of inter-cable shorting between thermoset (TS) 

cables; however, only one of these cases involved a clear-cut case of a sustained inter-cable 

short circuit between two TS cables (IRMS in Test IT-1) that could have led to a spurious 

operation. In other cases, the interactions were secondary or tertiary failure modes for at least 

one of the two involved cables. However, the test data clearly showed that TS-to-TS 

interactions are plausible, although the likelihood of risk-relevant interactions appears to be low, 

especially in comparison to the likelihood of intra-cable interactions leading to spurious 

operation [NUREG/CR-6931]. 
 

4-1 

4. INTRA-CABLE – DIRECT CURRENT CIRCUITS 

All of the fire-induced DC circuit failure data and information available for the analysis 

documented in this report came from the U.S. Nuclear Regulatory Commission (NRC)–

sponsored Direct Current Electrical Shorting In Response to Exposure Fire (DESIREE-FIRE) 

project. A substantial amount of effort was required to convert the dc data into a usable format 

for this work. The formatting was handled by Sandia National Laboratories (SNL), and led to 

identification of several errors documented in the draft test report for the DESIREE-FIRE 

project. These errors were subsequently corrected in the final version of NUREG/CR-7100, 

“Direct Current Electrical Shorting In Response to Exposure Fire (DESIREE-FIRE): Test 

Results.” 

The only dc test data removed from the analysis were instances where the cable did not reach a 

failure point at the end of the test. The majority of these cases were for the Kerite cable testing, 

where it was important to stop the test prior to cable failure to evaluate the physical damage to 

the cable materials. Tests excluded from further analysis in this report included the following: 

 D-P-27-MOV1

 D-P-27-MOV2

 D-P-26-SOV1

 D-P-26-SOV2

 D-P-38-SOV1

 D-P-38-SOV2

 D-IT-P1-1-Vlv

 D-IT-P1-LargeCoil

Section 4.1 details the specific set points used to clean up the data and a brief description of the 

five dc circuits. The rest of the section provides failure mode likelihood and duration information 

based on specific parameters, as was done for the AC test data. 

4.1 DC Data Analysis Approach 

The analysis for the dc is discussed in this section. The data that was analyzed corresponds to 

the experiments performed under the DESIREE-FIRE testing program [5]. For the intra-cable 

experiments, there were five different circuit types (1-in Valve, Large Coil, motor-operated valve 

(MOV), solenoid-operated valve (SOV), and switchgear (SWGR)); the analysis for each will be 

discussed here in detail. 

The dc data required additional review and processing to ensure a consistent method of 

determining the specific failure points of concern. To accomplish this, threshold voltage levels 

were identified for specific conductors that corresponded with a specific failure mode. This 

information is presented below. These voltage levels were then used on the specific circuit data 

to generate state diagrams, which present a clear view of the circuit status, gleaned from the 

noisy data signals collected during testing. It was from these state diagrams that the failure 

mode timelines and duration information were imported into the database. Each circuit is 

discussed below, along with the criteria for evaluating each conductor for specific failure modes. 

4.1.1 1-inch valve control circuit 

The 1-inch valve circuit that was tested is shown below in Figure 4-1. As seen in the figure, 

seven conductors were monitored during the test. From these seven conductors, the electrical 

measurement data were analyzed based on the information displayed in Table 4-1 and Table 

4-2 for the penlight and intermediate-scale tests, respectively. There is a slight difference in the 

logic for the penlight and intermediate-scale tests, due to the fact that the switches (normally 
 

4-2 

open (NO) and normally closed (NC) contacts) on the G and R conductors had worn out during 

the penlight tests. Thus, the switches were both physically wired closed for all the intermediatescale tests. This data processing effort has taken this into account. 

For the 1-inch valve circuit, conductor S was the hot short (HS)/spurious operation (SA) target, 

and conductors G and R were the HS targets for the penlight tests. For intermediate-scale 

tests, conductor S was the HS/SA target, and conductors G and R were not used for fuse 

status. The SP conductor was a non-energized target that could either short to the positive or 

negative sides of the circuit for all tests. The other conductors were used to determine whether 

a fuse had blown. Once the positive or negative fuse had blown, the durations for the HS 

and/or HS/SA were assumed to be complete. 

Figure 4-1. Line drawing of the DC-SIM panel layout for a 1-inch coil circuit 

Note: The NO contact on the “R” conductors and the NC contact on the “G” conductor were 

wired closed for all intermediate-scale tests. 

 

P

G

R

S

N1

N2

SP

A

A

A

A

A

V

V

V

V

V

V

V

5A

1-INCH

COIL

1750

1750

+

-125 VDC

DCCCS CABLE UNDER TEST FROM DISTRIBUTION 

CIRCUIT BREAKER

FUSE BLOCK

5A NC

NO

A
 

4-3 

Table 4-1. Analysis logic for 1-in valve Penlight tests 

Conductor 

Spurious 

Operation 

(Status 2) 

Hot Short 

(Status 1) 

Normal 

(Status 0) 

Fuse Clear or Spare 

Conductor Short 

(Status -1) 

P VPModified>100V VPModified<10V 

[Positive Fuse Clear]

G 

S=2 & 

VGModified>100V 

[Hot Short]

VGModified>100V 

R 

S≠2 & 

VRModified>100V 

[Hot Short]

VRModified<10V 

S 

VSModified>48 V

[Hot Short-Induced 

Spurious Operation]

VSModified<48 V

N1 VN1Modified<10V VN1Modified>100V 

[Negative Fuse Clear]

N2 VN2Modified<10V VN2Modified>100V 

[Negative Fuse Clear]

SP VSp Raw >30V 

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V 

[Short to Negative]

Raw – voltage reference is ground Modified – voltage level is approximately battery negative 

Table 4-2. Analysis logic for 1-in valve intermediate-scale tests 

Conductor 

Spurious 

Operation 

(Status 2) 

Hot Short 

(Status 1) 

Normal 

(Status 0)

Fuse Clear or Spare 

Conductor Short

(Status - 1)

P VPModified>100V VPModified<10V

[Positive Fuse Clear]

G VGModified>100V VGModified<10V 

[Positive Fuse Clear]

R VRModified>100V VRModified<10V 

[Positive Fuse Clear]

S 

VSModified>48 V 

[Hot Short-Induced 

Spurious Operation]

 VSModified<48 V 

N1 VN1Modified<10V VN1Modified>100V 

[Negative Fuse Clear]

N2 VN2Modified<10V VN2Modified>100V 

[Negative Fuse Clear]

SP VSp Raw >30V 

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V 

[Short to Negative]

 
 

4-4 

4.1.2 Large coil control circuit 

The large coil circuit that was tested is shown below in Figure 4-2. As seen in the figure, there 

are seven conductors that were monitored during the test. For those seven conductors, the 

electrical measurement data was analyzed based on the information displayed in Table 4-3 for 

all tests. For this, circuit conductor S was the HS/SA target, and conductor R was an HS target 

for all tests. The SP conductor was a non-energized target that could either short to the positive 

or negative sides of the circuit for all tests. The other conductors were used to determine 

whether a fuse had blown. Once the positive or negative fuse had blown, the durations for the 

HS and/or HS/SA were assumed to be complete. 

Figure 4-2. Line drawing for the DC large coil circuit 

 

P

G

R

S

N1

N2

SP

A

A

A

A

A

V

V

V

V

V

V

V

10A

LARGE

COIL

1750

1750

+

-125 VDC

DCCCS CABLE UNDER TEST FROM DISTRIBUTION 

CIRCUIT BREAKER

FUSE BLOCK

10A
 

4-5 

Table 4-3. Analysis logic for large coil Penlight and intermediate-scale tests 

Conductor 

Spurious 

Operation 

(Status 2) 

Hot Short 

(Status 1) 

Normal 

(Status 0) 

Fuse Clear or Spare 

Conductor Short 

(Status - 1) 

P VPModified>100V VPModified<10V 

[Positive Fuse Clear]

G VGModified>100V VGModified<10V 

[Positive Fuse Clear]

R VRModified>60V 

[Hot Short]

VRModified<60V 

S 

VSModified>60 V

[Hot ShortInduced Spurious 

Operation]

VSModified<60 V

N1 VN1Modified<10V VN1Modified>100V 

[Negative Fuse Clear]

N2 VN2Modified<10V VN2Modified>100V 

[Negative Fuse Clear]

SP VSp Raw >30V 

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V 

[Short to Negative]

4.1.3 dc MOV control circuit 

The MOV circuit that was tested is shown below in Figure 4-3. As seen in the figure, there are 

seven conductors that were monitored during the test. Those seven conductors’ electrical 

measurement data was analyzed based on the information displayed in Table 4-4 for all tests. 

Each test had two MOV circuits designated as MOV1 and MOV2. Conductors YO1 and YC1 for 

MOV1 were HS/SA and HS targets. With MOV1, there were mechanical interlocks that caused 

YC1 to lock out if YO1 was engaged; thus, if YO1 had an HS/SA while YC1 got an HS, YC1 

would not engage. Conductors G and R were HS targets. The SP conductor was a nonenergized target that could short to either the positive or the negative side of the circuit for all 

tests. The other conductors were used to determine whether a fuse had blown. Once the 

positive or negative fuse had blown, the durations for the HS and/or HS/SA were assumed to be 

complete. 
 

4-6 

Figure 4-3. Line drawing for DC MOV circuit 

Table 4-4. Analysis logic for MOV Penlight and intermediate-scale tests 

Conductor 

Spurious 

Operation 

(Status 2) 

Hot Short 

(Status 1) 

Normal 

(Status 0) 

Fuse Clear or 

Spare 

Conductor 

Short 

(Status - 1) 

G 

 VYO1Modified>100V 

& VGModified>100V 

VGModified>100V 

N 

 VNModified<10V VNModified>100V 

[Negative Fuse 

Clear]

P VPModified>100V VPModified<10V 

[Positive Fuse Clear]

R VYO1Modified>100V 

& VRModified>100V 

VRModified>100V 

YC1 (MOV1) VYC1Modified>89.3V 

& IYC1>0.06A 

YO1=2 & 

VYC1Modified>89.3V 

VYC1Modified<10V & 

VYO1Modified<10V 

YC1 (MOV2) VYC1Modified>50.7V 

& YO1 ≠ 2 

YO1=2 & 

VYC1Modified>50.7V 

VYC1Modified<10V & 

VYO1Modified<10V 

YO1 (MOV1) VYO1Modified>29.0V 

& IYO1>0.06A 

YC1=2 & 

VYO1Modified>29.0V 

VYC1Modified<10V & 

VYO1Modified<10V 

YO1 (MOV2) VYO1Modified>50.7V 

& IYO1>0.06A 

YC1=2 & 

VYO1Modified>50.7V 

VYC1Modified<10V & 

VYO1Modified<10V 

SP VSp Raw >30V 

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V 

[Short to Negative]

G

P

YC1

YO1

R

N

SP

A

A

A

A

V

V

V

V

V

V

V

NC

NC

1750

+

-125 VDC

O

NO

NC

C

A

A

1750

DCCCS CABLE UNDER TEST FROM DISTRIBUTION 

CIRCUIT BREAKER

FUSE BLOCK

10A

10A

A

A

B

C
 

4-7 

4.1.4 Small pilot SOV control circuit 

The SOV circuit that was tested is shown below in Figure 4-4. As seen in the figure, there are 

seven conductors that were monitored during the test. Those seven conductors’ electrical 

measurement data was analyzed based on the information displayed in Table 4-5 for all tests. 

For this circuit conductor, S2 was the HS/SA target, and conductor R was an HS target for all 

tests. The SP conductor was a non-energized target that could short to either the positive or the 

negative side of the circuit for all tests. The other conductors were used to determine whether a 

fuse had blown. Once the positive or negative fuse had blown, the durations for the HS and/or 

HS/SA were assumed to be complete. 

Figure 4-4. Line drawing for DC SOV circuit 

 

S1

G

R

S2

N

SP

A P

A

A

A

A

V

V

V

V

V

V

V

5A

5A

SOV

1750

1750

+

-125 VDC

DCCCS CABLE UNDER TEST

FROM DISTRIBUTION 

CIRCUIT BREAKER

FUSE BLOCK
 

4-8 

Table 4-5. Analysis logic for SOV penlight and intermediate-scale tests 

Conductor 

Spurious 

Operation 

(Status 2) 

Hot Short 

(Status 1) 

Normal 

(Status 0) 

Fuse Clear or 

Spare 

Conductor 

Short 

(Status - 1) 

P,G,S1 VModified>100V VModified<10V 

[Positive Fuse Clear]

N VNModified<10V VNModified>100V 

[Negative Fuse 

Clear]

R VRModified>60V 

[Hot Short]

VRModified<60V 

S2 VS2Modified>56.05V VS2Modified<60V 

SP VSp Raw >30V 

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V 

[Short to Negative]

4.1.5 Medium-voltage circuit breaker dc control circuit 

There were two different medium-voltage circuit breakers (SWGR) circuits used during 

DESIREE testing. As mentioned in the report, there was a problem with the first breaker during 

intermediate-scale Test #8. The first SWGR circuit is displayed in Figure 4-5, with the 

instrumentation’s data analysis displayed in Table 4-6. The internal manufacturer wired this 

SWGR in reverse, which is depicted in Figure 4-5. The wiring did not affect the functionality of 

the SWGR, the only difference being that the red light was not energized. Table 4-6 has a 

different set-up than the tables for the previous circuits analyzed. The SWGR circuits were 

more complex to analyze, resulting in the different format. Conductors G, T, and C1 were hot 

short targets, while T and C1 were used to determine whether the breaker had tripped or closed 

(HS/SA target). The duration for the HS/SA was never more than one time step. Conductor R 

was treated as a energized spare. The two SP conductors were non-energized targets that 

could short to either the positive or the negative side of the circuit for all tests. The other 

conductors were used to determine whether a fuse had blown. Once the positive or negative 

fuse had blown, the durations for the HS and/or HS/SA were assumed to be complete. The 

second SWGR circuit is displayed in Figure 4-6, with the instrumentation’s data analysis 

displayed in Table 4-7. The only difference with this SWGR in terms of the data analysis logic 

was that R was an HS target and not an energized spare. It is also noted in Table 4-6 and 

Table 4-7 that there were two cables tested for each SWGR test. One cable was connected to 

the close circuit, and the other was connected to the trip circuit. The conductors associated with 

each are identified in the tables. 
 

4-9 

Figure 4-5. Line drawing for DC SWGR 1 circuit 
 

4-10 

Figure 4-6. Line drawing for DC SWGR 2 circuit 

 
 

4-11 

Table 4-6. Analysis logic for SWGR Penlight tests and intermediate-scale 

 

Conductor Logic Statements (adjusted 

voltage used) Notes 

Close Cable 

C1 If(VC1<10V, “EtC”, if(45V< VC1<75V, 

“Floating,” if VC1>100V, “HS,” “HS or 

Floating”)) 

EtC means enable to close. If a 

fuse clears on the close circuit, 

this conductor state becomes 

Not_EtC (not enable to close). 

HS means hot short. 

PC If(VP>100V, “Normal,” “Pos. Fuse 

Blown”) 

N1 If(VN1<10V, “Normal,” “Neg. Fuse 

Blown”) 

Trip Cable 

G If(VG<10V, “G_On”, “G_Off”) If the green light is off and T is 

floating, then there is a hot 

short. 

R If(VR<60V, “HS,” “Normal”) Internal wiring was reversed; R 

was treated as a hot spare. 

PT If(VPT>100V, “Normal,” “Pos. Fuse 

Blown”) 

N2 If(VN2<10V, “Normal,” “Neg. Fuse 

Blown”)

T If(VT<10V, “EtT”, if( VT>100V, “HS,” 

“Floating”)) 

EtT means enable to trip. If a 

fuse clears on the trip circuit, this 

conductor state becomes 

Not_EtT (not enable to trip). 

SP1 If(VS1<30V, “Short_to_-,” If(VS1>90V, 

“Short_to_+,” “Floating/Normal”)) 

SP2 If(VS2<30V, “Short_to_-,” If(VS1>90V, 

“Short_to_+,” “Floating/Normal”)) 

 Breaker Position Breaker position was determined by 

analysis of the conductors’ behavior, 

as well as of the experimental field 

notes. This was necessary because 

of the interdependencies between 

the trip and close circuits. 

 
 

4-12 

Table 4-7. Analysis logic for SWGR intermediate scale tests 1, 3, 5, 6, 7, 8, 9, 10, Cont. 

1, and Cont. 2 

Conductor If Statements (adjusted voltage 

used) Notes 

Close Cable 

C1 If(VC1<10V, “EtC,” if(45V< 

VC1<75V, “Floating,” if VC1>100V, 

“HS,” “HS or Floating”)) 

EtC means enable to close. If a 

fuse clears on the close circuit, this 

conductor state becomes Not_EtC 

(not enable to close). HS means 

hot short. 

PC If(VP>100V, “Normal,” “Pos. Fuse 

Blown”) 

N1 If(VN1<10V, “Normal,” “Neg. Fuse 

Blown”) 

Trip Cable 

G If(VG<10V, “G_On,” “G_Off”) If the green light is off and T is 

floating, then there is a hot short. 

R If(VR<10V, “R_On,” “R_Off”) If the red light is on and T is floating, 

then there is a hot short. 

PT If(VPT>100V, “Normal,” “Pos. Fuse 

Blown”) 

N2 If(VN2<10V, “Normal,” “Neg. Fuse 

Blown”)

T If(VT<10V, “EtT,” if( VT>100V, 

“HS,” “Floating”)) 

EtT means enable to trip. If a fuse 

clears on the trip circuit, this 

conductor state becomes Not_EtT 

(not enable to trip). 

SP1 If(VS1<30V, “Short_to_-,” 

If(VS1>90V, “Short_to_+,” 

“Floating/Normal”)) 

SP2 If(VS2<30V, “Short_to_-,” 

If(VS1>90V, “Short_to_+,” 

“Floating/Normal”)) 

 Breaker Position Breaker position was determined 

by analysis of the conductors’ 

behavior, as well as of the 

experimental field notes. This 

was necessary because of the 

interdependencies between the 

trip and close circuits. 

 
 

4-13 

4.2 Conductor Count 

The test data used to evaluate the effect cable conductor count has on failure modes included 

multi-conductor cables with 2-6, 7-9, and 10-15 conductors. Table 4-8 provides summaries of 

the dc test data, separated into these three conductor count ranges. These ranges were 

suggested by the electrical Phenomena Identification and Ranking Table (PIRT) expert panel. 

Figure 4-7 provides a graphical representation of this data. 

Table 4-8. Conductor count, global approach, DC tests 

Global Approach 1/C 2-6/C 7-9/C 10-15/C >15/C 

Fuse Clear - 1 22 1 - 

Hot Short - 4 142 5 - 

Spurious Operation - 3 89 2 - 

HS/SO Possible - 5 164 6 - 

Figure 4-7. Conductor count column plot, global approach, DC tests 

These fire-induced cable failure mode plots provide little insight into how conductor count affects 

the likelihood of any one failure mode. This is partially due to the abundance of conductor count 

data available for 7/C cables, as well as the fact that the data shows consistent results among 

the three bins even with minimal data for the other two bins. Table 4-9 and Figure 4-8 provide 

dc test data for hot short and spurious operation durations, separated by these same conductor 

count ranges. 

 

1/C 2-6/C 7-9/C 10-15/C >15/C

Count

0

50

100

150

200

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

54%

87%

20%

80%

60%

100%

100%

13%

17%

83%

33%
 

4-14 

Table 4-9. Conductor count, duration data, DC tests 

Hot Short Spurious Operation 

1/C 2-6/C 7-9/C 10-15/C >15/C 1/C 2-6/C 7-9/C 10-15/C >15/C 

q1 - 101.5 14 18 - - 203.5 10 105 - 

min - 1 1 7 - - 193 1 105 - 

median - 193 47 63 - - 214 31 105 - 

max - 1082 8545 2873 - - 235 6417 105 - 

q3 - 265 254 242 - - 224 80 105 - 

mean - 302 409 471 - - 214 195 105 - 

Figure 4-8. Conductor count box plot, duration, DC tests 

4.3 Thermal Exposure Conditions 

This section presents the dc data evaluated by thermal exposure conditions’ effects on fireinduced failure modes. The thermal exposure conditions include flame, hot gas layer (HGL), 

plume, and radiant conditions. The flame, hot gas layer, and plume data are from the 

intermediate-scale testing, while the radiant test data are from the Penlight (small-scale) radiant 

testing. These thermal exposure conditions are discussed in more detail in Section 2.3. Table 

4-10 provides summaries of the dc test data failure mode evaluation by thermal exposure 

conditions, while Figure 4-9 presents this information graphically. 

 

0

50

100

150

200

250

300

350

400

450

500

2‐6/C 7‐9/C 10‐15/C 2‐6/C 7‐9/C 10‐15/C

Hot Short SpuriousOperation

q1

min

median

max

q3

1082s 8545s 2873s 6417s
 

4-15 

Table 4-10. Thermal exposure conditions, global approach, DC tests 

Global Approach Flame Plume HGL Radiant 

Fuse Clear 9 3 5 7 

Hot Short 43 25 13 70 

Spurious Operation 26 11 5 52 

HS/SO Possible 52 28 18 77 

Figure 4-9. Thermal exposure conditions column plot, global approach, DC tests 

The failure mode data indicates that the HGL exposure data is an outlier compared to the other 

exposure conditions. The HGL test data shows a lower likelihood of experiencing a spurious 

operation (28%) and a higher chance of having the circuit protective fusing clear (28%). It is 

interesting to note that it was believed that the Penlight radiant exposure simulated an HGL 

exposure, due to the high radiative heat transfer that occurs in a sooty HGL. This assumption 

may be accurate for comparisons of the thermal conditions, but the failure mode data does not 

show this relation. This data tends to indicate that fire-induced cable failure modes do not follow 

this same logic, and, more specifically, that the radiant failure mode likelihood data is similar to 

the plume and flame exposure condition failure mode results. This may be due to the high 

intensity of the radiant exposure. 

Table 4-11 and Figure 4-10 present the dc test’s hot short and spurious operation duration data, 

separated by thermal exposure conditions. The data shows a weak trend (based on the median 

of the data) for shorter duration hot shorts in flame and radiant exposures as opposed to HGL 

exposure, with the plume exposure durations lying somewhere in the middle. There is a similar 

trend in the AC test data results (Section 2.3). 

 

Flame Plume HGL Radiant

Count

0

20

40

60

80

100

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

39%

89%

11%

100%

50%

83%

17%

100%

28%

78%

28%

100%

68%

91%

9%
 

4-16 

Table 4-11. Thermal exposure conditions, duration data, DC tests 

 Hot Short Spurious Operation 

 Flame Plum

e 

HGL Radiant Flame Plume HGL Radiant 

q1 16.4 27.5 57.95 12 13 10.7 34.8 10 

min 2 2 7 1 3 3.4 26 1 

median 40 154 115 43 34 20.6 70 31 

max 2873 2590 4871 8545 124 198.4 115 6417 

q3 119.2 740 714 210 66.7 60.5 90.0 98.3 

mean 61.6 468.7 587.8 428.4 45.1 146.6 111.9 301.0 

Figure 4-10. Thermal exposure conditions box plot, duration, DC tests 

4.4 Raceway Routing 

The two raceway routing configurations used during testing were open ladder-back cable trays 

and rigid steel conduit configurations that were tested in DESIREE-FIRE. The dominant use of 

ladder-back cable tray configurations makes it difficult to determine the effects that these 

configurations have on cable failure. A summary of these results is shown in Table 4-12 and 

Figure 4-11. The data evaluated shows no difference in failure mode between cable tray and 

conduit configurations for dc circuits. 

Table 4-12. Raceway routing, global approach, DC tests 

Global Approach Conduit Tray 

Fuse Clear 4 20 

Hot Short 18 133 

Spurious Operation 13 81 

HS/SO Possible 22 153 

0

100

200

300

400

500

600

700

800

Flame Plume HGL Radiant Flame Plume HGL Radiant

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

2873s 2590s 8545s 4871s 6417s
 

4-17 

Figure 4-11. Raceway routing column plot, global approach, DC tests 

Table 4-13 and Figure 4-12 present the data that was evaluated for raceway routing against hot 

short and spurious operation durations. The interquartile range, shown in Figure 4-12, is wider 

for the hot short durations than for the spurious operation durations, with the median for hot 

shorts being about 13-17 seconds longer. 

Table 4-13. Raceway routing, duration data, DC data 

 Hot Short Spurious Operation 

 Conduit Tray Conduit Tray 

q1 14.1 16.0 16.4 10.0 

min 1 1 3 1 

median 56 50 39 33.5 

max 2804 8545 431 6417 

q3 278.5 255 87 90 

mean 405.8 408.8 80.8 212.0 

Figure 4-12. Raceway routing box plot, duration, DC tests 

CONDUIT TRAY

Count

0

20

40

60

80

100

120

140

160

180

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

14%

86% 68% 13%

87%

53%

0

100

200

300

400

500

CONDUIT TRAY CONDUIT TRAY

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

2804s 6417s 8545s
 

4-18 

4.5 Cable Orientation 

DESIREE-FIRE only tested cables in the horizontal orientation; thus, no comparison can be 

made on this parameter for dc circuits. 

4.6 Raceway Fill 

The dc test data was evaluated based on the raceway fill conditions (single, medium, 

partitioned) and their effect on the failure mode. The single cable raceway fill configurations are 

shown below in Figure 4-13. Most of this single-fill data came from the Penlight tests, with a few 

data points coming from the intermediate-scale tests. If two single cables were in a raceway 

(e.g., Figure 4-14, Fill Tray H), it was also considered a single cable fill. Cables next to a 

partitioned cable group but separate (e.g., Bundle Trays D & H), as shown in Figure 4-15 with 

the single cable off to the right, were also considered single cables for this specific analysis. 

Besides the few instances mentioned above, all fill trays represented in Figure 4-14 and Figure 

4-16 were analyzed as medium-fill, and the fill trays represented in Figure 4-15 were analyzed 

as partitioned cable tray raceway fill. In Section 2.6, bundles represent cable groups held 

together by tie wraps. Tie wraps were not used in the dc testing to group cables together; 

instead, thin steel right-angle plates were connected to the cable tray rungs. 

