NUREG/CR-7244

Response of Nuclear Power

Plant Instrumentation Cables 

Exposed to Fire Conditions

Office of Nuclear Regulatory Research

SAND2017-10346R
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SR-CR 10/2017
NUREG/CR-7244

Office of Nuclear Regulatory Research

Response of Nuclear Power

Plant Instrumentation Cables

Exposed to Fire Conditions

Manuscript Completed: November 2017 

Date Published: January 2019

Prepared by:

A. Muna

C. LaFleur

D. Brooks

Sandia National Laboratories 

Risk and Reliability Analysis, Department 8851

P.O. Box 5800 

Albuquerque, NM 87185-0748

Gabriel Taylor, NRC Project Manager 

SAND2017-10346R
Sandia National Laboratories is a multi-mission laboratory managed and operated by National 

Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell 

International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration 

under contract DE-NA-0003525.
iii

ABSTRACT 

This report presents the results of instrumentation cable tests sponsored by the US Nuclear 

Regulatory Commission (NRC) Office of Nuclear Regulatory Research and performed at Sandia 

National Laboratories (SNL). The goal of the tests was to assess thermal and electrical response 

behavior under fire-exposure conditions for instrumentation cables and circuits. The test objective 

was to assess how severe radiant heating conditions surrounding an instrumentation cable affect 

current or voltage signals in an instrumentation circuit. 

A total of thirty-nine small-scale tests were conducted. Ten different instrumentation cables were 

tested, ranging from one conductor to eight-twisted pairs. Based on a previous study, the focus of 

the tests was thermoset (TS) cables. As such, only two of the ten cables had thermoplastic (TP) 

insulation and jacket material and the remaining eight cables were one of three different TS 

insulation and jacket material. Two instrumentation cables from previous cable fire testing were 

included, one TS and one TP. Three test circuits were used to simulate instrumentation circuits 

present in nuclear power plants: a 4–20 mA current loop, a 1

0–50 mA current loop and a 1–5 VDC 

voltage loop. A regression analysis was conducted to determine key variables affecting signal 

leakage time. 

v 

TABLE OF CONTENTS 

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

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

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

LIST OF TABLES......................................................................................................................... ix

ACKNOWLEDGMENTS.............................................................................................................xiii

EXECUTIVE SUMMARY............................................................................................................xi

ABBREVIATIONS AND ACRONYMS...................................................................................... xv

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

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

1.2 Purpose and Objectives .................................................................................................... 1-2

1.3 Project Planning and General Approach ........................................................................... 1-2

1.4 Scope................................................................................................................................ 1-3

2 OVERVIEW OF TESTING NEEDS ..................................................................................... 2-1

2.1 Instrumentation Circuit Background................................................................................... 2-1

2.2 Instrumentation Cable Background ................................................................................... 2-2

2.3 Cable Failures and Circuit Faults....................................................................................... 2-2

2.3.1 Cable Failures ........................................................................................................ 2-2

2.3.2 Circuit Faults .......................................................................................................... 2-3

2.4 Instrumentation Needed for Safe Shutdown ...................................................................... 2-4

2.4.1 Instrumentation Needed for Pressurized Water Reactors ....................................... 2-4

2.4.2 Instrumentation Needed for Boiling Water Reactors ............................................... 2-4

3 APPROACH........................................................................................................................... 3-1

3.1 Project Planning and General Approach ........................................................................... 3-1

3.2 Cable Selection ................................................................................................................. 3-1

3.3 Test Circuits ...................................................................................................................... 3-4

3.3.1 4–20 mA Test Circuit .............................................................................................. 3-5

3.3.2 10–50 mA Test Circuit ............................................................................................ 3-6

3.3.3 1–5 VDC Test Circuit .............................................................................................. 3-7

3.4 Small-Scale Radiant Heater .............................................................................................. 3-7

3.5 Temperature Heating Profiles.......................................................................................... 3-11

3.6 Diagnostic Instrumentation Summary.............................................................................. 3-14

3.6.1 Cable Electrical Performance Monitoring .............................................................. 3-14

3.6.2 Thermal Response Monitoring.............................................................................. 3-15

4 TEST MATRIX ....................................................................................................................... 4-1

5 SMALL-SCALE TEST RESULTS....................................................................................... 5-1

5.1 Organization and Content ................................................................................................. 5-1

5.2 Calculating Signal Degradation, Failure and Leakage Times............................................. 5-1

5.3 Regression Analysis.......................................................................................................... 5-5

5.4 Experimental Results ........................................................................................................ 5-8

5.4.1 Number of Conductors Results............................................................................... 5-8
vi 

5.4.2 FR-EPR/CPE Cable Material Results ................................................................... 5-10

5.4.3 TS and TP Cable Results ..................................................................................... 5-12

6 CONCLUSIONS AND RECOMMENDATIONS................................................................. 6-1

6.1 General Conclusions Regarding Instrumentation Cable Failures....................................... 6-1

6.2 Recommendations for Follow-On Work............................................................................. 6-2

7 REFERENCES ...................................................................................................................... 7-1

APPENDIX A TEST RESULTS ............................................................................................ A-1

APPENDIX B LITERATURE SEARCH ............................................................................... B-1

APPENDIX C FINAL TEST PLAN ....................................................................................... C-1
vii 

LIST OF FIGURES 

Figure 1-1 Degradation of Signal Data from Thermoset Test (Ref. 4) ................................... 1-2

Figure 2-1 4–20 mA Current Loop Example .......................................................................... 2-1

Figure 3-1 4–20 mA Instrumentation Circuit for Fire Test, Grounded .................................... 3-5

Figure 3-2 4–20 mA Instrumentation Circuit for Fire Test, Ungrounded ................................ 3-5

Figure 3-3 10–50 mA Instrumentation Circuit for Fire Test .................................................... 3-6

Figure 3-4 1–5 VDC Instrumentation Circuit for Fire Test...................................................... 3-7

Figure 3-5 Picture of Cable Test Setup (Left) and Ceramic Heater (Right) ........................... 3-8

Figure 3-6 Emissivity of Heat Surface for Watlow Ceramic Fiber Heater .............................. 3-8

Figure 3-7 Representative Cable Setup (Test 28) ............................................................... 3-10

Figure 3-8 Stainless Steel Rod Test Setup .......................................................................... 3-10

Figure 3-9 Shroud Thermocouple Test with Two SS Rods.................................................. 3-10

Figure 3-10 Thermoplastic Cable Heating Profile - 325°C ..................................................... 3-13

Figure 3-11 Thermoset Cable Heating Profile - 470°C .......................................................... 3-14

Figure 3-12 Example Thermocouple Arrangement for Monitoring of 7-Conductor Cable 

near the Electrically Monitored Cable in Tray ..................................................... 3-16

Figure 3-13 Representative Cable Setup Illustrating TC Placement (Test 21) ...................... 3-16

Figure 5-1 Test 8A Noise Example ........................................................................................ 5-2

Figure 5-2 Temperature at Signal Failure .............................................................................. 5-5

Figure 5-3 Regression Analysis Decision Tree with cp=0.01................................................. 5-7

Figure 5-4 Number of Conductors and Corresponding Signal Leakage Time ....................... 5-9

Figure 5-5 Signal Leakage by Cable Material Type ............................................................. 5-10

Figure 5-6 Signal Leakage Time for FR-EPR/CPE Cables.................................................. 5-11

Figure 5-7 Test 14 (2-Pair FR-EPR/CPE Cable) and Test 15 (8-Pair FR-EPR/CPE 

Cable)................................................................................................................. 5-12

Figure 5-8 Signal Leakage Time for TP and TS Cables...................................................... 5-13

Figure 5-9 Test 23 (TP Cable) and Test 26 (TS Cable)....................................................... 5-14

ix 

LIST OF TABLES 

Table 3-1

Table 3-2

Radiant Heat Flux Based on Measured Emissivity of 0.85..................................3-9

Table 3-3 Heat Fluxes and Temperatures from Previous Instrumentation Cable Testing....3-11

Table 4-1 Matrix of Small-Scale Instrumentation Cable Tests..............................................4-2

Table 4-2 &KURQRORJ\RI,QVWUXPHQWDWLRQ7HVWV

Table 5-1 Signal Degradation, Failure, and Leakage Times for All Tests............................. 5-3

Table 5-2 Regression Analysis for Leakage Time ................................................................ 5-7

Table 5-3 Model Coefficients for Leakage Time ................................................................... 5-8

Table 5-4 Summary of Number of Conductors Testing ........................................................ 5-9

Table 5-5 Summary of Cable Material Testing ................................................................... 5-10

Table 5-6 Current Loop Test Data from 2001 Tests ........................................................... 5-12

3URMHFW&DEOH/LVW

Relationship Between the Ceramic Fiber Heater Shroud Temperature and 

xi

EXECUTIVE SUMMARY 

PRIMARY AUDIENCE: Fire Probabilistic Risk Assessment (PRA) and Human Reliability Analysis 

(HRA) methodology developers, NRC staff, and other stakeholders concerned with determining 

impact of delayed signal degradation for instrumentation circuits exposed to fire conditions. 

SECONDARY AUDIENCE: Engineers, reviewers, utility managers, and other stakeholders who 

conduct, review, or manage PRAs and HRAs and engineers that route and plan instrument 

circuits.

KEY RESEARCH QUESTION 

What are the fire-induced failure modes of instrumentation cables and circuits? 

RESEARCH OVERVIEW 

In 2001, a series of cable fire tests was performed by the Nuclear Energy Institute (NEI) and the 

Electric Power Research Institute (EPRI) which were designed to address specific aspects of the 

cable failure and circuit fault issues of concern (Ref. 1). These early tests concluded that 

thermoplastic (TP) cables generally displayed no characteristics of signal degradation prior to 

complete loss of signal and thermoset (TS) cables displayed up to ten minutes of signal 

degradation prior to complete loss of signal. The conclusions made in the 2001 study were based 

on a limited series of testing. To obtain better insights into this type of failure behavior on and a 

wider variety of cables and circuit configurations, a series of small-scale instrumentation cable

tests sponsored by NRC/RES and performed at Sandia National Laboratories (SNL).

The objectives of this report are to document the bench-scale testing efforts and identify focus 

areas for further testing necessary to address the research question comprehensively. 

KEY FINDINGS 

This research provides insights into the performance and signal response of low voltage 

instrumentation circuits in fire conditions. A total of 39 small-scale tests were conducted, primarily 

on TS cables. The signal leakage time during the fire test were monitored and reported as a 

measure of circuit response. Signal leakage time represents the time from when a signal has 

dropped 0.25 percent from its starting value to when the single has fallen to zero percent of the 

measurement (i.e., less than 4 mA for 4–20 mA circuits, less than 10 mA for 10–50 mA circuits, 

and less than 1 V for 1–5 VDC circuits). 

The tests provided evidence that under the appropriate circumstances, instrumentation cables can 

have a slow signal leakage time under fire-exposure conditions. The signal leakage time varied 

from 0 seconds to slightly over 2 1⁄2 minutes for TP cables. The signal leakage time for TS cables 

ranged from 0 seconds to over 21 minutes. 

There are three note-worthy general observations on the performance of instrumentation cables: 

x The results from the testing of TP cables showed some differences when compared to the

findings from prior, limited 2001 testing which stated that TP cables had no signal leakage

characteristics prior to signal loss. TP cables were found to have a smaller leakage time

on average when compared with TS cables and most TP cables failed instantly; however,
xii 

one TP test had a leakage time of 2.6 minutes. Therefore, TP cables may have some 

signal degradation prior to failure. 

x Conclusions from the 2001 testing stated that TS cables displayed some amount of signal

leakage before the signal failed. During this series of testing, twelve out of the thirty-two

tests had less than one minute of signal leakage before failure and four of these tests

experience no signal leakage. Four other tests had signal leakage for longer than ten

minutes. Therefore, this testing does not support the previous conclusion that TS cables

will always experience signal leakage before failure.

x A regression analysis was performed on the test data to determine key variables that

contributed to longer leakage times. The fitted model coefficient methodology concluded

that there is a significant relationship between the number of conductors and the signal

leakage time.

WHY THIS MATTERS 

Fire scenarios in a plant could include a fire affecting a thermoset instrument cable causing the 

indicator to display an intermediate, but not obviously erroneous, value due to signal degradation. 

This misleading information in a single indicator circuit could potentially cause operators to take an 

action based on faulty information depending on the nature of the signal and the direction of the 

signal leakage. The current tests were designed as a first step in better understanding the failure 

behavior for fire PRA and HRA applications. 

HOW TO APPLY RESULTS 

The results can be used to inform full-scale testing to better address the research problem and its 

implications for HRA. Several areas were identified that would further the understanding of 

parameters affecting signal time delay in instrumentation circuits. These areas are summarized as 

follows: 

x Assess the performance of instrumentation in various—likely cable-tray—configurations.

This includes bundling of cables, vertical and horizontal positions, and more realistic

configurations.

x Determine the implications of prolonged signal leakage on HRA.

x Assess the potential heating effects on digital transmitters and receivers.

x Assess the performance of different TP insulation/jacket cables materials. The focus of

this testing was on TS cables; however, TP cables were shown to have some signal

leakage before failure. Different TP insulation/jacket materials should be tested for a more

comprehensive understanding of the signal leakage.

LEARNING AND ENGAGEMENT OPPORTUNITIES 

Users of this report may be interested in the annual fire PRA training, Module III – Fire PRA, 

sponsored jointly between EPRI and the US NRC-RES. 
ACKNOWLEDGMENTS 

The authors gratefully acknowledge the contributions of the many people who helped to ensure 

the success of this project. Within the NRC, we especially acknowledge Gabriel Taylor and Mark 

Henry Salley, who have continued to support nuclear power plant fire research and the Sandia fire 

risk program. 

The authors thank the members of the RES/EPRI working group for their contributions to the 

project: 

Scott Bareham (NIST) 

Susan Cooper (NRC) 

Alan Jelalian (EPM) 

Ming Li (NRC) 

Ashley Lindeman (EPRI) 

Eric Lysiak (NRC) 

Christopher Pragman (Exelon) 

Anthony Putorti (NIST) 

Andy Ratchford (JENSEN HUGHES) 

Tammie Rivera (NRC) 

Kiang Zee (JENSEN HUGHES) 

The draft test plan was issued for a 30-day public comment period in November 2016 in the 

Federal Register (81 FR 80688). The authors would like to thank the comment received from 

David Helker of Exelon Generating Company. Those comments were dispositioned prior to 

performance of testing. 

We also gratefully acknowledge the help of Ethan Sena and Brian Ehrhart of SNL who assisted in 

the preparation of this document and with graphing test results. Finally, the authors also gratefully 

acknowledge Steve Nowlen, a retired Sandia employee, for his many contributions to Sandia’s fire 

program. 

xiii

xv 

ABBREVIATIONS AND ACRONYMS 

A or Amp Ampere

AC Alternating Current

AWG American Wire Gauge

CAROLFIRE Cable Response to Live Fire

CFR Code of Federal Regulations

cp Complexity Parameter

CPE Chlorinated Polyethylene

CSPE Chloro-Sulphonated Polyethylene

DAQ Data Acquisition

DC Direct Current

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

EPDM Ethylene Propylene Diene Monomer

EPR Ethylene-Propylene Rubber

EPRI Electric Power Research Institute

EQ Equipment Qualification

ESFAS Engineering Safeguard Feature Actuation System

FR Flame-Retardant 

HRA Human Reliability Analysis

IR Insulation Resistance

JACQUE-FIRE Joint Assessment of Cable Damage and Quantification of Effects from Fire

LSZH Low Smoke Zero Halogen

mA Milliamps 

MOU Memorandum of Understanding

MS Mean Square

NEI Nuclear Energy Institute

NIST National Institute of Standards and Technology

NPP Nuclear Power Plant

NRC Nuclear Regulatory Commission

PE Polyethylene

PIRT Phenomena Identification and Ranking Table

PRA Probabilistic Risk Assessment

PVC Polyvinyl Chloride

RES Office of Nuclear Regulatory Research (at NRC)

SNL Sandia National Laboratories

SS Stainless Steel

TC Thermocouple
xvi 

THIEF Thermally-Induced Electrical Failure 

TP Thermoplastic

TS Thermoset

V Volt

XLPE Cross-Linked Polyethylene
1-1

1 INTRODUCTION

This report describes a series of cable fire tests performed by Sandia National Laboratories (SNL)

under the sponsorship of the U.S. Nuclear Regulatory Commission (NRC) Office of Nuclear

Regulatory Research (RES). This effort was conducted in collaboration with the Electric Power

Research Institute (EPRI) as a working group under the memorandum of understanding (MOU)

for collaborative research. This effort provides data to better understand the failure behavior of

instrumentation cables subjected to damaging fire conditions. 

1.1 Background

In 1990, the NRC sponsored a series of tests at SNL to investigate the effects of thermal aging on 

fire damageability, documented in NUREG/CR-5546, “An Investigation of the Effects of Thermal 

Aging on the Fire Damageability of Electric Cables” (Ref. 2). An instrumentation cable was tested 

to determine the failure time and temperature for both aged and unaged cables. During the 

testing, levels of leakage current on the order of 15 mA were observed prior to the onset of

catastrophic failure. This phenomenon was not explored further as the damage thresholds and

times were based only on the failure of a 2 Ampere (A) fuse in the circuit.

In 2001, the Nuclear Energy Institute (NEI) and EPRI, together hereafter referred to as “industry,” 

conducted a series of cable fire tests designed to address specific aspects of cable failure and

circuit fault issues of concern (Ref. 1). “Issues of concern” refers to the problems associated with

post-fire safe-shutdown circuit analysis, as presented in NRC Information Notice 99-17: “Problems 

Associated with Post-Fire Safe-Shutdown Circuit Analyses” (Ref. 3). The NRC observed and 

participated in the 2001 tests by providing supplemental cable performance monitoring equipment

for the tests. The NRC contracted SNL who provided instrumentation designed to monitor cable 

degradation through the measurement of insulation resistance (IR) for several of the NEI/EPRI

tests. In addition to the IR tests, a separate surrogate instrument circuit was used in six of the

tests. This circuit simulated a 4–20 mA instrument circuit loop with a constant current source set to 

15 mA. The instrument wire transmitting the signal was exposed to fire conditions and the output

signal was monitored for degradation of the transmitted signal. These tests are documented in 

NUREG/CR-6776, “Cable Insulation Resistance Measurements Made During Cable Fire Tests”

(Ref. 4). 

These tests concluded that there are pronounced behavior differences observed between the 

failure of the thermoplastic (TP) and thermoset (TS) cables. TP cables generally displayed no 

characteristics of signal degradation prior to complete loss of signal. TS cables displayed a 

substantial amount of signal degradation, the worst case had signal degradation for approximately

ten minutes prior to the total loss of the signal, as shown in Figure 1-1. Fire scenarios in a plant 

could postulate a fire affecting a TS instrumentation cable to cause the indicator to read an 

intermediate, but not obviously erroneous, value. This misleading indication could potentially

cause operators to take an action based on faulty information (depending on the nature of the 

signal and the direction of the signal leakage). In contrast, a fire affecting a TP cable would likely

cause an abrupt and obviously faulty off-scale indication. This would be far less likely to mislead 

operators who would likely diagnose the instrumentation failure.
1-2

Figure 1-1 Degradation of Signal Data from Thermoset Test (Ref. 4) 

1.2 Purpose and Objectives

The objective of this research is to better understand the fire-induced failure modes of 

instrumentation cables. This research is intended to better quantify the cable failure 

characteristics (i.e., leaks in current) that may occur before catastrophic failure in 

instrumentation circuits. 

The Joint Assessment of Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE), 

Volume 1 report documented the results of a Phenomena Identification and Ranking Table 

(PIRT) exercise that was performed on fire-induced electrical circuit failures that may occur in 

nuclear power plants as a result of fire damage to cables (Ref. 5). The PIRT panel ranked 

instrumentation circuits as the top research priority and recommended additional testing due to 

the low level of knowledge and potential high consequences of fire-induced failure. The 

Probabilistic Expert Elicitation (PEE) panel indicated that the spurious operation and duration 

conditional probabilities developed for control and power circuits should not be used for 

instrumentation circuits (Ref. 6). The panel restated the need to advance the knowledge of fireinduced circuit failure for instrumentation circuits. 

1.3 Project Planning and General Approach

The draft project plan was developed over the course of several months and included several 

rounds of review and revision. The first draft of the test plan was issued to NRC on August 25, 

2016, and included a subsequent 30-day public comment period (see Federal Register notice 81 

FR 80688) starting November 16, 2016 and ending December 16, 2016. The project plan was 

revised based on public comments. Industry input led to refinements of various aspects 

of the project plan including defining industry practices for grounding the circuit. The draft test 

plan can be found on the NRC website, titled “Response of Nuclear Power Plant Instrumentation 

Cables When Exposed to Fire Conditions – Test Plan” (Ref. 7); the final test plan is included in 

APPENDIX C . 

Tests were performed between February 16, 2017 and March 9, 2017 using SNL fire test 

facilities in Albuquerque, New Mexico. 
1-3

The project employed basic quality assurance provisions, but was not subject to a strict quality 

assurance program. The instruments (voltage and current transducers) were covered by 

manufacturer supplied certificates of calibration and were included in the SNL instrument 

calibration system for verification or re-certification at the completion of testing. All other 

instruments used in testing, particularly the various thermocouples (TC) and temperature 

measurement instrumentation, were subject to the SNL calibration process which provides 

calibration services traceable to National Institute of Standards and Technology (NIST) 

standards. 

Field notes were maintained by the lead test engineer documenting all variable aspects of the 

individual tests and recording other observations during each test. All data processing and 

plotting was performed using commercial software (Microsoft Excel®). The regression analysis 

presented in Section 5 was performed using the R Project software. The original data files in 

their native format have been preserved for archival purposes. All data from the testing program 

is publicly available without restriction on a CD. 

1.4 Scope 

While the project involved collaboration between the RES and EPRI, SNL acted as the primary 

test laboratory and produced the contents of this report. This project complements previous 

research conducted in the Cable Response to Live Fire (CAROLFIRE) project in 2006 (Ref. 8), 

the Kerite Analysis in Thermal Environment of FIRE project in 2011 (Ref. 9), and the Direct 

Current Electrical Shorting in Response to Exposure Fire (DESIREE-Fire) project in 2012 (Ref. 

10). Although this report provides a general overview of the testing approach, the reader 

unfamiliar with these two tests should consult Vol. 1 of NUREG/CR-6931 (Ref. 8) and 

NUREG/CR-7100 (Ref. 10) for full understanding of the approach and reasoning. 

This report includes a summary description of all tests performed including experimental setups, 

test matrices, and a description of instrumentation fielded during each experiment. APPENDIX A 

contains the processed test data. A detailed timeline of the onset of signal degradation and failure 

is included. A regression analysis was performed on the data to focus the analysis on key 

variables which lead to longer signal leakage times. Additional interpretation of the test results 

applied to risk analysis is outside the scope of this project. In addition, the potential overheating of 

digital transmitters and receivers themselves is not in the scope of this test. 

This balance of this report is organized as follows: 

x Section 2 provides general background discussions describing previous test programs 

investigating related phenomena. Section 2 also provides an overview of the 

testing needs addressed by this project. 

x Section 3 describes the general approach taken in this project. Included in this section 

are summary descriptions of the test facilities, protocols, circuits, and 

cables used.

x Section 4 presents the test matrix. 

x Section 5 provides a description of the regression analysis performed on test results. In 

addition, there is a discussion on key variables in the results. 

x Section 6 presents summary discussions highlighting general insights gained from the 

testing and future recommendations. 

x Section 7 identifies referenced documents. 

2-1

2 OVERVIEW OF TESTING NEEDS 

Instrument circuits (also known as instrumentation and control circuits) provide critical information 

to operators regarding the status of plant conditions. Circuit fault effects on instrument systems

are unique and more complex than power and control circuits. Instrument sensors typically

convert process variable values (temperature, pressure, level, flow, etc.) to an electric signal (e.g., 

voltage and current) for transmission to a remote readout or display. Instrumentation readings can 

also be used to actuate an automatic plant response, as instrumentation circuits can be tied to 

process equipment, such as the reactor protection system and engineered safety features

actuation system (ESFAS). The current loop typically exists in two forms: 10–50 mA (old 

standard) and 4–20 mA (new standard). The 4–20 mA became the industry standard because it

has lower circuit voltages and current levels so there is less chance for personal shock injury or

the generation of sparks.

In either case, the principle of operation is the same; current produced by the loop power supply is

sent around the loop, flowing through every device and load—or burden device—in the circuit. 

The current is modulated into a process variable by a transmitter, which converts a sensor’s

measurement into a current signal and amplifies and conditions the output. A sensor typically

measures temperature, humidity, flow, level, or pressure. The current loop also has a receiver, a 

device that interprets the current signal into units that can be easily understood by the operators.

The receiver converts the 4-20 mA current back into a voltage which can be displayed, or actuate 

another component based on its start/stop logic. In this setup, 4 mA represents 0 percent of the 

measurement, 20 mA represents 100 percent; when the current is between 4 mA and 20 mA the 

voltage across the resistor is in direct proportion to that current. See Figure 2-1 for an example 

current loop showing the components discussed above.

Figure 2-1 4–20 mA Current Loop Example1

Current loops are extremely robust systems; they are impervious to electrical noise, and routing 

the signal through shielded, twisted-pair cables further reduces noise. Grounding the negative of 

the power supply to the shield provides additional noise protection. It is ideal for long distances as 

current does not degrade over long connections, unlike voltage which can degrade. It is also 

easier to detect and troubleshoot a fault in the system. One disadvantage to the current loop 

1 Figure derived from: https://www.predig.com/indicatorpage/back-basics-fundamentals-4-20-ma-current-loops

2.1 Instrumentation Circuit Background
2-2

design is that it can only transmit one process signal. However, programmable logic controllers or

other digital control systems are designed to take inputs from multiple current loops. 

2.2 Instrumentation Cable Background

Instrumentation cables transmit low-level signals from the instrument sensor to an indicator,

controller, or recorder. Instrumentation cables are low voltage and low ampacity (Ref. 11). They

are used for digital or analog transmission from various types of transducers. Resistance

temperature detectors, pressure transducers, and TCs are usually of a shielded twisted-pair

configuration whereas radiation detection and neutron monitoring circuits often use coaxial or

triaxial shielded configurations (Ref. 11). Instrumentation cables typically use single, shielded

twisted-pair conductor cables or much larger multi-conductor cables consisting of fifty or more

conductors. Each instrument conductor is typically size 16 American Wire Gauge (AWG) or

smaller. These cables frequently enclose several shielded twisted pairs of conductors contained

within a protective outer jacket. The twisting of conductors reduces magnetic noise, while the

shield and drain wire reduce electrostatic and radio-frequency interference. The shield consists of

a conductive material that is wrapped around the twisted pair of conductors. The uninsulated drain

wire, which is in physical and electrical contact with the shield, provides for easier termination of

the foil shield to a common ground point.

2.3 Cable Failures and Circuit Faults

2.3.1 Cable Failures

Cable failure implies that the cable is no longer able to perform its intended function, which is to

maintain the electrical integrity and continuity of the associated circuit sufficiently to ensure proper

operation of the circuit (Ref. 12). Hence, cable failure implies that one or more of the cable

conductors have lost electrical integrity or continuity. Cables can fail in the following ways. 

Open Circuit: An open circuit is failure condition that results when a circuit (either a cable or 

individual conductor within a cable) has a loss of continuity (Ref. 13). Such failures would likely be

diagnosed as a circuit fault by operators. However, a complete loss of several signals may mean

that operators would not know the actual reactor status, depending on available independent and

redundant sensors. 

Short Circuit: A short circuit is an abnormal connection (including an arc) of relatively low 

impedance, whether made accidentally or intentionally, between two points of different potential

(Ref. 13). 

A short circuit does not involve an external ground. Twisted pairs, especially shielded twisted

pairs, would be more likely to short-to-ground rather than form a short circuit given the proximity of

the ground (i.e., properly grounded shield). If the power for the current loop is provided by a power

supply that is physically independent of the loop’s transmitter, a conductor-to-conductor short

across the transmitter could possibly drive the loop current high and give a false reading. Both

intra-cable and inter-cable faults are possible, but again the possibility decreases with the addition

of shielding (properly grounded) protecting the twisted pairs and/or the cables.

Hot Short: Hot shorts occur when individual conductors of the same or different cables come in 

contact with each other and may result in a voltage or current on the circuit being analyzed

(Ref. 13).
2-3

Short-to-Ground: A short-to-ground is a short circuit between a conductor and a grounded 

reference point (e.g., grounded conductor, conduit or other raceway, metal enclosure, shield wrap,

or drain wire within a cable) (Ref. 13). Twisted pairs, shields for the pairs, and overall shields can 

be grounded in instrumentation circuits, so shorts-to-ground may occur more than hot shorts. 

2.3.2 Circuit Faults 

A circuit fault is undesired or unplanned behavior in an electrical circuit induced by the failure of 

one or more elements of the circuit, including the failure of an associated electrical cable (Ref. 13).

For the purposes of this test plan, this term refers to effects that postulated cable failures have on 

the associated electrical circuits and components. Circuit faults that could be applicable to 

instrumentation circuits are as follows. 

Loss of circuit operability: Some cable failures may lead to a total loss of circuit operability. 

This may result from failures involving instrumentation and control interlocks and permissive 

signals. For example, the failure of an oil pressure signal cable in such a manner that a false low 

oil pressure was indicated may lead to the loss of function of an associated pump or motor due 

to an oil pressure interlock (Ref. 13). 

Loss of indication: In some cases, cable failures may leave a system or component nominally 

operational, but will compromise the indication functions of the circuit. This may lead, for example, 

to status indicator lights going dark (Ref. 13). 

Inaccurate indications: Some cable failures may result in misleading or even conflicting 

instrument signals. A relatively low level of degradation in the insulation of an instrumentation 

cable may be sufficient to substantially bias an instrument’s readout (Ref. 13). For example, a 

false low water level signal could lead operators to activate additional water sources leading to the 

reactor vessel being overfilled. A false high reading could lead operators to shut down or throttle 

coolant injection systems, potentially leading to low water levels in the reactor.

Spurious operation: Spurious operation is the undesired or unplanned operation or activation 

of a system or component. Spurious operations are most commonly associated with cable hot 

short failures, although various cable failure modes may lead to spurious operations 

(depending on circuit design), and not all hot shorts will lead to spurious operations (Ref. 13). 

The functional impact of cable failures and circuit faults on plant systems, components, and 

functions can vary. This unpredictability in the process variable as a result of cable failures may 

elicit undesired automatic or human responses that may complicate or compromise the overall 

response to the effects of fire. 

The other unknown is the change of voltage that would indicate a change of state to the operator 

if the signal has a binary output. For example, a valve position indicator could be designed to alert 

the operator only if the valve is open or closed. If a voltage change is minimal for a long period of 

time, the operator may not know something is wrong until several minutes have passed. If

controlled by a digital device, the setting determines the voltage or amperage at which a system 

problem is indicated. Because the digital transmitter set points vary by plant, set points were not 

analyzed during testing. 
2-4

2.4 Instrumentation Needed for Safe Shutdown 

For the purposes of this test, there are two concerns for instrumentation readings. First, an 

instrumentation reading for a component that is time-sensitive and operator-dependent could 

cause unanalyzed problems if the signal is delayed or failed. Second, instrumentation readings 

that automatically actuate a plant response are also of interest. For example, a pump (dependent 

on the operation of a lubrication system) commonly has a permissive tie to an oil pressure 

reading. If the instrument cable failure led to an inaccurate indication of a loss of oil pressure, the 

pump may trip or fail to start on demand (Ref. 13). 

Information Notice 84-09, titled “Lessons Learned from NRC Inspections of Fire Protection Safe 

Shutdown Systems” provides guidance for licensees implementing requirements of 10 CFR 50, 

Appendix R (Ref. 14). Section III.L.1 of Appendix R requires that alternative shutdown capability 

achieve and maintain subcritical reactivity conditions in the reactor for III.G.3 fire areas. Section 

III.L.2 requires provision for direct readings of the process variables necessary to perform and 

control the reactor shutdown function. The minimum process monitoring capability described in IN 

84-09 includes the following instruments:

2.4.1 Instrumentation Needed for Pressurized Water Reactors 

x Pressurizer pressure and level

x Reactor coolant hot leg temperature or exit core TCs, and cold leg temperature

x Steam generator pressure and level (wide range)

x Source range flux monitor

x Diagnostic instrumentation for shutdown systems

x Level indication for all tanks used (e.g., condensate storage tank)

2.4.2 Instrumentation Needed for Boiling Water Reactors 

x Reactor water level and pressure

x Suppression pool level and temperature

x Emergency or isolation condenser level

x Diagnostic instrumentation for shutdown systems

x Level Indication for all tanks used

Diagnostic instrumentation is instrumentation needed to ensure the proper actuation and 

functioning of safe-shutdown equipment and associated support equipment (e.g., instrumentation 

for flow rate, pump discharge pressure, etc.). The diagnostic instrumentation needed is plantspecific and should be based on the design of the alternative shutdown capability. All of the 

instrumentation listed have multiple channels and within any given fire area, fire detection may 

alert the operators to a fire. However, this analysis is applicable if fire detectors are not present or 

have not yet sensed the fire or for single instrument circuits, such as battery/bus voltages or pump 

oil pressure. 
3-1

3 APPROACH 

3.1 Project Planning and General Approach 

An extended process of project planning was undertaken to ensure that the testing program and 

protocols would address the identified data needs. Based on early discussions, a definition of the

overall project goals and technical approach was developed. Several key parameters that would 

need to be decided upon as a part of test planning were identified as follows: 

x Selection of instrumentation test circuits

x Circuit monitoring objectives and instruments

x Power source characteristics (e.g., current source and voltage source)

x Power source, circuit and instrument grounding

x Cable types to be used in testing

A RES/EPRI working group was established to discuss test parameters and the test plan. From 

these working group discussions, SNL developed a preliminary test plan that was issued by the 

NRC for public comment in November 2016. The public comment process resulted in several 

comments which were addressed in subsequent revisions. In addition, the RES/EPRI working 

group also reviewed the test plan and provided feedback. The test plan was nominally finalized in 

January 2017. However, it should be noted that while the final test plan was “frozen” as a 

document, additional changes and adjustments were made throughout testing to address minor 

issues identified as the test plan was implemented. The final test matrix is found in Section 4. 

To meet the project goals, a fairly large number of tests involving varied arrays of cable types, 

heating conditions, and circuit types were performed. Preliminary testing was conducted on a 

small-scale radiant heat testing apparatus. Small-scale heating apparatus is described more 

completely in Section 3.4. The ceramic heater used in the small-scale tests allows for wellcontrolled heat exposures that are beneficial for comparison purposes. The small-scale radiant 

heat tests can be conducted very efficiently so that many tests can be conducted in a short time 

and at relatively low cost. 

The test design was optimized to allow for considerable flexibility as the testing proceeded. As 

noted above, the test plan document was nominally frozen in January 2017. However, the actual 

implementation of the test matrix allowed for considerable flexibility. Changes were made to cable, 

circuit, and instrumentation configurations and to test procedures to reflect insights gained as the 

tests progressed. That is, as experience was gained through the performance of the tests, 

opportunities for improvement were identified and implemented. Hence, the test matrix in the final 

test plan was modified. The final test matrix is presented in Section 4.

The small-scale tests for this project were conducted at the Thermal Test Complex at Sandia 

National Laboratories in Albuquerque, NM using a ceramic heater for the radiant heating 

apparatus. Volume 2 of the CAROLFIRE report provides a detailed description of the smallscale test facilities and the general test protocols that were followed during this series of tests. 

3.2 Cable Selection 

Surveys conducted under the equipment qualification (EQ) research programs in the 1980s and 

1990s were an important factor in determining cable insulation materials for the CAROLFIRE and 

DESIREE-Fire tests. Instrumentation circuits were also analyzed in the EQ program and 
3-2

comprised almost 20 percent of the various types of circuits found at one nuclear power plant 

during this study.2 The NRC EQ inspections identified that a common instrumentation cable is a 

2-conductor, twisted shielded pair, 16 AWG (Ref. 15).

During the 2001 cable tests, manufacturers and specific cable properties were not included in the 

documentation (Ref. 4). The types of cable insulations and jackets recorded are listed below. 

x Ethylene-propylene rubber (EPR)/Chloro-Sulphonated Polyethylene (CSPE) 8/Conductor

armored cable

x Polyethylene (PE)/ Polyvinyl Chloride (PVC) 2/Conductor shielded cable

x PVC/PVC

x Ethylene Propylene Diene Monomer (EPDM)/CSPE

None of the common suppliers of EPR cables still advertise them according to the CAROLFIRE 

project plan. The CAROLFIRE project explored a wide range of cable types and the results 

indicated that TS and TP insulated cables behaved differently; however, the various TS cable 

types behaved similarly, as did the various TP cable types. The four instrumentation cables 

tested during the CAROLFIRE project included:

x Cross-linked Polyethylene (XLPE)/CSPE, 16 AWG, 2/Conductor, Shielded RockbestosSurprenant Cable

x XLPE/CSPE, 18 AWG, 12/Conductor, Rockbestos-Surprenant Cable

x PVC/PVC, 16 AWG, 2/Conductor, Shielded General Cable

x PVC/PVC, 18 AWG, 12/Conductor General Cable

The CAROLFIRE report stated that the single most popular insulation material used in the US 

nuclear power industry is the TS material XLPE. The most popular jacket with the XLPE insulation 

type is CSPE, also known by the trade name Hypalon. The most common TP insulation material 

in use at US Nuclear Power Plants (NPPs) is PE, while another very popular material is PVC. The 

types of cables from the 2001 tests were unavailable so other cables and cable manufacturers 

were used. 

The tested cables are described below with summary information provided in Table 3-1. For this 

testing project, TP cable tests were limited because the scope of this project is to define the failure 

characteristics of TS cables based on the 2001 testing. All cables are rated for 600 V. 

For convenience, this report identifies the cable materials in the format ‘insulation/jacket’ (e.g., 

PE/PVC corresponds to a cable with PE insulation surrounding the individual conductors and a 

PVC jacket encapsulating the collection of insulated conductors). 

General descriptions of the TS-insulated and jacketed cables are as follows: 

x XLPE/CSPE: As stated above, XLPE/CSPE is the most popular cable insulation/jacket

combination found in U.S. NPPs. The cables tested were Rockbestos Firewall® III

products in various configurations, shown in Table 3-1. The cables have an overall shield

2 There were a number of US NRC-sponsored cable aging research efforts at Sandia National Laboratories in the 

1980s associated with the Nuclear Plant Aging Research (NPAR) programs, and at EPRI and the U.S. Department 

of Energy relative to Plant Life Extension (PLEX) programs. The work cited here can be found in the reference 

SAND 96-0344, “Aging Management Guideline for Commercial Nuclear Power Plants – Electrical Cable and 

Terminations,” September 1996.
3-3

that is helically applied aluminum/polyester laminated tape shield in continuous contact 

with a flexible strand, tin-coated copper drain wire. The cables with shielded pairs have a 

helically applied aluminum/polyester laminated tape shield with a flexible strand, tin-coated 

copper drain wire. 

x FR-EPR/CPE: EPR is the second most popular insulation material and is another TS

used during this testing. This Flame-Retardant (FR) EPR insulated, Chlorinated

Polyethylene (CPE) jacketed cable was procured from Houston Wire & Cable Company

and manufactured by Belden.

General descriptions of the TP-insulated and jacketed cables are as follows: 

x PVC/PVC-Nylon: PVC is a very popular TP material in the U.S. and abroad as a

general commercial and industrial grade cable. The cable jacket consists of PVC with a

thin layer of nylon material between the jacket and the insulation. This cable was

procured from Houston Wire & Cable Company and manufactured by Belden.

In addition to the purchased cables, two instrumentation cables from the CAROLFIRE project 

were included in the test matrix. All cables are new and have not been in service. These are 

shown, along with the recently purchased cables, in Table 3-1. 

Table 3-1 Project Cable List 

Cable type Cable Characteristics

Manufacturer

Insulation 

& Jacket 

Materials

TS TP

Num. of 

Twisted 

Pairs or 

Conductors

Part 

Number

Overall 

Shield

Shielded 

Pairs Notes

Rockbestos 

Firewall III

XLPE/CS

PE x 2/c

I46-

5700 x

From the 

Firewall III 

product line, a 

nuclear 

qualified cable 

brand. 

Equipment 

qualification 

certificates 

were not 

requested.

Rockbestos 

Firewall III

XLPE/CS

PE x 4/c

I46-

5844 x

Rockbestos 

Firewall III

XLPE/CS

PE x 2

I46-

0021 x x

Rockbestos 

Firewall III

XLPE/CS

PE x 4

I46-

3433 x x

Belden

PVC/PVC

-Nylon x 2

HW105

01602 x Industrialgrade cable

Belden

PVC/PVC 

Nylon x 8

HW105

01608 x

• XLPE/LSZH: The cable insulation consists of XLPE and the jacket is low smoke zero

halogen (LSZH). This cable was procured from Houston Wire & Cable Company and

manufactured by Belden.
3-4

Cable type Cable Characteristics

Manufacturer

Insulation 

& Jacket 

Materials

TS TP

Num. of 

Twisted 

Pairs or 

Conductors

Part 

Number

Overall 

Shield

Shielded 

Pairs Notes

Belden

FREPR/CPE x 2HW110

01602 x x

Belden

FREPR/CPE x 8HW110

01608 x x

Belden

XLPE/LS

ZH x 1

HW120

01601 x x

Belden

XLPE/LS

ZH x 8

HW120

01608 x x

General 

Cable PVC/PVC x 2/c 230830 x

CAROLFIRE 

Test Cable 4

RockbestosSurprenantXLPE/CS

PE x 2/c

I57-

0120 x

CAROLFIRE 

Test Cable 7

Additional Notes:

Insulation and jacket materials shown as: (insulation type) / (jacket type).