Figure 4-13. Circuit cable orientation within the cable trays for single fill 
 

4-19 

Figure 4-14. Circuit cable orientation for filled trays 

Tray Fill A Tray Fill B

Tray Fill C Tray Fill D

Tray Fill E Tray Fill F

Tray Fill G Tray Fill H
 

4-20 

Figure 4-15. Circuit cable orientation for partitioned trays 
 

4-21 

Figure 4-16. Circuit cable orientation for specialized trays 

Table 4-14 provides summaries of the dc failure mode test data, separated by raceway fill type. 

The graphical representation of this data is shown in Figure 4-17. As shown in these figures, 

there is not a significant effect on failure modes based on raceway fill configurations. One 

observation of note is the slightly lower likelihood of experiencing a spurious operation in the 

partitioned tray configuration. However, this was not observed in the medium-full 

configurations, making it difficult to explain this result as the shielding effect of the other cables 

surrounding the monitored cables. 

Table 4-14. Raceway fill, global approach, DC tests 

Global Approach Partitioned Medium Single 

Fuse Clear 8 6 10 

Hot Short 35 39 77 

Spurious Operation 16 21 57 

HS/SO Possible 43 45 87 

Figure 4-17. Raceway fill column plot, global approach, DC tests 

1 2 TC 3 4 

Specialized Tray 

A

1 TC 2

3 TC 4 TC 

Specialized Tray 

B

1 TC 2 TC 3 TC

Specialized Tray 

C

Partitioned Medium Single

Count

0

20

40

60

80

100

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

37%

81%

19%

13%

87%

47%

11%

66%

89%
 

4-22 

The duration data was also evaluated against the raceway fill configurations. The analysis 

results are shown below in Table 4-15 and Figure 4-18. No trend was identified for the duration 

data based on raceway fill. 

Table 4-15. Raceway fill, duration data, DC tests 

Hot Short Spurious Operation 

 Bundle Medium Single Bundle Medium Single 

q1 31 17.6 12.6 14.4 13 10.2 

min 2 2 1 3 2 1 

median 115 42 46 34 35 31 

max 4871 2873 8545 198 124 6417 

q3 675 124 240.5 73.6 82.5 97.2 

mean 530 219 444 53 47 289 

Figure 4-18. Raceway fill box plot, duration, DC tests 

 

0

100

200

300

400

500

600

700

Bundle Medium Single Bundle Medium Single

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

4871s 8545s 6417s
 

4-23 

4.7 Insulation Type 

The insulation type parameter separates insulation materials into two categories of polymer 

types, thermoset (TS) and thermoplastic (TP). Table 4-16 provides a breakdown of how 

insulation materials are classified by insulation type. Table 4-17 and Figure 4-19 present the 

failure mode test data separated by cable conductor insulation type, TS and TP. Section 4.8 

provides information on failure characteristics based on insulation materials, and Section 4.9 

presents the data segregated by insulation and jacket type combinations. 

Table 4-16. Breakdown of insulation material by type, DC tests 

Thermoset Materials (TS) Thermoplastic Materials (TP) 

EPR – ethylene propylene rubber PE – polyethylene 

FR-Kerite – Flame Retardant KeriteTM PVC – polyvinyl chloride 

XLPE – cross-linked polyethylene TEF – Tefzel 

XLPO – cross-linked polyolefin 

Table 4-17. Insulation type, global approach, DC tests 

Global Approach TP TS 

Fuse Clear 16 7 

Hot Short 48 99 

Spurious Operation 36 55 

HS/SO Possible 64 106 

Figure 4-19. Insulation type column plot, global approach, DC tests 

The data indicates that insulation type has little effect on the likelihood of spurious operation, but 

has a minor effect on the likelihood of experiencing a fuse clear failure. Here the TS insulation 

has a lower likelihood of experiencing a fuse clear (7%), and, thus, a higher likelihood of 

experiencing a hot short than a TP-insulated cable. Once again, as was shown in the AC test 

results, there is no difference between cable insulation types relative to the likelihood of 

experiencing a spurious operation. 

TP TS

Count

0

20

40

60

80

100

120

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

25%

75%

56%

7%

93%

52%
 

4-24 

The insulation type data was used to determine its effect on failure mode durations, which is 

shown below in Table 4-18 and Figure 4-20. The TP-insulated cables showed slightly longer 

hot short and spurious operation duration, based on the median and inter-quartile range. 

Table 4-18. Insulation type, duration data, DC tests 

 Hot Short Spurious Operation 

 TP TS TP TS 

q1 23.3 12.8 27.5 5.0 

min 1 1 1 1 

median 79 42 90 22 

max 6417 8545 6417 1195 

q3 372.8 212.2 142.6 36.8 

mean 476 376 420 57 

Figure 4-20. Insulation type box plot, duration, DC tests 

4.8 Insulation Material 

The next cut-set evaluates the different types of cable insulation materials. The cable insulation 

materials used during the dc testing were ethylene propylene rubber (EPR), cross-linked 

polyethylene (XLPE), flame-retardant keriteTM (FR-Kerite), polyethylene (PE), polyvinyl chloride 

(PVC), and TefzelTM (TEF), which can also be separated into TS and TP materials. These 

materials were analyzed for a better understanding of their effects on cable failure modes, as 

shown in Table 4-19. This data is presented graphically in Figure 4-21. The data suggests that 

conductors insulated with PE or PVC have a higher likelihood (20% and 17%, respectively) of 

experiencing a fuse clear failure than the other materials. It is interesting to note that both PE 

and PVC are TP materials, and that TEF, another TP material, experienced zero fuse clear 

failures, while the TS material also experienced a low number of fuse clear failures (~6%). 

0

100

200

300

400

500

TP TS TP TS

Hot Short SpuriousOperation

Duration

q1

min

median

max

q3

6417s 1195s 8545s 6417s
 

4-25 

Table 4-19. Insulation material, global approach, DC tests 

Global Approach TS TP

EPR XLPE FR-Kerite PE PVC TEF

Fuse Clear 1 4 1 15 1 0

Hot Short 17 66 15 35 5 8

Spurious Operation 5 41 8 26 4 6

HS/SO Possible 18 70 16 50 6 8

Figure 4-21. Insulation material column plot, global approach, DC tests 

This data set was analyzed with the failure durations summarized in Table 4-20 and displayed in 

Figure 4-22. The data shows that the PVC- and EPR-insulated cables have a very short 

duration; however, only a limited number of PVC cables were tested (6 total). 

Table 4-20. Insulation material, duration data, DC tests

Hot Short Spurious Operation

TS TP TS TP

EPR XLPE PE PVC TEF EPR XLPE PE PVC TEF

q1 7.3 12.3 33.9 1.3 17 3.9 10 28 1 425

min 1 1 1 1 2 3 1 10 1 91

median 53 38 95 13 72 5 23 90 1 759

max 724 4871 6417 84 1433 34 115 6417 1 1427

q3 149 115 676 28.8 290 9.5 37 124 1 1093

mean 146 289 575 22 293 10 28 409 1 759

EPR XLPE FR-Kerite PE PVC TEF

Count

0

20

40

60

80

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

100%

100%

100%

28%

94%

6%

6%

94%

59%

6%

94%

50%

30%

70%

52%

17%

83%

67%

100%

75%

0%
 

4-26 

Figure 4-22. Insulation material box plot, duration, DC tests 

4.9 Insulation-Jacket Type Combinations 

The test data was next evaluated based on the combination of cable insulation and jacket types. 

There are three combinations identified from the data, namely (1) thermoplastic-insulated, 

thermoplastic-jacketed, (2) thermoset-insulated, thermoset-jacketed, and (3) thermosetinsulated, thermoplastic-jacketed. Table 4-21 provides summaries of the dc test data, divided 

into these three categories. This information is displayed in column plots in Figure 4-23, which 

shows that when TS-TS cables are compared to TP-TP cables, the failure mode likelihood data 

is similar to the results obtained from the comparison of the insulation type. It is probable and 

logical that insulation material is the dominant influencing factor for the failure mode likelihood. 

The TS-TP category comprises a single cable type, namely, the armored cable provided 

through the NRC-RES/EPRI Memorandum of Understanding (MOU). The failure modes show a 

high likelihood of experiencing a spurious operation and hot short. These results are consistent 

with industry testing of armored cable. The high percentage of spurious operation and hot 

shorts is a result of an ungrounded power supply and electrical interactions with the armor 

during fire-induced failure. 

Table 4-21. Insulation-jacket type, global approach, DC tests 

Global Approach TP-TP TS-TS Armored (TS-TP) 

Fuse Clear 16 6 0 

Hot Short 48 70 12 

Spurious Operation 36 41 9 

HS/SA Possible 64 76 12 

0

200

400

600

800

1000

1200

EPR XLPE PE PVC TEF EPR XLPE PE PVC TEF

TS TP TS TP

Hot Short SpuriousOperation

Secnods

q1

min

median

max

q3

4871s 6417s 6417s 1427s 1433s
 

4-27 

Figure 4-23. Insulation-jacket type column plot, global approach, DC tests 

The durations for the hot shorts and spurious operations for the jacket types were evaluated 

using the global approach. The data is presented in Table 4-22 with the box plots shown in 

Figure 4-24. Similar to what was shown in the insulation type analysis of Section 4.7, the TP-TP 

material cables show longer duration than the TS-TS cables. The mechanism for this 

phenomenon is unclear to the authors, but it may be the insulation polymer material’s sequence 

of physical thermal degradation. 

Table 4-22. Insulation-jacket type, duration data, DC tests 

Hot Short Spurious Operation 

 TP-TP TS-TS Armored (TS-TP) TP-TP TS-TS Armored (TS-TP)

q1 23.3 14 19.8 27.5 9 4.8 

min 1 1 1 1 1 4 

median 79 42 39 90 24 21 

max 6417 8545 2590 6417 1195 42 

q3 372.8 255.8 182 142.6 37 37.5 

mean 476 429 298 420 73 22 

 

TP-TP TS-TS Armored (TS-TP)

Count

0

20

40

60

80

100

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

25%

75%

56%

8%

92%

54%

100%

0%

100%

75%

100%
 

4-28 

Figure 4-24. Insulation-jacket type box plot, duration, DC tests 

4.10 Wiring Configuration 

The test data used to evaluate the wiring configuration effects on failure modes included five 

types of configurations. These configurations are shown in Table 4-23, identifying the number 

of source, target, and common return conductors within a test cable, along with the associated 

circuit type. 

Table 4-23. DC test data wiring configurations 

 # Sources # Targets # Returns dc Circuit 

Configuration 1 2 4 1 MOV 

Configuration 2 2 3 1 N/A 

Configuration 3 2 2 1 N/A 

Configuration 4 3 3 1 SOV 

Configuration 5 2 3 2 1-IN & LG COIL 

Configuration 6 1 1 1 SWGR - C 

Configuration 7 1 5 1 SWGR - T 

Table 4-24 provides summaries of the dc test data, divided into the different types of 

configurations. This information is shown graphically in Figure 4-25. Configuration 6 had zero 

fuse clears, and configuration 7 had the highest percentage of fuse clears. Configuration 1 had 

the highest percentage (61%) of spurious operations, while configuration 6 had the lowest 

(41%). Configuration 7 had the lowest percentage of hot shorts (65%), as well as the lowest 

source-to-target ratio (1:5). 

 

0

100

200

300

400

500

TP‐TP TS‐TS Armored (TS‐TP) TP‐TP TS‐TS Armored (TS‐TP)

Hot Short SpuriousOperation

q1

min

median

max

q3

6417s 8545s 6417s 2590s 1195s
 

4-29 

Table 4-24. Wiring configuration, global approach, DC tests 

Global Approach Config. 1 Config. 4 Config. 5 Config. 6 Config. 7 

Fuse Clear 4 7 5 0 8 

Hot Short 50 35 29 22 15 

Spurious Operation 33 19 19 9 14 

HS/SO Possible 54 42 34 22 23 

Figure 4-25. Wiring configuration column plot, global approach, DC tests 

This data set was analyzed to determine wiring configuration influence on hot short duration. 

This is shown below in Table 4-25 and Figure 4-26. It should be noted that the durations for 

spurious operations for configurations 6 and 7 are not calculated, as mentioned above. Since 

these are the close and trip circuits of the switchgear, the duration is less than a second, and is 

never continuous; therefore, it is not relevant to this analysis. Configuration 6 had a significantly 

longer median for hot short duration. 

Table 4-25. Wiring configuration, duration data, DC tests 

Hot Short 

 Config. 1 Config. 4 Config. 5 Config. 6 Config. 7 

q1 11 17.5 13.2 35.2 8.9 

min 1 1 1 2 1 

median 37 59 46.5 176 76 

max 8545 724 1143 4871 1397 

q3 173.2 96.2 121.8 1085.8 709 

mean 405 110 195 736 351 

 Spurious Operation 

 Config. 1 Config. 4 Config. 5 Config. 6 Config. 7 

q1 10.8 23 7 N/A N/A 

min 1 3 1 N/A N/A 

median 33.5 37 13 N/A N/A 

max 6417 198.4 1052 N/A N/A 

q3 96.0 69.6 90 N/A N/A 

mean 286 53 129 N/A N/A 

Config. 1 Config. 4 Config. 5 Config. 6 Config. 7

Count

0

10

20

30

40

50

60

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

100%

100%

61%

93%

7%

17%

83%

45%

15%

85%

56%

0%

100%

41%

65%

61%

35%
 

4-30 

Figure 4-26. Wiring configuration box plot, duration, DC tests 

4.11 Conductor Size 

The test data was used to evaluate the effect that conductor size has on failure modes (12 AWG 

vs. 14 AWG). Table 4-26 provides summaries of the dc test data, divided into the different 

conductor sizes. The majority of the test data is for 12 WG cables, with only 8% being of the 14 

AWG variety. The global approach does not result in any significant differences among failure 

modes as a result of cable conductor size. Figure 4-27 provides the graphical representation of 

the failure mode characteristics for cable conductor size. 

Table 4-26. Conductor size, global approach, DC tests 

Global Approach 12 AWG 14 AWG 

Fuse Clear 23 1 

Hot Short 138 13 

Spurious Operation 86 8 

HS/SA Possible 161 14 

 

0

400

800

1200

1600

Config. 1 Config. 4 Config. 5 Config. 6 Config. 7 Config. 1 Config. 4 Config. 5 Config. 6 Config. 7

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

8537s 4871s 6417s
 

4-31 

Figure 4-27. Conductor size column plot, global approach, DC tests 

Table 4-27 and Figure 4-28 display the data that was analyzed based on conductor size for 

failure mode durations. The data shows that the 14 AWG cables experience longer-lasting hot 

shorts and spurious operations, which is based on a limited set of data for the 14 AWG cables. 

Table 4-27. Conductor size, duration data, DC tests 

Hot Short Spurious Operation 

12 AWG 14 AWG 12 AWG 14 AWG 

q1 14 20.8 11 15.5 

min 1 1 1 1 

median 47 194 33 193 

max 6417 8545 6417 1195 

q3 211.2 898.5 80 270.5 

mean 355 965 186 280 

Figure 4-28. Conductor size box plot, duration, DC tests 

12 AWG 14 AWG

Count

0

20

40

60

80

100

120

140

160

180

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

14%

86%

100%

7%

93%

57%

53%

0

200

400

600

800

1000

1200

1400

12 AWG 14 AWG 12 AWG 14 AWG

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

6417s 6417s 8545s
 

4-32 

4.12 Circuit Type 

This cut-set separates the test data by circuit type (MOV, SOV, SWGR, 1-inch, and Large Coil). 

These circuits are explained above in Section 4.1. Table 4-28 presents the data for the circuit 

type’s effect on failure mode occurrence. Figure 4-29 presents this data graphically. 

The MOV and 1-inch valve circuits show a higher likelihood for spurious operation at 76% than 

the SOV, switchgear, and large coil circuit at 55%, 51%, and 53%, respectively. No specific 

mechanism for this has been identified. Circuit type has no significant bearing on the likelihood 

of fuse clears and hot shorts. 

Table 4-28. Circuit type, global approach - DC tests 

Global Approach MOV SOV SWGR 1-inch Large Coil 

Fuse Clear 4 7 8 2 3 

Hot Short 50 35 37 15 14 

Spurious Operation 33 19 23 12 7 

HS/SO Possible 54 42 45 17 17 

Figure 4-29. Circuit type column plot, global approach, DC tests 

The circuit types were also evaluated to determine whether circuit type had an effect on failure 

mode durations. This information is displayed below in Table 4-29 and Table 4-30, and is 

shown graphically in Figure 4-30. It should be noted that in Table 4-30 the duration for SWGR 

spurious operations were not analyzed for this data set because the duration of a breaker 

tripping or closing in only about one time step in data collection would skew the duration data. 

Hot short duration is unaffected by the circuit design, and the durations of hot shorts have been 

reviewed. The switchgear and large coil circuits have the longest median hot short durations 

(136.5s and 71.5s respectively). The large coil has the longest median spurious operation 

duration (52s), while the 1-inch coil has the shortest median spurious operation duration (13s). 

No specific mechanism for this has been identified. 

 

MOV SOV SWGR 1-Inch Large Coil

Count

0

20

40

60

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

100%

100%

61%

93%

7%

17%

83%

45%

18%

82%

51%

12%

88%

71%

18%

82%

41%
 

4-33 

Table 4-29. Circuit type hot short only, duration data, DC tests 

Hot Short 

 MOV SOV SWGR 1-inch Large Coil 

q1 11 17.5 32.2 11.0 21.5 

min 1 1 1 1 3 

median 37 59 136.5 33 75.5 

max 8545 724 4871 855 1143 

q3 173.2 96.2 1082.8 91.5 124 

mean 405 110 695 154 239 

Table 4-30. Circuit type spurious operation only, duration data, DC tests 

Spurious Operation 

MOV SOV SWGR 1-inch Large Coil 

q1 10.8 23 N/A 9.8 4.3 

min 1 3 N/A 1 3 

median 33.5 37 N/A 12.5 90 

max 6417 198.4 N/A 811 1052 

q3 96 69.6 N/A 37.2 111 

mean 286 53 N/A 90 197 

Figure 4-30. Circuit type box plot, duration, DC tests 

 

0

200

400

600

800

1000

1200

1400

MOV SOV SWGR 1‐Inch Large Coil MOV SOV SWGR 1‐Inch Large Coil

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

8545s 4871s 6417s
 

4-34 

4.13 Fuse Size 

The effects of fuse size on failure mode likelihood and duration were evaluated at the request of 

the PIRT panel. Although this evaluation only slightly differentiated the data from the previous 

evaluation based on the circuit type, the PIRT panel thought that the effects of fuse size on 

failure mode and duration could be significant and warranted an evaluation here. The dc testing 

data is the only data that was binned by fuse size, and there were four (4) fuse sizes used in the 

circuits tested in the dc testing program (DESIREE-FIRE). Table 4-31 presents the failure mode 

data, and Figure 4-31 presents the information from the tables in column plots. 

The data for the 35A and 15A fuse bins are entirely from the switchgear circuit and the trip and 

close portions of that circuit, respectively. The 35A bin is an outlier, based on its lack of fuse 

clear failures and lower likelihood of spurious operation (41%). The lack of fuse clear failures is 

likely a result of finite insulation impedance during fire-induced failures, limiting the fault current 

enough that it doesn’t exceed the fuse clear limits. 

Table 4-31. Fuse size, global approach, DC tests 

Global Approach 35A 15A 10A 5A 

Fuse Clear 0 8 7 9 

Hot Short 22 15 64 50 

Spurious Operation 9 14 40 31 

HS/SO Possible 22 23 71 59 

Figure 4-31. Fuse size column plot, global approach, DC tests 

The effects of fuse size on duration are presented in Table 4-32, and a box plot is provided in 

Figure 4-32 to graphically illustrate this information. There is a clear trend (based on median 

and inter-quartile range) indicating that, as the fuse size decreases, so does the duration of the 

hot shorts and spurious operations. 

 

35A 15A 10A 5A

Count

0

20

40

60

80

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

41%

100%

0%

35%

65%

61%

10%

90%

56%

85%

53%

15%

100%
 

4-35 

Table 4-32. Fuse size, duration data, DC tests 

Hot Short Spurious Operation

35A 15A 10A 5A 35A 15A 10A 5A

q1 35.2 8.9 12 12.3 N/A N/A 10 12

min 2 1 1 1 N/A N/A 1 1

median 176 76 42 43 N/A N/A 36 33

max 4871 1397 8545 855 N/A N/A 6417 811

q3 1085.8 709 171.8 96 N/A N/A 98.5 64

mean 736 351 382 123 N/A N/A 273 68

Figure 4-32. Fuse size box plot, duration, DC tests 

4.14 Cable Shielding 

This section evaluates the effect a cable shield has on the failure modes of electrical cables 

exposed to damaging thermal conditions. The data that represents the cable shield category is 

from two different cables. The first is a cable donated to the testing program by JNES. The 

shield in this cable is described in NUREG/CR-7100: 

“The cable included a spiral-wound copper shield wrap approximately 0.23 mm 

(0.009 in) thick. Both inside and outside this shield wrap was a counter-wrapped 

thin natural fiber fabric strip (e.g., a cotton canvas type material).” 

The other shield-wrapped cable was a FR-Kerite insulated cable with a zinc shield wrap, 

described in NUREG/CR-7102 as follows: 

“A zinc tape is spiral-wound directly beneath the jacketing material and two fabric 

wraps separate the insulated conductors from the zinc material.” 

‐100

100

300

500

700

900

1100

1300

1500

35A 15A 10A 5A 35A 15A 10A 5A

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

4871s 8545s 6417s NotApplicable NotApplicable
 

4-36 

Thus, these two cable constructions represent shield wraps with substantial physical 

characteristics and not shield wraps made from aluminized Mylar, a shield wrap commonly 

found in instrumentation cable noise reduction. Also, this section is only intended to evaluate 

the shield, and all armored cable data has been removed from this analysis. Table 4-33 and 

Figure 4-33 present the failure mode likelihood data in tabular and graphical form. The results 

of this analysis show no significant difference for the global approach based on cable shielding. 

Table 4-33. Cable shielding, global approach, DC tests 

Global Approach Shield No Shield 

Fuse Clear 2 22 

Hot Short 10 141 

Spurious Operation 6 88 

HS/SO Possible 12 163 

Figure 4-33. Cable shielding column plot, global approach, DC tests 

The effects of shielding on hot short durations are presented below in Table 4-34 and Figure 4-

34. This comparison doesn’t present any characteristics that differentiate the length of hot short 

durations among cables with or without shields. 

Table 4-34. Cable shielding, duration data, DC tests 

 Hot Short Spurious Operation 

 Shield No Shield Shield No Shield 

q1 18 14 80.9 10.8 

min 1 1 9 1 

median 161 47 149 32 

max 2873 8545 235 6417 

q3 268.5 252 203.5 82.5 

mean 398 409 135 198 

 

Shield No Shield

Count

0

20

40

60

80

100

120

140

160

180

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

17% 83% 50%

13%

87%

54%
 

4-37 

Figure 4-34. Cable Shielding box plot, duration, DC tests 

4.15 DC Concurrence of Hot Short-Induced Spurious Operations 

Concurrence of hot short-induced spurious operations, as discussed in this report, occurs when 

more than one circuit (or cable) experiences individual hot shorts at the same time (i.e., 

concurrence). The intermediate-scale tests performed in DESIREE-FIRE consisted of 12 tests, 

which included six to seven DC circuits per test. This section documents how the test results 

were analyzed to identify times when hot short-induced spurious operations occurred 

concurrently. 

The DESIREE-FIRE project tested five different types of dc surrogate circuits: solenoidoperated valves (SOVs), motor-operated valves (MOVs), 1-inch valve solenoids, large coils 

similar in size to a power-operated relief valve, and a medium-voltage circuit breaker, referred to 

as switchgear (SWGR). The testing included two SOV and two MOV circuits, resulting in a total 

of eight circuits (SOV-1, SOV-2, MOV-1, MOV-2, 1-inch valve, large coil, and switchgear trip 

and close circuits). Most circuits were included in every intermediate-scale test. Since the 

intermediate-scale tests have the most realistic fire exposure conditions, this information has the 

most applicability to plant configuration, and is the focus of this discussion. 

Two approaches were taken to evaluate the concurrence of the DC data set. The first approach 

evaluates the DC data set for concurrence of spurious operations within a single test. The 

second approach is identical to what was done for the AC results and evaluates the data from 

all tests, but within specific fire exposure locations. Note that the draft version of this report only 

evaluated the former, and a public comment received on that draft noted the value of performing 

a similar analysis of the DC data for comparison purposes. This analysis has been added to the 

final report and is presented at the end of this section, following the analysis of concurrence 

among individual DC tests. 

 

0.0

100.0

200.0

300.0

400.0

500.0

Shield No Shield Shield No Shield

Hot Short Spurious Actuation

Duration

q1

min

median

max

q3

2873s 6417s 8545s
 

4-38 

Analysis of spurious operation concurrence within individual tests 

Table 4-35 presents a listing of the four tests in which concurrent spurious operations occurred. 

Although all concurrences occurred between cables of the same insulation type, the testing 

configurations only tested one cable type per test; thus, the possibility of concurrence among 

different cable insulation types was never present. 

Table 4-35. Listing of concurrent spurious operations during intermediate-scale DC 

testing (concurrences that occurred during an individual test) 

Test # 

Circuit 

Experiencing 

Concurrent SO 

Duration of 

individual SO 

(seconds) 

Duration of 

Concurrent 

SO (seconds) 

Cable 

Physical 

Location 

Cable 

Insulation 

Type 

5 SOV-2 

SOV-1 

211 

12 3 D B in Conduit 

TP 

TP 

5 SOV-2 

DC MOV-1 Open 

211 

16 16 D B in Conduit 

TP 

TP 

6 1-inch valve 

SWGR-Close 

89 

1 1 C B in Conduit 

TP 

TP 

6 1-inch valve 

SWGR-Trip 

89 

1 1 C B in Conduit 

TP 

TP 

8 Large coil 

SOV-1 

123 

90 90 A A 

TP 

TP 

8 Large coil 

DC MOV-1 close 

123 

95 9 A A 

TP 

TP 

9 SOV-1 

DC MOV-1 close 

112 

7 7 B B 

TS 

TS 

9 SOV-1 

DC MOV-1 close 

112 

1 1 B 

B 

TS 

TS 

The following discussion provides additional information related to the individual concurrent hot 

shorts in each test identified in Table 4-35. The plots that follow identify the circuit, times of 

failure, and concurrence duration of the hot short. The figures show the start of a hot short, 

represented as a diamond, while the squares indicate the end and the black lines represent the 

duration of a hot short. The information on the horizontal axis of the figure indicates the circuitnaming convention: 

 test series (D = DESIREE) 

 testing scale (IT = Intermediate) 

 test number 

 the circuit that experienced the hot short 

 
 

4-39 

Figure 4-35. Time plot of concurrent hot shorts for DESIREE-FIRE 

intermediate-scale test 5 

Figure 4-35 depicts the DC hot short concurrence between SOV-2, SOV-1, and MOV-1 for 

intermediate-scale Test #5. It is important to note the physical location of the cables because 

thermal exposure conditions can influence the timing of cable failure. The SOV-2 cable is 

located in position D (upper plume), while the SOV-1 and MOV-1 cables are both located in a 

conduit in position B (lower plume). As referenced in Table 4-35, SOV-2 and SOV-1 have 

concurrent spurious operation duration of three seconds, while SOV-2 and MOV-1 have 

concurrent spurious operation duration of 16 seconds. Figure 4-36 provides the temperature 

profile for the two cable locations that experienced concurrent hot shorts. The vertical line 

represents the time of failure. 

Figure 4-36. Plot of intermediate-scale test 5 for MOV and SOV cable locations 

Time (s)

0 500 1000 1500 2000 2500 3000

Temperature (C)

0

200

400

600

800

B Position - Conduit - Middle 

D Position - Middle 

635 C

584 C
 

4-40 

To summarize the data presented in Figure 4-36 and Table 4-35, intermediate-scale test #5 

experienced two concurrent hot shorts among three circuits; the cables are physically located in 

Location D and Location B (inside the conduit). All of the cable insulation is thermoplastic. 

Figure 4-36 plots temperature versus time for MOV and SOV cable locations in intermediatescale test #5. According to Figure 4-36, the cables located in the B Position fail at 

approximately 600 °C, whereas the cable located in the D Position fails at approximately 

630 °C. This indicates the importance of understanding thermal exposure conditions and the 

effect that they have on concurrent failure timing. Although the cables are in different locations, 

each has a similar temperature profile, which leads to failure at approximately the same time. 

Figure 4-37 depicts the DC hot short concurrence between the1-inch valve circuit and 

switchgear circuits for intermediate-scale Test #6. There are two data points for the SWGR 

circuits, since one is for the close function and the other for the trip function. The 1-inch valve 

cable is located in position C (hot gas layer), while the switchgear close and trip cables are both 

located inside a conduit at position B (lower plume). As referenced in Table 4-35, the 1-inch 

valve and switchgear (close) circuits have concurrent spurious operation duration of one 

second, as do the 1-inch valve and switchgear (trip) circuits. 

Figure 4-37. Concurrent hot shorts - test 6 
 

4-41 

Figure 4-38. Plot of intermediate-scale test 6 for 1-inch valve and switchgear cable 

locations 

To summarize the data presented in Figure 4-37 and Table 4-35 intermediate-scale test #6 

experienced two concurrent hot shorts among three circuits; the cables are physically located in 

Locations C and B inside the conduit. All of the cable insulation is thermoplastic. Figure 4-38 

plots temperature versus time for intermediate-scale test #6 for 1-inch valve and switchgear 

cable locations. According to the plot, cables located in B Position fail at approximately 460 °C, 

whereas the cable located in C Position fails at approximately 340 °C. Both of these 

temperatures fall within the typical range of cable failures for this cable type. This plot provides 

an analytical representation of the importance of cable location and the thermal exposure 

conditions due to the HGL effects. 

Figure 4-39 depicts the dc circuit hot short concurrence between Large Coil, SOV-1, and MOV-1 

for intermediate-scale test #8. In the case of the two concurrent hot shorts observed in this test, 

all circuit cables were located in Position A (flame exposure). As referenced in Table 4-35, 

large coil and SOV-1 have concurrent spurious operation durations of 90 seconds, while the 

large coil and MOV-1 have concurrent spurious operation durations of nine seconds. All of the 

cable insulation is thermoplastic. All of the cables are located in A, in the flame; this is 

consistent with the concurrent failure timing because all cables are experiencing similar thermal 

insult. 

 

Time (s)

0 500 1000 1500 2000 2500

Temperature (C)

0

100

200

300

400

500

600

C Position - Middle 

B Position - Conduit Avg 

412 C

343 C
 

4-42 

Figure 4-39. Concurrent hot shorts - test 8 

Figure 4-40 depicts the dc hot short concurrence as falling between SOV1 and MOV1 for 

intermediate-scale test #9. In this test, all cables involved in the concurrent hot shorts were 

located in the same tray, namely Position B (lower plume). As referenced in Table 4-35, SOV1 

and MOV1 have concurrent spurious operation durations of seven seconds, while SOV1 and 

MOV1 have concurrent spurious operation durations of one second. All of the cable insulation 

is thermoset. All of the cables are located in B, in the plume; this is consistent with the 

concurrent failure timing as a result of being exposed to similar thermal insults. 

 
 

4-43 

Figure 4-40. Concurrent hot shorts - test 9 

Analysis of concurrence among all tests for a specific exposure location 

As mentioned above, a comment on the draft version of this report suggested that the data 

should be analyzed to evaluate the concurrence of spurious operations among all tests for 

specific fire exposure locations, as was done for the AC results. For the intermediate-scale 

tests, the data from all tests was binned in exposure locations A, B, and D. Locations C and E 

are geometrically identical, and were grouped into one bin. Since the DC test data used the 

surrogate circuits in the penlight exposure (AC data did not), that data was also analyzed and 

binned by the following shroud temperature ranges: Bin 1 consisted of data from cables 

exposed to 325 – 375C shroud temperatures, Bin 2 had a temperature range of 400 – 480C, 

and Bin 3 had a temperature range of 500 – 525C. There was no strict rule or basis for the 

selection of these bins. However, binning was chosen to make the analysis simpler, and on the 

assumption that cables exposed to high heat flux (i.e., penlight shroud temperatures) should fail 

earlier than cables exposed to lower heat fluxes. Additionally, binning makes the presentation 

of the data cleaner and easier to understand. However, cables tend to exhibit aleatory 

uncertainty with regard to their thermal fragility (i.e., cables don’t all fail at the same 

temperature); thus, to provide a complete analysis of the concurrence observed during testing, 

the last part of this analysis evaluates concurrences among data in these bins. 

Location A in the DESIREE-FIRE tests places cables in a flame exposure location, as shown in 

Figure 2-32. Location A had a total of 14 cables instrumented for circuit response during all of 

the DESIREE-FIRE tests, of which eight experienced spurious operations. Of those eight test 

cases, five were involved in a total of six concurrent spurious operations, and are presented in 

Figure 4-41 and Table 4-36. 
 

4-44 

Figure 4-41. Time plot of concurrent spurious operations for DESIREE-FIRE among all 

test circuits in Location A 

Table 4-36. Test data for Location A of DESIREE-FIRE for cases where concurrent 

spurious operations occurred Test ID D-IT-8-SOV1

D-IT-2-SOV2D-IT-8-MOV1D-IT-2-MOV2D-IT-8-LGCOIL# of concurrent cable SO’s

Test ID

D-IT-8-SOV1 22 - - 92 3

D-IT-2-SOV2 22 56 - 34 4

D-IT-8-MOV1 - 56 7 10 4

D-IT-2-MOV2 - - 7 - 2

D-IT-8-LGCOIL 92 34 10 - 4

Start Time (s) 960 1030 1054 1116 940

Stop Time (s) 1052 1110 1123 1139 1064

Duration (s) 92 80 69 23 124

900

950

1000

1050

1100

1150

D‐IT‐8‐SOV1 D‐IT‐2‐SOV2 D‐IT‐8‐MOV1 D‐IT‐2‐MOV2 D‐IT‐8‐LrgCl

Start

Stop
 

4-45 

Location B in the DESIREE-FIRE tests places cables in a flame/plume exposure location 

dependent on the cable loading in Location A, as shown in Figure 2-32. Location B had a total 

of 38 cables instrumented for circuit response during all of the DESIREE-FIRE tests, of which 

23 tests resulted in spurious operations. Of those 23 tests, 11 were involved in a total of six 

concurrent spurious operations, and are presented in Table 4-37. Due to the concurrence 

durations and the range of failure times among tests, a graph of these results is not presented. 

Table 4-37. Test data for Location B of DESIREE-FIRE for cases where concurrent 

spurious operations occurred Test ID D-IT-7-SOV1 D-IT-C2-TRP D-IT-C2-CLS D-IT-5-LGCOIL

D-IT-6-TRPD-IT-1-1”VLVD-IT-3-SOV2D-IT-1-LGCOILD-IT-3-CLSD-IT-9-SOV1D-IT-9-MOV2# of concurrent cable SO’s

Test ID

D-IT-7-SOV1 1 1 - - - - - - - - 3

D-IT-C2-TRP 1 - - - - - - - - - 2

D-IT-C2-CLS 1 - - - - - - - - - 2

D-IT-5-

LGCOIL - - - 1 - - - - - - 2

D-IT-6-TRP - - - 1 - - - - - - 2

D-IT-1-1”VLV - - - - - 30 - - - - 2

D-IT-3-SOV2 - - - - - 30 - - - - 2

D-IT-1-

LGCOIL - - - - - - - 1 - - 2

D-IT-3-CLS - - - - - - - 1 - - 2

D-IT-9-SOV1 - - - - - - - - - 10 2

D-IT-9-MOV1 - - - - - - - - - 10 2

Start Time (s) 302 334 354 819 850 1358 1361 1446 1460 2584 2613

Stop Time (s) 364 335 355 909 851 1391 1397 1465 1461 2689 2623

Duration (s) 62 1 1 90 1 33 36 19 1 105 10

The data from locations C and E was combined, due to geometric similarities with respect to the 

fire exposure conditions. As such, these two locations consisted of 18 circuit trials, in which 7 

spurious operations occurred. Of the seven spurious operations, none were concurrent. 

Location D in the DESIREE-FIRE tests places cables in a plume exposure location, as shown in 

Figure 2-32. Location D had a total of 28 cables instrumented for circuit response during all of 

the DESIREE-FIRE tests, during which 16 circuits experienced spurious operations. Of these 

16 spurious operations, eight were involved in a total of four concurrent spurious operations, 

and are presented in Figure 4-42 and Table 4-38. 
 

4-46 

Figure 4-42. Time plot of concurrent spurious operations for DESIREE-FIRE among all 

test circuits in Location D 

Table 4-38. Test data for Location D of DESIREE-FIRE for cases where concurrent 

spurious operations occurred Test ID D-IT-5-MOV2 D-IT-9-SOV2 D-IT-1-MOV2

D-IT-10-1”VlvD-IT-12-LgCoilD-IT-3-MOV1D-IT-11-SOV2D-IT-3-SOV1# of concurrent cable SO’s

Test ID

D-IT-5-MOV2 23 - - - - - - 2

D-IT-9-SOV2 23 - - - - - - 2

D-IT-1-MOV2 - - 9 - - - - 2

D-IT-10-1”Vlv - - 9 - - - - 2

D-IT-12-LgCoil - - - - 3 - - 2

D-IT-3-MOV1 - - - - 3 - - 2

D-IT-11-SOV2 - - - - - - 21 2

D-IT-3-SOV1 - - - - - - 21 2

Start Time (s) 1500 1552 2617 2635 2746 2784 2858 2860

Stop Time (s) 1575 1581 2663 2644 2798 2787 2917 2881

Duration (s) 75 29 46 9 52 3 59 21

 

1400

1600

1800

2000

2200

2400

2600

2800

3000

Stop

Start
 

4-47 

For the penlight test cases exposed to shroud temperature in the range of 325 - 375C a total of 

25 cables were instrumented for circuit response, 17 circuits experienced spurious operations. 

Of these 17 spurious operations, Figure 4-43 and Table 4-39 present the 11 test cases that 

were involved in a total of 13 concurrent spurious operations. 

Figure 4-43. Time plot of concurrent spurious operations for DESIREE-FIRE among all 

Penlight test with exposure temperatures in the range of 325-375C 

Table 4-39. Test data for DESIREE-FIRE cases where concurrent spurious operations 

occurred during Penlight exposures in the range of 325 - 375C 

Test ID 

Test ID 

D-P-9-SOV2

D-P-12-MOV1D-P-9-SOV2D-P-30-MOV2D-P-11-LgCoilD-P-11-1”VlvD-P-30-MOV1D-P-JPN1-CLSD-P-JPN3-MOV2D-P-44-MOV1D-P-44-MOV2# of concurrent cable SO’s

D-P-9-SOV2 28 23 - - - - - - - - 3 

D-P-12-MOV1 28 23 - - - - - - - - 3 

D-P-9-SOV2 23 23 - - - - - - - - 3 

D-P-30-MOV2 - - - 1052 811 91 1 193 - - 6 

D-P-11-LgCoil - - - 1052 811 91 1 - - - 5 

D-P-11-1”Vlv - - - 811 811 91 - - - - 4 

D-P-30-MOV1 - - - 91 91 91 - - - - 4 

D-P-JPN1-CLS - - - 1 1 - - - - - 3 

D-P-JPN3-MOV2 - - - 193 - - - - - - 2 

D-P-44-MOV1 - - - - - - - - - 225 2 

D-P-44-MOV2 - - - - - - - - - 225 2 

Start Time (s) 827 863 864 1076 1089 1108 1435 1977 2308 9073 10043 

Stop Time (s) 891 1066 887 2503 2141 1919 1526 1978 2501 10268 10349

Duration (s) 64 203 23 1427 1052 811 91 1 193 1195 306 

0

2000

4000

6000

8000

10000

12000

Stop

Start
 

4-48 

For the penlight test cases exposed to shroud temperature in the range of 400 - 480C a total of 

36 cables instrumented for circuit response, 23 circuits experienced spurious operations. Of 

these 23 spurious operations, Figure 4-44 and Table 4-40 present the 15 test cases that were 

involved in a total of 12 concurrent spurious operations. 

Figure 4-44. Time plot of concurrent spurious operations for DESIREE-FIRE among all 

Penlight test with exposure temperatures in the range of 400-480C 

470

490

510

530

550

570

590

610

630

650

Stop

Start
Table 4-40. Test data for DESIREE-FIRE cases where concurrent spurious operations occurred during 

Penlight exposures in the range of 400 - 480C

Test ID 

D-P-8-MOV1 

D-P-20-SOV1 

D-P-20-SOV2 

D-P-7-MOV1

D-P-2-SOV2

D-P-25-MOV2

D-P-25-MOV2

D-P-4-TRP

D-P-22-MOV1

D-P-22-MOV2

D-P-6-1”Vlv

D-P-25-MOV1

D-P-5-LgCoil

D-P-5-LgCoil

D-P-4-CLS

# of concurrent 

cable SOs Test ID 

D-P-8-MOV1 9 3 - - - - - - - - - - - - 3D-P-20-SOV1 9 17 4 - - - - - - - - - - - 4D-P-20-SOV2 3 17 34 13 - - - - - - - - - - 5D-P-7-MOV1 - 4 34 15 - - - - - - - - - - 4D-P-1-SOV2 - - 13 15 20 - - - - - - - - - 4D-P-2-SOV2 - - - - 20

3

5

3

3 - - - - - 6

D-P-25-MOV2 - - - - - 3 - - - - - - - - 2D-P-25-MOV2 - - - - - 5 - 3

3 - - - - - 4

D-P-4-TRP - - - - - 3 - 3

4 1 - - - - 5

D-P-22-MOV1 - - - - - 3 - 3

4 33 1 9

3 - 8

D-P-22-MOV2 - - - - - - - - 1 33 1 11

3 1 7

D-P-6-1”Vlv - - - - - - - - - 1 1 - - - 3D-P-25-MOV1 - - - - - - - - - 9 11 - 3 - 4D-P-5-LrgCoil - - - - - - - - - 3

3 - 3 - 4

D-P-4-CLS - - - - - - - - - - 1 - - - 2

Start Time (s) 501 502 508 521 542 559 580 584 586 586 589 598 613 616 625

Stop Time (s) 511 525 555 557 579 589 583 589 590 622 631 599 624 619 626

Duration (s) 10 23 47 36 37 30

3

5

4 36 42 1 11

3 1

4-49
 

4-50 

For the penlight test cases exposed to shroud temperature in the range of 500 - 525C a total of 

12 cables instrumented for circuit response, nine circuits experienced spurious operations. Of 

these nine spurious operations, Figure 4-45 and Table 4-41 present the six test cases that were 

involved in a total of three concurrent spurious operations. 

Figure 4-45. Time plot of concurrent spurious operations for DESIREE-FIRE among all 

Penlight test with exposure temperatures in the range of 500-525C 

Table 4-41. Test data for DESIREE-FIRE cases where concurrent spurious operations 

occurred during Penlight exposures in the range of 500 - 525C Test ID D-P-37-MOV1 D-P-35-CLS D-P-37-MOV2 D-P-34-SOV1 D-P-41-MOV2 D-P-41-MOV1 # of concurrent cable SO’s

Test ID 

D-P-37-MOV1 1 - - - - 2

D-P-35-CLS 1 - - - - 2

D-P-37-MOV2 - - 12 - - 2

D-P-34-SOV1 - - 12 - - 2

D-P-41-MOV2 - - - - 54 2

D-P-41-MOV1 - - - - 54 2

Start Time (s) 1681 1693 1724 1728 2463 2702

Stop Time (s) 1712 1694 1740 1743 2894 2756

Duration (s) 31 1 16 15 431 54

The above information completes the evaluation of penlight data for individual bins, however, 

since there was no strict rule for developing these bins, among other reasons stated previously, 

1600

1800

2000

2200

2400

2600

2800

3000

Start

Stop
 

4-51 

the following and final concurrence analysis evaluates concurrent spurious operations occurring 

between test cases in different bins. Of the 73 penlight tests, 51 spurious operations occurred. 

Out of the 51 spurious operations, there were 76 instances of concurrent spurious operations 

and of those 76 concurrences, 34 instances of concurrent spurious operation occurred between 

test cases in different bins. Thus, the binning provided a method to easily present the data, but 

the basis for selecting the bins is weak. Table 4-42 presents the cases where spurious 

operation concurrence was identified between test cases in different bins. The “*” symbol is 

used in the table to indicate spurious operation concurrence for test cases in the same bin, thus, 

the table below does not represent duplicate concurrences previously presented. 

Conclusions 

Upon reviewing the test data for AC and DC circuits with respect to the observation of 

concurrence, several insights have been gained. First the lack of concurrence within any 

individual AC intermediate-scale test provides no bases for excluding plausibility of this 

phenomena. The experimental arrangement of cables within the test apparatus somewhat 

biased the results to decrease the possibility of observing concurrent spurious operations. This 

was because of the limited number of cables instrumented for circuit response (four SCDUs) 

and the placement of cables in different locations or in the same locations but with different 

bundling configurations caused the cables to receive different thermal exposures. What would 

be more commonly found in NPP applications would be cable raceways loaded with cables of 

the same insulation type (TS, TP) and exposures to the same thermal insult. With this 

arrangement groups of cables within the same cable tray would be exposed to almost identical 

thermal conditions and with similar cable failure thresholds it is likely that concurrent spurious 

operations would be observed. 

The DC results provided a better understanding of the concurrent spurious operation 

phenomena. Here up to eight cables could be instrumented for circuit response per test and of 

the five exposure locations within the testing apparatus, typically only two locations were used. 

This resulted in multiple cables in the same location being exposed to similar thermal 

conditions. The flame (location A) concurrence in the intermediate-scale DC tests reflect the 

data obtained from the DC Penlight experiments showing the likelihood of concurrent spurious 

operations to be in the range of 36-52%. For the DC intermediate-scale locations other than 

location A (flame) the results showed a lower likelihood of concurrence, in the range of 29%. 

This result is difficult to explain, but is likely linked to the likelihood of individual spurious 

operation results presented previously in section 2 and 4 when evaluation the parameter effect 

of thermal exposure conditions where it was shown that the likelihood of spurious operation for 

the flame and radiant exposures were higher than the plume or hot gas layer results. 

The final insight gained from this review of the data was that the duration of spurious operations 

can influence the likelihood of concurrent spurious operations. This finding is easily understood 

and Table 4-42 shows instances where long duration spurious operations resulted in numerous 

concurrent spurious operations (e.g., D-P-MOV2, D-P-11-LgCoil, D-P-11-1”Vlv). 
Table 4-42. Test data for DESIREE-FIRE cases where concurrent spurious operations occurred during 

Penlight exposures among tests not binned together in the analysis presented previously. 

* indicates a concurrent spurious operation that was between tests within the same bin and captured in the bin analysis above.

Test ID

D-P-20-SOV1

D-P-20-SOV2

D-P-31-SOV1

D-P-1-SOV2

D-P-2-SOV2

D-P-33-MOV2

D-P-22-MOV1

D-P-22-MOV2

D-P-32-Cls

D-P-25-MOV1

D-P-32-Trp

D-P-12-MOV1

D-P-21-Cls

D-P-30-MOV2

D-P-11-lrgCl

D-P-11-1"Vlv

D-P-50-MOV2

D-P-41-MOV2

D-P-30-MOV1

D-P-36-1"Vlv

D-P-37-MOV1

D-P-35-Cls

D-P-37-MOV2

D-P-34-SOV1

D-P-JPN3-MOV2

D-P-41-MOV2

D-P-JPN3-MOV1

D-P-41-MOV1

D-P-20-SOV1 * 3 ‐‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐D-P-20-SOV2 * 3 * ‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐D-P-31-SOV1 3 3 ‐‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐D-P-1-SOV2 ‐ * ‐ * 1 ‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-2-SOV2 ‐‐‐ * 1 * ‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-33-MOV2 ‐‐‐ 1 1 ‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-22-MOV1 ‐‐‐‐ * ‐ * 1 * 1 ‐‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

D-P-22-MOV2 ‐‐‐‐‐‐ * 1 * 1 ‐‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐D-P-32-Cls ‐‐‐‐‐‐ 1 1 ‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

D-P-25-MOV1 ‐‐‐‐‐‐ * * ‐ 1 ‐‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

D-P-32-Trp ‐‐‐‐‐‐ 1 1 ‐ 1 ‐‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐D-P-12-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ 1 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-21-Cls ‐‐‐‐‐‐‐‐‐‐‐ 1 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-30-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * * 24 99 * 13 31 1 16 15 * * ‐ ‐

D-P-11-lrgCl ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * * 24 99 * 13 31 1 16 15 ‐‐‐‐

D-P-11-1"Vlv ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * * 24 99 * 13 31 1 16 15 ‐‐‐‐

D-P-50-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 24 24 24 ‐‐‐‐‐‐‐‐‐‐‐D-P-41-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 99 99 99 ‐ ‐‐‐‐‐‐‐‐‐‐

D-P-30-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ *** ‐‐ ‐‐‐‐‐‐‐‐‐

D-P-36-1"Vlv ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 13 13 13 ‐‐‐ ‐‐‐‐‐‐‐‐

D-P-37-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 31 31 31 ‐‐‐‐ * ‐‐‐‐‐‐

D-P-35-Cls ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 111 ‐‐‐‐ * ‐‐‐‐‐‐

D-P-37-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 16 16 16 ‐‐‐‐‐‐ * ‐‐‐‐

D-P-34-SOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 15 15 15 ‐‐‐‐‐‐ * ‐‐‐‐

D-P-JPN3-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * ‐‐‐‐‐‐‐‐‐‐ 38 ‐ ‐

D-P-41-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * ‐‐‐‐‐‐‐‐‐‐ 38 235 *

D-P-JPN3-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐ 235 54

D-P-41-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐ 54

Start 502 508 518 542 559 574 586 589 607 613 620 863 962 1076 1089 1108 1241 1307 1435 1611 1681 1693 1724 1728 2308 2463 2632 2702Stop 525 555 521 579 589 575 622 631 608 624 621 1066 963 2503 2141 1919 1265 1406 1526 1624 1712 1694 1740 1743 2501 2894 2867 2756Duration 23 47 3 37 30 1 36 42 1 11 1 203 1 1427 1052 811 24 99 91 13 31 1 16 15 193 431 235 54

4-52
 

5-1 

5. INTER-CABLE – DIRECT CURRENT CIRCUITS 

5.1 Traditional Inter-Cable Failure Analysis for DESIREE-FIRE 

Results 

As was done in other testing projects, the Direct Current Electrical Shorting in Response to 

Exposure Fire (DESIREE-FIRE) project attempted to evaluate inter-cable interactions using 

multiple methods. To explicitly explore this failure mode, an inter-cable test configuration was 

used. In addition, the data (voltage and current measurements) from the surrogate circuits 

could be analyzed post-test to evaluate inter-cable shorting behavior. 

The inter-cable test configuration used during the DESIREE-FIRE testing focused on arranging 

the cables to evaluate the likelihood of proper polarity in inter-cable shorting. These tests 

stacked the deck by placing the cables on an insulated marinite board located in a cable tray 

and having multiple source cables surrounding a single target cable. This configuration is 

shown in Figure 5-1, with a target cable co-located in the center of the arrangement and two 

positive source cables and two negative source cables located on the side and above a target 

cable. The target cable conductors were all connected to a network of resistors and monitored 

for voltage response only (no current transducers were used). Each source conductor was 

powered by one side of a nominal 125Vdc battery and protected with a 10-amp fuse. 