XLPE = Cross-linked polyethylene; CSPE = Chlorosulfunated polyethylene (also known as Hypalon); PVC = 

Polyvinyl chloride; FR-EPR = Flame-retardant ethylene-propylene rubber; CPE = Chlorinated Polyethylene; 

LSZH = Low smoke zero halogen

TS = Thermoset; TP = Thermoplastic. 

All cables are 16 AWG.

“2/c” represents a 2-conductor cable, “2” represents a cable containing 2 twisted pairs of conductors

3.3 Test Circuits 

Three test circuits were used to simulate instrumentation circuits similar to what may be seen in 

industry. The most popular instrumentation circuit is the 4–20 mA current loop, given its 

insensitivity to electrical noise, was one of the instrumentation circuits that was tested. The 4–20

mA current loop is also the standard output signal, according to ANSI/ISA-50.00.01-1975 (R2012),

“Compatibility of Analog Signals for Electronic Industrial Process Instruments” (Ref. 5). The 10–50

mA control signal circuit design began back in the days of vacuum tubes where high line voltages 

were required to power up the circuitry. Since transistor circuits have become more widely used 

(and are more stable and accurate), the 10–50 mA current loop is not as prevalent in industry, 

however, these types of circuits may be present in older NPPs and were therefore included in 

testing. Finally, a 1–5 VDC instrumentation circuit was also included in the testing to understand 

how a voltage loop reacts in response to a fire. Each cable type was tested three times for the 

three different test circuit configurations. 

Table 3-1 (Cont'd.)

Project Cable List 

Project Cable List 
3-5

3.3.1 4–20 mA Test Circuit 

A schematic representation that simulates a typical 4–20 mA current loop is shown in Figure 3-1. 

Figure 3-2 illustrates the same 4–20 mA current loop, but not connected to a ground. The 

instrument loop design for the test consisted of a low-power current source, two 10 Ω resistors to 

simulate a long run of instrument cable (in this case 610 m (2,000 ft.), as opposed to the short 

length exposed during the fire test), a 250 Ω load resistor, and a National Instruments LabVIEW 

module to provide the simulated readout circuit. Note that the 250 Ω load resistor is analogous to 

a shunt resistor in an output meter that would convert the 4–20 mA signal into a 1–5 V signal. Use 

of such a shunt resistor at the output device is typical of many instrumentation circuit designs; 250 

Ω is the maximum for a 4–20 mA standard current input (Ref. 5). If twisted pairs had grounded 

shielding, they were grounded at one and not both ends based on discussions with the project 

industry working group, who determined this as a common industry practice.

250 Ω Constant 

Current: 15mA

1 – 5 V 

(Expected 

3.75V)

+

-

Fire Test Cell

10 Ω

10 Ω

1/8 A

Figure 3-1 4–20 mA Instrumentation Circuit for Fire Test, Grounded 

250 Ω Constant 

Current: 15mA

1 – 5 V 

(Expected 

3.75V)

+

-

Fire Test Cell

10 Ω

10 Ω

1/8 A

Figure 3-2 4–20 mA Instrumentation Circuit for Fire Test, Ungrounded 

The circuit was driven by a constant current output from a current source of approximately 15 mA. 

In typical instrumentation circuits, DC voltages are converted to current at the transmitter based 
3-6

on sensor signals. To simulate this, a current source was used to maintain consistency instead of 

adding another variable to the fire test. A fire is assumed to only affect the instrumentation cable; 

the transmitter or receiver are assumed to be located in other rooms. Consequently, a constant 

current is expected from the transmitter, which is emulated through the current source. 

As the fire degrades the instrument cable, some current can leak between the cable conductors, 

resulting in an apparent change in the instrument signal at the display device. That is, portions of 

the fixed 15 mA current signal may leak directly from conductor to conductor, bypassing the 

load/shunt resistor. This behavior was reflected as an inaccurate reading at the load 

resistor/voltmeter assembly. 

Note that in presenting the data from this device, the actual measured output voltage was 

converted to an equivalent 0 to 100 percent process variable scale to ease the interpretation of 

the results. That is, an output reading of 1 V corresponds to 0 percent on the process variable 

scale, and an output reading of 5 V corresponds to 100 percent on the process variable scale. 

Given the constant input current of 15 mA, a reading of about 68 percent on the process variable 

scale is expected. If the two conductors form a “hard” (or very low impedance) short, the reading 

would go off-scale low on the process variable scale (i.e., a zero voltage would be off-scale low 

because the minimum anticipated current load under normal circuit conditions is 4 mA). Since the 

circuit is of such a simplistic nature, robust circuit simulators that Sandia has used in the past, 

specifically Surrogate Circuit Diagnostic Unit (SCDU), were not necessary. 

3.3.2 10–50 mA Test Circuit 

The 10–50 mA current loop design is similar to the 4–20 mA because a constant current source is 

used instead of a transmitter. Two 10 Ω resistors were again used to simulate a long length of 

instrument cable, and a 100 Ω load resistor acted as a shunt resistor. A LabVIEW module was 

again used to capture the voltage across the shunt resistor in the range of a 1–5 V signal. 

The constant current output from the current source was approximately 37.5 mA. The output was 

chosen to have the same expected output as the 4–20 mA circuit: 3.75 V. The rest of the setup

was the same as the ungrounded 4–20 mA instrumentation circuit. The fire behavior was reflected 

as an inaccurate reading at the shunt resistor and LabVIEW module assembly. See Figure 3-3 for 

the 10–50 mA current loop test setup. 

100 Ω Constant 

Current: 37.5 

mA

1 – 5 V 

(Expected 

3.75V)

+

-

Fire Test Cell

10 Ω

10 Ω

1/8 A

Figure 3-3 10–50 mA Instrumentation Circuit for Fire Test 
3-7

3.3.3 1–5 VDC Test Circuit 

A 24 VDC power supply was used instead of a current source. A resistor with a 620 Ω load, along 

with a line drop of 100 Ω and an intrinsic safety resistor of 250 Ω were included in the 

instrumentation circuit in place of a transmitter. The voltage drops across these loads equaled the 

constant voltage of 24 V. The load resistor was 250 Ω, which provided a standard output of 5 V, 

instead of the 3.75 V in the previous two instrumentation circuits. This is the maximum load for the 

voltage source, and in the field the transmitter load drop would be less than 620 Ω, but for the 

purposes of this test we decided to test the loop at 100 percent of its normal operating 

characteristics. A LabVIEW module was again used to measure the expected voltage from the 

shunt resistor. This ungrounded test circuit is illustrated in Figure 3-4. 

250 Ω

Constant 

Voltage: 24V

1 – 5 V 

(Expected 5V)

Fire Test Cell

20 mA

100 Ω

(Line drop 2V)

250 Ω

(Intrinsic Safety 

Resistor 5V)

1/8 A

620 Ω

Figure 3-4 1–5 VDC Instrumentation Circuit for Fire Test 

3.4 Small-Scale Radiant Heater 

The ceramic fiber heater is constructed of ceramic fiber insulation, which isolates the heating 

chamber from the outside. The heater is light-weight, and its low-density properties make it

ideally suited for high temperature applications requiring low thermal mass. The heater size was 

customized with the same cylindrical ring configuration that the Penlight heating apparatus 

utilized in previous testing. Penlight consisted of a cylindrical ring of 0.61 m (24 in) long watercooled quartz lamps with a stainless cylindrical shroud 0.46 m (18 in) in diameter and 0.6 m (24 

in) long. The ceramic fiber heater has an inner diameter of 0.41 m (16 in) and is 0.6 m (24 in)

long. Similar to Penlight, the ceramic heater transferred heat radially onto the surface of the 

cables. 

The exposure temperature was controlled and monitored by TCs mounted on the inner surface 

of the shroud. This created a radiant heating environment analogous to that seen by an object 

enveloped in a fire-induced, hot gas layer or in a fire plume outside the flame zone. The ceramic 

fiber heater simulates these conditions with shroud temperature and heat flux, assuming a 

constant emissivity of 0.85, listed in Table 3-2. The heater has a high emissivity coating which 

enables constant emissivity, shown in Figure 3-6. 
3-8

Figure 3-6 Emissivity of Heat Surface for Watlow Ceramic Fiber Heater3

3 Source: Performance Data for Ceramic Fiber Heaters, Watlow Heaters 

http://catalog.watlow.com/Asset/Performance-Data-for-Ceramic-Fiber-Heaters.pdf

Figure 3-5 Picture of Cable Test Setup (Left) and Ceramic Heater (Right) 
3-9

Table 3-2 Relationship between the Ceramic Fiber Heater Shroud Temperature and 

Radiant Heat Flux Based on Measured Emissivity of 0.85. 

Temperature (°C) Heat Flux (kW/m2)

200 2.42

225 2.97

250 3.61

275 4.35

300 5.20

325 6.17

350 7.27

375 8.51

400 9.90

425 11.45

450 13.18

475 15.10

500 17.22

525 19.56

Tests were conducted using paired cable lengths supported on a 30 cm (12 in) wide ladder-back 

style cable tray suspended through the center of the ceramic heater. There were no tests 

conducted using a conduit or air drop configuration. The cable tray and other physical test 

conditions are effectively identical to those used in CAROLFIRE and DESIREE-Fire. The plan for 

this series of testing was to lay the cables on a B-line ladder-back style cable tray suspended

through the center of the ceramic fiber heating shroud. In every test, two cables were placed on 

the cable tray, shown in Figure 3-7. The tray was placed inside the heating apparatus. One of the 

cables was used for thermal monitoring and one for electrical monitoring, described further in 

Section 3.6. One additional test, not in the initial test plan, was conducted to determine whether 

the two parallel cables were receiving the same radiant heat flux from the ceramic heater. The 

Sandia team determined that, to properly test the TCs, an object with enough mass to represent 

the size of the cable had to be included. Two stainless steel rods were placed on the cable tray 

with one TC placed on the outside of each rod. This is shown in Figure 3-8. 
3-10

Figure 3-7 Representative Cable Setup (Test 28) 

Figure 3-8 Stainless Steel Rod Test Setup 

The heating apparatus was set to 470°C with a ramp of 45°C/min. The difference in temperatures 

between the stainless steel (SS) rods was at maximum 4°C, which is a tolerable difference 

between cable temperatures. The final results of the test are shown in Figure 3-9. 

Figure 3-9 Shroud Thermocouple Test with Two SS Rods 

The results of the testing determined that the difference in temperature between the two cables is 

negligible. For the testing results analysis, the TC temperature was used to determine the 

temperature at failure for the electrically monitored cables. 

0

100

200

300

400

500

600

0:000:050:100:150:200:250:300:350:40

Temperature (°C)

Time (hour:min)

Cable 1 Temp Cable 2 Temp Shroud Temp
3-11

3.5 Temperature Heating Profiles 

For comparison, heat profile information for the 2001 tests is included here, as the objective of this 

test plan was to confirm circuit behavior demonstrated in the 2001 tests. The 2001 testing took 

place in a 10 ft. by 10 ft. steel enclosure serving as a test chamber. A diffusion flame burner was 

used for all tests, with the radiant heat flux, shown in Table 3-3, calculated using the Oxygen 

Consumption Calorimetry principle described in ASTM E 1537. Cables were tested on a 

horizontal raceway in either a plume exposure, where the burner is placed directly under the 

cables, or a hot gas layer exposure, where the burner is offset approximately two feet toward the 

center of the room. Tests 14 and 16 were in plume exposure; Tests 13, 15, and 18 were in hot 

gas layer exposure. Test 17 was tested vertically with a radiant exposure. More details on test 

exposures can be found EPRI TR-1003326 (Ref. 16). 

The CAROLFIRE and DESIREE-Fire series of tests used Penlight which has a maximum shroud 

temperature of about 900°C. Although one test was conducted at this temperature during the 

CAROLFIRE project, the rest of the tests used shroud temperatures ranging from 260–675°C to 

gauge when failure occurs. The instrumentation cables that were tested during the CAROLFIRE 

project were tested with a shroud temperature of 325°C for TP cables, and 470 or 475°C for the 

two TS cables. The thermal response cable for the TS cables ignited prior to electrical failure. 

Table 3-3 Heat Fluxes and Temperatures from Previous Instrumentation Cable Testing 

Test Cable Description 

Radiant 

Heat Flux 

Tested 

(kW/m2) 

Heat 

Release 

Rate (kW) 

Shroud 

Temp. 

(°C) 

Cable 

Temp. at 

Failure 

IRMS_13 EPR/CSPE 8/c Armored 

(TS/TS) n/a 350 n/a unknown 

IRMS_14 PE/PVC 2/c Shielded 16 

AWG (TP/TP) n/a 145 n/a unknown 

IRMS_15

Thermoset1, 1/pair 

shielded 16 AWG 

(TS/TS) 

n/a

Variable 

(350/200/4

50) 

n/a unknown 

IRMS_16 PVC/PVC 3/pair 

shielded (TP/TP) n/a 145 n/a unknown 

IRMS_17 EPDM/CSPE 2/c 

(TS/TS) n/a 200 n/a unknown 

IRMS_18 EPR/CSPE (TS/TS) n/a 250 n/a unknown 

CAROLFIRE_62 XLPE/CSPE 12/c 18 

AWG (TS/TS) 14.5 n/a 475 n/a

CAROLFIRE_63 PVC/PVC 12/c 18 AWG 

(TP/TP) 5.9 n/a 325 205

CAROLFIRE_64 XLPE/CSPE 2/c 16 

AWG (TS/TS) 14.1 n/a 470 n/a

CAROLFIRE_65 PVC/PVC 2/c 16 AWG 

(TP/TP) 5.9 n/a 325 225

1

Although the exact cable material couldn’t be found, based on the information from the cable 

notebook the material is most likely FR-XLPE/CSPE. 
3-12

As in previous tests, the goal was to characterize the degradation of cable integrity and behavior, 

nominally on the order of 10–30 minutes. This amount of time to failure was selected given the 

nature of typical NPP fires and the types of fire scenarios found to be important in risk analysis. 

TP cables fail electrically when their inner (under the jacket) temperatures reach somewhere 

between 200°C and 250°C (Ref. 17). The failure temperature of 200°C is used in the NRC 

Thermally-Induced Electrical Failure (THIEF) Model (Ref. 18) for TP instrumentation cables. A 

ramp-and-hold profile was used to achieve this failure within the target time frame of 10–30

minutes. The intent of the ramp-and-hold profile is not to explicitly represent any particular fire 

profile but to generically represent typical fire behavior. The temperature of the heating shroud 

was 325°C for TP cables in the DESIREE-Fire series of tests. This temperature provides a heat 

flux of 6.17 kW/m2 and is expected to cause longer TP failure times. When this testing was 

conducted, the heating apparatus was set to the desired temperature, which it achieved quickly 

and maintained. Times to failure were expected to be longer than the CAROLFIRE and 

DESIREE-Fire results due to the gradual increase in temperature, which is more representative of 

fire behavior. 

The ceramic fiber heater was started at ambient temperature, around 20°C (68°F). The first test 

for both TP and TS cables was intended to determine the appropriate temperature to achieve 

failure within the target time frame of 10–30 minutes and were performed at lower temperature 

levels. The damage criteria for generic electrical cables in a fire probabilistic risk assessment is 

205°C for TP cables and 330°C for TS cables, according to the EPRI/NRC-RES Fire PRA 

Methodology for Nuclear Power Facilities (Ref. 19).

Preliminary Test 1 was conducted with a temperature rate of rise of 10°C/min to a maximum 

temperature of 205°C for a TP cable. After an hour of heating, the cable had not failed, so the 

temperature was raised incrementally until failure occurred. The test director determined that the 

higher heater temperature would align better to the desired failure time of 10–30 minutes, and 

reflect realistically expected heating profiles in a fire. Preliminary Test 3 ramped to a higher 

temperature of 325°C, and failure of the TP cable occurred around 30 min. Therefore, the ramp 

slope was increased from 10°C/min to 45°C/min. This heating ramp reaches the maximum 

temperature at 410 seconds (6.8 min). The heating apparatus held this constant temperature until 

failures were observed. Note that time t=0 was defined as the time when the primary ramp was 

initiated. Figure 3-10 illustrates the final heating profile that was used during all non-preliminary TP 

cable tests.
3-13

Figure 3-10 Thermoplastic Cable Heating Profile - 325°C 

To test the TS cables, a similar heating profile was created. TS cables failed electrically when their 

inner (under the jacket) temperatures reached somewhere between 400°C and 450°C (Ref. 17).

The failure temperature of 400°C is used in the THIEF model (Ref. 18) for TS instrumentation 

cables. The temperature of the heating shroud was 470°C for TS cables in the DESIREE-Fire 

tests. This temperature provides a heat flux of 14.1 kW/m2 and is expected to cause longer TS 

failure times. TS cables fail earlier than the desired time at a heat flux of 26.9 kW/m2 (600°C)

(Ref. 10).

Preliminary Test 2 was conducted with a rise of 10°C/minute to a maximum temperature of 330°C

for a TS cable. After an hour of heating, the cable had not failed, so the test was concluded. 

Again, the test director determined that the higher heater temperature would align better to the 

desired failure time of between 10–30 minutes reflecting a realistic expected heating profile in a 

fire. Preliminary Test 3 ramped to a higher temperature (470°C) using the same 10°C/min ramp 

and failure occurred around 48 minutes for the TS cable. Therefore, the ramp slope was 

increased from 10°C/min to 45°C/min. The ramp began from 20°C to 470°C at the rate of 45°C 

(113°F) per minute. The shroud should reach 470°C at 600 seconds (10 min). The higher 

temperatures for TS cables correspond to the higher temperature failure rates observed in the 

CAROLFIRE series of tests. Again, time t=0 is defined as the time when the primary ramp was 

initiated and the maximum temperature (470°C) was held until failures are observed. Figure 3-11

illustrates the final heating profile that was used during all subsequent TP cable tests. 

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14 16 18 20 22 24

Shroud Temperature (°C)

Time (min)
3-14

Figure 3-11 Thermoset Cable Heating Profile - 470°C 

The exact heating protocol for each test is specified in the detailed test matrix provided in 

Section 4.

3.6 Diagnostic Instrumentation Summary 

As a general practice, cables were tested in symmetric pairs; one cable was instrumented with 

Type-K TCs and inserted just below the outer cable jacket to measure the cable temperature 

response, while a second length of cable was routed in a symmetric position on the tray (relative 

to the shroud) and connected to energized electrical integrity test circuits to monitor electrical 

performance. This cable pairing approach allowed for a direct correlation of temperature response 

to electrical performance without compromising the electrical integrity of the energized cable. It is 

not appropriate to instrument any single cable for both thermal and electrical response, because 

the instillation of a TC on or within a cable could impact the electrical failure behavior. Given the 

results of testing performed, the temperature and electrical signal can be correlated because the 

temperature difference between the two cables is negligible, as discussed in Section 3.4. The 

conductor number used for electrical monitoring was documented in lab notebooks during testing. 

Raceways used were B-Line Brand Series 268, ladder back, 12 in-wide galvanized steel trays. 

3.6.1 Cable Electrical Performance Monitoring 

National Instruments LabVIEW modules were used to read current and voltage from the circuits 

as described in Section 3.3. The power supply is a Keithley 2400 Source Meter. LabVIEW 

outputted the following information: 

x Upper Shell Temperature from a TC on the upper part of the heating shroud

x Lower Shell Temperature from a TC on the lower part of the heating shroud

x Internal Shell Temperature from a TC placed on the side of the heating shroud

x Tray Temperature from a TC placed on the cable tray

x Cable Temperature from a TC placed in the thermally monitored cable

x Cable Voltage captured at the load resistor

x Heater Setpoint captured the temperature at which the heater was set

0

50

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10 12 14 16 18 20 22 24

Shroud Temperature (°C)

Time (min)
3-15

heater setpoint. 

For the analysis of the results, upper shell temperature was used to compare the shroud 

temperature. Lower shell temperature, internal shell temperature and the cable tray temperature 

were not included in the analysis or the graphs but was preserved in the original documentation. 

Heater setpoint and heater power were also not included in the analysis, but again are preserved 

in the original documentation. Cable temperature and cable voltage were the primary variables 

analyzed. 