Figure 5-1. DESIREE-FIRE inter-cable configuration 

Thirteen intermediate-scale and four penlight tests were conducted using the five-cable intercable arrangement shown above. Of those tests, only one showed weak signs of multiple 

external shorts to separate conductors within the target cable. This particular case is shown in 

Figure 5-2, where the maximum induced voltage difference is roughly 20Vdc. In all other tests, 

the data shows that internal faults occurred prior to inter-cable faulting of the target cable. 
 

5-2 

Figure 5-2. DESIREE-FIRE inter-cable test results penlight test 47 

The second method involved reviewing the voltage and current data from individual tests. Intercable short circuit failures involve conductors of separate cables coming in electrical contact 

with each other due to fire damage. When analyzing the data for these types of failures, voltage 

and current traces are needed to understand which conductors are involved (i.e., voltage alone 

will not provide sufficient information to identify source and target conductors). In addition, 

knowledge of fuse operability is beneficial so that potential sources can be ruled out following 

the clearing of these protective devices. The DC test circuits all had two fuses, one on the 

positive battery side and one on the negative battery side of the circuit. When a circuit’s positive 

battery side fuse cleared, it could no longer be considered a potential source; likewise, when its 

negative fuse cleared, its target conductors could no longer be considered targets (i.e., hot 

shorts to active and passive devices could no longer occur). However, if only one of the two 

circuit fuses cleared, then the circuit could still experience inter-cable shorting faults that could 

cause spurious operations. 

The small-scale penlight tests were simpler to evaluate for inter-cable shorting because there 

were typically no more than two circuits in any individual test. The intermediate-scale testing, 

however, used all seven circuits (eight energized cables), along with the inter-cable testing 

configuration. The larger number of circuits provided additional source and target conductor 

shorting opportunities, and complicated the evaluation of the inter-cable shorting events. 

The ungrounded battery supply also provided complications in analyzing the data for inter-cable 

shorting. If the dc battery is ungrounded, which is common practice in U.S. nuclear power 

plants (NPPs), a single short to ground from a positively or negatively energized conductor 

would not cause a fuse to clear in and of itself. To have a fuse clear either a plus or a minus, a 

conductor-to-conductor short would be required, or multiple shorts to a ground plane (plus and 

minus) of sufficiently low resistance to result in over current, either of which would clear a circuit 

Time (seconds)

2000 3000 4000 5000 6000 7000 8000

Voltage (Vdc)

40

50

60

70

80

T1-V(Batt-) 

T2-V(Batt-) 

T3-V(Batt-) 

T4-V(Batt-) 

T5-V(Batt-) 

T6-V(Batt-) 

T7-V(Batt-) 

T5

T2
 

5-3 

protective device. However, because the dc circuit had two fuses per circuit, one on the positive 

side and one on the negative side, the fuses would not always clear simultaneously. Thus, in 

about half of the cases, only one fuse in a particular circuit would clear at any time. This singlefuse clearing would eliminate the possibility of intra-cable shorting, but the side of the circuit 

whose fuse did not clear would still be functional from an inter-cable shorting perspective. For 

example, if circuit A experienced a low-resistance short when its positive side fuse cleared, but 

its negative fuse remained intact, then this circuit could still experience a short from another 

conductor in another cable, which could lead to a spurious operation if the respective 

conductors shorted together. 

The purpose of this lengthy discussion is to identify a unique failure mode that has not been 

observed thus far in the associated testing. With a common ungrounded power supply, the 

ground plane (cable trays, conduit, and ground conductors) can act as an electrical conductive 

pathway to aid in inter-cable shorting. This observation results in the need to analyze hot shorts 

and spurious operations more closely to identify the failure mode type (inter- or intra-cable). In 

the AC tests, the control power transformer (CPT) was typically grounded (as is done in the 

majority of U.S. NPPs), and any energized conductor experiencing a low-resistance short to the 

reference ground (due to fire damage) would experience a high-current rush, resulting in the 

clearing of an upstream protective device (fuse or circuit breaker) and the de-energizing of the 

circuit. 

To aid in identifying inter-cable shorting, a simple yet beneficial approach was taken. For an 

individual circuit (MOV-1, SOV-2, Lg Coil, etc.), the current within that circuit was summed, that 

is, the currents coming from the positive battery terminal were added and the currents returning 

to the negative battery terminal were subtracted. Figure 5-3 and Equation 5-1 provide the 

graphical and mathematical representations of this approach. Under normal conditions, 

Kirchoff’s current law states that the currents within a circuit sum up to zero. This law also holds 

under intra-cable-only circuit failures, in that the current within the circuit/cable remains inside 

the cable, and the sum is equal to zero. However, when inter-cable interactions occur, the 

current from one circuit leaves the electrical circuit and enters another; thus, for the inter-cable 

case, the individual circuit currents do not sum up to zero, and there is a net current (negative if 

the circuit is receiving currents from some other circuit, positive if the circuit is supplying 

currents to some other circuit). 

 
 

5-4 

Figure 5-3. DC MOV schematic showing current summation used in identifying intercable shorting behavior 

 isum_dcMOV = iP + iG + iR - ( iYC1 + iYO1 + iN ) Equation 5-1

Although this method provides an efficient tool to quickly identify which circuits were involved in 

inter-cable shorting, there are a few drawbacks. First, this method only shows which circuits 

were involved, and not which conductors. To compensate for this, the analyst must review the 

data from the respective circuits and determine which conductors were involved. Secondly, in 

the intermediate-scale testing, the inter-cable circuit was included, but it was not monitored for 

current. Thus, in some cases the analysis could not identify the source of the inter-cable short, 

although it can be assumed that the source was the inter-cable circuit. Thirdly, there were a few 

circuits (small SOVs in particular) that had a very low operating current (0.042A) when 

energized. Although they were typically discernible in the analysis, they were not as apparent 

as the other circuits’ inter-cable shorts. Fourthly, there may be cases where a circuit is leaking 

current and gaining current from other circuits simultaneously; these interactions can cancel 

each other out, and can lead to difficulties in identifying the inter-cable short. Lastly, there were 

several cases where a single circuit shorted abruptly to the common ground plane and caused 

several circuit protective devices to clear without direct indication of which circuit initiated the 

event. It is assumed that because there were multiple simultaneous fuse clears, there was a 

very abrupt current spike, followed by fuse clearing, which the data acquisition system (DAQ) 

was unable to capture. 

As a result of these aspects, the analysis for this section is focused on identifying spurious 

operations that resulted from inter-cable (cable-to-cable) shorting. There were some cases 

where it was possible to determine how individual circuit fuses cleared via inter-cable shorting; 

that information is noted in the summary tables. At this time, an evaluation of inter-cable hot 

shorting of the passive targets has not been conducted, mainly due to the low-level currents 

required to energize these devices and the complications associated with the auxiliary contacts 

and reed switches used to control the passive target sources. 
 

5-5 

The following two sections present the inter-cable analysis of the surrogate circuit data for the 

small-scale Penlight and intermediate-scale open-flame tests. Due to the number of circuits 

used in the intermediate-scale testing and the use of actual flaming combustions, those results 

are analyzed in more detail than they are in the penlight tests, where only two circuits were colocated within the same cable tray. The intermediate-scale results also show unique failures in 

which cables located within a rigid steel conduit interact with other cables located in cable trays 

at different locations. 

5.2 Penlight Tests – Ground Fault Equivalent Hot Short 

Penlight tests for the DESIREE-FIRE project typically consisted of two cables, each connected 

to an individual circuit. The only exception for this type of configuration was the medium-voltage 

circuit breaker test, where two cables were connected to one circuit. In all tests using a cable 

tray, the cables were not in physical contact with anything except the cable tray. A cable 

instrumented for thermal response was typically placed between the two cables instrumented 

for electrical response, as shown in Figure 5-4. Thus, any inter-cable interactions are a direct 

result of cable interactions with the cable tray. In conduit tests, the two electrically monitored 

cables may be in physical contact, and a more detailed evaluation of any inter-cable interactions 

is necessary. 

Figure 5-4. Penlight cable tray typical loading, showing two electrically instrumented 

cables and a thermal response (temperature recording) cable located in the 

center. 

The Penlight results of the ground equivalent hot shorting analysis are documented in Appendix 

A. A summary of this analysis is presented here in Table 5-1. 

 
 

5-6 

Table 5-1. Results of inter-cable shorting during Penlight DESIREE-Fire tests. 

Test # Failure Mode Description 

PT-8 MOV-2 hot short to “R” conductor from MOV-1 “P” conductor at 478 seconds 

(duration = 3 seconds). 

PT-12 Interactions between MOV-1 “N” conductor and MOV-2 “P” conductor. This is a 

case of a high-resistance short between conductors connected to positive and 

negative battery potential. 

PT-22 Four separate ground fault equivalent spurious operations occurred in this test. 

MOV-1 Open coil SO for 2 seconds, short from MOV-2 “G” conductor (starts at 585s) 

MOV-1 Open coil SO for 2 seconds, short from MOV-2 “G” conductor (starts at 589s) 

MOV-1 Open coil SO for 40 seconds, short from MOV-2 “G” conductor (starts at 

593s) 

MOV-2 Open coil SO for 38 seconds, short from MOV-1 “G” conductor (starts at 

595s) 

PT-33 Interactions between MOV-1 “P” conductor and MOV-2 “N” and “YC” conductors (No 

SO or HS occur). 

PT-37 MOV-2 Close coil SO for 16 seconds, short from MOV-1 “G” conductor to MOV-2 

“YC” conductor. 

PT-41 Two separate ground fault equivalent spurious operations occurred in this test. 

MOV-2 Close coil SO for 6 seconds, short from MOV-1 “G” conductor to MOV-2 “YC” 

conductor (starts at 2753s) 

MOV-1 Open coil SO for 1 second, short from MOV-2 “G” conductor to MOV-1 “YO” 

Interactions between MOV-1 “P” conductor and MOV-2 “N” conductor were also 

observed for approximately 9 seconds, starting at 2825 seconds. 

PT-49 MOV-2 Open coil SO for <1 second, source is difficult to identify due to other 

conductor interactions among cable trays. 

PT-50 MOV-2 Close coil SO for 22s, short from MOV-1 “G” conductor to MOV-2 “YC” 

conductor. 

Inter-cable interactions also cause a fuse clear on MOV-2 circuit. 

PT-JPN3 False indication on MOV-1 Red lamp ON, due to inter-cable shorting with MOV-2. 

PT-20 SOV-2 SO for 20 seconds, short from SOV-1 “G” conductor (starts at 508s). 

PT-28 SOV-2 SO for 297secodns, short from SOV-1 “P” conductor (starts at 3393s). 

PT-31 False indication on SOV-2 Green lamp ON, due to inter-cable shorting with SOV-1. 

PT-11 Two separate ground equivalent hot shorts were observed in this test. 

Large coil SO for 52 seconds, short from 1-inch valve “G” and “R” conductors 

1-inch valve SO for 798 seconds, short from large coil “P” conductor 

PT-40 Large coil SO for 64 seconds, short from 1-inch valve “G” and R” conductors (starts 

at 4100s). 

PT-4 SWGR-trip SO (breaker opens), short from SWGR-Close “N1” conductor. 

PT-JPN2 False indication Red lamp ON, inter-cable interaction between SWGR-Trip “R” 

conductor and SWGR-Close “N1” conductor. 

5.3 Intermediate-Scale Tests – Ground Fault Equivalent Hot Short 

5.3.1 Preliminary Test #1 

Figure 5-5 presents an illustration of the test set-up for preliminary test #1. Location A contains 

fill cable that is represented by the gray area located within the cable tray, and is located directly 
 

5-7 

above the fire source (200 kW propene diffusion sand burner). Location B contains two cables 

connected to the switchgear trip and close coil circuitry, location C contains two cables 

connected to two separate AC surrogate circuit diagnostic units (SCDUs), location D contains 

the inter-cable test configuration of cables, and location E contains two cables connected to the 

1-inch valve and the large coil. During testing, the openings in the hood in which the cable trays 

and conduits are located are enclosed with a ceramic fiber material to develop and maintain a 

hot gas layer that is sufficient to damage the cables. The illustration does not show ceramic 

fiber. 

Figure 5-5. Intermediate-scale test preliminary 1 cable loading configuration 

Table 5-2 presents the failure mode sequence of events of preliminary test #1. The AC SCDU 

and inter-cable testing results are not discussed. Cables in location E did not fail during the 

test. 

Table 5-2. Intermediate-scale preliminary test 1 

Time (s) Failure Observation 

502 SWGR-C SA 

504 SWGR-C Fuse Clear – Positive 

515 SWGR-T Fuse Clear – Negative 

540 SWGR-C Fuse Clear – Negative (INTER-CABLE with SWGR-T cond. ‘P’) 

NOTE: 1-inch valve and Lg Coil circuit did not fail max temp (~380 C for both 

TS cables) 

5.3.2 Preliminary Test #2 

Figure 5-6 and Table 5-3 provide an illustration of the intermediate-scale layout and a summary 

of the test circuit failure sequence, respectively. Bold font is used to identify inter-cable 

interactions. Figure 5-7 presents the summed current plots for all circuits in this test. This plot 

indicates that MOV-2 open coil experiences an inter-cable hot short-induced spurious operation 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

+/- : power source cable 35A

NOT TO SCALE

Inter-cable Circuit

SG-C SG-T

ac3 ac4 1V LC
 

5-8 

from SOV-2. Although the cables associated with MOV-2 and SOV-2 are in the same cable 

tray, they are not in physical contact with each other; thus, the only means for this interaction is 

by ground plane equivalent hot short failure mode. In this specific spurious operation, 

conductors “S1,” “P,” and “G” of the SOV-2 circuit are supplying power to the MOV-2 open coil 

contact conductor. 

Figure 5-6. Intermediate-scale test preliminary 2 cable loading configuration 

Table 5-3. Intermediate-scale preliminary test 2 

Time (s) Failure Observation 

312 SOV-1 Fuse Clear – Positive 

343 MOV-1 Fuse Clear – Positive & Negative 

820 – 1221 MOV-2 SO Open Coil 

 INTER-CABLE shorting with SOV-2 conductor S1, P, G 

888 – 1221 MOV-2 HS Close Coil (likely from inter-cable) 

953 – 1020 SOV-2 SO (voltage but no corresponding current – unlikely an SO per SNL 

report) 

1020 SOV-2 Fuse Clear – Negative 

1221 MOV-2 Fuse Clear – Negative 

1221 SOV-2 Fuse Clear – Positive 
 

5-9 

Figure 5-7. Intermediate-scale test preliminary 2 – inter-cable shorting between SOV-2 

and MOV-2 

5.3.3 Test 1 

Figure 5-8 and Table 5-4 present an illustration of the intermediate-scale cable layout and the 

circuit response summary information, with inter-cable interactions shown in boldface type. 

Figure 5-9 provides an indication that the 1-inch valve circuit experienced interactions with the 

large coil and MOV-1 circuits. Upon closer review of the test data, it was determined that 

conductor “P” of the 1-inch valve circuit energized the conductor “S” of the large coil circuit, 

causing an inter-cable spurious operation. Shortly after the large coil spurious operation 

cleared, MOV-1 conductor YO1 on the open coil was energized by the same “P” conductor of 

the 1-inch valve circuit, causing spurious operation on the MOV-1 circuit. The 1-inch valve 

source conductor “P” energized two individual conductors in different cables and separate 

raceways. In addition, review of the ground fault circuitry measurements indicates that the 

positive side of the battery was grounded during these interactions. These results provide a 

clear indication that the ground plane was involved during both inter-cable hot shorts. 

Time (s)

800 900 1000 1100 1200 1300

Current (A)

-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

1-inch Valve 

Large Coil 

MOV-1 

MOV-2 

SOV-1 

SOV-1 

SOV-2 

Switchgear 
 

5-10 

Figure 5-8. Intermediate-scale test 1 cable loading configuration 

Table 5-4. Intermediate-scale test 1 

Time (s) Failure Observation 

1361-1377 1-inch Valve SA 

1375 SOV-1 Fuse Clear – Negative 

1382 – 1384 1-inch Valve SA 

1396 1-inch Fuse Clear – Negative 

1449 Lg Coil SA 

 INTER-CABLE from 1-inch valve conductor P via Ground 

1452 Lg Coil SA 

 INTER-CABLE from 1-inch valve conductor P via Ground

1460 – 1463 Lg Coil SA 

 INTER-CABLE from 1-inch valve conductor P via Ground

1467 Lg Coil Fuse Clear – Negative 

1475 – 1558 MOV-1 SO Open Coil 

 INTER-CABLE from 1-inch valve conductors P and G via Ground

1516 – 1558 MOV-1 HS Close Coil 

1558 MOV-1 Fuse Clear – Negative 

1560 1-inch Valve Fuse Clear – Positive 

2196 SWGR-C Fuse Clear – Negative 

2269 MOV-1 Fuse Clear – Positive 

2295 SOV-1 Fuse Clear – Positive 

2512-2523 SOV-2 SA 

2617 – 2661 MOV-2 HS Close Coil 

2649 SOV-2 Fuse Clear – Positive & Negative 

2654 – 2661 MOV-2 SO Open Coil 

2663 MOV-2 Fuse Clear – Positive & Negative 

2934 Lg Coil Fuse Clear – Positive 

3938 – 4028 SWGR-T HS 
 

5-11 

Figure 5-9. Outstanding current hot shorting for intermediate-scale test 1 between 1-inch 

valve, large coil, and MOV-1 circuits 

5.3.4 Test 2 

Table 5-5 presents the circuit failure chronologically. No inter-cable hot shorts occurred during 

this test. However, the cause of the fuse clear on SOV-2 is a result of inter-cable shorting 

between the SOV-2 and MOV-2 cables. These two cables were located in the same cable tray 

in the middle of the tray cable fill (see Figure 5-10). Review of the ground fault circuit data 

indicates that the battery negative was shorted to ground prior to the SOV-2 fuse clear. Thus, it 

is likely that the “N” conductor in SOV-2 shorted to ground initially, followed by MOV-2’s “P” 

conductor shorting to ground, resulting in an increased current, which would have caused the 

fuse in SOV-2 to clear. The current summation plot showing these interactions is presented in 

Figure 5-11. 

Time (s)

1350 1400 1450 1500 1550 1600

Current (A)

-4

-2

0

2

4

1-inch Valve 

Large Coil 

MOV-1 

MOV-2 

SOV-1 

SOV-2 

Switchgear 
 

5-12 

Figure 5-10. Intermediate-scale test 2 cable loading 

Table 5-5. Intermediate-scale test 2 

Time (s) Failure Observation 

1030-1109 SOV-2 SA 

1116 - 1142 MOV-2 HS Close 

1145 - 1152 MOV-2 HS Close 

1145 - 1152 MOV-2 HS Open 

1156 - 1175 MOV-2 HS Close 

1156 - 1173 MOV-2 HS Open 

1164 SOV-2 Fuse Clear – Positive and Negative 

 Due to INTER-CABLE shorting with MOV-2 conductor P via Gnd 

3909-3977 SOV-1 SA 

3979 SOV-1 Fuse Clear – Negative 

3975 1-inch Valve Fuse Clear – Positive 

4247 - 4362 MOV-1 SO Open 

4492 Lg Coil Fuse Clear - Negative 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

IC : Inter-cable circuit

M2 S2

M1 S1

1V LC

NOT TO SCALE

Inter-cable Circuit
 

5-13 

Figure 5-11. Outstanding current shorting in intermediate-scale test 2, between SOV-2 

and MOV-2 

5.3.5 Test 3 

Three circuits were involved in inter-cable hot shorting during Intermediate-Scale Test #3. 

Figure 5-12 illustrates the cable loading arrangement, and Table 5-6 provides a circuit fault 

summary for Intermediate-Scale test 3. SOV-2 experienced two spurious operations as a result 

of an inter-cable hot short from the Switchgear Trip circuit cable located in a conduit. Because 

the switchgear cables were isolated from the other cables by their location in a conduit, the only 

possible way for this shorting to occur was through the ground plane. Figure 5-13 provides the 

current sum method plot showing the SOV-2 and switchgear circuit interactions. 

Following the SOV-2 spurious operations, the 1-inch valve circuit also experienced two spurious 

operations. Upon review of the voltage and current data, both 1-inch valve spurious operations 

were also caused by inter-cable shorting through the ground plane from the switchgear trip 

circuit. Figure 5-14 provides the current sum method plot showing the 1-inch valve and 

switchgear interaction. 

Time (s)

1100 1120 1140 1160 1180 1200

Current (A)

-5

0

5

10

1-inch Valve 

Large Coil 

MOV-1 

MOV-2 

SOV-1 

SOV-2 

Switchgear 
 

5-14 

Figure 5-12. Intermediate-scale test 3 cable loading 

Table 5-6. Intermediate-scale test 3 

Time (s) Failure Observation 

1078 – 1090 MOV-2 SO Open Coil 

1097 – 1128 MOV-2 SO Open Coil 

1108 MOV-2 HS Close Coil 

1111 – 1113 MOV-2 HS Close Coil 

1127 MOV-2 HS Close Coil 

1130 MOV-2 Fuse Clear – Positive 

1168 MOV-2 Fuse Clear – Negative 

1262 SOV-2 Fuse Clear – Positive 

1361 – 1363 SOV-2 SO 

INTER-CABLE from SWGR-T conductor P via Ground

1375 – 1406 SOV-2 SO 

 INTER-CABLE from SWGR-T conductor P via Ground

1419 SOV-2 Fuse Clear – Negative 

1460 – 1468 SWGR-C SO 

1468 SWGR-C Fuse Clear Positive and Negative 

2188 – 2221 1-inch Valve SO 

INTER-CABLE from SWGR-T conductor P via Ground 

2226 – 2229 1-inch Valve SO 

INTER-CABLE from SWGR-T conductor P via Ground 

2231 1-inch Valve Fuse Clear – Negative 

2286 1-inch Valve Fuse Clear – Positive 

2288 Lg Coil Fuse Clear – Positive & Negative 

 INTER-CABLE SWGR-T conductor PT 

2784 – 2787 MOV-1 SO Open Coil 

2787 MOV-1 SO Fuse Clear – Positive and Negative 

3066 SOV-1 Fuse Clear – Positive and Negative 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

M2 S2 SG-C

M1 S1

SG-T

1V LC

NOT TO SCALE Inter-cable Circuit
 

5-15 

Figure 5-13. Outstanding current shorting in intermediate-scale test 3, between SOV-2 

and SWGR-T 

Figure 5-14. Outstanding current shorting in intermediate-scale test 3, between 1 inch 

valve and SWGR-T 

 

Time (s)

1340 1360 1380 1400 1420

Current (A)

-4

-2

0

2

4

1-inch Valve 

Large Coil 

MOV-1 

MOV-2 

SOV-1 

SOV-2 

Switchgear 

Time (s)

2140 2160 2180 2200 2220 2240

Current (A)

-1.0

-0.5

0.0

0.5

1.0

1-inch Valve 

Large Coil 

MOV-1 

MOV-2 

SOV-1 

SOV-2 

Switchgear 
 

5-16 

5.3.6 Test 4 

No inter-cable spurious operations were observed during this test. Figure 5-15 provides a cable 

loading illustration, and Table 5-7 provides the chronology of circuit failures. The fuse clearing 

for the 1-inch valve circuit and the large coil circuit were caused by inter-cable shorting from the 

inter-cable circuit. 

Figure 5-15. Intermediate-scale test 4 cable loading 

Table 5-7. Intermediate-scale test 4 

Time (s) Failure Observation 

1530 1-inch valve Fuse Clear – Positive 

1585 SOV-1 Fuse Clear – Positive – inter-cable with 1-inch valve conductor N 

1671 Lg coil Fuse Clear – Positive 

INTER-CABLE shorting from 1-inch valve conductor “N” 

1671 1-inch valve Fuse Clear – Negative 

INTER-CABLE shorting from Lg coil conductor “G” 

1859 – 1895 MOV-1 SO Open Coil 

1895 MOV-1 Fuse Clear – Positive and Negative 

4766 SWGR-C Fuse Clear – Positive and Negative 

4974 MOV-2 Fuse Clear – Positive and Negative 

5216 – 5249 SOV-2 SO 

5249 SOV-2 Fuse Clear – Positive and Negative 

5305 SOV-1 Fuse Clear – Negative 

5307 Lg coil Fuse Clear – Negative 

 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

IC : Inter-cable circuit

ac1-4 : SCDU circuits

ac1 ac2

ac3 ac4

NOT TO SCALE

Inter-cable Circuit

LC M1 S1 1V

M2 S2 SG-C SG-T
 

5-17 

5.3.7 Test 5 

Figure 5-16 provides intermediate-scale test 5 cable loading, while Table 5-8 presents the circuit 

failure mode information in chronological order. As shown in Figure 5-17, SOV-1 experienced 

an inter-cable hot short at 1637 seconds from the SWGRSWGR-T circuit, which resulted in a 

spurious operation of the SOV-1 circuit. Conductor “PT” of the switchgear trip circuit shorted to 

ground, as did the SOV-1 coil conductor “S.” These two cables were located in different areas 

of the enclosure, and SOV-1 was actually located in a rigid steel conduit. Thus, these 

interactions required the ground plan. No other inter-cable spurious operations were identified. 

Figure 5-16. Intermediate-scale test 5 cable loading 

Table 5-8. Intermediate-scale test 5 

Time (s) Failure Observation 

655 1-inch valve Fuse Clear – Negative 

819 – 908 Lg Coil SA 

908 1-inch Valve Fuse Clear – Positive 

910 Lg Coil Fuse Clear – Negative and Positive 

1424-1429 SWGR-C SO Close 

1429 SWGR-C Fuse Clear – Positive 

1500 – 1573 MOV-2 Hot Short Close Coil 

1510 – 1532 MOV-2 Hot Short Open Coil 

1542 – 1573 MOV-2 Hot Short Open Coil 

1556 SOV-1 Fuse Clear – Positive 

1575 MOV-2 Fuse Clear – Positive and Negative 

1596 SWGR-C Fuse Clear – Negative 

1637 – 1649 SOV-1 SA 

 INTER-CABLE shorting from SWGR-T conductor PT 

1646 – 1658 SOV-2 SA 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

IC : Inter-cable circuit

ac1-4 : SCDU circuits

1V LC S1

M2 S2

M1

SG-C SG-T

NOT TO SCALE

Inter-cable Circuit
 

5-18 

Table 5-8. Intermediate-scale test 5 

Time (s) Failure Observation 

1651 SOV-1 Fuse Clear – Negative 

1667 – 1857 SOV-2 SA 

1859 SOV-2 Fuse Clear – Negative 

2255 SOV-2 Fuse Clear – Positive 

1717 – 1734 MOV-1 SO Open Coil 

1717 – 1734 MOV-1 HS Close Coil 

1734 MOV-1 Fuse Clear – Positive and Negative 

Figure 5-17. Outstanding current shorting in intermediate-scale test 5, between SOV-1 

and SWGR-T 

5.3.8 Test 6 

No inter-cable hot shorts resulted in spurious operation of any device in intermediate-scale 

test 6. Figure 5-18 illustrates the cable loading and arrangement for intermediate-scale test 6. 

Table 5-9 presents the summary of circuit failure modes in chronological order. There were 

several inter-cable interactions observed in the data set involving the MOV-2 circuit fuses 

clearing as a result of inter-cable shorting with the SOV-2 and SWGR-T circuits. There were 

also several current spikes in several circuit data plots, which were a result of inter-cable 

shorting. Although MOV-2 and SOV-2 were collocated in the same raceway, the switchgear 

circuit was in a different location, and shorting via the ground plane was likely the cause of 

these interactions. 

Time (s)

1500 1550 1600 1650 1700

Current (A)

-0.1

0.0

0.1

0.2

1-inch Valve 

Large Coil 
 

5-19 

Figure 5-18. Intermediate-scale test 6 cable loading 

Table 5-9. Intermediate-scale test 6 

Time (s) Failure Observation 

191 SOV-2 Fuse Clear – Negative 

230 MOV-2 Fuse Clear – Negative 

 INTER-CABLE with SOV-2 

850 SWGR-T SO [Breaker Open] 

1168 SOV-2 Fuse Clear – Positive 

1170 MOV-2 Fuse Clear – Positive 

INTER-CABLE with SWGR-T conductor N2 

1317 Lg Coil Fuse Clear – Positive and Negative 

1400 – 1502 SOV-1 SO 

1480 – 1507 MOV-1 SO Close Coil 

1534 – 1567 Short between SOV-1 conductor G and SWGR-C conductor N1 

1567 SOV-1 Fuse Clear – Positive and Negative 

1548 – 1637 1-inch Valve SO 

1603-1607 SWGR-C SO [Breaker Close] 

1603-1607 SWGR-T SO [Breaker Open] 

1638 1-inch Valve Fuse Clear – Negative 

1728 SWGR-C and SWGR-T Fuse Clear – Negative 

5.3.9 Test 7 

No inter-cable hot shorts were identified in intermediate-scale test 7. Figure 5-19 and 

Table 5-10 provide the cable loading configurations and summarize the circuit failure modes in 

chronological order. Ground plane influences can be associated with the concurrent fuse 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

M2 S2

SG-C

1V LC

SG-T

M1 S1

NOT TO SCALE

Inter-cable Circuit
 

5-20 

clearing of MOV-1, MOV-2, and SOV-2 1286 seconds into the test. At this point, the battery 

transitioned from being grounded on its positive side to being grounded on its negative side. 

Figure 5-19. Intermediate-scale test 7 cable loading 

Table 5-10. Intermediate-scale test 7 

Time (s) Failure Observation 

302 – 363 SOV-1 SO 

324 MOV-1 Fuse Clear – Negative 

363 SOV-1 Fuse Clear – Positive and Negative 

466 SOV-2 Fuse Clear – Negative 

535 MOV-2 Fuse Clear – Negative 

1095 SWGR-T SO [Breaker Open] 

1258 SWGR-C Fuse Clear – Negative 

1286 MOV-1 Fuse Clear – Positive 

1286 MOV-2 Fuse Clear – Negative 

1286 SOV-2 Fuse Clear Positive 

1388 SWGR-T Fuse Clear – Negative 

1426 Lg Coil Fuse Clear – Negative 

1713 – 1762 1-inch Valve SO 

1762 1-inch Valve Fuse Clear – Negative 

5.3.10 Test 8 

Figure 5-20 shows the cable loading configuration for intermediate-scale test 8 while Table 5-11 

contains the failure mode summary information, presented in chronological order. One intercable hot short was observed, which resulted in the spurious operation of MOV-1 close coil. 

This short occurred when the G conductor of the large coil cable came into electrical contact 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

M1 S1 LC

SG-C SG-T

1V

M2 S2

NOT TO SCALE Inter-cable Circuit
 

5-21 

with close coil conductor YC1 of the MOV-1 circuit via a ground path. Figure 5-21 shows the 

unbalanced current profiles for large coil and MOV-1. Note that these two cables were located 

adjacent to each other in the same cable tray in location A, “flame exposure region.” Review of 

the ground fault circuit data indicates that the positive side of the battery shorted to ground at 

approximately 900 seconds and remained grounded for the duration of the test. 

Figure 5-20. Intermediate-scale test 8 cable loading 

Table 5-11. Intermediate-scale test 8 

Time (s) Failure Observation 

900 1-inch Valve Fuse Clear – Negative 

943 – 1060 Lg Coil SO 

960 – 1052 SOV-1 SO 

1052 SOV-1 Fuse Clear – Positive and Negative 

1052 – 1149 MOV-1 SO Close Coil 

 INTER-CABLE with Lg Coil conductor G via ground 

1060 Lg Coil Fuse Clear – Negative 

1149 MOV-1 Fuse Clear – Negative 

1743 MOV-2 Fuse Clear – Negative 

2354 SOV-2 Fuse Clear – Positive and Negative 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

M2 S2

SG-C SG-T

NOT TO SCALE

Inter-cable Circuit

1V M1 S1 LC

ac1 ac2

ac3 ac4
 

5-22 

Figure 5-21. Outstanding current shorting in intermediate-scale test 8, between MOV-1 

and Lg Coil 

5.3.11 Test 9 

Figure 5-22 presents the cable loading configuration for intermediate-scale test 9, and Table 5-

12 provides the chronological order of the failure modes identified during this test. Three intercable spurious operations were observed during this test. MOV-2 open coil went through 

spurious operation for 24 seconds via inter-cable shorting from conductors “G” and “P” of the 

large coil circuit. Note that these two cables are set in different locations in the hood: MOV-2 is 

in location D, while the large coil circuit is in the cable tray immediately below in Location B. At 

1552 seconds into the test, the SOV-2 circuit experienced an inter-cable spurious operation 

from the same source conductors as MOV-2 (namely conductors “G” and “P” from the large coil 

circuit). This spurious operation lasted for 28 seconds. Again, both cables involved in the 

shorting were set in different cable tray locations. The third and final inter-cable spurious 

operation occurred when the MOV-1 close coil actuated after being energized by the switchgear 

trip circuit. This spurious operation lasted for 16 seconds. In this case, the cables involved 

were located in the same cable tray and were not adjacent to each other, but were separated by 

a fill cable. 

Time (s)

1000 1050 1100 1150 1200

Current (A)

-1.0

-0.5

0.0

0.5

1.0

1-inch Valve 

Large Coil 

MOV-1 

MOV-2 

SOV-1 

SOV-2 

Switchgear 
 

5-23 

Figure 5-22. Intermediate-scale test 9 cable loading 

Table 5-12. Intermediate-scale test 9 

Time (s) Failure Observation 

628 – 638 1-inch Valve SA 

765 Lg Coil Fuse Clear – Negative 

765 1-inch Valve Fuse Clear – Positive and Negative 

1253 – 1277 MOV-2 SO Open Coil 

INTER-CABLE shorting with Lg Coil conductors G & P via ground 

1278 MOV-2 Fuse Clear – Negative 

1552 – 1580 SOV-2 SA 

INTER-CABLE shorting with Lg Coil conductors G & P via ground 

1583 SOV-2 Fuse Clear – Negative 

1602 Lg Coil Fuse Clear – Positive – Short w/SWGR-T cond. N2 via ground 

1604 SOV-2 Fuse Clear – Positive – Short w/SWGR-T cond. N2 via ground 

1605 MOV-2 Fuse Clear – Positive – Short w/SWGR-T cond. N2 via ground 

1920 SWGR-C Fuse Clear – Positive 

2420 SWGR-C Fuse Clear – Negative – Short w/SOV-1 cond. P via ground 

2584 – 2696 SOV-1 SO 

2611 – 2627 MOV-1 SO Close Coil 

 INTER-CABLE shorting with SWGR-T conductor P via ground 

2638 MOV-1 Fuse Clear – Negative 

2699 SOV-1 Fuse Clear – Positive and Negative – Short w/SWGR-T cond. P 

 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

NOT TO SCALE

Inter-cable Circuit

TC

TC TC

1V

LC M1 S1

TC

M2 S2 SG-C SG-T
 

5-24 

5.3.12 Test 10 

The cable configuration used in intermediate-scale test 10 is shown in Figure 5-23, and the 

chronological order of the cable failures is presented in Table 5-13. The results show that there 

were three spurious operations and one hot short as a result of ground fault equivalent shorting. 

In all four instances, the source of the interactions could not be identified; however, this test 

configuration has the inter-cable testing configuration in location A, directly above the fire. This 

experimental set-up likely caused the inter-cable source conductors (which were not monitored 

for current) to short to the ground plane and aid in the four cases of inter-cable shorting. 

The first inter-cable spurious operation involved the MOV-2 close coil. It actuated at 2798s for 

37 seconds, and the cable associated with this circuit was set in location B, directly above 

location A, where the inter-cable test configuration was located. The second inter-cable 

spurious operation occurred in location C and involved the MOV-1 open coil, which actuated at 

3579s for 15 seconds. 

Figure 5-23. Intermediate-scale test 10 cable loading 

Table 5-13. Intermediate-scale test 10 

Time (s) Failure Observation 

2502 SOV-2 Fuse Clear – Negative 

2635 – 2644 1-inch Valve SO 

2646 1-inch Valve Fuse Clear – Positive and Negative 

2798 – 2835 MOV-2 SO Close Coil 

 INTER-CABLE unknown source – likely inter-cable test circuit 

2890 Lg Coil Fuse Clear – Positive and Negative 

3108 SWGR-T SO [Breaker Open] 

3177 SWGR-C Fuse Clear – Positive 

3236 SWGR-C Fuse Clear – Negative 

3579 – 3594 MOV-1 SO Open Coil 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

TC

TC

1V

LC

NOT TO SCALE Inter-cable Circuit

TC

TC

S1

M1

TC TC TC

M2 SG-T/C S2
 

5-25 

Table 5-13. Intermediate-scale test 10 

Time (s) Failure Observation 

INTER-CABLE unknown source – likely inter-cable test circuit 

3594 – 3646 MOV-1 SO Close Coil 

INTER-CABLE unknown source – likely inter-cable test circuit

3594 – 3605 MOV-1 HS Open Coil 

INTER-CABLE unknown source – likely inter-cable test circuit

3646 SOV-2 Fuse Clear – Positive 

3646 SOV-1 Fuse Clear – Positive and Negative 

3646 MOV-1 Fuse Clear – Positive 

The inter-cable interactions that occurred during intermediate-scale test #10 could not be linked 

to any of the circuits that monitored current. Thus, these inter-cable interactions are likely a 

result of interactions from the inter-cable circuit, which was not equipped with current-monitoring 

transducers. These inter-cable interactions occurred in the MOV-2 and MOV-1 circuits. 

5.3.13 Test 11 

Intermediate-scale test 11 experienced one inter-cable ground equivalent hot short. Figure 5-24 

illustrates the cable loading configuration for test 11, and Table 5-14 presents the chronological 

fault mode sequence. The SOV-2 circuit went through spurious operation 2858s into the test, 

and was powered by the “P” conductor of the large coil circuit. This interaction is shown in 

Figure 5-25, where the large coil circuit is supplying power (positive current) and the SOV-2 

circuit is absorbing power (negative current). The cables that are connected to this circuit are 

located in different exposure locations; SOV-2 is in location D, directly above the large coil cable 

in location B. The different locations and a review of the ground fault detection circuit response, 

which shows that the battery positive shorted to ground at approximately 1440 seconds, indicate 

that this inter-cable interaction is a result of ground equivalent hot shorting. 

Figure 5-24. Intermediate-scale test 11 cable loading 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

+/- : power source cable

NOT TO SCALE

Inter-cable Circuit

1V M1 S1 LC

M2 S2

TC

ac1 ac3

+/-

ac2
 

5-26 

Table 5-14. Intermediate-scale test 11 

Time (s) Failure Observation 

1179 – 1197 MOV-1 SO Open Coil 

1182 – 1197 MOV-1 HS Close Coil 

1197 MOV-1 Fuse Clear – Positive and Negative 

1310 – 1312 1-inch Valve SO 

1319 – 1323 1-inch Valve SO 

1429 1-inch Valve Fuse Clear – Negative 

1432 Lg Coil SO 

1437 Lg Coil Fuse Clear – Negative 

1569 SOV-1 Fuse Clear – Positive and Negative 

2749 MOV-2 Fuse Clear – Negative – short with Lg Coil cond. P & G 

2858 – 2917 SOV-2 SA 

 INTER-CABLE shorting from Lg Coil conductors P 

2917 SOV-2 Fuse Clear – Negative 

3351 MOV-2 Fuse Clear – Positive 

3352 SOV-2 Fuse Clear – Positive 

Figure 5-25. Intermediate-scale test 11 current summation 

 

Time (s)

2840 2860 2880 2900 2920

Current (A)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

1-inch Valve 

Large Coil 

MOV-1 

MOV-2 

SOV-1 

SOV-2 
 

5-27 

5.3.14 Test 12 

The cable loading configuration for this test is shown in Figure 5-26. Intermediate-scale test 12 

experienced four inter-cable hot short-induced spurious operations. The source of the first two 

spurious operations could not be identified, and, due to the location of the inter-cable test 

configuration (location A), it is likely that the source came from this circuit. The other possible 

source is a 35A +/- cable that was used to evaluate the response of the high-current 

transducers. The current transducers did not pick up any current measurements; however, the 

laboratory had difficulties getting these high-current transducers to function properly, so, 

although it is unlikely that the 35A +/- cable was the source of the inter-cable interactions, the 

lack of reliable data for the large 500A current transducers does not completely rule out the 35A 

+/- cable. Fuses of the inter-cable circuit cleared at approximately 3125 seconds. After this 

time, the remaining two inter-cable spurious operations occurred, and the source cables for 

these interactions could be identified. The last piece of information that pointed to the intercable test cables being the source of the first two inter-cable spurious operations was that the 

inter-cable test configuration was located in Location A, as was done in intermediate-scale test 

10, which also experienced inter-cable shorting that could not identify the source cables. From 

all of these observations, it is highly probable that the source cable for the first two inter-cable 

shorting events is from the inter-cable test configuration in location A. 

Figure 5-26. Intermediate-scale test 12 cable loading 

Current summation plots are presented in Figure 5-27(a-d) for each of the inter-cable spurious 

operations. As shown in Figure 5-27(a) and (b), there is no source current in these plots from 

any of the surrogate circuits. Figure 5-27(c) and (d) show the source current from the 1-inch 

and large coil circuits, respectively. It is interesting to note that in Figure 5-27(d), the large coil 

cable is shorting via the ground to MOV-1 and 1-inch valve circuit, but no spurious operation 

results. 

 

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

+/- : power source cable 35A

M2 S2

TC

TC

M1

1V

NOT TO SCALE Inter-cable Circuit

ac1 ac2

LC

S1

TC

ac3

+/-
 

5-28 

Figure 5-27. Intermediate-scale test 12 current summation plot 

Table 5-15 presents the circuit failure mode summary for intermediate-scale test 12. The first 

inter-cable ground fault equivalent hot short-induced spurious operation involved energizing the 

MOV-2 close coil. The MOV-2 circuits-associated cable is in Location B, while the probable 

source (the inter-cable test configuration) is located directly below in Location A. Even if the 

35A +/- cable is the source, it is located in a different tray than the MOV-2 circuit, specifically in 

location C in the hot gas layer exposure. The next inter-cable spurious operation involves the 

Time (s)

2100 2150 2200 2250 2300 2350 2400

Current (A)

-1.0

-0.5

0.0

0.5

1.0

1-inch 

Large Coil 

MOV-1 

MOV-2 

SOV-1 

SOV-2 

SwGr 

Time (s)

2700 2720 2740 2760 2780 2800 2820 2840

Current (A)

-6

-4

-2

0

2

4

6

Time (s)

2860 2880 2900 2920 2940 2960 2980

Current (A)

-6

-4

-2

0

2

4

6

Time (s)

3100 3110 3120 3130 3140 3150 3160

Current (A)

-8

-6

-4

-2

0

2

4

6

8

(a) (b)

(c) (d)
 

5-29 

large coil circuit at 2746 seconds. This cable is located at the highest exposure position in the 

plume (location D). The probable source cable is the inter-cable test configuration located in the 

flame exposure, Location A. 

For the last two instances of spurious operation, it was possible to identify the source cables. 

The third ground equivalent hot short-induced spurious operation involved the 1-inch valve 

cable providing the source power to energize the large coil. In this case, both cables are in 

location D, and are located adjacent to each other (they make physical contact). The 

interactions between the ground plane and the battery potentials, as shown in Figure 5-28, 

indicate that this failure is associated with ground-plane interactions, so it is unlikely that this 

spurious operation was a cable-to-cable failure, and more likely that it was a ground equivalent 

hot short-induced spurious operation. 

Table 5-15. Intermediate-scale test 12 

Time (s) Failure Observation 

2233 – 2340 MOV-2 SO Close Coil 

 INTER-CABLE unknown source (not from 35A +/- cable) 

2314 SOV-2 Fuse Clear – Negative 

2343 MOV-2 Fuse Clear – Positive and Negative 

2540 SOV-2 Fuse Clear – Positive 

2746 – 2797 Lg Coil SO 

 INTER-CABLE unknown source (not from 35A +/- cable) 

2901 – 2939 Lg Coil SO 

INTER-CABLE 1-inch Valve conductor R via ground 

2939 1-inch Valve Fuse Clear – Positive 

3031 MOV-1 Fuse Clear – Positive 

3129 1-inch Valve Fuse Clear – Negative – shorting with Lg Coil 

3131 – 3136 SOV-1 SO 

INTER-CABLE Lg Coil conductor P via ground 

3141 SOV-1 Fuse Clear – Positive and Negative 

3143 Lg Coil SO 

3146 – 3154 Lg Coil SO 

3155 Lg Coil Fuse Clear – Positive 
 

5-30 

Figure 5-28. Ground fault detection voltage response for second large coil SO 

5.3.15 Contingency test A 

Contingency test A evaluated the anti-pump circuit of the medium-voltage switchgear and only 

two cables co-located in the same cable tray (location B) connected to the trip and close 

circuitry. This test’s cable loading configuration is shown in Figure 5-29, and a summary of the 

failure behavior is provided in Table 5-16. There were no inter-cable hot short-induced spurious 

operations observed during this test. 

Figure 5-29. Intermediate-scale test contingency A cable loading configuration 

Time (seconds)

2890 2900 2910 2920 2930 2940 2950

Voltage (Vdc)

-150

0

150

Fire Time (s) vs Ground_VT7_1 

Fire Time (s) vs Ground_VTU_1 

Fire Time (s) vs Ground_VTU_2 
 

5-31 

Table 5-16. Intermediate-scale contingency test A 

Time (s) Failure Observation 

 Note: Breaker is closed, and jumper is installed between C1 (close coil) and 

PC (positive power conductor); this is to evaluate anti-pump ckt 

406 SWGR-T SO [Breaker open] 

408 SWGR-C SO (self-induced due to jumper) [Breaker closed] 

409 SWGR-T SO [Breaker open] 

423 SWGR-C Fuse Clear – Negative 

5.3.16 Contingency test B 

Contingency test B is a repeat of contingency test A. The experimental set-up is the same as 

before, and is shown in Figure 5-29 above. Table 5-17 provides the circuit failure mode 

summary, indicating that no inter-cable hot short-induced spurious operations were observed 

during this test. 

Table 5-17. Intermediate-scale contingency test B 

Time (s) Failure Observation 

337 SWGR-T Fuse Clear – Negative 

354 SWGR-C Fuse Clear – Positive 

458 SWGR-C Fuse Clear – Negative 

5.3.17 Intermediate Scale – Inter-cable hot short induced spurious operation 

conclusions 

Table 5-18 summarizes the failure modes for each test by breaking down the initial failure mode 

into either intra-cable spurious operation, ground fault equivalent spurious operation, or a fuse 

clear. The table identifies the number of each failure type, and also lists the circuits that 

experienced those failures immediately below the number. 

It is interesting to note that a fair portion of inter-cable hot short-induced spurious operations 

occurred in the intermediate-scale testing. In particular, these types of failures occurred 

between cable trays located in different thermal exposure conditions. The fact that location E 

was only used in one test (Test 4) causes the authors to question whether there would have 

been more hot short inter-cable spurious operation with similar exposure conditions and cable 

loading configurations in locations C and E. Had these two locations used similar cable types 

and loading, this may have resulted in cable failures occurring within a similar time frame, and 

may have resulted in more inter-cable interactions. This is strictly the authors’ observation, and 

no data is available to confirm this hypothesis. However, this observation does bring into 

question the conservatism of the number of inter-cable hot short interactions that may have 

resulted in more realistic scenarios. The number of ground fault equivalent hot short induced 

spurious operations would depend on the cable loading within the affected fire area, the 

associated components that the cables are connected to, and the availability of a common 

power supply among the affected cables. 

 
 

5-32 

Table 5-18. Summary of initial failure mode for inter-cable test circuits 

Test 

# Intra-cable SO 

Inter-cable SO 

(Gnd equivalent 

SO) Fuse Clear 

1 3 

1-inch, MOV-2, SOV-2 

2 

Lg Coil, MOV-1 

2 

SOV-1, SWGR 

2 3 

MOV-1, MOV-2, SOV-2 

0 3 

1-inch, Lg Coil, SOV-1 

3 3 

MOV-1, MOV-2, SWGR 

2 

1-inch, SOV-2 

2 

Lg Coil, SOV-1 

4 2 

MOV-1, SOV-2 

0 5 

1-inch, Lg Coil, MOV-2, SOV-1, 

SWGR 

5 5 

Lg Coil, MOV-1, MOV-2, 

SOV-2, SWGR 

1 

SOV-1 

1 

1-inch 

6 4 

1-inch, MOV-1, SOV-1, 

SWGR 

0 3 

MOV-2, SOV-2, SWGR 

7 3 

1-inch, SOV-1, SWGR 

0 4 

Lg Coil, MOV-1, MOV-2, SOV-2 

8 2 

Lg Coil, SOV-1 

1 

MOV-1 

3 

1-inch, MOV-2, SOV-2 

9 2 

1-inch, SOV-1 

3 

MOV-1, MOV-2, 

SOV-2 

2 

Lg Coil, SWGR 

10 2 

1-inch, SWGR 

2 

MOV-1, MOV-2 

3 

Lg Coil, SOV-1, SOV-2 

11 4 

1-inch, Lg Coil, MOV-1, 

SWGR 

1 

SOV-2 

2 

MOV-2, SOV-1 

12 0 3 

Lg Coil, MOV-2, 

SOV-1 

4 

1-inch, MOV-1, SOV-2, SWGR 

Avg. 2.75/test 

40.25% of population 

1.25/test 

18.25% of population

3.83/test 

41.5% of population 
 

6-1 

6. SUMMARY OF FINDINGS 

6.1 Alternating Current Test Results 

(NEI/EPRI, CAROLFIRE, DESIREE-FIRE) 

Section 2 evaluated the experimental alternating current (AC) data by looking at various 

physical attributes that may influence the likelihood of an AC circuit experiencing a particular 

fire-induced fault mode, and also by evaluating the effects that these parameters have on hot 

short duration. This evaluation has proven difficult in numerous instances because the 

experimental set-up was based on configurations typically encountered in U.S. nuclear power 

plants (NPPs). Thus, in many cases, there is a large amount of data for one particular bin or 

configuration and minimal to no data to allow other configurations to provide an adequate 

comparison. The following parameters showed this to be true for the AC circuit fire-induced 

fault mode likelihood evaluation: 

 Conductor count (95% of data for 7-9/C count) 

 Cable orientation (95% of data for horizontal orientation) 

 Raceway routing (95% of data for cable tray; 3% conduit; 2% air drop) 

 Circuit grounding (88% of data is for grounded circuits) 

 Wiring configuration (95% of data has two sources, four targets, and one return) 

This review also showed that additional data may be useful in providing a more detailed 

evaluation of thermal exposure conditions. Here radiant exposures only contribute to 4.5% of 

the data set. 

Note that these recommendations only identify areas where additional data is needed to provide 

more information to better understand the associated physical configuration effect of the 

parameter under evaluation. These recommendations are not based on the applicability of the 

parameter’s actual use in U.S. NPPs. For instance, although it may be beneficial to have more 

data on ungrounded circuits to better evaluate their fault modes and hot short durations, it is 

likely that only a small portion of U.S. NPPs actually use ungrounded AC configurations. In this 

instance, priorities and resources may be better served collecting data to evaluate the effects of 

other parameters, such as cable orientation or cables in conduits. 

Parameters that showed signs of influencing the fault mode likelihood of fire-induced damage 

include: 

 Thermal exposure conditions 

o In the flame region, there is a higher likelihood of experiencing hot shorts (72%) 

and spurious operations (68%) than there is in the plume (46% SA, 59% HS) or 

hot gas layer (51% SA, 58% HS) exposures. 

 Raceway fill 

o Bundle configurations show a higher likelihood of hot shorts (74%) and spurious 

operations (70%) than cable trays with intermediate fill (47% HS, 37% SA) or 

single fill (48% HS, 35% SA). 