The corresponding data for the tests contain two sets of time records. The first set of time records 

is a “raw” data acquisition time and is labeled “DAQ time” for Data Acquisition time. The “DAQ 

Time” starts at time=0 and is the time when the data acquisition time was started. This is the time 

that is original to the data files. The second set of time records is labeled “Heater Time” and this 

set is indexed such that time time=0 corresponds to when the heater ramp was initiated. The 

difference between the “DAQ Time” and the “Heater Time” is a simple constant offset that reflects 

the length of time over which baseline data was collected prior to initiation of initial conditions and 

proper operation of data acquisition systems. For the purposes of data reporting, all time 

references use the “DAQ Time” records, unless otherwise noted. APPENDIX A lists the 

difference in “DAQ Time” and “Heater Time.”

3.6.2 Thermal Response Monitoring 

The cable’s temperature response was measured using a TC inserted below a cable’s outer 

jacket. This technique has been used in several prior test programs and has been shown to 

provide good correlation between cable temperature and electrical failure behaviors (e.g., see 

NUREG/CR-6931 (Ref. 8)). That is, prior testing has shown that the cable insulation temperature 

is well correlated to electrical failure, and subjacket TCs provide a reasonable measure of cable 

insulation temperature. Insertion of a TC potentially compromises a cable’s electrical integrity, so 

temperature response cables were not monitored for electrical performance. The cable used for 

monitoring temperature response was the same instrumentation cable type as the cable used for 

determining electrical failure. 

The TCs were Omega, Type-K (part number KMQIN-040U-18) and were placed just below the 

cable jacket. A small slit in the cable jacket allowed for TC bead insertion. The bead itself was 

inserted at a distance of approximately 2.5–10 cm (1–4 in) along the length of the cable, placing it 

well away from the cut in the outer jacket, shown in Figure 3-13. The slit was then closed and 

secured with a single layer of fiberglass tape. In Figure 3-13, the tape indicates where the slit was 

made and the silver mark on the cable shows where the TC ended. Figure 3-12 demonstrates the 

placement of the TC under the jacket and shows the relation of the temperature monitored cable 

to the electrically monitored cable. TCs were electrically isolated from conductors. 

x Heater Setpoint captured the temperature at which the heater was set

x Heater Power percent captured the power the heater was consuming to reach the
3-16

Figure 3-12 Example Thermocouple Arrangement for Monitoring of 7-Conductor Cable 

near the Electrically Monitored Cable in Tray 

Figure 3-13 Representative Cable Setup Illustrating TC Placement (Test 21) 

TC

~4 in.

Electrically Monitored

Cable

Temperature Monitored 

Cable
4-1

4 TEST MATRIX 

Table 4-1 provides test matrices details for small-scale tests performed at Sandia National 

Laboratories. The goal of the program was to maintain the option to adjust test matrices based on 

insights gained as the program progressed. Test matrices described here document tests 

performed. The test numbers were designated in the initial test plan matrix. Tests were not 

performed sequentially in the same order as would indicate the test number; therefore Table 4-2 

provides an alternate listing of the tests arranged by order performed, with comments relating to 

test anomalies, changes in test configurations, or changes in test protocols implemented during 

testing. The order varied according to logistics and productivity optimization. A total of thirty-eight 

tests were conducted with cables, in addition to four preliminary tests, and one test designed to 

examine heat applied to the cable tray. 

Four preliminary tests were conducted prior to entering the primary test matrix and are numbered 

separately from the primary tests. Data from these tests was used to determine the optimal 

setpoint and ramp rate to simulate cable failure between 10–30 minutes, the target time frame as 

documented in the test plan. A 45°C ramp was deemed sufficient to achieve the 325°C setpoint for 

TP and 470°C setpoint for TS cables. 

For the other cited test parameters, an “X” in any given column indicates the active choice for each 

experimental variable. The primary test variables are as follows: 

x Cable manufacturer specifies the cable manufacturer

x Cable insulation and jacket material specifies the cable insulation and jacket material for

the cables tested 

x Number of twisted pairs or conductors specifies the number of twisted pairs in each cable

or the number of individual conductors in each cable

x Shielded pairs specifies whether the twisted pairs have a shield

x Thermal exposure defines the initial setpoint temperature of the heating apparatus; the final

set point is either 325°C or 470°C (617°F or 878°F), for TP and TS samples, respectively.

Two tests were done on a lower heating setting of 205°C or 330°C or (401°F or 626°F) for

TP and TS samples to analyze the failure in a less severe but still damaging condition.

x Instrumentation circuit specifies which instrumentation circuit was utilized

For all tests, conductor size was 16 AWG. All cables had overall shields between insulated 

conductors and the cable jacket. When twisted pairs were grounded, overall shields were also 

grounded. Three additional variables warrant further discussion. First, as shown in Table 4-1

there was variability in whether the circuit was grounded. As discussed in the CAROLFIRE report, 

grounding the power supply had a pronounced effect on the testing of armored cables in 2001

tests. As a result, CAROLFIRE test data revealed no significant differences between ungrounded 

and grounded circuits for non-armored cables. In this series of testing, tests were conducted with 

the circuit grounded and ungrounded, as many instrumentation circuits are ungrounded for 

increased reliability. Second, industry practice defines that in most instances cable shields are 

grounded at one end to the station ground. This was also included as a variable for a few tests to 

determine if grounding the shield made a difference in the failure of the cable. Finally, the 

inclusion of a fuse between the power supply and circuit was considered a variable. The fuse was 

initially included to match the 2001 tests; however, the impact of the fuse addition was considered 

minimal, and therefore was included as a variable. 
Table 4-1 Matrix of Small-Scale Instrumentation Cable Tests 

Burn Test Number

CableNumber

Manufacturer

Cable Insulation/ Jacket Material Number of Twisted 

Pairs/Conductors

Pairs Shielded Thermal Exposure (°C) 

Circuit

Grounded to Circuit 

Power Supply

Cable Shielding 

Grounded

Circuit Included Fuse Date Completed

Notes

TP TS

20 mA 4–

50 mA– 10

1-5 VDC

PVC/PVC

XLPE/CSPE

EPR/CPE- FR

XLPE/LSZH 1 2 4 8 2/c 4/c

Prelim 1 1004 B x x 205 x x 2/16/2017Prelim 2 1008 B x x x 330 x x 2/17/2017Prelim 3 1004 B x x 325 x x 2/17/2017Prelim 4 1008 B x x x 470 x x 2/20/20171 1004 B x x 325 x x 2/20/20172 1005 B x x 325 x x 2/21/20173A 1006 B x x x 470 x x 2/21/20173B 1006 B x x x 470 x x 2/21/2017 13C 1006 B x x x 470 x x 2/21/2017 14A 1007 B x x x 470 x x 2/23/20174B 1007 B x x x 470 x x 2/23/2017 15 1008 B x x 470 x x 2/27/20176A 1009 B x x x 470 x x x 2/27/2017 26B 1009 B x x x 470 x x 2/27/2017 27 1000 RB x x 470 x x 2/22/2017 38A 1001 RB x x 470 x x 2/22/2017 48B 1002 RB x x 470 x 2/22/2017 49 1003 RB x x x 470 x x 2/23/201710 1004 B x x x 470 x x 2/23/201711 1000 RB x x 470 x 2/22/2017 312 1004 B x x 325 x x x 3/2/2017

4-2
Table 4-1 Matrix of Small-Scale Instrumentation Cable Tests (Cont'd.) 

Burn Test Number

CableNumber

Manufacturer

Cable Insulation/ Jacket Material Number of Twisted 

Pairs/Conductors

Pairs Shielded Thermal Exposure (°C) 

Circuit

Circuit Grounded to 

Power Supply

Cable Shielding 

Grounded

Circuit Included Fuse Date Completed

Notes

TP TS

20 mA 4–

50 mA– 10

1-5 VDC

PVC/PVC

XLPE/CSPE

EPR/CPE- FR

XLPE/LSZH 1 2 4 8 2/c 4/c

13 1005 B x x 325 x x x 3/2/201714 1006 B x x x 470 x x x 2/28/201715 1007 B x x x 470 x x x 3/2/201716 1008 B x x 470 x x x 2/28/201717 1009 B x x x 470 x x x 3/1/201718A 1000 RB x x 470 x x x 2/28/2017 518B 1000 RB x x 470 x x x x 3/3/2017 519 1001 RB x x 470 x x x 3/1/201720 1002 RB x x x 470 x x x 3/1/201721 1003 RB x x x 470 x x x 3/1/201722 1004 B x x 325 x x x x 3/6/201723 1005 B x x 325 x x x x 3/6/201724 1006 B x x x 470 x x x x 3/6/201725 1007 B x x x 470 x x x x 3/7/201726 1008 B x x 470 x x x x 3/6/201727 1009 B x x x 470 x x x x 3/8/201728 1000 RB x x 470 x x x x 3/6/201729 1001 RB x x 470 x x x x 3/7/201730 1002 RB x x x 470 x x x x 3/7/201731 1003 RB x x x 470 x x x x 3/7/201732 CC4 GC x x x 325 x x x 3/8/201733 CC7 RB-S x x x 470 x x x 3/8/201734 SS Rod n/a 470 3/9/2017 6

4-3
Notes 

Conductors for all experiments were 16 AWG. 

A cable tray was used for all experiments. 

Manufacturers: Rockbestos (RB), Belden (B), General Cable (GC) and Rockbestos-Surprenant (RB-S)

1: These tests are repeats to determine the reproducibility of the test. 2: The difference between these tests is the cable shield was ungrounded for 6B. 3: The difference between these tests is the circuit is grounded for Test 7 and ungrounded for 11. 

4: The difference between these tests is the circuit is grounded for Test 8A and ungrounded for 8B. 

5: The difference between these tests is Test 18B had a fuse addition. 

6: This test analyzed the TC response for two stainless steel tubes. 

4-4
4-5

Table 4-2: Chronology of Instrumentation Tests

Date Burn Test 

#

Cable 

Number Comments including changes to test protocols

Begin Small Scale Testing 2/16/2017

2/16/2017 Prelim 1 1004

2/17/2017 Prelim 2 1008

2/17/2017 Prelim 3 1004

2/20/2017 Prelim 4 1008

2/20/2017 1 1004

2/21/2017 2 1005

2/21/2017 3A 1006

2/21/2017 3B 1006

2/21/2017 3C 1006

2/22/2017 7A 1000 Moved to nuclear grade Rockbestos cables to try to see 

the delayed failure behavior.

2/22/2017 11 1000

This test is listed as test 7-U (ungrounded) in the lab 

notebook. In this test, 7A was repeated except the circuit 

was ungrounded. 

2/22/2017 8A 1001

2/22/2017 8B-U 1001

This test repeated 8A except the circuit was ungrounded. 

After seeing no apparent difference between grounding 

and not circuit, the remaining tests grounded all the 

circuits.

2/23/2017 9 1002

2/23/2017 10 1003

2/23/2017 4A 1007

2/23/2017 4B 1007

Repeated Test 4A to determine if 20+ minute leakage time 

is an anomaly. The same long leakage was seen during 

this test.
4-6

Table 4-2: Chronology of Instrumentation Tests (Cont'd)

Date Burn Test 

#

Cable 

Number Comments including changes to test protocols

2/27/2017 5 1008

2/27/2017 6A 1009

This is the first test where the shield was grounded. Likely, 

the shield touches the cable tray so it becomes ground, 

however industry practice is to ground one end of the 

shield. 

2/27/2017 6B 1009

This test repeats 6A but the shield is ungrounded to 

determine if there is a difference. There was not a 

substantial difference between test 6A and 6B so from 

here the cable shield and, if available the twisted pair 

shield, will be grounded to the facility ground.

2/28/2017 14 1006

2/28/2017 16 1008

2/28/2017 18A 1000

3/1/2017 19 1001

3/1/2017 20 1002

3/1/2017 21 1003

3/1/2017 17 HW6

3/2/2017 15 1007

3/2/2017 12 1004

3/2/2017 13 1005

3/3/2017 18B 1000

This test added a fuse to the circuit. The intent was to 

determine if there was a difference with the addition of the 

fuse. Due to no significant difference, remaining tests 

included a fuse in the circuit.

3/6/2017 22 1004

3/6/2017 23 1005

3/6/2017 24 1006
4-7

Table 4-2: Chronology of Instrumentation Tests (Cont'd)

Date Burn Test 

#

Cable 

Number Comments including changes to test protocols

3/6/2017 26 1008

3/6/2017 28 1000

3/7/2017 29 1001

3/7/2017 30 1002

3/7/2017 31 1003

3/7/2017 25 1007

3/8/2017 27 1009

3/8/2017 32 CC4

The CAROLFIRE cables were added at the end of the test 

plan. Although CAROLFIRE had a faster ramp rate, we 

decided to test these cables according to our test plan.

3/8/2017 33 CC7

3/9/2017 34 SS Rod

This test looked at the difference in heating profile between 

the cable with the thermocouple verses the cable that 

carries the electrical signal. Two stainless steel rods with 

thermocouples were tested to determine if there was a 

difference in the heater's profile. The difference was 

minimal so no additional testing is needed.

5-1 

5 SMALL-SCALE TEST RESULTS 

5.1 Organization and Content 

Test results are presented in this section with specific plots to illustrate key aspects of testing. 

Section organization is as follows: 

x Section 5.2 includes the calculation of signal degradation, failure and leakage times 

x Section 5.3 introduces the regression analysis 

x Section 5.4 reviews the experimental test results in the order of the regression analysis 

Test results have been presented in a summarized form and only those plots that illustrate an 

important point or test result have been reproduced here. A detailed summary and graphs for 

every test are included in APPENDIX A . 

5.2 Calculating Signal Degradation, Failure and Leakage Times 

An important part of analysis is the definition of the time the signal begins to degrade and the time 

the signal fails. After a discussion with a Sandia research reactor operator who has previous 

experience with a commercial plant, the significance criteria for signal degradation varies widely 

from 0.25 percent to 2 percent, depending on what is being measured and the required accuracy 

(Ref. 20). For the purposes of this analysis, the conservative 0.25 percent degradation was used 

to designate signal degradation times for all tests. 

The next step is to determine signal failure times. Typical 4–20 mA circuits are designed to show 

circuit failure when the current is less than 4 mA. For example, a loss of power would indicate 0 

mA, instead of the expected 0 percent output of 4 mA for a typical 4–20 mA design. For this 

analysis, anything less than 4 mA was designated a signal failure time for the 4–20 mA circuit. For 

the 10–50 mA circuit, the signal failure time was less than 10 mA. Finally, for the 1–5 VDC circuit 

the failure point was when the voltage was less than 1 V. 

For both cable insulation/jacket material types, as the temperature was nearing the failure 

temperature, at times a sudden drop and restoration of the current was seen, as shown in detail in 

Appendix A. This noise is shown in Test 8A and Figure 5-1, and illustrates how the current could 

drop to 0 mA and restore itself quickly. Signal failure was designated as the first time the current 

or voltage fell below 4 mA, 10 mA, or 1 V, depending on the circuit design, since this would be the 

first indication of an issue. 
5-2

Figure 5-1 Test 8A Noise Example 

To summarize, signal degradation time is when the signal has dropped 0.25 percent from its 

starting value. Signal failure time is when the current or voltage has fallen to less than 4 mA for 

4-20 mA circuits, less than 10 mA for 10–50 mA circuits, and less than 1 V for 1–5 VDC circuits.

The difference between the signal failure time and the signal degradation time is called signal

leakage time.

The signal degradation, failure, and leakage times and the temperature of the cable at signal 

degradation and failure for all tests are shown in Table 5-1. Figure 5-2 illustrates the temperatures 

for the cables at signal failure by TP or TS cable type and number of conductors. 

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:220:240:26

Current (mA)

Signal Percentage

Time (hour:min)
Table 5-1 Signal Degradation, Failure, and Leakage Times for All Tests 

Burn Test Number 

Cable Number 

Insulation/ Jacket Material 

TS or TP 

Number of Conductors 

Signal Degradation Time (s)1

Temp. at Signal Degradation Time (°C) 

Signal Failure Time (s) 

Temp. at Signal Failure Time (°C) 

Signal Leakage Time (min:sec)2

1 1004 PVC/PVC TP 4 674 226 675 226 00:01 2 1005 PVC/PVC TP 16 835 229 835 229 00:00 3A 1006 FR-EPR/CPE TS 4 912 445 963 461 00:513B 1006 FR-EPR/CPE TS 4 958 420 989 444 00:31 3C 1006 FR-EPR/CPE TS 4 911 483 951 489 00:40 4A 1007 FR-EPR/CPE TS 16 1134 404 1739 516 10:05 4B 1007 FR-EPR/CPE TS 16 1142 428 1975 494 13:53 5 1008 XLPE-LSZH TS 2 1023 499 1023 499 00:00 6A 1009 XLPE-LSZH TS 16 1804 444 1804 444 00:00 6B 1009 XLPE-LSZH TS 16 1665 449 1665 449 00:00 7 1000 XLPE/CSPE TS 2 745 418 839 476 01:34 8A 1001 XLPE/CSPE TS 4 750 406 847 476 01:37 8B 1001 XLPE/CSPE TS 4 746 416 860 477 01:54 9 1002 XLPE/CSPE TS 4 858 384 1013 452 02:35 10 1003 XLPE/CSPE TS 8 926 376 1130 443 03:24 11 1000 XLPE/CSPE TS 2 745 415 833 502 01:28 12 1004 PVC/PVC TP 4 621 242 621 242 00:0013 1005 PVC/PVC TP 16 922 226 923 226 00:01 14 1006 FR-EPR/CPE TS 4 909 443 946 451 00:37 15 1007 FR-EPR/CPE TS 16 1113 380 2382 475 21:09 16 1008 XLPE/LSZH TS 2 897 501 898 501 00:01 17 1009 XLPE/LSZH TS 16 1820 421 1821 421 00:01 18A 1000 XLPE/CSPE TS 2 738 406 845 463 01:47 18B 1000 XLPE/CSPE TS 2 767 398 896 454 02:09 19 1001 XLPE/CSPE TS 4 763 404 898 456 02:15 20 1002 XLPE/CSPE TS 4 865 402 1013 453 02:28 

5-3
Burn Test 

Number

Cable Number

Insulation/ Jacket Material

TS or TP

Number of Conductors

Signal Degradation Time (s)1

Temp. at Signal Degradation Time (°C)

Signal Failure Time (s)

Temp. at Signal Failure Time (°C)

Signal LeakageTime (min:sec)2

21 1003 XLPE/CSPE TS 8 971 376 1235 443 04:2422 1004 PVC/PVC TP 4 657 242 660 244 00:0323 1005 PVC/PVC TP 16 875 236 1031 250 02:3624 1006 FR-EPR/CPE TS 4 900 422 959 451 00:5925 1007 FR-EPR/CPE TS 16 1116 383 2379 460 21:0326 1008 XLPE/LSZH TS 2 939 465 940 465 00:0127 1009 XLPE/LSZH TS 16 1820 423 1820 423 00:0028 1000 XLPE/CSPE TS 2 741 380 872 461 02:1129 1001 XLPE/CSPE TS 4 744 386 895 453 02:3130 1002 XLPE/CSPE TS 4 843 377 1023 446 03:0031 1003 XLPE/CSPE TS 8 949 369 1222 434 04:3332 CC4 PVC/PVC TP 2 549 229 549 229 00:0033 CC7 XLPE/CSPE TS 2 725 401 818 452 01:331Signal Degradation Time is based on a 0.25 percent degradation2Signal Leakage Time is equal to Signal Failure Time minus Signal Degradation Time.

5-4

Table 5-1 Signal Degradation, Failure, and Leakage Times for All Tests (Cont'd.) 
5-5

Figure 5-2 Temperature at Signal Failure 

At first glance, the FR-EPR/CPE eight-twisted pair cable had a significant signal leakage time 

compared to the other cables. However, a regression analysis was performed to better 

understand the key variables that drive signal leakage time. 

5.3 Regression Analysis 

A linear regression analysis was performed on the test data to determine the key variables that 

contribute to longer leakage times. Regression analysis is used to predict the value of one 

variable on the basis of other variables (Ref. 21). The dependent variable is the variable to 

forecast (i.e., the variable of interest to understand dependencies); for this analysis, it is the time it 

takes for the cable to lose signal below a certain threshold, or signal leakage time. The other 

variables are called independent variables. In our analysis, the independent variables are: 

x Manufacturer 

x Insulation/jacket material combination 

x Thermoset or thermoplastic 

x Number of conductors 

x Pairs shielded or not shielded 

x Circuit type 

x Circuit grounded or not grounded 

x Shield grounded or not grounded 

x Circuit with a fuse or circuit without a fuse 

0

100

200

300

400

500

600

Temperature (°C)

Number of Conductors

TP Temp at Signal Failure TS Temp at Signal Failure

2 4 8 16
5-6

The independent and dependent variables were put into the RPART package4 in R5, a program 

for statistical and computing graphics, which performs recursive partitioning for the analysis. 

Recursive partitioning was optimal for this analysis because it detects how the leakage time might 

be affected by two parameters interacting, versus a linear regression which can only detect linear 

trends and not the effects of two interacting parameters. 

R constructed a decision tree by splitting or not splitting nodes to best classify or estimate a 

response variable. The advantage of using a decision tree is that is easier to understand because 

of its binary nature and visual representation (Ref. 22). The top node of a decision tree is called 

the parent node and shows the independent variable with the most influence over leakage time. 

This top node is split at a determined value along a range of values for a variable, thus producing 

two child nodes with greater homogeneity than the parent node. R iterates all possible values of 

independent variables to identify the first split, as well as the cut point for the split, to result in one 

group having a strong link to signal leakage time. The terminal or bottom nodes of the tree are 

where the data is not split further and shows the different regions of data categorization. 

The decision tree is shown in Figure 5-3. The node color gradient represents the magnitude of the 

leakage time (i.e., the darker the color the longer the leakage time). Percentages at each node 

indicate the percentage of data in that node. For example, the top node is set to 100 percent 

because it encompasses the entire data set. The ‘n’ value is the number of data points (i.e., tests) 

in that node; the number on top of each node is the mean leakage time for that node. The 

complexity parameter (cp) value determines the cutoff valve for improvements to the model Rsquared value, or whether to split a node. The main role of the cp value is to prune splits from the 

tree that are not worthwhile (Ref. 9). The cp value for this tree was set to 0.01, which means only 

the most significant parameters were identified. A smaller cp leads to a larger decision tree. 

As shown, the first split is material type, separating out FR-EPR/CPE cables with other 

insulation/jacket material types (PVC/PVC, XLPE/LSZH, XLPE/CSPE). These next layer of nodes 

are then recursively treated as parent nodes, thereby continuously splitting the data to further sift 

out key variables with the most impact on leakage time. For this analysis, the FR-EPR/CPE node 

is split between number of conductors and the remaining insulation/jacket material types. 

The decision tree shows the regression analysis in an understandable manner. The results for a 

linear regression are shown in 

Table 5-2. These results include the number of degrees of freedom (related to the number of data 

points and variables used), the sum of the squares which is a measure of the variability in the 

data, and the mean square (MS) which is the sum of squares divided by the degrees of freedom 

for normalization. The f-test compares the variance in the data explained by the model (row titled 

“Regression”) to the variation in the data that is seemingly due to random error (row titled 

“Residual”). If the regression model is explaining some of the variance in the data, then the MS 

Regression value increases compared to the MS Residual. Therefore, because the f-test value is 

greater than 1, there is evidence that more of the variation in the data is explained by the model 

than random chance, highlighted in the table. The significance level for this test is at a typical 

cutoff point, so the model is explaining some variance but more investigative work can be done. 

4 Recursive partitioning for classification, regression and survival trees. An implementation of most of the 

functionality of the 1984 book by Breiman, Friedman, Olshen and Stone. 

5 R is a free software environment for statistical computing and graphics. https://www.r-project.org/ 
5-7

Figure 5-3 Regression Analysis Decision Tree with cp=0.01 

Table 5-2 Regression Analysis for Leakage Time 

Degrees of 

Freedom 

(df)

Sum of the Squared 

Deviations 

Mean Square 

(MS)

F-test Significance F

Regression 4 804539 201135 2.5 0.06

Residual 34 2737162 80505

Total 38 3541701

Table 5-3 shows fitted model coefficients (with confidence intervals around those coefficients) as 

well as standard error values, t-test statistics, and p-values for each independent variable. The 

intercept row in the table does not have a physical interpretation, but it is required for the linear 

regression model to prevent bias in the other coefficients. Mathematically, the intercept is the 

estimated value of the output when all other parameters are zero; however, it is not possible for all 

parameters in our data set to be zero. It is included here because it adjusts the position of the 

model so it is not required to contain the origin. If a confidence interval for a variable coefficient 

contains the value of zero, there is not enough evidence to conclude that parameter has a 

significant impact on the leakage time. 
5-8

Table 5-3 Model Coefficients for Leakage Time 

Based on the table, the only conclusion that we can make with a 95 percent confidence is that 

there is a significant relationship between the number of conductors and leakage time. This is 

highlighted in the table. 

5.4 Experimental Results 

Based on the regression analysis, the experimental results are presented according to variables 

that influence leakage time the most: the number of conductors and whether the insulation/jacket 

material is FR-EPR/CPE. In addition, the conclusions drawn from the 2001 testing [4] on the 

difference between TS and TP cables are reinvestigated. 

5.4.1 Number of Conductors Results 

The number of conductors was a key variable in the regression analysis performed and discussed 

in Section 5.3. The decision tree first split branches based on material type, separating out FREPR/CPE cable materials from other cable insulation/jacket materials. In the FR-EPR/CPE 

section the cables are further split by the number of conductors. For the other insulation/jacket 

materials, only the Rockbestos cables (XLPE/CSPE) are split up by number of conductors. The 

number of conductors tested varied from two to sixteen. As shown in Table 5-4, the 8/c and 16/c 

cables had longer leakage times than the 2/c and 4/c cables. 

Coefficients Standard Error T Stat P-value

Lower 95 

percent 

Upper 95 

percent 

Intercept -11.28 143.91 -0.078 0.938 -303.7 281.2 

Material -15.03 16.56 -0.907 0.370 -48.7 18.6 

Number of 

Conductors 26.79 8.79 3.048 0.004 8.9 44.7 

Circuit 

Type 74.31 121.8 0.61 0.546 -173.2 321.8

Grounding 

Types -26.19 82.75 -0.317 0.754 -194.4 142.0 
5-9 

 

Table 5-4 Summary of Number of Conductors Testing 

Number of Conductors Number of Tests 

Average Leakage Time 

(s)

2 10 64 

4 15 80 

8 3 247 

16 11 375 

The number of conductors is a key variable because the heat transfer rate into the cable is 

dependent upon the heat transfer area and material thickness. Cables with the most conductors 

had the largest mass per linear foot, and were found to have a longer signal leakage time than 

cables with a small number of conductors. A graphical representation of the number of conductors 

and their corresponding leakage time is shown in Figure 5-4. 

Overall, the number of conductors appears to impact the signal leakage time, with more 

conductors generally leading to a longer signal leakage time. However, there are exceptions to 

this analysis. For example, the 16/c XLPE/LSZH cables had a short leakage time. This will be 

discussed more in the next section. 

Figure 5-4 Number of Conductors and Corresponding Signal Leakage Time 

0 2 4 6 8 10 12 14 16 18 20 22

Number of Conductors (Number of Tests)

2 (10) 4 (15) 8 (3) 16 (11)

Leakage Time (min)
5-10

5.4.2 FR-EPR/CPE Cable Material Results 

The regression analysis decision trees indicated the driving key variable as insulation/jacket cable 

material, as discussed in Section 5.3. The highest four leakage times in the testing all had the 

same insulation/jacket material: FR-EPR/CPE. Table 5-5 summarizes the number of tests and 

average leakage times for different insulation/jacket material combinations, and Figure 5-5 shows 

the difference in leakage times between the four-cable insulation/jacket materials tested. As 

shown, FR-EPR/CPE cables have the longest signal leakage times, with the maximum leakage 

time equaling 1,269 seconds (21.15 min). XLPE/LSZH cables had the shortest leakage time. 

Table 5-5 Summary of Cable Material Testing 

Cable Material Type TP or TS Number of Tests Average Leakage

Time (s)

XLPE/LSZH TS 7 0.4

PVC/PVC TP 7 23

XLPE/CSPE TS 16 148

FR-EPR/CPE TS 9 465

Figure 5-5 Signal Leakage by Cable Material Type 

0 2 4 6 8 10 12 14 16 18 20 22

Cable Material Type (Number of Tests)

PVC/PVC FR-EP/CPE XLPE/CSPE XLP-LSZH

Leakage Time (min)
5-11 

 

However, not all FR-EPR/CPE cables demonstrated the same long leakage time. The two-twisted 

pair (four conductors) cables had a significantly shorter leakage time than the eight-twisted pair 

cables (sixteen conductors). The split in the decision tree for the number of conductors is simply 

the average of ten between four and sixteen conductors in the FR-EPR/CPE cables. The 

difference in leakage time between the two-twisted pair and eight-twisted pair FR-EPR/CPE 

cables is shown in Figure 5-6. Figure 5-7 illustrates typical cable temperatures and voltage drop 

for all FR-EPR/CPE cables. This figure shows Tests 14 and 15. 

Figure 5-6 Signal Leakage Time for FR-EPR/CPE Cables 

0 2 4 6 8 10 12 14 16 18 20 22

Number of Conductors (Number of Tests)

2-Pair (5) 8-pair (4)

Leakage Time (min)

0 2 4 6 8 10 12 14 16 18 20 22

Number of Conductors (Number of Tests)

2-Pair (5) 8-pair (4)

Leakage Time (min)
5-12

Figure 5-7 Test 14 (2-pair FR-EPR/CPE Cable) and Test 15 (8-pair FR-EPR/CPE Cable) 

5.4.3 TS and TP Cable Results 

The TS versus TP variable was not found to be a key variable in the regression analysis; however 

a discussion is included to reassess the conclusions found during 2001 testing (Ref. 4). The 2001

tests concluded the following (Ref. 4):

“The most notable result of these tests is the pronounced behavioral differences observed 

between the failure of the thermoplastic cables and that of the thermoset cables. Thermoplastic 

cables generally displayed no characteristics of signal degradation prior to the complete loss of 

signal. On the other hand, the thermoset cables usually displayed some substantial amount of 

signal degradation for a relatively prolonged time period prior to the total loss of signal.”

The analysis is based on the industry current loop test, results shown in Table 5-6. 

Table 5-6 Current Loop Test Data from 2001 Tests 

Test 

Number

Cable 

Material

Raceway 

Type

Time of Signal 

Degradation1 (s)

Time of Signal 

Loss1 (s)

Signal Leakage

Time2 (s)

13 TS Horiz. Tray 1100 2390 1290

14 TP Conduit — 2225 —

15 TS Horiz. Tray 1100 1500 400

16 TP Horiz. Tray — 100 —

17 TS Vert. Tray 930 1600 670

18 TP Conduit 1140 1325 185

1Although these are the similar names to the calculations performed in Table, the methodology used to designate the signal degradation and signal loss time was not documented. Therefore, 

these values cannot be used for a direct comparison. 

2Not included in the report, however it is simply calculated as the time of signal loss minus the 

time of signal degradation. 

0

0.5

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1.5

2

2.5

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4

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0:000:040:080:120:170:210:250:290:340:380:420:460:510:550:591:031:081:121:161:201:25

Voltage (V)

Temperature (°C)

Time (hour:min)

Shroud Temp 8-Pair Load Resistor Voltage 2-Pair Load Resistor Voltage
5-13

Although the TP and TS designator was listed as a key variable in the regression analysis, it was 

not found to be significant in the decision tree or confidence interval analysis. Part of this reason 

could be that the TS material was further deconstructed into material type as another variable so 

that was more dominant. The difference in leakage times is shown in Figure 5-8.

Figure 5-8 Signal Leakage Time for TP and TS Cables 

As shown, the TP cables overall have a shorter leakage time than the TS cables on average. 

However, there were a number of TS tests that had a shorter leakage time than the maximum TP 

leakage time. An example is shown in Figure 5-9. Tests 23 and 26 were both using the same 1–5

VDC circuit; however, Test 23 was conducted on a TP cable and Test 26 was conducted on a TS 

cable. As shown, the TS cable has a 1 sec leakage time, smaller than the TP cable which had a 

156 seconds leakage time. 

0 2 4 6 8 10 12 14 16 18 20 22

Insulation/Jacket Material Type (Number of 

Tests)

TP (7) TS(32)

Leakage Time (min)
5-14

Figure 5-9 Test 23 (TP Cable) and Test 26 (TS Cable) 

This example illustrates that the TP or TS designation does not necessarily correlate to a long 

signal leakage time. The results of the regression analysis show that other key variables 

contribute more to the signal leakage time than the TP or TS cable designation. 

0

1

2

3

4

5

6

0

50

100

150

200

250

300

350

400

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:170:180:190:200:21

Voltage (V)

Temperature (°C)

Time (hour:min)

Shroud Temp TP Load Resistor Voltage for Test 23

TS Load Resistor Voltage for Test 26
6-1 

6 CONCLUSIONS AND RECOMMENDATIONS 

6.1 General Conclusions Regarding Instrumentation Cable Failures 

A total of thirty-nine small-scale tests were conducted. Tests provide evidence that 

instrumentation cables can, under certain circumstances, have a slow signal leakage time 

under fire-exposure conditions. General observations are included in this section. 

Conclusions from the 2001 testing stated that TP cables had “no characteristics of signal 

degradation prior to the complete loss of a signal,” documented in NUREG/CR-6776 (Ref. 4). In 

the industry series of tests, the term signal degradation is equivalent to this report’s usage of the 

term signal leakage. The results of this testing series determined that, in one out of seven tests, 

TP cables may not fail instantaneously. Although, most TP cables failed instantaneously, one TP 

test had a leakage time of 2.6 min. There were a limited number of TP tests (seven out of the total 

thirty-nine) because the focus of the test series was on TS cables. Additional TP testing, which 

varies the number of conductors and TP insulation/jacket material, has been included in the 

recommendation section. 

The focus of this series of testing was on TS cables. Regarding TS cables, the conclusions of 

prior 2001 testing stated that they “usually displayed some substantial amount of signal leakage 

for a relatively prolonged time period prior to the total loss of signal” (Ref. 4). During this series of 

testing, twelve out of the thirty-two tests had less than 1 min of signal leakage before failure and 

four of these tests experienced no signal leakage. Four other TS tests had a signal leakage longer 

than 10 min. Therefore, it is difficult to conclude that TS cables will always experience signal 

leakage before failure. 

A regression analysis was performed on the test data to determine key variables that contributed 

to longer leakage times. The dependent variable is the variable to forecast (i.e., the variable of 

interest to understand dependencies); for this analysis, it is the time it takes for the cable to lose 

signal below a certain threshold (signal leakage time). The other variables are called independent 

variables. In our analysis, the independent variables are: 

x Manufacturer 

x Insulation/jacket material combination 

x Thermoset or thermoplastic 

x Number of conductors 

x Presence or absence of shielding 

x Circuit type 

x Presence or absence of circuit grounding 

x Presence or absence of shield grounding 

x Presence or absence of a circuit fuse 

Two analyses were conducted for the regression analysis: fitted model coefficients and a decision 

tree. Based on the fitted model coefficients method, the number of conductors is the only key 

variable where the confidence interval does not include the value of zero. Therefore, it is the only 

parameter that has a significant impact on leakage time. The only conclusion that can be made 

with this regression methodology with a 95 percent level of statistical confidence is that there is a 

significant relationship between the number of conductors and the signal leakage time. 
6-2

The second regression methodology performed consisted of utilized the R program to construct a 

decision tree by splitting or not splitting each node on the tree to best classify or estimate a 

response variable. The top node of a decision tree is called the parent node and shows the 

independent variable with the most influence over leakage time. This top node is split at a 

determined value along a range of values for a variable, thus producing two child nodes with 

greater homogeneity than the parent node. The first split in the decision tree was material type 

where FR-EPR/CPE cables were split away from the other insulation/jacket material types 

(PVC/PVC, XLPE/LSZH, XLPE/CSPE). However, material was not a key variable, according to 

the linear regression analysis and model coefficient table. This could also be because only eighttwisted pair FR-EPR/CPE cables had significant signal leakage times, versus the two-pair FREPR/CPE cable with leakage times of less than 2 min. The decision tree corroborated visual 

results that FR-EPR/CPE eight-twisted pair cables had the highest leakage times for all thirty-nine 

tests. 

6.2 Recommendations for Follow-On Work 

This series of instrumentation cable tests were limited to small-scale radiant heater tests. Full 

scale testing that is more representative of in-plant conditions is recommended to gain better 

understanding of the key parameters during signal leakage time. It is especially recommended to 

assess the performance of instrumentation in various, likely cable-tray configurations including 

varying the bundling of cables and positions, both vertical and horizontal. Configuration changes 

may have an impact on signal leakage; exposing cables to more varied and representative 

conditions would provide a more complete understanding of instrumentation cable failure. 

Signal leakage times, defined as the time difference between where the signal has dropped 0.25 

percent from its starting value to the time of failure based on the circuit’s current or voltage (4 mA 

for 4–20 mA circuits, 10 mA for 10–50 mA circuits, and less than 1 V for 1–5 VDC circuits), ranged 

from 0 to over 21 min. If a signal does not fail immediately, then the delay may have an impact on 

nuclear power plant operators and the timely decisions they must make. Therefore, it is 

recommended that Fire PRA and HRA evaluation be performed to analyze the potential impacts 

of a long signal delay to operators. Testing realistic circuit configurations that have the potential of 

being single point items, for example battery/bus voltage or pump oil pressure, will be important to 

HRA of realistic NPP scenarios. 

The impact of heating on digital transmitters and receivers was not explored in this test series. 

Sandia has conducted testing on the impact of smoke on digital instrumentation and controls, 

documented in “Results and Insights on the Impact of Smoke on Digital Instrumentation and 

Control” (Ref. 23), which concluded that smoke can cause interruptions and upsets in active 

electronics. The impact of heating on the digital instrumentation and controls was not analyzed in 

the report, but reviewing it is recommended to understand the comprehensive effects of fire on 

digital transmitters and receivers. 

This series of instrumentation cable testing was predominantly focused on TS cable tests; 

however, seven out of twenty-nine tests were performed on TP cables. The results of the testing 

determined that TP cables may not fail instantaneously, with one test having a leakage time of 2.6 

min. Additional testing on TP cables is recommended, particularly to vary the number of 

conductors and insulation/jacket material. Testing a variety of TP cables would provide a more 

comprehensive understanding of the signal leakage behavior. 
7-1 

7 REFERENCES 

[1] TR-1006961, "Spurious Actuation of Electrical Circuits Due to Cable Fires, Results of an 

Expert Elicitation," Institution, Palo Alto, CA, 2002. 

[2] NUREG/CR-5546, SAND90-0696, "An Investigation of the Effects of Thermal Aging on 

the Fire Damageability of Electric Cables," Institution, May 1991. 

[3] Information Notice 99-17, "Problems Associated with Post-Fire Safe-Shutdown Circuit 

Analyses," United States Nuclear Regulatory Commission, June 3 1999, (available in 

ADAMS under Accession #ML023510114). 

[4] NUREG/CR-6776, SAND2002-0447P "Cable Insulation Resistance Measurements 

Made During Cable Fire Tests " Sandia National Laboratories, June 2002, (available in 

ADAMS under Accession #ML15167A477). 

[5] NUREG/CR-7150, BNL-NUREG-98204-2012, EPRI 1026424 "Joint Assessment of 

Cable Damage and Quantification of Effects from Fire (JACQUE-Fire), Volume 1: 

Phenomena Identification and Ranking Table (PIRT) Exercise for Nuclear Power Plant 

Fire-Induced Electrical Circuit Failure," Department of Energy, Science and Technology 

Brookhaven National Laboratory, October 2012, (available in ADAMS under Accession 

#ML12313A105). 

[6] NUREG/CR-7150, EPRI 3002001989, BNL-NUREG-98204-2012, "Joint Assessment of 

Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE) Volume 2: 

Expert Elicitation Exercise for Nuclear Power Plant Fire-Induced Electrical Circuit 

Failure," Brookhaven National Laboratory, May 2014, (available in ADAMS under 

Accession #ML14141A129). 

[7] SAND2016-10803 R, "Response of Nuclear Power Plant Instrumentation Cables When 

Exposed to Fire Conditions - Test Plan " Sandia National Laboratories, November 2016, 

(available in ADAMS under Accession #ML16309A608). 

[8] NUREG/CR-6931, SAND2007-600/V1, "Cable Response to Live Fire (CAROLFIRE) 

Volume 1: Test Descriptions and Analysis of Circuit Response Data " Sandia National 

Laboratories, April 2008, (available in ADAMS under Accession #ML081190230). 

[9] NUREG/CR-7102, "Kerite Analysis in Thermal Environment of FIRE (KATE-Fire): Test 

Results," Sandia National Laboratories, December 2011, (available in ADAMS under 

Accession #ML11333A033). 

[10] NUREG/CR-7100, SAND2012-0323P, "Direct Current Electrical Shorting in Response to 

Exposure Fire (DESIREE-Fire): Test Results," Institution, April 2012. 

[11] SAND 96-0344, "Aging Management Guideline for Commercial Nuclear Power Plants – 

Electrical Cable and Terminations," Sandia National Laboratories, September 1996, 

(available in ADAMS under Accession #ML003759038). 