An interesting observation from analysis of the data is the fact that thermoset (TS)- and 

thermoplastic (TP)-insulated cables have nearly the same likelihood of experiencing a spurious 

operation. The NEI/EPRI data report identifies that thermoset insulated cables spuriously 

operated 26 out of 126 trials (20.6%), while the thermoplastic insulated cables spuriously 
 

6-2 

operated 19 out of 39 trials (48.7%). During the EPRI expert elicitation panel, one member 

identified this cable insulation material influence on spurious operation likelihood as a moderate 

dependence for intra-cable and significant for inter-cable hot shorts, while other members were 

silent on the insulation material influence on spurious operation likelihood. However, the EPRI 

expert elicitation report states the following with regard to the differences between thermoset 

and thermoplastic cables; 

“It is important to point out that, once cable damage has occurred, 

be it manifested as a hot short or as another phenomenon, the 

probability of spurious actuation given cable damage (PSACD) does 

not display significant differences between thermoset and 

thermoplastic cables” 

NUREG/CR-6850 adopted the conclusion from the EPRI expert elicitation report that insulation 

type does not influence spurious operation likelihood. At the beginning of the electrical expert 

PIRT panel a common belief among the panel members was that the two cable insulation types 

would have different likelihood of experiencing hot short-induced spurious operations; however, 

the data presented in this report does not substantiate this effect, and in fact shows that TPinsulated cables have a 51% likelihood of spurious operation, while TS-insulated cables have a 

52% likelihood, based on the data. After the material contained in this report was presented to 

the PIRT panel, they agreed unanimously that insulation type has no effect on spurious 

operation likelihood. Therefore, the data presented here and the PIRT panel’s conclusions 

suggest that insulation type makes no difference to the likelihood of experiencing one failure 

mode over another for the intra-cable category, although the polymer properties do influence the 

thermal failure point, that is, the point where the cable begins to degrade physically. 

In addition to evaluating the fault mode likelihoods, this report also explored the parameter 

effects on the duration of hot shorts and spurious operations. Those parameters where the data 

indicated an effect on the duration of hot shorts or spurious operations included: 

 Thermal exposure conditions 

o As the thermal exposure conditions become less intense, the durations of the hot 

shorts/spurious operations increase. 

 Raceway routing 

o Data indicated that air drops and conduit raceways have a longer duration than 

cable trays; however, there is only a limited data set for the air drop (2 tests) and 

conduit (4 tests) configurations. 

 Raceway fill 

o Intermediate raceway loading configurations have longer-lasting hot 

shorts/spurious operations than the other two configurations (bundle, single). 

 Conductor size 

The data shows that cables with 14 AWG conductors experience longer durations than cables 

with 12 AWG conductors. 

 
 

6-3 

6.2 Direct Current Test Results (DESIREE-FIRE) 

Section 4 evaluated the experimental data by looking at various physical attributes that may 

influence the likelihood of a DC circuit experiencing a particular fire-induced fault mode, and 

also by evaluating the effects that these parameters have on hot short duration of dc circuits. 

The entire dc test data set came from a single test series, namely, the U.S. Nuclear Regulatory 

Commission (NRC)-sponsored DESIREE-FIRE project. As a result of this being the first and 

only testing of dc circuits, not every configuration could be tested with the limited amount of 

resources available to perform the testing. This resulted in a number of configurations that 

lacked a sufficient variety of configurations to provide comparisons for the parameter under 

evaluation in this effort. Examples include: 

 Conductor count (94% 7-9/C, 3% 2-6/C, and 3% 10-15/C) 

 Cable orientation (100% of dc data utilized horizontal orientation) 

 Raceway routing (87% cable tray, 13% conduit, 0% air drop) 

 Conductor size (92% for #12 AWG conductors) 

 Cable shielding (93% non-shielded cable) 

Parameters that showed signs of influencing the fault mode likelihood of fire-induced damage 

include: 

 Raceway Fill (bundled configurations showed lower likelihood of spurious operations) 

 Armor (non-grounded circuits result in high spurious operation likelihood) 

 Circuit Type (motor-operated valve (MOV) circuit has larger likelihood of experiencing a 

spurious operation – two active targets) 

In the evaluation of the dc test data, the following parameters showed signs of influencing hot 

short duration: 

 Insulation type (TP longer than TS) 

 Insulation/Jacket type (TP-TP longest, followed by TS-TS, followed by TS-TP) 

 Conductor size (12 AWG has shorter durations than 14 AWG) 

 Fuse Size (larger fuses have longer hot short durations) 

6.3 Ground Equivalent Hot Shorts 

The analysis of the dc testing results has shown that shorts through ground plane or common 

conductors are possible, provided that the circuits involved are ungrounded and use a common 

power supply. Although this phenomenon was only observed in dc tests, it is likely that similar 

results would have occurred in the AC testing, had that testing been set up in a similar manner. 

Since the NRC AC tests only had one circuit ungrounded, there was no chance for such a 

failure mode to present itself in the NRC AC tests. 

This testing is the first observation of the ground equivalent hot short phenomenon. This 

phenomenon was theorized in NUREG/CR-6834, “Circuit Analysis – Failure Mode and 

Likelihood Analysis,” as multiple shorts to ground. However, little to no evidence was available 

at that time to substantiate the likelihood of such events. 
 

6-4 

The results from the DESIREE-FIRE testing now show that these events occurred quite 

frequently during the intermediate-scale testing. An important concept to take away from the 

data is that a maximum of eight circuits could be instrumented in each test, thus limiting the 

likelihood of multiple circuits shorting to ground at the same time to cause these ground fault 

equivalent hot shorts. Had the cable trays been loaded to the more typical loading 

configurations found in plants, it could be postulated that a higher percentage of ground 

equivalent hot shorts would have occurred. Another complicating factor is the fact that most dc 

circuits have fuses on both ends of the circuit. Thus, clearing a single fuse does not eliminate 

the possibility of experiencing a short to ground that may interact with another circuit shorted to 

ground. The last thought on this phenomenon is that some licensees have placed safetysignificant cables in dedicated conduits to provide some sort of separation or protection. The dc 

testing results have shown that, from a fire-induced failure standpoint, these cables are still 

vulnerable to ground equivalent hot shorts. 
 

7-1 

7. CONCLUSIONS AND FUTURE RESEARCH RECOMMENDATIONS 

Fire-induced circuit failure testing has evolved over the years, and today’s focus on obtaining 

realistic test results to advance the state-of-the-art in fire probabilistic risk assessment (PRA) 

has allowed the scientific community to better understand the failure modes of fire-induced 

electrical cable damage. The consolidation of the three major fire testing programs has allowed 

for a better understanding of key circuit parameters that can affect the likelihood of a circuit 

experiencing a particular failure mode and the duration of hot shorts. 

This report has identified that cable armor, raceway fill configurations, and circuit type can 

influence the fire-induced failure modes of electrical cable. To better understand the effect 

armor has, it is suggested that additional testing be conducted on armor and cables with 

metallic shields or drain wires. 

This consolidation has identified that concurrent hot shorts can occur and have occurred during 

testing. The opportunities for concurrent hot shorts to occur are increased when fire conditions 

exist to cause cable to fail at the same time. The information presented here shows that even 

different cable insulation types can experience concurrent spurious operation hot shorts due to 

different thermal exposure conditions causing the different cable types to fail during the same 

timeframe. 

This work has determined that multiple cable shorts to ground are plausible failure modes, and 

should be addressed in both deterministic and performance-based methods. Provided that an 

ungrounded power supply is used (such as is common for station batteries), the fire damage to 

control circuits powered from the same common power supply can result in shorts to ground 

causing system spurious operations. Although this failure mode was identified in NUREG/CR6834,”Circuit Analysis – Failure Mode and Likelihood Analysis,” it wasn’t until the DESIREE-Fire 

results were thoroughly reviewed that this failure mode was actually identified as actually 

occurring. 

This report has also identified areas where additional data would provide a better understanding 

of a parameter’s effect on a cable failure mode. Such areas include, expanding the range of 

conductor count within a multi-conductor control cable. The core set of data collected thus far 

has focused on 7-9/C cables. In the field, large multi-conductor cables commonly referred to as 

“trunk cables” are used to transmit control signals from the main control room to relay rooms, 

and auxiliary control rooms. There is no publicly available data on the fire-induced failures of 

these types of cables which commonly have 37 or more conductors per cable. 

The variation of cable types and failure criteria has also been limited in past testing. The 

majority of the cables tested was of a control type, and even when instrumentation or power 

cables were tested, the failure criteria were not tailored to the specific thresholds that would 

constitute a failure of the associated system in the field. As such the authors believe that there 

should be a fire testing standard developed to standardize the testing methods and 

acceptance/failure criteria of when cables experience functional failure. This standard would 

likely reduce the costs associated with testing and allow for an entity such as EPRI or NEI to 

collect such data for improvement of fire PRA estimation of conditional probabilities of cable 

damage. 

With the exception of a limited set of the NEI/EPRI test data, the cables were tested in a 

horizontal straight configuration. In field applications, there are commonly cable runs in vertical 
 

7-2 

and inclined configurations as well as bends and t-connections. Future testing should consider 

such configurations. 

A large majority of the AC testing has been limited to testing grounded AC circuits as this is a 

common configuration found in the field. However, the authors are aware of some plants that 

use ungrounded AC systems, and, as such, it is suggested that future research include a larger 

portion of typical ungrounded AC circuits to generate a more substantial set of data from which 

to develop conclusions. In particular, the likelihood of hot short and subsequent hot short 

durations for common ungrounded AC circuit designs should be evaluated. In addition, the AC 

data is sparse, and the use of conduits and any AC grounded/ungrounded tests should include 

conduit raceways to better understand the applicability of the current methodology in 

NUREG/CR-6850, relative to the credit given for reducing the likelihood of spurious operation 

when a cable is routed in conduit. 
 

8-1 

8. REFERENCES 

NRC NUREG/CR-6931, Vol. 1, “Cable Response to Live Fire (CAROLFIRE) Volume 1: Test 

Descriptions and Analysis of Circuit Response Data,” April 2008. 

NRC NUREG/CR-6931, Vol. 2, “Cable Response to Live Fire (CAROLFIRE) Volume 2: Cable 

Fire Response Data for Fire Model Improvement,” April 2008. 

NRC NUREG/CR-6931, Vol. 3, “Cable Response to Live Fire (CAROLFIRE) Volume 3: 

Thermally-Induced Electrical Failure (THIEF) Model,” April 2008. 

EPRI TR1003326, “Characterization of Fire-Induced Circuit Faults, Results of Cable Fire 

Testing,” December 2002. 

NRC NUREG/CR-7100, “Direct Current Electrical Shorting in Response to Exposure Fire 

(DESIREE-FIRE): Test Result” April 2012. 

Freund, J. and Perles, B., “A New Look at Quartiles of Ungrouped Data,” The American 

Statistician, Volume 41, Number 3, pgs 200-203, 1978. 

Anixter wire and cable handbook. 

NRC NUREG-1475, “Applying Statistics,” March 2011. 

NRC NUREG/CR-6834, “Circuit Analysis – Failure Mode and Likelihood Analysis,” September 

2003 

NRC NUREG/CR-6850, “EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities, 

Volume 2: Detailed Methodology” September 2005. 
 
Appendix A: Penlight Ground Fault Equivalent Inter-Cable 

Failure Mode Evaluation 

 

A-1 

A. Penlight Ground Fault Equivalent Inter-Cable Failure 

Mode Evaluation 

This section is going to review the inter-cable interactions for the direct current (DC) penlight 

tests. They will be discussed based on circuit (solenoid-operated valve (SOV), motor-operated 

valve (MOV), Large Coil, 1-inch valve, and switchgear (SWGR)). Since these tests were 

performed in Penlight, the only route for inter-cable interaction is through the ground via the 

cable tray. The tests displayed in this section are the tests that displayed inter-cable 

interactions. 

A.1 Penlight MOV Tests 

A.1.1 Penlight MOV Test #8 

The first MOV test to display inter-cable interactions was Penlight Test #8. The timeline for this 

experiment is shown below in Table A-1. Figure A-1 shows the outstanding current plot for this 

test, displaying inter-cable interactions between MOV-1 and MOV-2. Figure A-2 and Figure A-3 

display the current plots for MOV-1 and MOV-2, respectively, during the same time period as 

the outstanding current displayed in Figure A-1. From this, it is apparent that the red lamp on 

MOV-2 is flickering between times 478-480 because of the inter-cable interaction with MOV-1 

conductor P via the ground plane. 

Table A-1: Penlight test #8 sequence of events 

Time (s) Event/Observation 

0 Penlight on 

300 Cable Ignition 

465-514 Chatter – MOV-2 – Open & Close Coils 

467-513 

False Indication – MOV-2 – Green & Red lamps flicker 

ON/OFF 

478-480 

MOV-2 Red lamp flicker due to inter-cable interactions 

with MOV-1 conductor P via ground. 

498-502 Chatter – MOV-1 Open Coil 

502 False Indication – MOV-1 – Green Flickers Off/On 

505-538 False Indication – MOV-1 – Green lamp OFF 

514 Fuse Clear – MOV-2 

538-546 

MOV-1 SO – Open Coil (8s duration) 

False Indication – MOV-2 – Green lamp ON & Red lamp OFF 

546 Fuse Clear – MOV-1 

780 Penlight off 
 

A-2 

Figure A-1: Outstanding current shorting in Penlight MOV test #8 

Figure A-2: Penlight MOV-1 test #8 current plot 

Time (s)

476 478 480 482 484

Current (A)

-0.3

-0.2

-0.1

0.0

0.1

0.2

8-MOV1 

8-MOV2 

Time (s)

476 478 480 482 484

Current (A)

-0.2

-0.1

0.0

0.1

0.2

0.3

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 
 

A-3 

Figure A-3: Penlight MOV-2 test #8 current plot 

A.1.2 Penlight MOV Test #12 

The timeline for Penlight MOV Test #12 is shown below in Table A-2. Highlighted in red type 

are the inter-cable interactions between MOV-1 conductor N and MOV-2 conductor P via the 

ground plane. These low-current interactions did not cause any failure mode effects. This is 

represented graphically in Figure A-4, which shows the outstanding current shorting for this test. 

Figure A-5 and Figure A-6 display the conductors’ current for MOV-1 and MOV-2, respectively. 

Table A-2: Penlight test #12 sequence of events 

Time (s) Event/Observation 

0 Penlight on 

863-1066 MOV-1 SO – Open Coil (203s duration) 

863-966 False Indication (Red off - No Voltage Pickup on R) 

945-1062 HS MOV-1 – Close Coil 

990-1066 Grounding of Positive battery lead 

1066 Fuse Clear MOV-1 – Positive 

1066 Grounding of Negative battery lead 

1066 Current increase to 0.08A on Negative of MOV-2 

1323-2321 

Inter-cable interactions off and on between MOV-1 conductor N and MOV-2 

conductor P via ground 

1335 Penlight off 

1350 Fuse Clear – MOV-2 – Negative 

1635 Penlight turned back on 

2350 Fuse Clear – MOV-1 – Negative 

2400 Penlight off 

Time (s)

476 478 480 482 484

Current (A)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-4 

Figure A-4: Outstanding current shorting in Penlight MOV test #12 

Figure A-5: Penlight MOV-1 test #12 current plot 

Time (s)

1200 1400 1600 1800 2000 2200 2400

Current (A)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

MOV1 

MOV2 

Time (s)

1200 1400 1600 1800 2000 2200 2400

Current (A)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 
 

A-5 

Figure A-6: Penlight MOV-2 test #12 current plot 

A.1.3 Penlight MOV Test #22 

The sequence of events for Penlight MOV Test #22 is presented below in Table A-3. As shown, 

there are four spurious operations caused by inter-cable interactions. These are highlighted in 

red in Table A-3. Figure A-7 displays the outstanding current shorting for this test relative to the 

time frame of those four spurious operations. The specific conductors causing the inter-cable 

interactions were identified from the conductors’ current plots for MOV-1 and MOV-2 (Figure A-8 

and Figure A-9, respectively),. 

Table A-3: Penlight test #22 sequence of events 

Time (s) Event/Observation 

0 Penlight on 

174 Smoke observed 

285-572 Cable ignition of the outer jacket material 

585-592 Intermittent grounding of battery positive and negative 

585-587 

SA MOV-1 – Open Coil (2s duration) due to inter-cable interactions 

between MOV-1 conductor YO and MOV-2 conductor G via ground 

586-595 Chatter – MOV-1 & MOV-2 – Open & Close coils 

589-591 

SA MOV-1 – Open Coil (2s duration) due to inter-cable interactions 

between MOV-1 conductor YO and MOV-2 conductor G via ground 

595-631 Grounding of positive lead 

593-633 

SA MOV-1 – Open Coil (40s duration) due to inter-cable interactions 

between MOV-1 conductor YO and MOV-2 conductor G via ground 

Battery Positive shorts to ground 

595-633 

SA MOV-2 – Open Coil (38s duration) due to inter-cable interactions 

between MOV-2 conductor YO and MOV-1 conductor G via ground 

False Indication – MOV-2 – Green lamp ON 

Time (s)

1200 1400 1600 1800 2000 2200 2400

Current (A)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-6 

Table A-3: Penlight test #22 sequence of events 

Time (s) Event/Observation 

596-633 HS MOV-2 – Close Coil (37s duration) 

633 Fuse Clear - MOV-1 

633 Fuse Clear - MOV-2 

785 Penlight off 

Figure A-7: Outstanding current shorting in Penlight MOV test #22 

Figure A-8: Penlight MOV-1 test #22 current plot 

Time (s)

580 590 600 610 620 630 640

Current (A)

-1

0

1

2

MOV1 

MOV2 

Time (s)

580 590 600 610 620 630 640

Current (A)

0

1

2

3

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 
 

A-7 

Figure A-9: Penlight MOV-2 Test #22 current plot 

A.1.4 Penlight MOV Test #33 

For Penlight MOV Test #33, the sequence of events is displayed in Table A-4. As shown, there 

is one inter-cable interaction between MOV-1 and MOV-2 that does not cause any cable failure 

modes to occur. This is shown to display a sharp single spike in the outstanding current 

calculation (Figure A-10). From this current spike and looking at Figure A-11 and Figure A-12 

(MOV-1’s and MOV-2’s conductors’ current plots, respectively), the inter-cable interaction was 

identified as occurring between MOV-1 conductor P with MOV-2 conductors N and YC via the 

ground plane. 

Table A-4: Penlight test #33 sequence of events 

Time (s) Event/Observation 

0 Penlight on 

538-626 Battery Negative Shorts to Ground 

575 Fuse Clear – MOV-2 

611-626 HS MOV-1 – Close coil – no corresponding current 

620-621 

Inter-cable interactions with MOV-1 conductor P with MOV-2 conductor N, 

and YC via ground 

627 Fuse Clear – MOV-1 

705 Penlight off 

Time (s)

580 590 600 610 620 630 640

Current (A)

0

1

2

3

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-8 

Figure A-10: Outstanding current shorting in Penlight MOV test #33 

Figure A-11: Penlight MOV-1 test #33 current plot 

Time (s)

500 550 600 650 700

Current (A)

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

MOV1 

MOV2 

Time (s)

500 550 600 650 700

Current (A)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 
 

A-9 

Figure A-12: Penlight MOV-2 test #33 current plot 

A.1.5 Penlight MOV Test #37 

For Penlight MOV Test #37, there was one spurious operation caused by inter-cable 

interactions. This is highlighted below in Table A-5 in the sequence of events for this test. 

Figure A-13 displays the outstanding current calculation for MOV-1 and MOV-2. From this plot, 

it is noted that there are inter-cable interactions during the time of the spurious operation on 

MOV-1 close coil. From Figure A-14 and Figure A-15 (MOV-1 and MOV-2 conductor current 

plots respectively), the inter-cable interaction is between MOV-1 conductor G and MOV-2 

conductor YC via the ground plane. 

Table A-5: Penlight test #37 sequence of events 

Time (s) Event/Observation 

0 Penlight on 

1681-1711 SA MOV-1 – Close Coil (30s duration) 

1692-1712 

False Indication – MOV-1 – Red ON 

 (note: auxiliary contact failure) 

1712 Fuse Clear – MOV-1 

1723-1739 

SA MOV-2 – Close Coil (16s duration) Inter-cable interactions 

between MOV-1 conductor G and MOV-2 conductor YC via ground 

1731-1739 

False Indication – MOV-2 – Red ON 

 (note: auxiliary contact failure) 

1740 Fuse Clear - MOV-2 

1830 Penlight off 

Time (s)

500 550 600 650 700

Current (A)

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-10 

Figure A-13. Outstanding current shorting in Penlight MOV Test #37 

Figure A-14. Penlight MOV-1 Test #37 current plot 

Time (s)

1600 1650 1700 1750 1800 1850

Current (A)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

MOV1 

MOV2 

Time (s)

1600 1650 1700 1750 1800 1850

Current (A)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 
 

A-11 

Figure A-15. Penlight MOV-2 Test #37 current plot 

A.1.6 Penlight MOV Test #41 

The sequence of events for Penlight MOV Test #41 is presented below in Table A-6. As shown, 

there are two spurious operations caused by inter-cable interactions and one inter-cable 

interaction that does not cause an immediate failure mode effect. These are highlighted in red 

in Table A-6. Figure A-16 displays the outstanding current shorting for this test relative to the 

time frame of those four spurious operations. The specific conductors causing the inter-cable 

interactions were identified from the conductors’ current plots for MOV-1 and MOV-2 (Figure A17 and Figure A-18, respectively). 

Table A-6. Penlight Test #41 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

317 Smoke observed 

1307-1405 SA MOV-2 – Close Coil (98s duration) 

2462-2894 HS MOV-2 – Open Coil 

2560-2649 Battery Negative shorts to ground 

2562 – 2895 Cable thermocouple within conduit displaying off-normal readings 

2626-2648 SA MOV-2 – Close Coil (22s duration) 

2692-2755 Battery Positive shorts to ground 

2699-2759 SA MOV-1 – Open Coil (60s duration) 

2753-2759 

SA MOV-2 – Close Coil (6s duration) due to inter-cable interactions with 

MOV-1 conductor G via ground. 

2755-2790 Battery Negative shorts to ground 

2776-2777 

SA MOV-1 – Open Coil (1s duration) weak signs of inter-cable interactions 

with MOV-2 conductor G via ground.

Time (s)

1600 1650 1700 1750 1800 1850

Current (A)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-12 

Table A-6. Penlight Test #41 sequence of events. 

Time (s) Event/Observation 

2776-2838 HS MOV-1 – Open & Close coils – 118 & 112 Vdc, respectively 

2790-2791 SA MOV-1 – Open Coil (1s duration) 

2790-2840 Battery Positive shorts to ground 

2825-2834 

Inter-cable interactions with MOV-1 conductor P and MOV-2 conductor N 

via ground. 

2837-2838 SA MOV-1 – Open Coil (1s duration) 

2839 Fuse Clear – MOV-1 

2872-2874 SA MOV-2 – Close Coil (2s duration) 

2894 Fuse Clear – MOV-2 

3255 Penlight off 

Figure A-16. Outstanding current shorting in Penlight MOV Test #41 

Time (s)

2700 2720 2740 2760 2780 2800 2820 2840

Current (A)

-1.0

-0.5

0.0

0.5

1.0

MOV1 

MOV2 
 

A-13 

Figure A-17. Penlight MOV-1 Test #41 current plot 

Figure A-18. Penlight MOV-2 Test #41 current plot 

 

Time (s)

2700 2720 2740 2760 2780 2800 2820 2840

Current (A)

-2

-1

0

1

2

3

4

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 

Time (s)

2700 2720 2740 2760 2780 2800 2820 2840

Current (A)

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-14 

A.1.7 Penlight MOV Test #49 

The sequence of events for Penlight MOV Test #49 is presented below in Table A-7. As shown, 

there is one spurious operation and one fuse clear caused by inter-cable interactions. These 

are highlighted in red in Table A-7. Figure 19 displays the outstanding current shorting for this 

test relative to the time frame of those four spurious operations. The specific conductors 

causing the inter-cable interactions were identified from the conductors’ current plots for MOV-1 

and MOV-2 (Figure 20 and Figure 21, respectively). 

Table A-7. Penlight Test #49 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

755 Liquid exiting TC cable 

2400 Penlight increased to 440 °C 

4394-4401 SA MOV-1 – Close Coil (7s duration) 

4402 MOV-1 Fuse Clear 

4402-4824 Battery Negative shorts to ground 

4620 Penlight off 

~4820 Interactions between MOV-1 and MOV-2 circuits 

4823 

SA MOV-2 – Open Coil (<1s duration) with intra-cable interactions 

with conductors P and N also with inter-cable interaction with MOV-1 

conductor N via ground. 

4824 

MOV-2 Fuse Clear caused by inter-cable interactions between MOV-1 

conductor N and MOV-2 conductors R and N. 

Figure A-19. Outstanding current shorting in Penlight MOV Test #49 

Time (s)

4800 4810 4820 4830 4840

Current (A)

-2

-1

0

1

2

MOV1 

MOV2 
 

A-15 

Figure A-20. Penlight MOV-1 Test #49 current plot 

Figure A-21. Penlight MOV-2 Test #49 current plot 

 

Time (s)

4800 4810 4820 4830 4840

Current (A)

-0.5

0.0

0.5

1.0

1.5

2.0

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 

Time (s)

4800 4810 4820 4830 4840

Current (A)

0

1

2

3

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-16 

A.1.8 Penlight MOV Test #50 

The sequence of events for Penlight MOV Test #50 is presented below in Table A-8. As shown, 

there is one hot short and one fuse clear caused by inter-cable interactions. These are 

highlighted in red in Table A-8. Figure A-22 displays the outstanding current shorting for this 

test relative to the time frame of those four spurious operations. The specific conductors 

causing the inter-cable interactions were identified from the conductors’ current plots for MOV-1 

and MOV-2 (Figure A-23 and Figure A-24, respectively). 

Table A-8. Penlight Test #50 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

420 Liquid exiting end of TC cable 

822 Cable Ignition 

1164-1181 False Indication MOV-2 – Red lamp ON 

1242-1334 Battery Positive shorts to ground 

1242-1264 

SA MOV-2 – Close Coil (22s duration) caused by inter-cable 

interactions between MOV-2 conductor YC and MOV-1 conductor 

G via ground. 

1267 

Fuse Clear – MOV-2 caused by inter-cable interactions between 

MOV-2 conductor YC and N with MOV-1 conductor N via ground. 

1279-1300 False Indication – MOV-1 – Red lamp ON 

1334 Fuse Clear – MOV-1 

1440 Penlight off 

Figure A-22. Outstanding current shorting in Penlight MOV Test #50 

Time (s)

1200 1220 1240 1260 1280 1300 1320 1340

Current (A)

-6

-4

-2

0

2

4

MOV1 

MOV2 
 

A-17 

Figure A-23. Penlight MOV-1 Test #50 current plot 

Figure A-24. Penlight MOV-2 Test #50 current plot 

A.1.9 Penlight MOV Test #JPN-3 

For Penlight MOV Test #JPN-3, the sequence of events is displayed in Table A-9. As shown, 

there is one inter-cable interaction between MOV-1 and MOV-2 that caused the red light to turn 

on. The outstanding current shorting is displayed in Figure A-25 for MOV-1 and MOV-2. From 

this current spike and from looking at Figure A-26 and Figure A-27 (MOV-1 and MOV-2 

conductor current plots, respectively), the inter-cable interaction was identified as occurring 

between MOV-1 conductor R with MOV-2 conductors N and P via the ground plane. 

 

Time (s)

1200 1220 1240 1260 1280 1300 1320 1340

Current (A)

0

1

2

3

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 

Time (s)

1200 1220 1240 1260 1280 1300 1320 1340

Current (A)

0

1

2

3

4

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-18 

Table A-9. Penlight Test #JPN-3 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

1974-2501 Battery Positive shorts to ground 

2308-2502 

SA MOV-2 – Open Coil (194s duration) 

HS MOV-2 – Close Coil 

2318-2501 False Indication – MOV-2 – Green lamp ON 

2320-2502 

False Indication – MOV-1 – Red lamp ON due to inter-cable 

interactions with MOV-2 conductor N and P via ground. 

2463 Cable Ignition 

2502 Fuse Clear – MOV-2 

2626-2759 False Indication – MOV-1 – Red lamp OFF & Green lamp ON 

2626-2866 SA MOV-1 – Open Coil (240s duration) 

2761-2866 

Battery Negative shorts to ground 

False Indication – MOV-1 Red lamp OFF & Green lamp ON 

2866 Fuse Clear – MOV-1 

2930 Penlight off 

Figure A-25. Outstanding current shorting in Penlight MOV Test #JPN-3 

Time (s)

2200 2300 2400 2500 2600

Current (A)

-0.2

-0.1

0.0

0.1

MOV1 

MOV2 
 

A-19 

Figure A-26. Penlight MOV-1 Test # JPN-3 current plot 

Figure A-27. Penlight MOV-2 Test # JPN-3 current plot 

 

Time (s)

2000 2200 2400 2600 2800 3000

Current (A)

0.0

0.2

0.4

0.6

0.8

MOV1-P

MOV1-N

MOV1-G 

MOV1-R 

MOV1-YO 

MOV1-YC 

Time (s)

2000 2200 2400 2600 2800 3000

Current (A)

0.0

0.1

0.2

0.3

MOV2-P 

MOV2-N 

MOV2-G 

MOV2-R 

MOV2-YO 

MOV2-YC 
 

A-20 

A.2 Penlight SOV Tests 

This section will discuss the inter-cable interaction results for the Penlight SOV tests. The tests 

that showed inter-cable interactions will be discussed. There were some issues with some of 

the current transducers drifting during these tests, so the tests that clearly showed signs of intercable interactions are the ones described below. 

A.2.1 Penlight SOV Test #20 

For Penlight SOV Test #20, the sequence of events is displayed in Table A-10. The spurious 

operation caused by the inter-cable interaction is highlighted in red. The outstanding current 

plot, the SOV-1 conductors’ current plot, and the SOV-2 conductors’ current plot are shown in 

Figure A-28, Figure A-29, and Figure A-30, respectively. From these three plots, the inter-cable 

interaction was determined to occur between SOV-2 conductor S2 and SOV-1 conductor G via 

the ground plane. 

Table A-10. Penlight Test #20 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

250 Cable Ignition 

483-526 Battery Positive Shorts to Ground 

484-526 SOV-1 False Indication Red lamp ON 

502-526 SOV-1 SO (~0.078 A) [24s duration]

508-528 

SOV-2 SO (~0.059 A) [20s duration] due to inter-cable interactions with 

SOV-1 conductor G via ground. 

524-528 SOV-2 False Indication Red lamp ON 

526 SOV-1 Fuse Clear 

529-556 Battery Positive Shorts to Ground 

530-556 

SOV-2 SO (~0.082 A) [26s duration] and 

SOV-2 False Indication Red Lamp ON 

556 SOV-2 Fuse Clear 

646 Penlight off 
 

A-21 

Figure A-28. Outstanding current shorting in Penlight SOV Test #20 

Figure A-29. Penlight SOV-1 Test #20 current plot 

Time (s)

500 510 520 530 540 550

Current (A)

-0.2

-0.1

0.0

0.1

0.2

SOV1 

SOV2 

Time (s)

500 510 520 530 540 550

Current (A)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

SOV1-P

SOV1-S1

SOV1-G

SOV1-S2

SOV1-N 
 

A-22 

Figure A-30. Penlight SOV-2 Test #20 current plot 

A.2.2 Penlight SOV Test #28 

For Penlight SOV Test #28, the sequence of events is displayed in Table A-11. The spurious 

operation caused by the inter-cable interaction is highlighted in red. The outstanding current 

plot, SOV-1 conductors’ current plot, and SOV-2 conductors’ current plot are shown in Figure A31, Figure A-32, and Figure A-33, respectively. From these three plots, the inter-cable 

interaction was determined to occur between SOV-2 conductor S2 and SOV-1 conductor P via 

the ground plane. 

Table A-11. Penlight Test #28 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

2400 Penlight Increased to 350 °C 

2958-3384 SOV-1 False Indication Red lamp ON 

3360 Penlight Increased to 375 °C 

3384 SOV-1 Fuse Clear 

3393-3690 

SOV-2 SO (~0.071 A) [297s duration] due to inter-cable interactions 

between MOV-2 conductor P 

3597-3690 SOV-2 False Indication Red lamp ON 

3690 SOV-2 Fuse Clear 

3820 Penlight off 

Time (s)

500 510 520 530 540 550

Current (A)

-0.2

0.0

0.2

0.4

SOV2-P 

SOV2-S1

SOV2-G 

SOV2-S2 

SOV2-N 
 

A-23 

Figure A-31. Outstanding current shorting in Penlight SOV Test #28 

Figure A-32. Penlight SOV-1 Test #28 current plot 

Time (s)

3300 3400 3500 3600 3700 3800 3900

Current (A)

-0.08

-0.06

-0.04

-0.02

0.00

SOV1 

SOV2 

Time (s)

3300 3400 3500 3600 3700 3800 3900

Current (A)

-0.10

-0.05

0.00

0.05

0.10

0.15

SOV1-P

SOV1-S1

SOV1-G

SOV1-S2

SOV1-N 
 

A-24 

Figure A-33. Penlight SOV-2 Test #28 current plot

A.2.3 Penlight SOV Test #31 

For Penlight SOV Test #31, the sequence of events is displayed in Table A-12. The hot short 

caused by the inter-cable interaction is highlighted in red. The outstanding current plot, SOV-1 

conductors’ current plot, and SOV-2 conductors’ current plot are shown in Figure A-34, Figure 

A-35, and Figure A-36, respectively. From these three plots, the inter-cable interaction was 

determined to occur between SOV-2 conductor R and SOV-1 conductor N via the ground plane. 

Table A-12. Penlight Test #31 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

414 Battery Positive Shorts to Ground 

414-431 

SOV-2 False Indication Green Lamp ON caused by inter-cable 

interactions with SOV-1 conductor N. 

432 SOV-2 Fuse Clear 

455-420 

Battery Positive Shorts to Ground and 

SOV-1 False Indication Red lamp ON 

517-520 SOV-1 SO (~0.084 A) [3s duration]

520 SOV-1 Fuse Clear 

579 Penlight off 

Time (s)

3300 3400 3500 3600 3700 3800 3900

Current (A)

-0.10

-0.05

0.00

0.05

0.10

0.15

SOV2-P 

SOV2-S1

SOV2-G 

SOV2-S2 

SOV2-N 
 

A-25 

Figure A-34. Outstanding current shorting in Penlight SOV Test #31 

Figure A-35. Penlight SOV-1 Test #31 current plot 

Time (s)

400 420 440 460 480 500

Current (A)

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

SOV1 

SOV2 

Time (s)

400 420 440 460 480 500

Current (A)

0.00

0.05

0.10

0.15 SOV1-P

SOV1-S1

SOV1-G

SOV1-S2

SOV1-N 
 

A-26 

Figure A-36 Penlight SOV-2 Test #31 current plot 

A.3 Penlight large coil and 1-inch valve tests 

A.3.1 Penlight large coil and 1-inch valve Test #11 

For the Penlight large coil and the 1-inch valve circuit in Test #11, the sequence of events is 

displayed in Table A-13. There were two spurious operations caused by inter-cable 

interactions, which are highlighted in red. The outstanding current plot, 1-inch valve conductors’ 

current plot, and large coil conductors’ current plot are shown in Figure A-37, Figure A-38, and 

Figure A-39, respectively. From these three plots, the first inter-cable interaction was 

determined to occur between large coil conductor S and 1-inch valve conductors G and R via 

the ground plane. The second inter-cable interaction was determined to occur between 1-inch 

valve conductor S and large coil conductor P via the ground plane. 

Table A-13. Penlight Test #11 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

1087-1141 Battery Positive shorts to ground 

1089-1104 False Indication – 1-inch valve – Red lamp ON 

1089-1141 

SA – Large Coil (52s duration) – caused by inter-cable interaction with 1-

inch valve conductor G and R via ground. 

1109 

SA – 1-inch valve (<1s duration) 

False Indication – 1-inch valve – Green lamp ON 

1110-1130 False Indication – 1-inch valve – Red lamp ON 

1130-1141 

SA – 1-inch valve (11s duration) 

False Indication – 1-inch valve – Green lamp ON 

1142-1455 Battery Negative shorts to ground 

1142-1455 False Indication – 1-inch valve –Green lamp OFF 

Time (s)

400 420 440 460 480 500

Current (A)

0.0

0.1

0.2

0.3

SOV2-P 

SOV2-S1

SOV2-G 

SOV2-S2 

SOV2-N 
 

A-27 

Table A-13. Penlight Test #11 sequence of events. 

Time (s) Event/Observation 

1456-1464 False Indication – 1-inch valve – Red lamp ON 

1456-2457 SA – Large Coil (1001s duration) 

1464-1835 False Indication – 1-inch valve – Green lamp ON 

1464-2457 Battery Positive shorts to ground 

1464-2262 

SA – 1-inch valve (798s duration) due to inter-cable interaction between 

Large Coil conductor P via ground. 

1534-2457 False Indication – 1-inch valve – Red lamp ON 

1930-2262 False Indication – 1-inch valve – Green lamp ON 

2262 Fuse Clear – 1-inch valve (10A) 

2457 Fuse Clear – Large Coil (25A) 

2495 Cable Ignition 

2795 Penlight off 

Figure A-37. Outstanding current shorting in Penlight 1-inch valve and large coil Test #11 

Time (s)

1000 1500 2000 2500 3000

Current (A)

-4

-2

0

2

4

1-inch Valve

Large Coil
 

A-28 

Figure A-38. Penlight 1-inch valve Test #11 current plot 

Figure A-39. Penlight large coil Test #11 current plot 

A.3.2 Penlight Large Coil and 1-inch valve Test #40 

For the Penlight Large Coil and the 1-inch valve Test #40, the sequence of events is displayed 

in Table A-14. There were two spurious operations caused by inter-cable interactions, which 

are highlighted in red. The outstanding current plot, 1-inch valve conductors’ current plot, and 

Large Coil conductors’ current plot are shown in Figure A-40, Figure A-41, and Figure A-42, 

respectively. From these three plots, the first inter-cable interaction was determined to occur 

between Large Coil conductor S and 1-inch valve conductors G and R via the ground plane. 

The second inter-cable interaction was determined to occur between Large Coil conductor S 

and 1-inch valve conductors N2 and S via the ground plane. 

 

Time (s)

1000 1500 2000 2500 3000

Current (A)

-1

0

1

2

3

4

5

1-inch Valve - P

1-inch Valve - G

1-inch Valve - R

1-inch Valve - N2

1-inch Valve - S

1-inch Valve - N1

Time (s)

1000 1500 2000 2500 3000

Current (A)

0

1

2

3

4 Large Coil - P

Large Coil - G

Large Coil - N2

Large Coil - S

Large Coil - N1
 

A-29 

Table A-14. Penlight Test #40 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

3345 Penlight increased to 475 °C 

3985 Penlight increased to 500 °C 

4063-4166 Battery Positive shorts to ground 

4068-4166 False Indication – Large Coil – Red lamp ON 

4100-4164 

SA – Large coil (64s duration) due to inter-cable interaction 

between 1”Valve conductors G and R via ground. 

4167-4312 Battery Negative shorts to ground 

4167 Fuse Clear – 1-inch valve (10A) 

4280 Penlight off 

4314-4329 

SA – Large coil (15s duration) cause by inter-cable interactions with 

1-inch valve conductors N2 and S via ground. 

4317-4329 False Indication – Large Coil – Red lamp ON 

4330-4330 Battery negative shorts to ground 

4330 Fuse Clear – Large coil (25A) 

Figure A-40. Outstanding current shorting in Penlight 1-inch valve and large Coil Test #40 

Time (s)

4000 4100 4200 4300 4400

Current (A)

-4

-2

0

2

4

1-inch Valve

Large Coil
 

A-30 

Figure A-41. Penlight 1-inch valve Test #40 current plot 

Figure A-42. Penlight large coil Test #40 current plot 

 

Time (s)

4000 4100 4200 4300 4400

Current (A)

0

1

2

3

4

1-inch Valve - P

1-inch Valve - G

1-inch Valve - R

1-inch Valve - N2

1-inch Valve - S

1-inch Valve - N1

Time (s)

4000 4100 4200 4300 4400

Current (A)

0

1

2

3

4

Large Coil - P

Large Coil - G

Large Coil - N2

Large Coil - S

Large Coil - N1
 

A-31 

A.4 Penlight SWGR Tests 

The last set of penlight tests to be discussed is the SWGR tests for both the trip and close 

circuits. This section will discuss the SWGR tests where inter-cable interactions were identified. 

A.4.1 Penlight SWGR Test #4 

For Penlight SWGR Test #4, the sequence of events is displayed in Table A-15. There was one 

spurious operation caused by inter-cable interactions, which is highlighted in red. The 

outstanding current plot, Close Circuit conductors’ current plot, and Trip Circuit conductors’ 

current plot are shown in Figure A-43, Figure A-44, and Figure A-45, respectively. From these 

three plots, the inter-cable interaction was determined to occur between Trip Circuit conductor 

PT and the Close Circuit conductor N1 via the ground plane. 

Table A-15. Penlight Test #4 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

299 Cable Ignition 

550-597 False Indication Red lamp ON 

568-640 

Cable thermocouples providing abnormal results, perhaps due to the arcing 

behavior 

577-581 False Indication Green lamp OFF 

589-625 HS Trip Coil (Breaker remains Open) 

598-625 False Indication Green lamp OFF 

623-638 Positive Battery Lead Shorts to Ground 

625 SA Close Coil (Breaker Closes) 

625-626 HS Close Coil (Breaker remains Closed) 

625-626 False Indication Red lamp OFF 

626 SA Trip Coil (Breaker Opens) 

626-632 False Indication Green lamp OFF 

632 SA Close Coil (Breaker Closes) 

632-634 HS Close Coil (Breaker remains Closed) 

632-635 False Indication Red lamp OFF 

635 

SA Trip Coil (Breaker Opens) due to inter-cable interaction with 

SWGR Close Circuit conductor N1 via ground. 

635-698 HS Trip Coil (Breaker remains Open) 

635-700 False Indication Green lamp OFF 

638 Fuse Clear Close Circuit (15A) 

639-1638 Battery Negative shorts to ground 

701-1440 False Indication Red lamp ON 

719-728 HS Trip Coil (Breaker remains Open) 

1441-1637 False Indication Green lamp OFF 

1638 Penlight off 
 

A-32 

Figure A-43. Outstanding current shorting in Penlight SWGR Test #4 

Figure A-44 Penlight SWGR Close Test #4 current plot 

Time (s)

620 625 630 635 640 645 650

Current (A)

0

1

2

3

4

Close

Trip

Time (s)

620 625 630 635 640 645 650

Current (A)

0

1

2

3

4

Close - PC

Close - N1
 

A-33 

Figure A-45 Penlight SWGR Trip Test #4 current plot 

A.4.2 Penlight SWGR Test #JPN-2 

For Penlight SWGR Test #JPN-2, the sequence of events is displayed in Table A-16. There 

was one false red lamp indication caused by inter-cable interactions, which is highlighted in red. 

The outstanding current plot, Close Circuit conductors’ current plot, and Trip Circuit conductors’ 

current plot are shown in Figure A-46, Figure A-47, and Figure A-48, respectively. From these 

three plots, the inter-cable interaction was determined to occur between Trip Circuit conductor R 

and the Close Circuit conductor N1 via the ground plane. This is a weak indication of an intercable interaction, and most of this current analysis may not have picked up all of these types of 

indications of inter-cable interactions. 

Table A-16. Penlight Test #JPN-2 sequence of events. 

Time (s) Event/Observation 

0 Penlight on 

978-1361 Voltage loss on Trip circuit “R” conductor (~100Vdc) 

1322-1456 Battery Negative shorts to Ground 

1362-1456 

False Indication Red lamp ON 

 This is an Inter-cable hot short between Trip cable “R” conductor and 

 Close cable N1 conductor via ground 

1457 Fuse Clear – Close Coil 

1457-2071 Battery Positive shorts to Ground 

2072-2120 False Indication Red lamp ON 

2072-2111 Battery Negative shorts to Ground 

2112-2430 Battery Positive shorts to Ground 

2121-2430 False Indication Red lamp ON 

2430 Penlight off 

Time (s)

620 625 630 635 640 645 650

Current (A)

0

1

2

3

4

Trip - PT

Trip - G

Trip - R

Trip - N2
 

A-34 

Figure A-46. Outstanding current shorting in Penlight SWGR Test #JPN-2 

Figure A-47. Penlight SWGR Close Test #JPN-2 current plot 

Time (s)

1300 1350 1400 1450 1500

Current (A)

-0.10

-0.05

0.00

0.05

0.10

Close

Trip

Time (s)

1300 1350 1400 1450 1500

Current (A)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Close - PC

Close - N1
 

A-35 

Figure A-48. Penlight SWGR Trip Test #JPN-2 current plot 

Time (s)

1300 1350 1400 1450 1500 1550 1600

Current (A)

-0.2

-0.1

0.0

0.1

0.2

Trip - PT

Trip - G

Trip - R

Trip - N2

Appendix B: Supplemental Information for the CAROLFIRE 

Reports, Including Additional Data Retrieval 

 

B-1 

B. Supplemental Information for the CAROLFIRE Reports, 

Including Additional Data Retrieval 

B.1. Introduction 

This document is meant to help readers of the Cable Response to Live Fire (CAROLFIRE) 

reports7

 to better understand the project, its diagnostic equipment, and certain of its data, 

including some that is not explicitly discussed in the reports. It is not intended to be a standalone document, and makes frequent reference to the CAROLFIRE reports and the extensive 

data files distributed with them. It is therefore essential that the referenced material be available 

to users of this document. This document provides a better explanation of certain aspects of 

the equipment and tests by collecting and organizing material that is scattered among different 

locations in Volumes 1 and 2, and it also presents additional details obtained from the Sandia 

National Laboratories (SNL) authors that are not in those volumes. 

CAROLFIRE utilized two different, complementary electrical performance monitoring systems, 

which together provided a comprehensive knowledge of fire damage to electric cables and its 

effects on electric circuits. The Insulation Resistance Measurement System (IRMS) provided a 

general overall knowledge of electric cable damage as the fire progressed by measuring the 

electrical insulation resistance (IR) between all pairs of conductors in the cable, and between 

each individual conductor and ground. IRMS measurements were totally independent of any 

circuit that might be connected to the cable in an actual nuclear power plant. The Surrogate 

Circuit Diagnostic System (SCDS) provided a detailed knowledge of the effects on one specific 

electric circuit of fire damage to an electric cable connected to that circuit. Both systems were 

necessary, because neither was capable of performing both functions by itself. 

B.2. The Insulation Resistance Measurement System (IRMS) 

B.2.1 Operating Principles 

The IRMS is described in detail in Appendix B of Volume 1. It determines the IR between a pair 

of conductors, each of which can be a single conductor or an electrically connected group of 

conductors, and between each of those conductors and the ground. It operates by energizing 

one conductor (the “source” conductor) with a known voltage source and then measuring the 

voltage across a known resistance connected in series with the source conductor, and also 

measuring the voltage across a separate known resistance connected in series with another 

conductor (the “target” conductor). It then switches the known voltage source to the opposite 

conductor (i.e., the former “target” becomes the “source,” and the former “source” becomes the 

“target”) and repeats the voltage measurements. The resulting two pairs of measurements, 

along with the known source voltage and the two known resistances, are mathematically 

sufficient to enable calculation of the above-specified IR values. The two pairs of 

measurements are made as described above (i.e., in immediate sequence—within two 

seconds8

) to minimize errors resulting from the implicit mathematical assumption that all four 

voltages exist at the exact same moment. 

 

7

 “Cable Response to Live Fire (CAROLFIRE) Volume 1: Test Descriptions and Analysis of Circuit Response Data,” NUREG/CR6931, Volume 1, April, 2008; and “Cable Response to Live Fire (CAROLFIRE) Volume 2: Cable Fire Response Data for Fire Model 

Development,” NUREG/CR-6931, Volume 2, April, 2008. 

8

 In earlier IRMS applications, (e.g., NUREG/CR-6776, “Cable Insulation Resistance Measurements Made During Cable Fire Tests,” 

June, 2002), IR measurements were made by connecting the source voltage to one conductor, sequentially measuring all other (i.e., 
 

B-2 

B.2.2 Uncertainties Due to IRMS Cycle Time 

SNL developed and patented two IRMSs for CAROLFIRE—each can be connected to as many 

as 14 conductors, and has sufficient switching and data recording equipment to determine the 

IR values between all pairs of those conductors and between each of those conductors and the 

ground. Depending on the number of conductors being monitored, however, one cycle (i.e., one 

measurement of the IR values for all pairs) can take from seconds (e.g., ~42 sec) to a few 

minutes (e.g., ~3 min). Thus, in practice, it is desirable to limit the number of monitored 

conductors, because long cycle times limit the data’s time resolution. That is, any event that 

occurs just after measurement of an IR value that would have been affected by the event would 

not be measured and recorded until that IR is again measured during the next cycle. If any 

additional events occurred before that next IR measurement, only the composite result of all 

such events would be measured and recorded (i.e., they would not be resolved in time and 

recorded as separate events). 

An important example is if a hot short occurs between two conductors just after measurement of 

those conductors’ IR values, and then, just before the next measurement of their IR values, they 

short to ground. The occurrence of the hot short would be missed—all that would be measured 

and recorded is that the conductors were, at the time of the second IR measurement, shorted to 

each other and to ground. Another important example is if a hot short occurs between two 

conductors just before measurement of their IR values, and then, just after that same 

measurement, one of the conductors shorts to ground—this termination by grounding of the hot 

short would not be measured and recorded until the next cycle’s measurement, resulting in the 

recording of a much longer-lasting hot short than actually occurred. The inaccuracies in both of 

these examples occur because the time resolution of IRMS data is limited by its cycle time, 

which increases as the number of monitored conductors increases. 

This is one of the reasons that surrogate circuit diagnostic units (SCDUs, discussed later) were 

also used in CAROLFIRE—SCDUs have a vastly better time resolution (0.2 seconds cycle 

time), but they lack the IRMS’s ability to detect progressive cable deterioration well before 

ultimate cable failure. The IRMS and SCDU systems thus complement each other, and 

together provide the most complete knowledge of electric cable behavior in fires. 

 B.2.3 Criteria for Spurious Operation (SA) 

The IRMS provided a stream of cable IR data indicating progressive degradation of the cables’ 

insulating ability. The numerical IR limit that should be considered sufficient to induce a 

spurious operation (SA) depends on the nature and sensitivity of the circuit. However, for 

CAROLFIRE, a specific criterion was applied to reflect a typical 120 VAC control circuit and to 

reflect the typical faulting behavior observed in previous testing. In particular, a control cable 

was considered to have caused an SO when it shorted to another conductor with an IR of less 

than or equal to 1000Ω. This IR limit was selected as a representative of expected failure onset 

conditions for control and instrument circuits because the typical behavior of such cables during 

fire exposure involves a fairly steady degradation of IR with rising temperature until the IR value 

degrades to some value considerably above 1000Ω, at which point the cable typically 

experiences rapid degradation to IR values typically under 100Ω. Thus, use of the 1000Ω

 “target”) conductors, then switching the source voltage to the second conductor, etc. That method required more time to collect the 

two pairs of measurements needed, and resulted in increased uncertainties in IR during the transition phase. 
 

B-3 

failure criterion should acceptably represent this behavior9

. The SO was considered to 

terminate when either conductor shorted to ground with an IR of less than or equal to 1000Ω. 

 B.2.4 Presentation of IRMS Data 

The IRMS results are provided in the form of extensive shorting sequence tables. Chapter 6 of 

Volume 1 provides the Penlight Test (PT) IRMS tables, and Chapter 7.1 provides the 

Intermediate-Scale Test (IT) IRMS tables. The tables provide specific sequences of observed 

short circuits between pairs of conductors (or conductor groups) and between each conductor 

(or conductor group) and ground. 