[12] NUREG/CR-6834, SAND2002-1942P, "Circuit Analysis - Failure Mode and Likelihood 

Analysis," Sandia National Laboratories, September 2003, (available in ADAMS under 

Accession #ML032731464). 

[13] Regulatory Guide 1.189, "Fire Protection for Nuclear Power Plants," U.S. Nuclear 

Regulatory Commission, October 2009, (available in ADAMS under Accession 

#ML092580550). 

[14] Information Notice 84-09, "Lessons Learned From NRC Inspections of Fire Protection 

Safe Shutdown Systems," February 13 1984, (available in ADAMS under Accession 

#ML070180073). 

[15] NUREG/CR-5461, SAND89-2369, "Aging of Cables, Connections, and Electrical 

Penetration Assemblies used in Nuclear Power Plants," Sandia National Laboratories, 

July 1990, (available in ADAMS under Accession #ML041280192). 
7-2

[16] TR-1003326, "Characterization of Fire-Induced Circuit Faults – Results of Cable Fire

Testing," Institution, Palo Alto, CA, December 2002.

[17] NUREG/CR-6931, NISTIR 7472, "Cable Response to Live Fire (CAROLFIRE) Volume 3:

Thermally-Induced Electrical Failure (THIEF) Model " Sandia National Laboratories, April

2008, (available in ADAMS under Accession #ML081190261).

[18] NUREG-1805, "Fire Dynamics Tools (FDTs) Quantitative Fire Hazard Analysis Methods

for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program,"

December 2004, (available in ADAMS under Accession #ML043290075).

[19] NUREG/CR-6850, "EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities:

Detailed Methodology, Volume 2," Sandia National Laboratory, Science Applications

International Corporation, September 2005, (available in ADAMS under Accession

#ML15167A411).

[20] "Telephone interview with J. Klein," Institution, March 29 2017.

[21] "Statistics for Management and Economics," Institution, 2003.

[22] "Bayesian Classification and Regression Trees," Institution, Chichester, UK, 2012.

[23] NUREG/CR-6597, SAND99-1320, "Results and Insights on the Impact of Smoke on

Digital Instrumentation and Control," Sandia National Laboratories, January 2001,

(available in ADAMS under Accession #ML011090023).
A-1

APPENDIX A TEST RESULTS 

A.1 Test 1 Results 

Test conditions: 2/21/17, 7:35 am 

Cable: HW2, 1005, TP, 16-AWG, PVC/PVC, 8-twisted pairs, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 325C, with a 45°/min ramp, nominal 6.17 

kW/m2 flux from shroud. 

Shroud power: Initiated after 30 seconds of baseline data monitoring. 

Figure A-1 Test 1 Temperature and Voltage 

Figure A-2 Test 1 Signal Percentage and Current 

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Voltage (V)

Temperature (°C)

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Cable Temp Shroud Temp Load Resistor Voltage

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Current (mA)

Signal Percentage

Time (hour:min)
A-2

A.2 Test 2 Results 

Test conditions: 2/21/17, 7:35 am 

Cable: HW2, 1005, TP, 16-AWG, PVC/PVC, 8-twisted pairs, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 325C, with a 45°/min ramp, nominal 6.17 

kW/m2 flux from shroud. 

Shroud power: Initiated after 30 seconds of baseline data monitoring. 

Figure A-3 Test 2 Temperature and Voltage 

Figure A-4 Test 2 Signal Percentage and Current 

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Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

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Current (mA)

Signal Percentage

Time (hour:min)
A-3

A.3 Test 3 A Results

Test conditions: 2/21/17, 9:17 am

Cable: HW3, 1006, TS, 16-AWG, FR-EP/CPE, 2-twisted pairs, pairs shielded.

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 45 seconds of baseline data monitoring. 

Figure A-5 Test 3 A Temperature and Voltage 

Figure A-6 Test 3 A Signal Percentage and Current 

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Voltage (V)

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Cable Temp Shroud Temp Load Resistor Voltage

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Current (mA)

Signal Percentage

Time (hour:min)
A-4

A.4 Test 3 B Results 

Test conditions: 2/21/17, 1:00 pm 

Cable: HW3, 1006, TS, 16-AWG, FR-EP/CPE, 2-twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-7 Test 3 B Temperature and Voltage 

Figure A-8 Test 3 B Signal Percentage and Current 

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Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

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Current (mA)

Signal Percentage

Time (hour:min)
A-5

A.5 Test 3 C Results

Test conditions: 2/21/17, 3:00 pm

Cable: HW3, 1006, TS, 16-AWG, FR-EP/CPE, 2-twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 30 seconds of baseline data monitoring. 

Figure A-9 Test 3 C Temperature and Voltage 

Figure A-10 Test 3 C Signal Percentage and Current 

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Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

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0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:17

Current (mA)

Signal Percentage

Time (hour:min)
A-6

A.6 Test 4 A Results 

Test conditions: 2/23/17, 11:59 am 

Cable: HW4, 1007, TS, 16-AWG, FR-EP/CPE, 8 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-11 Test 4 A Temperature and Voltage 

Figure A-12 Test 4 A Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

700

0:000:040:080:120:170:210:250:290:340:380:42

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:040:080:120:170:210:250:290:340:380:42

Current (mA)

Signal Percentage

Time (hour:min)
A-7

A.7 Test 4 B Results 

Test conditions: 2/23/17, 2:30 pm 

Cable: HW4, 1007, TS, 16-AWG, FR-EP/CPE, 8 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-13 Test 4 B Temperature and Voltage 

Figure A-14 Test 4 B Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

700

0:000:050:100:150:200:250:300:350:400:450:500:551:001:051:10

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:050:100:150:200:250:300:350:400:450:500:551:001:051:10

Current (mA)

Signal Percentage

Time (hour:min)
A-8

A.8 Test 5 Results 

Test conditions: 2/27/17, 8:04 am 

Cable: HW5, 1008, TS, 16-AWG, XLP-LSZH, 1 twisted pair, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-15 Test 5 Temperature and Voltage 

Figure A-16 Test 5 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:170:180:19

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:170:180:19

Current (mA)

Signal Percentage

Time (hour:min)
A-9 

 

A.9 Test 6 A Results 

Test conditions: 2/27/17, 9:58 am 

Cable: HW6, 1009, TS, 16-AWG, XLP-LSZH, 8 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-17 Test 6 A Temperature and Voltage 

Figure A-18 Test 6 A Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

700

0:000:020:040:060:080:100:120:140:160:180:200:220:240:260:280:300:320:34

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:220:240:260:280:300:320:34

Current (mA)

Signal Percentage

Time (hour:min)
A-10

A.10 Test 6 B Results 

Test conditions: 2/27/17, 2:30 pm 

Cable: HW6, 1009, TS, 16-AWG, XLP-LSZH, 8 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-19 Test 6 B Temperature and Voltage 

Figure A-20 Test 6 B Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:200:220:240:260:280:300:32

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:220:240:260:280:300:32

Current (mA)

Signal Percentage

Time (hour:min)
A-11 

 

A.11 Test 7 Results 

Test conditions: 2/22/17, 8:32 am 

Cable: RB1, 1000, TS, 16-AWG, XLPE/CSPE, 2 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-21 Test 7 Temperature and Voltage 

Figure A-22 Test 7 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:16

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:16

Current (mA)

Signal Percentage

Time (hour:min)
A-12

A.12 Test 8 A Results 

Test conditions: 2/22/17, 1:05 pm 

Cable: RB2, 1001, TS, 16-AWG, XLPE/CSPE, 4 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-23 Test 8 A Temperature and Voltage 

Figure A-24 Test 8 A Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

700

0:000:020:040:060:080:100:120:140:160:180:200:220:240:26

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:220:240:26

Current (mA)

Signal Percentage

Time (hour:min)
A-13 

 

A.13 Test 8 B Results 

Test conditions: 2/22/17, 3:30 pm 

Cable: RB2, 1001, TS, 16-AWG, XLPE/CSPE, 4 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-25 Test 8 B Temperature and Voltage 

Figure A-26 Test 8 B Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

700

0:000:020:040:060:080:100:120:140:160:180:200:220:24

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:220:24

Current (mA)

Signal Percentage

Time (hour:min)
A-14

A.14 Test 9 Results 

Test conditions: 2/23/17, 8:06 am 

Cable: RB3, 1002, TS, 16-AWG, XLPE/CSPE, 2 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-27 Test 9 Temperature and Voltage 

Figure A-28 Test 9 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:20

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:20

Current (mA)

Signal Percentage

Time (hour:min)
A-15 

 

A.15 Test 10 Results 

Test conditions: 2/23/17, 10:02 am 

Cable: RB4, 1003, TS, 16-AWG, XLPE/CSPE, 4 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-29 Test 10 Temperature and Voltage 

Figure A-30 Test 10 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:200:22

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:22

Current (mA)

Signal Percentage

Time (hour:min)
A-16

A.16 Test 11 Results

Test conditions: 2/22/17, 10:55 am 

Cable: RB1, 1000, TS, 16-AWG, XLPE/CSPE, 2 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Electrical response monitoring: Labview modules used to measure current. Cable tray was grounded. 

Shields were not grounded, circuit ungrounded to power supply. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-31 Test 11 Temperature and Voltage 

Figure A-32 Test 11 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:16

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:16

Current (mA)

Signal Percentage

Time (hour:min)
A-17

A.17 Test 12 Results 

Test conditions: 3/2/17, 11:00 am 

Cable: HW1, 1004, TP, 16-AWG, PVC/PVC, 2-twisted pairs, pairs not shielded, overall shield. 

Exposure conditions: Shroud set to temperature of 325C, with a 45°/min ramp, nominal 6.17 

kW/m2 flux from shroud. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-33 Test 12 Temperature and Voltage 

Figure A-34 Test 12 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

50

100

150

200

250

300

350

400

0:000:010:020:030:040:050:060:070:080:090:100:110:120:13

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:13

Current (mA)

Signal Percentage

Time (hour:min)
A-18

A.18 Test 13 Results 

Test conditions: 3/2/17, 1:20 pm 

Cable: HW2, 1005, TP, 16-AWG, PVC/PVC, 8-twisted pairs, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 325C, with a 45°/min ramp, nominal 6.17 

kW/m2 flux from shroud. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-35 Test 13 Temperature and Voltage 

Figure A-36 Test 13 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

50

100

150

200

250

300

350

400

0:000:020:040:060:080:100:120:140:160:180:200:22

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:22

Current (mA)

Signal Percentage

Time (hour:min)
A-19 

 

A.19 Test 14 Results 

Test conditions: 2/28/17, 11:21 am 

Cable: HW3, 1006, TS, 16-AWG, FR-EP/CPE, 2-twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 90 seconds of baseline data monitoring. 

Figure A-37 Test 14 Temperature and Voltage 

Figure A-38 Test 14 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:18

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:18

Current (mA)

Signal Percentage

Time (hour:min)
A-20

A.20 Test 15 Results 

Test conditions: 3/2/17, 8:00 am 

Cable: HW4, 1007, TS, 16-AWG, FR-EP/CPE, 8 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-39 Test 15 Temperature and Voltage 

Figure A-40 Test 15 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:040:080:120:170:210:250:290:340:380:420:460:510:550:591:031:081:121:161:201:25

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:040:080:120:170:210:250:290:340:380:420:460:510:550:591:031:081:121:161:201:25

Current (mA)

Signal Percentage

Time (hour:min)
A-21 

 

A.21 Test 16 Results 

Test conditions: 2/28/17, 1:45 pm 

Cable: HW5, 1008, TS, 16-AWG, XLP-LSZH, 1 twisted pair, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-41 Test 16 Temperature and Voltage 

Figure A-42 Test 16 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:18

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:18

Current (mA)

Signal Percentage

Time (hour:min)
A-22

A.22 Test 17 Results 

Test conditions: 3/1/17, 1:40 pm 

Cable: HW6, 1009, TS, 16-AWG, XLP-LSZH, 8 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-43 Test 17 Temperature and Voltage 

Figure A-44 Test 17 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:200:220:240:260:280:300:320:34

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:220:240:260:280:300:320:34

Current (mA)

Signal Percentage

Time (hour:min)
A-23 

 

A.23 Test 18 A Results 

Test conditions: 2/28/17, 3:22 pm 

Cable: RB1, 1000, TS, 16-AWG, XLPE/CSPE, 2 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-45 Test 18 A Temperature and Voltage 

Figure A-46 Test 18 A Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:17

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:17

Current (mA)

Signal Percentage

Time (hour:min)
A-24

A.24 Test 18 B Results 

Test conditions: 3/3/17 

Cable: RB1, 1000, TS, 16-AWG, XLPE/CSPE, 2 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Electrical response monitoring: Labview modules used to measure current. Cable tray was 

grounded. Shields were grounded, circuit grounded to power supply, circuit includes fuse. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-47 Test 18 B Temperature and Voltage 

Figure A-48 Test 18 B Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:20

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:20

Current (mA)

Signal Percentage

Time (hour:min)
A-25

A.25 Test 19 Results 

Test conditions: 3/1/17, 7:30 am 

Cable: RB2, 1001, TS, 16-AWG, XLPE/CSPE, 4 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-49 Test 19 Temperature and Voltage 

Figure A-50 Test 19 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:20

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:20

Current (mA)

Signal Percentage

Time (hour:min)
A-26

A.26 Test 20 Results 

Test conditions: 3/1/17, 9:30 am 

Cable: RB3, 1002, TS, 16-AWG, XLPE/CSPE, 2 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-51 Test 20 Temperature and Voltage 

Figure A-52 Test 20 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:20

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:20

Current (mA)

Signal Percentage

Time (hour:min)
A-27 

 

A.27 Test 21 Results 

Test conditions: 3/1/17, 11:30 am 

Cable: RB4, 1003, TS, 16-AWG, XLPE/CSPE, 4 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-53 Test 21 Temperature and Voltage 

Figure A-54 Test 21 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:200:22

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:020:040:060:080:100:120:140:160:180:200:22

Current (mA)

Signal Percentage

Time (hour:min)
A-28

A.28 Test 22 Results 

Test conditions: 3/6/17, 8:00 am 

Cable: HW1, 1004, TP, 16-AWG, PVC/PVC, 2-twisted pairs, pairs not shielded, overall shield. 

Exposure conditions: Shroud set to temperature of 325C, with a 45°/min ramp, nominal 6.17 

kW/m2 flux from shroud. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-55 Test 22 Temperature and Voltage 

Figure A-56 Test 22 Signal Percentage and Current 

0

1

2

3

4

5

6

0

50

100

150

200

250

300

350

400

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:14

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:14

Current (mA)

Signal Percentage

Time (hour:min)
A-29 

 

A.29 Test 23 Results 

Test conditions: 3/6/17, 9:30 pm 

Cable: HW2, 1005, TP, 16-AWG, PVC/PVC, 8-twisted pairs, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 325C, with a 45°/min ramp, nominal 6.17 

kW/m2 flux from shroud. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-57 Test 23 Temperature and Voltage 

Figure A-58 Test 23 Signal Percentage and Current 

0

1

2

3

4

5

6

0

50

100

150

200

250

300

350

400

0:000:020:040:060:080:100:120:140:160:180:20

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:020:040:060:080:100:120:140:160:180:20

Current (mA)

Signal Percentage

Time (hour:min)
A-30

A.30 Test 24 Results 

Test conditions: 3/6/17, 11:32 am 

Cable: HW3, 1006, TS, 16-AWG, FR-EP/CPE, 2-twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-59 Test 24 Temperature and Voltage 

Figure A-60 Test 24 Signal Percentage and Current 

0

1

2

3

4

5

6

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:18

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:020:040:060:080:100:120:140:160:18

Current (mA)

Signal Percentage

Time (hour:min)
A-31

A.31 Test 25 Results 

Test conditions: 3/7/17, 2:20 pm 

Cable: HW4, 1007, TS, 16-AWG, FR-EP/CPE, 8 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-61 Test 25 Temperature and Voltage 

Figure A-62 Test 25 Signal Percentage and Current 

0

1

2

3

4

5

6

0

100

200

300

400

500

600

0:000:040:080:120:170:210:250:290:340:380:420:460:510:550:591:03

Voltage (V)

Temperature (°C)

Time (hour:min) Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:040:080:120:170:210:250:290:340:380:420:460:510:550:591:03

Current (mA)

Signal Percentage

Time (hour:min)
A-32

A.32 Test 26 Results 

Test conditions: 3/6/17, 1:45 pm 

Cable: HW5, 1008, TS, 16-AWG, XLP-LSZH, 1 twisted pair, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-63 Test 26 Temperature and Voltage 

Figure A-64 Test 26 Signal Percentage and Current 

0

1

2

3

4

5

6

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:18

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:020:040:060:080:100:120:140:160:18

Current (mA)

Signal Percentage

Time (hour:min)
A-33 

 

A.33 Test 27 Results 

Test conditions: 3/8/17, 8:00 am 

Cable: HW6, 1009, TS, 16-AWG, XLP-LSZH, 8 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-65 Test 27 Temperature and Voltage 

Figure A-66 Test 27 Signal Percentage and Current 

0

1

2

3

4

5

6

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:200:220:240:260:280:300:32

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:020:040:060:080:100:120:140:160:180:200:220:240:260:280:300:32

Current (mA)

Signal Percentage

Time (hour:min)
A-34

A.34 Test 28 Results 

Test conditions: 3/6/17, 3:30 pm 

Cable: RB1, 1000, TS, 16-AWG, XLPE/CSPE, 2 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-67 Test 28 Temperature and Voltage 

Figure A-68 Test 28 Signal Percentage and Current 

0

1

2

3

4

5

6

0

100

200

300

400

500

600

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:170:18

Voltage (V)

Temperature (°C)

Time (hour:min) Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:170:18

Current (mA)

Signal Percentage

Time (hour:min)
A-35 

 

A.35 Test 29 Results 

Test conditions: 3/7/17, 8:17 am 

Cable: RB2, 1001, TS, 16-AWG, XLPE/CSPE, 4 Conductors, pairs not shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-69 Test 29 Temperature and Voltage 

Figure A-70 Test 29 Signal Percentage and Current 

0

1

2

3

4

5

6

0

100

200

300

400

500

600

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:170:18

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:170:18

Current (mA)

Signal Percentage

Time (hour:min)
A-36

A.36 Test 30 Results 

Test conditions: 3/1/17, 9:30 am 

Cable: RB3, 1002, TS, 16-AWG, XLPE/CSPE, 2 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-71 Test 30 Temperature and Voltage 

Figure A-72 Test 30 Signal Percentage and Current 

0

1

2

3

4

5

6

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:20

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:020:040:060:080:100:120:140:160:180:20

Current (mA)

Signal Percentage

Time (hour:min)
A-37 

 

A.37 Test 31 Results 

Test conditions: 3/7/17, 12:00 pm 

Cable: RB4, 1003, TS, 16-AWG, XLPE/CSPE, 4 twisted pairs, pairs shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-73 Test 31 Temperature and Voltage 

Figure A-74 Test 31 Signal Percentage and Current 

0

1

2

3

4

5

6

0

100

200

300

400

500

600

0:000:020:040:060:080:100:120:140:160:180:200:22

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

2

4

6

8

10

12

14

16

18

20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0:000:020:040:060:080:100:120:140:160:180:200:22

Current (mA)

Signal Percentage

Time (hour:min)
A-38

A.38 Test 32 Results 

Test conditions: 3/8/17, 11:00 am 

Cable: CC4, TP, 16-AWG, PVC/PVC, 2/c, pairs shielded. 

Exposure conditions: Shroud set to temperature of 325°C, with a 45°/min ramp, nominal 6.17 

kW/m2 flux from shroud. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-75 Test 32 Temperature and Voltage 

Figure A-76 Test 32 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

50

100

150

200

250

300

350

400

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:14

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:14

Current (mA)

Signal Percentage

Time (hour:min)
A-39

A.39 Test 33 Results 

Test conditions: 3/8/17 

Cable: CC7, TS, 16-AWG, XLPE/CSPE, 2/c, shielded. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Shroud power: Initiated after 60 seconds of baseline data monitoring. 

Figure A-77 Test 33 Temperature and Voltage 

Figure A-78 Test 33 Signal Percentage and Current 

0

0.5

1

1.5

2

2.5

3

3.5

4

0

100

200

300

400

500

600

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:17

Voltage (V)

Temperature (°C)

Time (hour:min)

Cable Temp Shroud Temp Load Resistor Voltage

0

5

10

15

20

25

30

35

40

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:000:010:020:030:040:050:060:070:080:090:100:110:120:130:140:150:160:17

Current (mA)

Signal Percentage

Time (hour:min)
A-40

A.40 Test 34 TCB Results 

Test conditions: 3/9/17, 10:00 am 

Specimens present: Two stainless steel rods both analyzed for thermocouple response. 

Raceway: 12" B-Line Series 2 tray. One thermocouple was attached to the inner surface of the 

side of the cable tray. 

Exposure conditions: Shroud set to temperature of 470°C, with a 45°/min ramp. 

Thermal response monitoring: Two shroud temperatures, one tray temperature, and two cable 

temperatures were measured by Labview modules for the two stainless steel rods. 

Figure A-79 Test 34 TCB Temperatures 

0

100

200

300

400

500

600

0:000:050:100:150:200:250:300:350:40

Temperature (°C)

Time (hour:min)

Cable 1 Temp Cable 2 Temp Shroud Temp
B-1

APPENDIX B LITERATURE SEARCH

B.1 Scope of Literature Review 

This literature review was undertaken to better understand instrumentation circuit fire testing 

conducted in the past with regards to time to signal degradation and time to electrical failure of the 

electrical cables in these circuit designs. The purpose of this work is to supplement the 

information provided in NUREG/CR-6850 and identify areas for improvement. The following 

documents were reviewed in completing this review: 

x NUREG/CR-5546, An Investigation of the Effects of Thermal Aging on the Fire

Damageability of Electric Cables, May 1991.

x J.M. Such, Programme Etude probiliste de Surete Incendie, (translated as: Probability Study

Program on Fire Safety), EF.30.15.R/96.442, ISPN, April 1997, as summarized in

NUREG/CR-6834, Circuit Analysis- Failure Mode and Likelihood Analysis, September 2003.

x NUREG/CR-6776, Cable Insulation Resistance Measurements Made During Cable Fire

Tests, June 2002.

x NUREG/CR-6931, Cable Response to Live Fire (CAROLFIRE) Volume 1-3, April 2008.

x NUREG/CR-7010, Cable Heat Release, Ignition, and Spread in Tray Instillations During Fire

(CHRISTIFIRE), July 2012.

x NUREG/CR-7150, Joint Assessment of Cable Damage and Quantification of Effects from

Fire (JACQUE-Fire), Volume 1: Phenomena Identification and Ranking Table (PIRT)

Exercise for Nuclear Power Plant Fire-Induced Electrical Circuit Failure, October 2012.

B.2 Cable Aging Effects on Cable Failure Thresholds Tests 

These tests were performed as part of the USNRC-sponsored Fire Vulnerability of Aged Electrical 

Components program. The objective of the test was to investigate the impact of cable aging on 

cable failure thresholds. During the series of tests, a 2-conductor 16 AWG Boston Insulated Wire 

(BIW) instrumentation cable with shield and drain was tested. The cable was energized during 

testing using a three-phase 208V power source and each conductor was connected to one phase 

of the power source and it was open-circuited at the opposite end. The drain wire was also 

energized as if it were a third conductor. The leakage currents on each phase/conductor were 

then monitored over time. Of note, the cables were thermally and electrically isolated from the 

supporting tray structure during tests which eliminated the potential for either cable-to-cable or 

conductor-to-tray failures. 

The conclusion of the test was that the degradation behavior of the aged BIW sample is more 

pronounced than that of the unaged BIW sample. During the tests, significant levels of leakage 

current were observed prior to the onset of catastrophic failure. This phenomenon was not 

investigated further as the damage threshold and damage times reported were all based on the 

failure of a 2-ampere fuse in any one leg of the energizing circuitry. The drain wire showed a 

pronounced tendency to experience the highest leakage currents of the three energized 

conductors, in most cases nearly twice of the individual insulated conductors. This indicated that 

for the aged samples there was a pronounced tendency of the insulated conductors to leak 

current to the shield and drain conductor rather than to each other. 
B-2

B.2.1 Conclusions

This test introduces the concept that leakage current could occur before the onset of catastrophic

failure. However, only one cable was tested and the characterization of the leakage current was

not captured. 

B.3 Probability Study Program on Fire Safety Tests (French nuclear regulatory, 

IRSN sponsored testing)

This report documents one cable fire test to assess the flammability behavior of certain specific 

cable products under fire exposure conditions. The fire test consisted of five cable trays, with each 

tray holding a single layer of cables arranged across the width of the tray. The source of the fire 

was 100 liters of light-weight pump lubricating oil pre-heated to 250°C and poured into a round 

pan with a 1 m2

 surface area. The anticipated burn duration was 91 minutes. One of the five types 

of cables used was a 2-conductor 20 AWG non-armored instrumentation cable. The cables 

carried an applied voltage and base current and were monitored for short circuits and leakage to 

ground. 

The instrument cable in each tray was energized using a 12-mA current source, to be 

representative of the mid-range current on a 4–20 mA device. One side of the supply was 

connected to the first cable conductor and the second conductor was connected to the return side 

of the source which was also grounded. The first and second conductors were connected in 

series through a 250 Ω load resistor. Three of the four circuits showed failure during the test. All 

illustrated a sharp failure behavior with little degradation noted prior to a circuit trip. 

B.3.1 Conclusions

This test is included to note that the instrumentation cables had little degradation noted prior to a 

circuit trip. Unfortunately, more information about the type of insulation and jacket wasn’t provided.

B.4 Cable Insulation Resistance Measurements Made During Cable Fire TestsIn 2002, Sandia National Laboratories (SNL) participated in six instrument circuit burn tests 

conducted by industry, simulating a 4 to 20 mA instrument circuit current loop at Omega Point 

Laboratories. The instrument wire transmitting the signal was exposed to fire environments and 

the output signal was monitored for degradation of the transmitted signal. 

A schematic of the instrument loop circuit used during the six tests is shown in Figure B-2 .

The instrument loop circuit consisted of a low-power current source, fuses to protect the 

components in the event of an unwanted voltage surge, two 10 Ω resistors to simulate a long 

run of instrument cable (~610 m (2000 ft.) as opposed to the short length exposed during the 

fire test), a 250 Ω load resistor, and a voltmeter to provide the simulate read-out circuit. The 

250 Ω load resistor acts in a way similar to a shunt resistor in an output meter that would 

convert the 4–20 mA signal into a 1 to 5 V signal. The circuit was driven by a constant current 

output from a current source of 15 mA. 

Instrumentation Testing
B-3

Figure B-1 Instrument Loop Circuit 

All tests were conducted in a steel chamber measuring 3 m wide, 3 m deep and 2.4 m high at 

Omega Point Laboratories, located in Elmendorf, Texas. The chamber had an opening ~76 cm 

wide by 2.1 m high in the center of one wall. The exposure fire was generated by flowing propane 

gas through a 30 cm x 30 cm diffusion burner, with a fire intensity ranging from 70 to 350 kW. 

The goal of the testing was to monitor the change in conductor IR occurring in at least one cable 

or bundle to determine the failure mode. During four of the tests for the instrumentation loop 

(Tests 13, 15, 16 and 17), the IR measurement system was compromised by a wiring fault. One of 

the instrumentation tests saw no substantive cable failures (Test 14). The IR measurement 

system was properly working for Test 18 and determined the failure mode to be short-to-ground. 

The SNL report does not provide specifics as to the cable manufacturer, instead saying that the 

cables were standard instrument cables. The instrument loop circuit was independent and 

separate from the IR measurements made concurrently during the tests; however, the data was 

gathered and stored by the same computer data acquisition system as the IR data. The current 

loop data was obtained and analyzed to determine the time of signal degradation and the time of 

signal loss. The actual measured voltage was converted to an equivalent 0 to 100% process 

variable scale to ease the interpretation of the results, for example an output reading of 1V 

corresponds to zero on the process variable scale and an output reading of 5 V corresponds to 

100%. The results of the tests are listed in Table B-1 Instrument Loop Test Data. 

Table B-1 Instrument Loop Test Data 

Test 

Number Cable Material Raceway Type

Heat Release 

Rate of Flame 

(kW)

Time of Signal 

Degradation (s)

Time of Signal 

Loss (s)

13 TS Horiz. Tray 350 1100 2390

14 TP Conduit 145 — 2225

15 TS Horiz. Tray Variable 

(350/200/450) 1100 1500

16 TP Horiz. Tray 145 — 100
B-4

17 TS Vert. Tray 200 930 1600

18 TS Conduit 250 1140 1325

B.4.1 Conclusions

This test demonstrated that there are pronounced behavior differences observed between the 

failure of the TP and TS cables. TP cables generally displayed no characteristics of signal 

degradation prior to complete loss of signal. TS cables displayed some substantial amount of 

signal degradation for a relatively prolonged time period prior to the total loss of the signal, shown 

in Figure B-2. As demonstrated in the TS tests, prolonged signal degradation could provide an 

operator with misleading information. Also noted was that instrument cables failed earlier than colocated control cables during the testing. 

B.5 Cable Response to Live Fire (CAROLFIRE) Instrumentation Cable Testing

During the Cable Response to Live Fire (CAROLFIRE) series of tests, a limited number of tests 

on instrumentation cables were performed. The two instrumentation cables tested were a 12-

conductor 18 AWG instrument cable and a 2-conductor 16 AWG instrument cable. These cable 

configurations were included primarily to support the fire model improvement need area. A 

detailed description of the cables tested is shown in Table B-1.

The results of the tests are found in Table B-2. For Tests 62 and 64, both TS cables, the thermal 

response cable ignited prior to electrical failure. Electrical failure for the CAROLFIRE tests is 

defined as a conductor to conductor short or short to ground. Because no temperature at failure 

was reported for these cases, the case was considered indeterminate and was not included in the 

resulting CAROLFIRE analysis. The TS cable experienced spontaneous ignition early in the test, 

compared to larger cables of the same insulation and jacket material, and did not have the same 

Table B-1 Instrument Loop Test Data (Cont'd.)

Figure B-2 Current Loop Data from Thermoset Test Number 13 
B-5

prolonged time to signal loss shown in the 2001 test. For Test 65, the thermal response cable 

ignited prior to electrical failure but the case met the criteria for inclusion in this analysis as 

described in CAROLFIRE, Vol. 2. 

B.5.1 Conclusions

Because of the indeterminate conclusion of Tests 62 and 64, they were not included in 

determining threshold temperature for TS cables in CAROLFIRE Vol. 3. Tests 63 and 65, which 

failed at 205 and 225 °C respectively, aligned with the threshold temperature chosen for TP 

cables: 200 °C. 
Table B-2 Physical Characteristics of the CAROLFIRE Instrumentation Cables 

Short Description Manufacturer Part 

Number

Cond. Count

Cond. Size AWG

Insulation Type

Jacket Type

Notes

PVC/PVC, 16 AWG, 2/C SH

General Cable 230830

2 16 TP TP Contains a foil shield

PVC/PVC, 18 AWG, 12/C General Cable 236120 12 18 TP TPXLPE/CSPE, 16 AWG, 2/C SH

RockbestosSurprenant 146-0021

2 16 TS TS Contains a foil shield.

XLPE/CSPE, 18 AWG, 12/C

RockbestosSurprenant 157-0120 12 18 TS TS

Table B-3 Summary of CAROLFIRE Test Results for Instrumentation Cables 

Test Number

Cable Insulation and Jacket Material

Conductor Count

Conductor Size (AWG)

Shroud Temperature °C (°F) 

Raceway Type

Time of FirstObserved ElectricalFailure (s)

Cable Temp.at Failure °C (°F)

62 XLPE/CSPE 

(TS/TS)

12 18 475 (887) Tray 502 n/a

63 PVC/PVC (TP/TP) 12 18 325 (617) Tray 333 205-208 (401-

406)

64 XLPE/CSPE 

(TS/TS)

2 16 470 (878) Tray 348 n/a

65 PVC/PVC (TP/TP)

2 16 325 (617) Tray 258 225 (437)

B-6
B-7

B.6 Cable Heat Release, Ignition, and Spread in Tray Instillations during Fire 

(CHRISTIFIRE) Tests 

The goal of the Cable Heat Release, Ignition, and Spread in Tray Instillations during Fire 

(CHRISTIFIRE) program was to provide data for the development of fire models that can predict 

the heat release rate of a cable fire. One instrumentation cable was tested during this program, a 

Brand-Rex XLPE/XLPE 18/c. This cable was tested with a mixture of other cables. Due to the 

nature and configuration of the tests, the results are not applicable to this project. 

B.7 Phenomena Identification and Ranking Table (PIRT) Exercise 

This report documented the results of a PIRT exercise that was performed on fire-induced 

electrical circuit failures that may occur in nuclear power plants as a result of fire damage to 

cables. The electrical expert PIRT panel was comprised of a group of electrical and fire protection

experts sponsored by NRC and EPRI. Due to the lack of fire test data, the PIRT panel could not 

rank the parameters influencing hot short-induced spurious operations in a similar manner as for 

the control circuits. The panel recommended future research in areas where the configurations 

were common and the consequences of fire-induced failures could be high. 

The PIRT panel discussed several different types of instrumentation control circuits and ruled 

out a number of them for further consideration and research for several reasons. Table B-4

gives a synopsis of the different types of circuits that the panel evaluated. The table briefly 

describes the configuration of each instrument control circuit, its usages in the nuclear industry, 

and the panel’s recommendations for future research. 

As shown in Table B-4, the panel was primarily concerned about testing instrument current 

loops and determining the failure modes and effects on those instrument circuits, which could 

be substantially different than those on control circuits. Some of the panel’s specifically 

identified instrumentation concerns on cable failures are listed below: 

x If the power for the loop is provided by a power supply that is physically independent of the

loop’s transmitter, a conductor-to-conductor short across the transmitter possibly could drive the

loop current high (20+ mA). The effect of this failure mode is contrary to the belief that loop

currents cannot be driven high by intra-cable shorting.

x Depending upon the electrical relationship of the shield with respect to the signal conductors, it

may be possible for leakage to occur between the two. This may occur as a result of intra-cable

shorts, or a combination of intra- and inter-cable shorts. It even may be possible to re-reference

a shield, via an inter-cable short, to allow the flow of current from one loop to another through

the shield or ground plane. This failure mode would challenge the concept that the shield would

protect the target loop from the influences of external loops.

x The leakage of signal current could be induced by intra-cable short(s) between the signal

conductors within a shielded, twisted pair cable. Due to low- energy characteristics of

instrumentation circuits, a prolonged short condition might be established, producing an

erroneous signal, fixed or variable, that is in the high-, low- or midscale-range. This failure mode

would be contrary to the concept that internal shorting is always of low impedance, and will

quickly drive the circuit to a single-failure state.
B-8

B.7.1 Conclusions 

Due to the low state of knowledge and potentially high consequences of fire-induced failure on 

instrumentation current loop circuits, the PIRT panel recommended that additional testing be 

conducted and the following circuits should be included in testing: 

x 10 mA to 50 mA instrumentation circuits

x 4 mA to 20 mA instrumentation circuits

x 1 VDC to 5 VDC instrumentation circuits
Table B- 4 PIRT Panel Table 

No. Instrumentation 

Control System 

Type

Description Usage in Nuclear 

Industry

PIRT Panel Recommendation

1 Current Loop In a current loop instrumentation controlsystem, the current produced by the loop’s 

power supply is sent around the loop, flowing through every device and load resistor in the circuit. Variations in the loop current are determined by changes in the process parameter, as measured by the instrument. The transmitter produces the output signal, either in the form of a 4–20

mA or a 10

–50 mA current that can be 

used for indication, operation, and other functions.

Current loops are used throughout the industry in a variety of control applications. The most common instrument loops in the nuclear industry are the 4–20 mA ones.

Since the 4

–20 mA current loop is 

prevalent in the industry, and the signal is transmitted through an electrical cable, very little prior testing has been conducted on the effects fire on the cables. Therefore, the PIRT panel highly recommended undertaking further research. Testing on the 10

–50 mA 

current loop, although not as prevalent at NPPs, was also recommended.

2 Full Pneumatic Full pneumatic-control systems utilize 

mechanical transducers to convert the process variable into a pneumatic signal for transmission around the plant via pneumatic tubing. Control pressures generally are 3-15 psig but can be amplified via mechanical amplifiers to greater pressures and volumes for the purposes of opening valves.

Used before the advent of the current loop (pre1950s). Found later insome commercial nuclear power plants for the trip logic of the emergency diesel generator.

Since these systems do not use electrical wiring, the PIRT panel did not recommend their future testing.

B-9
No. Instrumentation 

Control System 

Type

Description Usage in Nuclear 

Industry

PIRT Panel Recommendation

3 ElectroPneumatic Electro-pneumatic control systems use an electrical process variable signal and 

convert it to a proportional pressure signal via an electro-mechanical transducer.

Used extensively forvalve control.

Electrical portion is similar to the current loop in that a 4–20 mA

signal is transmitted through a cable. Future research recommended by the PIRT panel is addressed in number 1 above under Current Loop. Since the pneumatic portion does not employ electrical cabling, the PIRT panel did not recommend this type of system for future testing.

4 Electro-Hydraulic Electro-hydraulic systems employ a 

standard electrical control system via transducers. A typical example would be the conversion of an electrical process variable into a proportional hydraulic pressure for moving valves such as in the turbine control system.

Electro-hydraulic controls are found throughout the nuclear industry in the turbine control system and in the control system for many turbine driven pumps.

Electrical portion is similar to the current loop; therefore, future research is recommended by the PIRT panel and is addressed in number 1 above, Current Loop. Since the hydraulic portion does not employ electrical cabling, the PIRT panel did not recommend this type of system for future testing.

B-10

Table B- 4 PIRT Panel 

Table (Cont'd.)
No. Instrumentation 

Control System 

Type

Description Usage in Nuclear 

Industry

PIRT Panel Recommendation

5 Digital Control Digital-control systems employ high-order 

communication protocols, often with complex error-checking and loopregeneration capabilities. In general, the cabling is shielded, twisted pair, or more recently, specialty cabling that can carry power and other signals within the same cable. Sophisticated isolation an

d

synchronizing- capabilities often ensure 

seamless transfer when a fault is detected on a cable. Some protocols support the programming of loops so that they enter a “hold last state” mode upon loss of communications.

While digital-control systems are frequently used in non-nuclear 

industrial applications, they are not as common in the nuclear industry. This is primarily due to the complexity of the systems, and as a result, the uncertainty of, and vulnerability to, commoncause failures due to software related problems. Digital systems primarily are used in nonsafety and important- tosafety applications, such 

as feedwater-control and 

turbine-control systems. (use same type as in rest)

Because of the many variations of standards, protocols, cable media, adaptability, and programmability, a bounding testing- configuration for digital systems would be difficult to establish. Additionally, errorchecking schemes are employed 

by digital- control schemes that 

largely decrease the likelihood of fire- induced cable faults. Consequently, the PIRT panel does not recommend testing the cabling of digital- control systems. However, overheating effects of digital devices due to a fire may be a concern. It is important to understand the potential effects of exceeding the temperature ratings of the digital devices and the ultimate effects to the system that is being controlled.

6 Combination 

Analog and Digital

In this control system, digital data is carried over the same wires that the analog loop utilizes for control purposes with the digital signal riding in the carrier analog signal. Generally, the digital data is used to convey data such as system/device health, and environmental information.

While this type of device is “state-of-the-art” and 

often used in the nonnuclear industry, the PIRT panel was not aware of any nuclear plant that presently employs this type of system.

Since this type of system is rarely, if ever, used in the nuclear industry, the PIRT panel does not recommend further research.

B-11

Table B- 4 PIRT Panel 

Table (Cont'd.)
B-12

B.8 General Test Conclusions 

The limited testing performed in 2002 demonstrated that there are pronounced behavior 

differences observed between the failure of the TP and TS cables. The instrumentation cables 

tested during CAROLFIRE tests led to more insight into the failure time for TP cables only. The 

need to fully understand TS cables and the differences between them and TP cables was 

highlighted in the PIRT exercises conducted in 2012. 

B.9 Summary of NRC, IEEE and Industry Standards 

This section summarizes NRC, IEEE, and other industry standards applicable to the protection of 

instrumentation circuits. 

x GL 81-12 describes the systems and instrumentation that are generally necessary for

achieving post fire safe shutdown for existing PWRs and BWRs.

x IN 84-09 lists the minimum monitoring instrumentation needed to achieve safe shutdown

for both PWRs and BWRs.

x RG 1.189 states that a fire hazard analysis should identify and provide appropriate

protection for locations where the loss of instrumentation circuits important to safety can

occur.

x ANSI/ISA-50.00.01-1975 (R2012) applies to analog dc signals use din process control

and monitoring systems to transit information between subsystems or separated

elements of systems. The goal of the document is to provide for compatibility between

subsystems. It provides standard signals for transmitters and receivers. Applicable to this

project, the standard output signal of the transmitter should have a range of 4–20 mA.