The shorting sequence tables provide the most significant events (“highlights”) of each test, 

subject to the time resolution limits discussed previously. Full details are provided in the Excel 

data files on the CDs distributed with CAROLFIRE Volumes 1 and 2, and on the U.S. Nuclear 

Regulatory Commission (NRC) website. Those files include plots of the data, which can be 

enlarged on-screen. This method is recommended for viewing the data, because “hovering” 

over any plotted point will result in the appearance of its exact numerical coordinates, in addition 

to the plot showing how it fits into the overall test results. An example is provided in Figure 1, 

“IRMS Data Plot Example,” which represents one of the tests involving a single10 7-conductor 

cable. The relative location of the conductors in the cable is shown in Figure 2, “SevenConductor Cable,” which applies to all 7-conductor cables monitored during CAROLFIRE by 

either the IRMS or the SCDUs. 

 B.2.5 IRMS Set-Up to Detect Inter-Cable Hot Shorts 

A primary interest of the CAROLFIRE project was the interactions between cables (inter-cable 

shorts), as opposed to interactions between conductors within a singe cable (intra-cable shorts, 

such as the above example, in which each of the seven conductors in a single 7-conductor 

cable was monitored by an IRMS channel). This indicated that many tests should involve a 

bundle or bundles of multi-conductor electric cables. It was not possible to connect each 

conductor within such bundles to an IRMS channel, because each IRMS unit can only 

accommodate a maximum of 14 channels (and because of the need to minimize cycle times, as 

previously discussed). 

Thus, the typical IRMS practice was to group conductors from each of several co-located 

(bundled) cables into two groups. For a 7-conductor cable (Figure 2), there was one central 

conductor surrounded by six cables forming an outer ring. The six outer conductors were 

collected into two groups of three conductors each, with each group comprising alternate 

conductors in the outer ring. In this way, the IRMS was able to determine when one conductor 

group shorted internally to the other conductor group in the same cable (intra-cable shorting), 

when each conductor group shorted to ground, and when either conductor group in one cable 

shorted to either conductor group in another cable (inter-cable shorting). The typical conductor 

grouping, using the Figure 2 conductor numbering scheme, is shown in Figure 3, “Grouping of 

Seven Conductors.” Note that for these bundled tests (in contrast to the single cable example 

given above), the central conductor (“1” in Figure 2) was not connected to the IRMS and was 

not grounded (i.e., was a “spare” conductor, and so was not connected to anything). In some 

 

9

 Instrument cables might begin to cause instrument errors at IR values above 1000Ω, but fire damage is expected to cause IR 

decreases to begin considerably above 1000Ω and then proceed rapidly, so the 1000Ω criterion should be reasonably acceptable. 10 This “single cable” designation can be misleading, because in all cases (except the “Spec 1” test described on pg. 77 of Volume 

1) this actually means a single cable for electrical monitoring, plus a nearby (identical) single cable for thermal monitoring (i.e., two 

cables were actually used). 
 

B-4 

nuclear power plant (NPP) systems, spare conductors are grounded, so note that the 

CAROLFIRE IRMS data might be somewhat less representative of such cables11. Also note 

that for all tests involving the IRMS, the electrical raceway was grounded to a common ground, 

along with the IRMS power supply, and that none of the conductors or shields within the IRMSmonitored cables were grounded. Thus, conductor-to-ground IR values always indicated 

interactions between conductors and the raceway (i.e., cable tray or conduit). 

Given the above grouping of conductors, each cable was associated with two channels of the 

IRMS. In the data tables given in Chapters 6 and 7, this arrangement is designated by 

conductor labels that indicate the cable and IRMS channel. For example, Cable A was 

generally connected to IRMS channels 1 and 2, so the two Cable A conductor groups were 

referred to as “conductor A1” and “conductor A2.” Similarly, Cable B was generally connected 

to IRMS channels 3 and 4, so the two Cable B conductor groups were referred to as “conductor 

B3” and “conductor B4,” and so on for the rest of the monitored cables. Thus, if a data table 

entry says “conductors A1 and A2 shorted together” or “conductors B3 and B4 shorted 

together,” these entries indicate intra-cable, conductor group to conductor group shorts (i.e., 

between conductor groups within the same cable). If the entry says “conductors A1 and B1 

shorted together,” however, this indicates an inter-cable short between conductor groups (i.e., 

between conductor groups in separate cables). Cable bundles with three, six, and twelve 

individual cables arranged as shown in Figure 4 were used in CAROLFIRE. 

 B.2.6 Summary of IRMS Conductor-to-Conductor-Short Data 

As indicated above, the CAROLFIRE IRMS data are presented in Volume 1 in the form of 

extensive shorting sequence tables. These tables do not include summary tables like the ones 

provided for data from the CAROLFIRE surrogate circuit diagnostic units (SCDUs, discussed 

later in this document). Thus, for this document, the IRMS data were examined using the 

process described below, resulting in identification of 20 conductor-to-conductor-short data 

points in an IRMS summary table (attached). 

The IRMS data’s principal purpose was to indentify conductor-to-conductor-shorts that could 

likely cause spurious operations. Other conductor-to-conductor-shorts were of far less interest, 

and were not compatible with the SCDU data discussed later in this document. Therefore, the 

following process was applied to the IRMS shorting sequence tables: 

 - Only data from primary events were selected—that is, if either conductor group 

involved had previously shorted to ground at less than or equal to 1000Ω, then the event was 

not listed in the summary table because existence of the ground would likely prevent the 

availability of sufficient power for a spurious operation. 

 - The time when two conductor groups meeting the above condition shorted together at 

less than or equal to 1000Ω was taken as the short’s initiation time. If different times were given 

for the two conductor groups, the earlier of the two was used. 

 - The time when either conductor group shorted to ground at less than or equal to 

1000Ω was taken as the short’s termination time. If different times were given for the two 

conductor groups, the earlier of the two was used. However, the recorded time when conductor 

 

11 Since thermal damage to cables begins on the outside and proceeds inward, effects of this difference should be minimized - most 

shorts to ground would likely occur to the outside raceway, not to any inside grounded conductor. 
 

B-5 

groups shorted to ground is subject to the uncertainties discussed in Section 2.7, which can be 

of considerable importance, especially for hot shorts with shorter durations. 

 - The short’s duration time was defined as the difference between the above-described 

initiation and termination times. However, if the duration was less than one cycle, the short was 

not included in the summary table because of uncertainty resulting from the data’s time 

resolution (as discussed above). 

 B.2.7 Termination Time Uncertainties in IRMS-detected Hot Shorts 

These uncertainties are explained using the data given on page 55 of Volume 1 as an example; 

the second and third lines of the table “Results for Test PT-34” are: 

1304 seconds – Conductors A1 and A2 short together at 23Ω

130912-1332 seconds – Conductors A1 and A2 short to ground at 303 and 455Ω

These two entries indicate that a hot short occurred sometime during the previous cycle (i.e., 

the 185 seconds prior to 1304 seconds), and that it still existed at the indicated time (1304 

seconds). Furthermore, the entries indicate that the hot short continued to endure within the 

then-present cycle (i.e., after 1304 seconds) for between 5 and 28 additional seconds. 

According to previous explanations by the IRMS, however, the IR values between the 

conductors and between each of the conductors and the ground were all determined by the 

same voltage measurements, which were made within less than 2 seconds of the indicated time 

(1304 seconds). Thus, an uncertainty is indicated, because no relevant data would have been 

taken during those additional 5 to 28 seconds. However, looking in more detail at IRMS data 

recording processes reveals that relevant data was in fact taken during that time interval, as 

follows. 

In the Excel file for test PT-34, under the “Plot for Each Conductor” tab, the “Behavior of Cable 

A, Conductor 1” and the “Behavior of Cable A, Conductor 2” plots show the conductor-toconductor IR for A1-A2 and for A2-A1 (both at exactly 1303.999999 seconds penlight time) to 

be exactly 22.75434601Ω. This matches the first line of the “Results” table copied above. The 

IR values to ground given on the two referenced plots near 1304 seconds also match the IR 

values given in the second line of the “Results” table copied above; A1’s IR is 302.67Ω (at 

1309.7 seconds), and A2’s is 454.7Ω (at 1332.1 seconds). 

In the “key” block of the referenced plot for Cable A, Conductor 1, however, note that its IR to 

ground is referred to as “A1 – Grnd (min),” and that it appears below the column of entries A1 – 

A2, A1 – B3, A1 – B4, A1 – C5, and A1 – C6. Each of those five data pairs were taken at 

successively later times as the IRMS proceeded through its cycle, and each was used to make 

a separate “A1 – Grnd” IR calculation. Exact values for those successively later times can be 

obtained under the “A1-A2,” “A1-B3,” etc. tabs of the Excel data file. If all five times involving 

“A1” are noted and their average found, it is equal to 1309.7 sec, the “A1- Grnd (min)” time 

given in the “Results” table. Similarly, if the five successively later times for Cable A, Conductor 

2 are obtained under the “A1-A2,” “A2-B3,” “A2-B4,” “A2-C5,” and “A2-C6” tabs and their 

average found, it is equal to 1332.1 sec, the “A2 – Grnd (min)” time given in the “Results” table. 

 

12 Per the following discussion, this time is actually 1309.7 seconds and should have been shown as 1310 seconds in the “Results”

table, but was erroneously rounded to 1309 seconds. 
 

B-6 

These details demonstrate that the short-to-ground data are presented as the minimum IR value 

from the several calculations of each conductor’s IR-to-ground, at the average of the times 

when those measurements were taken. This is the origin of the noted uncertainty. It’s also 

noted in passing that the Excel data plots given under the “conductor-to-conductor mins” tabs 

use the same data averages described above for short-to-ground times, presented in a slightly 

different manner. In the above example, if the ten times (five times involving A1 to ground and 

five times involving A2 to ground) are averaged, the resulting time (1320.9 seconds) is used 

under the “A-B mins” and the “A-C mins” tabs for the time of the minimum IR for “A to Ground.” 

In the above example, taking the uncertainties into account, what the data actually indicate is 

that sometime during the 185-second cycle preceding 1304 seconds, conductors A1 and A2 

shorted to each other and also shorted to ground, but, due to the uncertainties, the data cannot 

support knowledge of which occurred first, nor of the time between them (if any). Thus, as 

stated previously, this hot short and others (some discussed below) given in the IRMS data that 

endured less than one cycle are not included in the attached IRMS data summary table. 

 B.2.8 Effects of Cycle and Termination Time Uncertainties on Results 

The two strongest IRMS indications of inter-cable hot shorts from the Penlight tests cited in 

Volume 1, Section 6.11, page 77, “Summary of Penlight Test Results in the Bin 2 Context,” are 

called into question by the cycle length issue. That section states that tests PT-45 and PT-60 

gave clear indications of inter-cable hot shorts, but the timing in both cases is such that it’s not 

possible to determine the time interval between the conductor-to-conductor shorts and the 

shorts to ground (which could be zero, making these invalid examples of “hot” shorts capable of 

causing an SA). Therefore, they were not included in the attached Inter-Cable section of the 

summary table. 

However, the two strongest IRMS indications of inter-cable hot shorts from the intermediatescale tests (ITs) cited in Volume 1, Section 7.1.16, page 109, “Summary of Intermediate-scale 

IRMS Results,” appear to be valid. On the attached Inter-Cable section of the summary table, 

the first of those indications is for the IT-1 test for the conductor C5 to conductor B4 hot short 

with a duration of five minutes (according to data from the Volume 1 table at the bottom of page 

83). Excel data indicates that even in the worst case (i.e., assuming the first conductor to short 

to ground does so one second after its last non-shorted measurement), the hot short endured 

for at least 144 seconds. Similarly, Excel data for the other IT-1 hot short on the summary table 

(the C5 to A1 short with duration 3.6 minutes, according to data from the Volume 1 table) show 

that it endured for at least 65 seconds. 

 B.2.9 Recommendations for Future IRMS Improvements 

Since the above discussions concern uncertainties in the IRMS data principally caused by the 

IRMS’s rather long cycle times, it is worth noting that those uncertainties could be reduced for 

future IRMS applications without reducing the amount of data provided. The data provided are 

for IR values between adjacent IRMS-monitored cables, but measurements were made for IR 

values between all possible pairs of IRMS-monitored cables. For example, with reference to the 

“Six-Cable Bundle Arrangement” shown in Figure 4, IR values were provided between 

conductor groups in Cable A and the adjacent Cables B and C, but IR values were also 

measured (but not reported) between Cable A and non-adjacent Cables D, E, and F. This same 

degree of over measurement existed for the other corner cables D and F, but a lesser degree of 

over measurement existed for the side cables B, C, and E because they each had only one non-
 

B-7 

adjacent cable. Re-programming the IRMS to eliminate the less important measurements 

would significantly shorten its cycle time and improve time resolution of the event sequences. 

B.3. Surrogate Circuit Diagnostic Units (SCDUs) 

 B.3.1 Introduction 

CAROLFIRE’s second electrical performance-monitoring system utilized SCDUs, which are 

described in detail in Appendix C of Volume 1. The SCDUs provided an opportunity to assess 

how various simulated circuits responded to fire-induced cable failures. They could be 

configured to represent a range of circuits, although, in practice, most of the CAROLFIRE tests 

used a standard AC-powered motor-operated valve (MOV) control circuit such as those used in 

both the Nuclear Energy Institute/Electric Power Research Institute (NEI/EPRI) (2001) and Duke 

Energy Corporation (2006) test programs. Some tests varied the number of energized source 

conductors and/or the number of grounded conductors present in the tested cable. 

 B.3.2 Differences Between the IRMS and the SCDU Tests 

These differences included: 

- most of the SCDU tests were configured with intra-cable shorting in mind, whereas most of 

the IRMS tests were configured with inter-cable shorting in mind; 

- each SCDU contained a specific circuit which was tested for the occurrence of an SA; thus, it 

was not subject to uncertainty resulting from the IRMS’s generic assumption that an IR of 

1000Ω or less represented an SA; 

- all 64 channels of SCDU data were recorded every 0.2 seconds (i.e., the SCDU’s cycle time 

was 0.2 seconds), as compared to the IRMS’s cycle time of 185 seconds (or less, in a few 

cases); 

- most of the SCDU test cables contained a grounded conductor, whereas none of the IRMS 

cables contained a grounded conductor or shield; 

- each SCDU tested only for the actual occurrence of a hot short or SO due to cable failure; it 

seldom gave any indication of cable degradation prior to cable failure, whereas the IRMS 

provided a complete history of IR degradation between all pairs of adjacent conductors prior to 

cable failure. 

 B.3.3 Individual SCDU Circuits 

SNL constructed four SCDUs for CAROLFIRE (Figure 5). Their permanent wiring was identical, 

with the exception that SCDU #1’s power supply was not grounded (it was grounded in the other 

three SCDUs). Although the electrical capacity of the Control Power Transformers (CPTs) used 

on the four SCDUs could be varied, in practice SCDUs #1 and #2 used 150 volt-amp (VA) 

CPTs, SCDU #3 used a 200 VA CPT, and SCDU #4 used a 100 VA CPT with the exception of 

four tests (IT-11, -12, -13, and -14) in which SCDU #4 was used without a CPT. 

 
 

B-8 

 B.3.4 Application Configurations 

Each of the four SCDUs could be connected in any of the four configurations discussed below. 

B.3.4.1 SCDU-MOV-1

As stated previously, the most frequently used configuration was SCDU-MOV-1 (see Figure 5). 

A hot short between Circuit Paths 1 or 2 (conductors 1 or 2) and Circuit Paths 4, 5, or 6 

(conductors 4, 3, or 7) would cause an SA. 

Note that Circuit Path 7 (conductor 5) was a return path to the power supply in all four SCDUs 

and was also grounded in SCDUs #2, #3, and #4, but not in SCDU #1 (this is one reason for the 

previous statement that “most of the SCDU test cables contained a grounded conductor”). The 

effect was that, for all four SCDUs, a hot short to Circuit Path 7 (conductor 5) would cause a 

fuse blow failure. However, whereas a single hot short to external ground (i.e., to the cable tray 

or conduit) would cause a fuse blow failure for SCDUs #2, #3, and #4, a single hot short to 

external ground would not cause a fuse blow failure for SCDU #1. Also, for SCDU #1, a short to 

ground on Circuit Paths 1 or 2 (conductors 1 or 2) and Circuit Paths 4, 5, or 6 (conductors 4, 3, 

or 7) would cause an SA, and a short to ground on Circuit Path 1 or 2 (conductor 1 or 2) and 

Circuit Path 7 (conductor 5) would cause a fuse blow. 

B.3.4.2 SCDU-MOV-1a

This configuration resulted from an inadvertent hookup wiring error made on all four SCDUs for 

test IP-4 only. The effects of this error were minor, and, once discovered, were negated by 

corrections to the recorded data. 

B.3.4.3 SCDU Operation Circuit 1

This configuration was used only in test IT-3, which included SCDU #4, connected to a 3-

conductor-plus-drain-wire cable. In this configuration, one of the three insulated conductors was 

connected to Circuit Path 1, which was energized (i.e., it became the single source conductor). 

The second insulated conductor was connected to Circuit Path 5, and the third insulated 

conductor was connected to Circuit Path 6, making two target conductors. The uninsulated 

drain wire was connected to Circuit Path 7 (grounded on SCDU #4). The other Circuit Paths 

were not connected to anything for this test (IT-3). This configuration, with a grounded drain 

wire within the cable, represented typical practice for cables with drain wires or shields. 

B.3.4.4 SCDU Inter-Cable Configuration (IC) 

Figure 6 shows the most frequently used (six-cable bundle) version of this configuration, which 

was used for a total of ten cable bundles in tests IT-2, IT-3, IT-4, and IT-5 (IT-2 also tested two 

twelve-cable bundles, which are discussed later). As shown in Figure 6, for all ten of the sixcable bundle IC tests, Circuit Path 1 was connected to all of the conductors of one 7-conductor 

cable, and Circuit Path 2 was connected to all of the conductors of another 7-conductor cable, 

thus creating two source cables. A third 7-conductor cable was used as the target cable and 

connected as shown: conductors 2 and 5 were connected to Circuit Path 4, conductors 3 and 6 

were connected to Circuit Path 5, and conductors 4 and 7 were connected to Circuit Path 6. 

Conductor 1 (the center conductor) was not connected to anything, becoming an “unconnected 

spare.” Since no target conductor was connected to Circuit Path 7, there were no conductors in 

the fire test structure that connected directly to the CPT return path. There were conductors 
 

B-9 

that led from the fire to the return path, but they led through the 1750Ω ballast resistor (from 

Source 1, the normal undamaged situation), through the 1750Ω passive operation device, or 

through the K1 or K2 active operation devices, all of which had sufficient resistance to preclude 

a fuse blow (energizing any of the three operation devices was the definition of an SO event). 

This was a significant difference from the other three SCDU configurations (i.e., the two “MOV1” and the “Operation Circuit 1” configurations), in which Circuit Path 7 (on all four SCDU 

circuits, both grounded and ungrounded) always served as a return path to the power supply 

from target conductor 5, as well as an internal ground for SCDUs #2, #3, and #4 (the grounded 

SCDUs). 

The three cables (two source cables and one target cable, as described above) were bundled 

as shown in the “Six-Cable Bundle Arrangement” part of Figure 4; Cables A and B were the 

source cables, Cable C was the target, and Cables D, E, and F (between Cables A, B, and C 

and the cable tray) were not connected to the SCDU and were not grounded, in keeping with 

their intended function of providing an additional level of isolation between the active cables and 

the grounded cable tray. 

For the above “IC” configurations using grounded SCDUs, hot shorts or spurious operations 

impacting the target cable could only occur given inter-cable shorting that remained 

independent of the external ground. Any short between an energized source conductor and the 

external ground (i.e., the raceway) would have caused a fuse blow. (Recall that there was no 

direct internal return path from the target conductors to the CPTs, so even for the grounded 

CPTs there was no internal ground). 

For the above “IC” configurations using the ungrounded SCDU #1, as with the grounded 

SCDUs, there was no direct internal return path to the CPTs, but, unlike the grounded SCDUs, 

there was also no external return path to the CPTs. Therefore, given fire damage to the cables, 

a fuse blow failure was not possible, and an SO was inevitable. An SO could result from direct 

interaction between either of the source cables and any of the three conductors in the target 

cable, or from multiple interactions with the ground (i.e., when either of the source cables 

shorted to ground and any of the three target conductors also shorted to ground). In principle, it 

might be possible to distinguish this latter case because voltage in the target conductor might 

tend to build slowly and never reach full source potential. 

As noted above, IT-2 also included two twelve-cable bundles. One bundle, consisting of twelve 

thermoset (TS) cables (cross-linked polyethylene/chlorosulfonated polyethylene (XLPE/CSPE), 

Cable ID #1013), was connected to SCDU Circuit #1 (ungrounded). The other bundle, consisting 

of a mixture of TS and thermoplastic (TP) cables (six XLPE/CSPE TS cables (Cable ID #10 - 

footnote 7 applies), and six polyethylene/polyvinyl chloride (PE/PVC) TP cables (Cable ID # 

15)), was connected to SCDU Circuit #2 (grounded). The response of both SCDUs to the 

various cable interactions was identical to that described above for the ten six-cable bundles. 

The only differences were the size and extent of the conductors used. The “Twelve-Cable 

Bundle Arrangement” part of Figure 4, and Figure 6, “SCDU IC Configuration for Six-Cable 

Bundles,” provide material that was created for six cable bundle purposes, but which can 

nevertheless be used to illustrate the following text about twelve-cable bundles. 

For SCDU Circuit #1 (connected to the all-TS twelve-cable bundle), Circuit Path 1 (source 1) 

was connected to 21 conductors, consisting of all 7 of the conductors in Cables J, G, and B. 

Circuit Path 2 (source 2) was connected to 21 conductors, consisting of all 7 of the conductors 

 

13 In Volume 1’s SCDU results table on page 115, the Cable ID # is incorrectly given as #3. 
 

B-10 

in Cables K, M, and C. Each of the three target paths (Circuit Paths 4, 5, and 6) was connected 

to all 7 of the conductors in a separate cable, H, A, or L, respectively. Thus, there were two 

sources, each consisting of all 21 conductors in three connected cables, and three targets, each 

consisting of all 7 conductors in a separate cable. Cables D, E, and F (between Cables G, B, C, 

M, and the cable tray) were not connected to the SCDU and were not grounded, in keeping with 

their intended function of providing an additional level of isolation between the active cables and 

the grounded cable tray. The above-described connections are consistent with the Excel 

datasheet for “Test IT_02 SCDU Data,” under the “Test Conditions” tab, in the “Circuit #1” 

column and the “Wiring Config:” row. 

For SCDU Circuit #2 (connected to the mixed TS and TP twelve-cable bundle), information 

presented in the Excel datasheet for “Test IT_02 SCDU Data,” under the “Test Conditions” tab, 

in the “Circuit #2” column and the “Wiring Config:” row, indicates that all six TP cables were 

connected. However, the information presented for IT-2 in Volume 2, page 110, indicates that 

Cables B, D, F, H, K, and M were the locations of the six TP cables14. Taken together, this 

means that two of the three “isolation” cables between the active cables and the tray (i.e., D and 

F) were connected to the SCDU. This would not have been consistent with the intended 

isolation function for the bottom row of cables (D, E, and F), and the SNL personnel who 

conducted the test stated that it was not something they would have done. After consulting all 

available records, the SNL personnel determined the most likely connections: Circuit Path 1 

(source 1) was connected to all seven conductors in each of two TS and one TP cables (Cables 

J, G, and B, respectively); Circuit Path 2 (source 2) was connected to all seven conductors in 

each of two TP and one TS cables (Cables K, M, and C, respectively); Circuit Path 4 (Passive 

Target 4) was connected to all seven conductors in TP Cable H; and Circuit Paths 5 and 6 

(Active Targets 5 and 6) were each connected to all seven conductors in TS Cables A and L, 

respectively. Cables D (TP), E (TS), and F (TP) were left unconnected to any Circuit Path (and 

were not grounded). 

 B.3.5 Summary of SCDU Conductor-to-Conductor-Short Data 

The SCDU data is well organized and sufficiently detailed to enable its use for many purposes. 

For example, the tables on pages 113 to 126 in Volume 1 proceed in columns from the left, 

giving the test number, the SCDU circuit number, the circuit configuration, CPT size and 

whether or not it’s grounded, cable type, number of conductors, cable ID number, bundle size, 

and an event summary (i.e., narration of the SAs and fuse blows that occurred due to both intraand inter-cable interactions). These items are discussed in this document, and should be 

understood to enable the selection of appropriate sets of data that avoid combining the results 

of vastly different tests. For example, an ungrounded SCDU in the IC configuration is quite 

different from a grounded SCDU in the MOV-1 configuration, and their data should be 

interpreted and used in significantly different ways. 

In addition, a two-page summary of the intra-cable interactions is presented on pages 131 and 

132 in Volume 1 (the nine inter-cable interactions are presented in the detailed tables on pages 

113 to 126, but are not repeated in the two-page summary). 

The Excel data files on the CDs distributed with CAROLFIRE Volumes 1 and 2 (and on the NRC 

website) provide detailed data recorded from the voltage and current transducers on Circuit 

Paths 1 through 8 (shown on Figures 5 and 6—note that Circuit Path 9 was not used, and was 

not monitored during any CAROLFIRE test). Since there was a voltage and a current 

 

14 Cables A, C, E, G, J, and L were the six TS cables. 
 

B-11 

transducer on each of the eight Circuit Paths, and four SCDUs were used in each CAROLFIRE 

IT, a total of 64 data points were collected during the CAROLFIRE ITs using a 64-channel data 

recorder (SCDUs were not used during the CAROLFIRE Penlight tests). 

All 64 data points were recorded every 0.2 seconds, and have been preserved for archival 

purposes. During the time intervals in which cable degradation occurred (i.e., immediately 

before, during, and after SAs and fuse blows), all data is presented in the Excel data files. 

However, during other times, intervals of 30 seconds to a minute are typically presented. The 

detailed data at 0.2-second intervals can be of interest in the many places where hot shorts of 

SO events are reported in the Volume 1 event summary tables, particularly when durations of a 

second or less are noted. 




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Final

Electrical Cable Test Results and Analysis 

During Fire Exposure (ELECTRA-FIRE)