The receiver should have a standard current input signal of 4–20 mA and a standard

voltage input signal of 1-5 VDC. It also states that the source resistance shall be no

higher than 250 Ω. This information is applicable for the 4–20 mA circuit.

x IEEE Std. 379-2014 states, “The principle of independence is basic to the effective use of

single-failure criterion. The design of a safety system shall be such that no single failure of

a component will interfere with the proper operation of an independent redundant

component or system.”

x IEEE Std. 384–2008 “Required independence. Physical separation and electrical isolation

shall be provided to maintain the independence of Class 1E circuits and equipment so

that the safety functions required during and following any design basis event can be

accomplished.”

B.10 References 

1. NUREG/CR-5546, An Investigation of the Effects of Thermal Aging on the Fire Damageability

of Electric Cables, May 1991.

2. J.M. Such, Programme Etude probiliste de Surete Incendie, (translated as: Probability Study

Program on Fire Safety), EF.30.15.R/96.442, ISPN, April 1997, as summarized in

NUREG/CR-6834, Circuit Analysis- Failure Mode and Likelihood Analysis, September 2003.

3. NUREG/CR-6776, Cable Insulation Resistance Measurements Made During Cable Fire Tests,

June 2002.

4. TR-1003326, Characterization of Fire-Induced Circuit Faults – Results of Cable Fire Testing,

EPRI, Palo Alto, CA, Dec. 2002.
B-13

5. NUREG/CR-6931, Vol. 1, Cable Response to Live Fire (CAROLFIRE) Volume 1: Test

Descriptions and Analysis of Circuit Response Data, April 2008.

6. NUREG/CR-6931, Vol. 2, Cable Response to Live Fire (CAROLFIRE) Volume 2: Cable Fire

Response Data for Fire Model Improvement, April 2008.

7. NUREG/CR-6931, Vol. 3, Cable Response to Live Fire (CAROLFIRE) Volume 3: ThermallyInduced Electrical Failure (THIEF) Model, April 2008.

8. NUREG/CR-7010, Vol. 1, Cable Heat Release, Ignition, and Spread in Tray Instillations

During Fire (CHRISTIFIRE), Phase 1: Horizontal Trays, July 2012.

9. NUREG/CR-7010, Vol. 2, Cable Heat Release, Ignition, and Spread in Tray Instillations

During Fire (CHRISTIFIRE), Phase 2: Vertical Shafts and Corridors, December 2013.

10. NUREG/CR-7150, Joint Assessment of Cable Damage and Quantification of Effects from Fire

(JACQUE-Fire), Volume 1: Phenomena Identification and Ranking Table (PIRT) Exercise for

Nuclear Power Plant Fire-Induced Electrical Circuit Failure, October 2012.

B.11 Regulatory Requirements Reviewed

A. ANSI/ISA-50.00.01-1975 (R2012), “Compatibility of Analog Signals for Electronic Industrial

Process Instruments,” 17 July 2012.

B. ANSI/ISA-67.01.01-2002, “Transducer and Transmitter Installation for Nuclear Safety

Applications,” 16 September 2002.

C. IEEE Std. 323, “IEEE Standard for Qualifying Class 1E Equipment for Nuclear Power

Generating Stations,” January 2004.

D. IEEE Std. 379, “Application of the Single-Failure Criterion to Nuclear Power Generating

Station Safety Systems,” May 2014.

E. IEEE Std. 384, “Criteria for Independence of Class 1E Equipment and Circuits,” December

2008.

B.12 Documents Reviewed, but not Summarized in the Report

A. Andrews, Ian, “Trends in Nuclear Instrumentation.” Electronics & Power. August 8, 1974.

B. Becker, P.H.B.; Gardos, M.; Hollenthoner, S.; Tanpraphan, T.; and Markowicz, A., “More than

20 years of Experience of the IAEA in Providing Training on Nuclear Instrumentation for

Developing Countries,” Advancements in Nuclear Instrumentation Measurement Methods and

their Applications (ANIMMAA) 2009 Conference.

C. DOE Standard 1162-2013, “Instrumentation and Control Functional Area Qualification

Standard.” June 2013.

D. IAEA-TECDOC-363, “Selected Topics in Nuclear Electronics.” January 1986.

E. IAEA-TECDOC-426, “Troubleshooting in Nuclear Instruments.” June 1987.

F. IAEA-TECDOC-530, “Nuclear Electronics Laboratory Manual.” October 1989.

G. IAEA-TECDOC-932, “Pilot Study on the management of ageing of instrumentation and

control cables.” March 1997.

H. IAEA-TECDOC-1188, Assessment and management of ageing of major nuclear power plant

components important to safety: In-containment instrumentation and control cables,

December 2000.

C-1

APPENDIX C FINALTEST PLAN 

C.1 OBJECTIVES, TECHNICAL BACKGROUND, AND APPROACH

C.1.1 Objectives

The objective of this research is to better understand the fire-induced failure modes of

instrumentation cables and evaluate the potential effect those failure modes could have on plant

instrumentation circuits (i.e., circuit, component, and/or system response). In particular, this

research is intended to better quantify the signal leakage that may occur before catastrophic

failure in instrumentation circuits. This work is intended to support future revisions to guidance

(e.g., RG1.189, NUREG/CR-6850) related to circuit analysis.

This test plan has been developed by Sandia National Laboratories (SNL) and sponsored by the

US Nuclear Regulatory Commission (NRC), Office of Regulatory Research (RES) Fire and 

External Hazards Analysis Branch. 

C.1.2 Technical Background

In 1990, the NRC sponsored a series of tests at SNL to investigate the effects of thermal aging on

fire damageability, documented in NUREG/CR-5546, “An Investigation of the Effects of Thermal

Aging on the Fire Damageability of Electric Cables.” An instrumentation cable was tested to

determine the failure time and temperature for both aged and unaged cables. During the testing,

levels of leakage current, on the order of 15 mA, were observed prior to the onset of catastrophic

failure. This phenomenon was not explored further as the damage thresholds and damage times

were only based on the failure of a 2-ampere fuse in the circuit.

In 2001, the Nuclear Energy Institute (NEI) and the Electric Power Research Institute (EPRI) and 

hereafter referred to as “industry,” conducted a series of cable fire tests designed to address 

specific aspects of the cable failure and circuit fault issues of concern.(6) The NRC was invited to 

observe and participate in the 2001 tests by including supplemental cable performance monitoring 

equipment during the tests. The NRC contracted with SNL who provided instrumentation

designed to monitor cable degradation through the measurement of insulation resistance (IR) for

several of the NEI/EPRI tests. In addition to the IR tests, a separate surrogate instrument circuit

was fielded by NRC/SNL in six of the NEI/EPRI tests. This circuit simulated a 4-to-20 mA

instrument circuit loop with a constant current source set to 15 mA. The instrument wire

transmitting the signal was exposed to fire conditions and the output signal was monitored for

degradation of the transmitted signal. These tests were documented in NUREG/CR-6776, “Cable

Insulation Resistance Measurements Made During Cable Fire Tests.”

These tests concluded that there are pronounced behavior differences observed between the

failure of the thermoplastic (TP) and thermoset (TS) cables. TP cables generally displayed no

characteristics of signal degradation prior to complete loss of signal. TS cables displayed a

substantial amount of signal degradation for approximately ten minutes prior to the total loss of the

signal, shown in Figure C-1. If a fire affected a TS instrument cable, it could cause the indicator to

read an intermediate, but not obviously erroneous, value. This misleading indication could

potentially cause operators to take an action based on faulty information (depending on the nature

of the signal and the direction of the signal leakage). In contrast, a fire affecting a TP cable would

6 “Issues of concern” refers to the problems associated with post-fire safe-shutdown circuit analysis, as presented in

Information Notice 99-17, “Problems Associated with Post-Fire Safe-Shutdown Circuit Analyses.”
C-2

likely cause an abrupt and obviously faulty off-scale indication. This would be far less likely to 

mislead operators who would likely diagnose the instrumentation failure. 

Figure C-1 Degradation of Signal Data from Thermoset Test 

These early tests identified potential issues that are unique to instrumentation cables; however, 

the parameters influencing hot short-induced spurious operations could not be identified and 

ranked in the same manner as control circuits, which have been evaluated in a more thorough 

manner. 

C.1.3 General Approach

The tests described in this test plan focus on the failure modes for instrumentation cables. The 

tests were designed to determine the failure modes, time of failure, and temperature at electrical 

failure. The tests are intended to supplement the 2001 testing done on instrumentation cables 

documented in NUREG/CR-6776 and to advance the state of knowledge, which has been 

determined to be low from a phenomena identification and ranking table exercise (NUREG/CR7150, Volume 1). For the purposes of this test, there are two concerns for instrumentation 

readings. First, an instrumentation reading for a component that an operator has to react to within 

a set time could cause unanalyzed problems if the time for the signal to fail is delayed. Second, 

instrumentation readings that automatically actuate an event are also of interest, since 

instrumentation circuits can be tied to component start/stop logic. 

To meet these objectives, SNL will perform a series of tests involving the following variables: 

cable manufacturers, insulation types, conductor sizes, number of twisted pairs or multi-conductor 

cables, and shielding variations. The tests are designed such that cable and instrumentation 

configuration changes can be made with little effort, allowing for flexibility as the testing 

progresses. The tests will utilize a ceramic fiber heater for the heating apparatus. This test plan 

will be reviewed by an NRC/RES and EPRI oversight panel and peer reviewed. Subsequent fullscale testing is planned to be performed by the National Institute of Standards and Technology 

(NIST). 
C-3

C.2 Cable Selection 

C.2.1 Instrumentation Circuit Background 

Instrument circuits (also known as instrumentation and control circuits) provide critical information 

regarding the status of plant conditions to operators. Circuit fault effects on instrument systems 

are unique and more complex than power and control circuits. Instrument sensors typically 

convert process variable values (temperature, pressure, level, flow, etc.) to an electric signal (e.g., 

voltage/current) for transmission to a remote readout or display. Instrumentation readings can also 

be used to automatically actuate an event, since instrumentation circuits can be tied to process 

equipment, such as the reactor protection system and engineering safeguard feature actuation 

system (ESFAS). The current loop typically exists in two forms: 10–50 mA (old standard) and 4–

20 mA (new standard). The 4–20 mA became the industry standard because it has lower circuit 

voltages and current levels so there is less chance for personal shock injury or the generation of 

sparks.

In either case, the principle of operation is the same: current produced by the loop power supply is 

sent around the loop, flowing through every device and load, or burden device, in the circuit. The 

current is modulated into a process variable by a transmitter which converts a sensor’s 

measurement into a current signal and amplifies and conditions the output. A sensor typically 

measures temperature, humidity, flow, level or pressure. The current loop also has a receiver 

which is a device that interprets the current signal into units that can be easily understood by the 

operators. It converts the 4–20 mA current back into a voltage which can be displayed or actuate 

another component based on its start/stop logic. In this setup, 4 mA represents 0 percent of the 

measurement, 20 mArepresents 100 percent and when the current is between 4 mAand 20 mA 

the voltage across the resistor is in direct proportion to that current. See Figure C-2 for an 

example current loop with components listed. 

Current loops are extremely robust systems as they are impervious to electrical noise, and routing 

the signal through shielded, twisted pair cables further reduces noise. Grounding the negative of 

the power supply to the shield provides additional noise protection. It is ideal for long distances as 

current does not degrade over long connections, unlike voltage which can degrade over long 

distances. It is also simple to detect a fault in the system. For example, a loss of power would 

indicate 0 mA, instead of the expected 0 percent output of 4 mA for a typical 4–20 mA design. 

Some designs of instrumentation circuits fail high, where a break in the circuit would read greater 

than 20 mA.

One downside for the current loop design is that it can only transmit one particular process signal. 

However programmable logic controllers or other digital control systems are designed to take 

inputs from multiple current loops. 
C-4

Figure C-2 4–20 mA Current Loop Example(7)

C.2.2 Instrumentation Cable Background

Instrument cables transmit low-level signals from the instrument sensor to an indicator, controller, 

or recorder. Instrumentation cables are low voltage, low ampacity cables (SAND 96-0344). They 

are used for digital or analog transmission from various types of transducers. Resistance 

temperature detectors, pressure transducers and thermocouples are usually of a shielded twisted 

pair configuration whereas radiation detection and neutron monitoring circuits often use coaxial or 

triaxial shielded configurations (SAND 96-0344). Instrument cables typically use single, twisted 

shielded pair conductor cables or much larger multi-conductor cables consisting of 50 or more 

conductors. Each instrument conductor typically is size 16 AWG or smaller. These cables 

frequently enclose several shielded twisted pairs of conductors contained within a protective outer 

jacket. The twisting of conductors reduces magnetic noise, while the shield and drain wire reduce 

electrostatic and radio-frequency interference. The shield consists of a conductive material that is 

wrapped around the twisted pair of conductors. The uninsulated drain wire, which is in physical 

and electrical contact with the shield, provides for easier termination of the foil shield to a common 

ground point. 

C.2.3 Cable Failures and Circuit Faults

C.2.3.1 Cable Failures

Cable failures and subsequent circuit faults are discussed in this section. Cable failure implies that 

the cable is no longer able to perform its intended function which is to maintain the electrical 

integrity and electrical continuity of the associated circuit sufficient to ensure proper operation of 

the circuit (NUREG/CR-6834). For a cable to perform its intended function, each individual 

conductor within the cable must maintain both electrical integrity and continuity. Hence, cable 

failure implies that one or more of the cable conductors have lost electrical integrity or continuity. 

Cables can fail in the following ways. 

Open Circuit: An open circuit is failure condition that results when a circuit (either a cable or 

individual conductor within a cable) has a loss of continuity (RG 1.189). Such failures would likely 

7

 Source: https://www.predig.com/indicatorpage/back-basics-fundamentals-4–20-ma-current-loops
C-5

be diagnosed as a circuit fault by operators. However, a complete loss of several signals may 

mean that operators would not know the actual reactor status, dependent on independent and 

redundant sensors available. 

Short Circuit: A short circuit is an abnormal connection (including an arc) of relatively low 

impedance, whether made accidentally or intentionally, between two points of different potential 

(RG 1.189). This scenario does not involve an external ground. Twisted pairs, especially shielded

twisted pairs, would be more likely to short-to-ground rather than form a short circuit given the 

proximity of the ground. If the power for the current loop is provided by a power supply that is 

physically independent of the loop’s transmitter, a conductor-to-conductor short across the 

transmitter could possibly drive the loop current high and give a false reading. Both intra-cable 

and inter-cable faults are possible, but again the possibility decreases with the addition of 

shielding (properly grounded) protecting the twisted pairs and/or the cables. It could be possible to 

re-reference a shield, via an inter-cable short, to allow the flow of current from one loop to another 

through the shield or ground plane. 

Hot Short: Hot shorts are where individual conductors of the same or different cables that come in 

contact with each other and may result in an impressed voltage or current on the circuit being 

analyzed (RG 1.189).

Short-to-Ground: A short-to-ground is a short circuit between a conductor and a grounded 

reference point (e.g., grounded conductor, conduit or other raceway, metal enclosure, shield wrap, 

or drain wire within a cable) (RG 1.189). Twisted pairs, shields for the pairs, and overall shields 

can be grounded in instrumentation circuits, so shorts-to-ground may occur more than hot shorts. 

C.2.3.2 Circuit Faults 

A circuit fault is undesired or unplanned behavior in an electrical circuit induced by the failure of 

one or more elements of the circuit, in particular, including the failure of an associated electrical 

cable (NUREG/CR-6834). For the purposes of this test plan, this term refers to effects that 

postulated cable failures have on the associated electrical circuits and components. Circuit faults 

that could be applicable to instrumentation circuits are: 

Loss of circuit operability: Some cable failures may lead to a total loss of circuit operability. This 

may result from failures involving instrumentation and control interlocks and permissive signals. 

For example, the failure of an oil pressure signal cable in such a manner that a false-low oil 

pressure was indicated may lead to the loss of function of an associated pump or motor due to an 

oil pressure interlock (NUREG/CR-6834). 

Loss of indication: Cable failures may leave a system or component nominally operational, but will 

compromise the indication functions of the circuit. This may lead, for example, to status-indicating 

lights going dark (NUREG/CR-6834). 

Inaccurate indications: Some cable failures may result in misleading or even conflicting instrument 

signals. For instrumentation circuits a relatively low level of degradation in the IR of signals 

carrying conductors may be sufficient to substantially bias an instrument’s readout (NUREG/CR6834). For example, a false low water level signal could lead operators to activate additional water 

sources leading to overcooling of the reactor vessel. A false high reading could lead operators to 

shut down or throttle coolant injection systems potentially leading to voiding of the core (Draft 

NUREG-1778). 
C-6

Spurious operation: Spurious operation is the undesired or unplanned operation or activation of a 

system or component. Spurious operations are most commonly associated with cable hot short 

failures, although various cable failure modes may lead to spurious operations (depending on 

circuit design) and not all hot shorts will lead to spurious operations (NUREG/CR-6834). 

The functional impact of the cable failures and circuit faults on the plants systems, components, 

and functions can vary. This unpredictability in the state of the process variable as a result of 

cable failures may elicit undesired automatic- or human-responses that may complicate or 

compromise the overall response to the effects of fire. 

The other unknown is determining the change of voltage that would indicate a change of state to 

the operator, if the signal has a binary output. For example, if a valve position indicator could only 

alert the operator if the valve is open or closed. If a voltage change is minimal for a long period of 

time, the operator may not know something is wrong until several minutes have passed. If 

controlled by a digital device, like the Dynamix 1444 Series Monitoring System, the operator 

setting up the system will determine the voltage or amperage at which to indicate a system 

problem. Because the digital transmitter set points will vary by plant, they will not be analyzed 

during the test. The overheating of digital devices themselves may also be a concern, but is not in 

the scope of this test. 

C.2.3.3 Instrumentation Needed for Safe Shutdown

For the purposes of this test, there are two concerns for instrumentation readings. First, an 

instrumentation reading for a component that an operator has to react to within a set time could 

cause unanalyzed problems if the time for the signal to fail is delayed. Second, instrumentation 

readings that automatically actuate an event are also of interest. For example, a pump (dependent 

on the operation of a lubrication system) commonly has a permissive tie to an oil pressure 

reading. If the instrument cable failure led to an inaccurate indication of a loss of oil pressure, the 

pump may trip or fail to start on demand (NUREG/CR-6834). 

Information Notice 84-09, titled “Lessons Learned from NRC Inspections of Fire Protection Safe 

Shutdown Systems” provides guidance for licensees implementing requirements of 10 CFR 50, 

Appendix R. Section III.L.1 of Appendix R requires that alternative shutdown capability achieve 

and maintain subcritical reactivity conditions in the reactor for III.G.3 fire areas. Section III.L.2 

requires provision for direct readings of the process variables necessary to perform and control 

the reactor shutdown function. The minimum process monitoring capability described in IN 84-09

includes the following instruments: 

Instrumentation Needed for PWRs 

x Pressurizer pressure and level

x Reactor coolant hot leg temperature or exit core thermocouples, and cold leg temperature

x Steam generator pressure and level (wide range)

x Source range flux monitor

x Diagnostic instrumentation for shutdown systems

x Level indication for all tanks used (e.g., CST)

Instrumentation Needed for BWRs 

x Reactor water level and pressure

x Suppression pool level and temperature
C-7

x Emergency or isolation condenser level

x Diagnostic instrumentation for shutdown systems

x Level Indication for all tanks used

Diagnostic instrumentation is instrumentation needed to ensure the proper actuation and 

functioning of safe-shutdown equipment and associated support equipment (e.g., flow rate, pump 

discharge pressure). The diagnostic instrumentation needed is plant-specific and should be based 

on the design of the alternative shutdown capability. 

C.2.4 Cable Identification 

Surveys conducted under the equipment qualification (EQ) research programs in the 1980’s and 

1990’s were an important factor in determining cable insulation materials for the Cable Response 

to Live Fire (CAROLFIRE) and Direct Current Electrical Shorting in Response to Exposure Fire 

(DESIREE-Fire) tests. Instrumentation circuits were also analyzed in the EQ program and 

composed almost 20% of the various types of circuits found at one nuclear power plant during 

this study(8). The NRC EQ inspections identified that a common instrumentation cable is a 2-

conductor, twisted shielded pair, 16 AWG (SAND 89-2369). 

During the industry cable tests, manufacturers and specific cable properties were not included in 

the documentation. The types of cable insulations and jackets, which were recorded, are listed 

below: 

x Ethylene-propylene rubber (EPR)/Chloro-Sulphonated Polyethylene (CSPE) 8/Conductor

armored cable

x Polyethylene (PE)/ Polyvinyl Chloride (PVC) 2/Conductor shielded cable

x PVC/PVC

x Ethylene Propylene Diene Monomer (EPDM)/CSPE

None of the common suppliers of EPR cables still advertise these cables, according to the 

CAROLFIRE project plan. The CAROLFIRE project explored a wide range of cable types and the 

results indicated that TS and TP insulated cables behaved differently; however, the various 

thermoset cable types behaved similarly, as did the various TP cable types. The four 

instrumentation cables tested during the CAROLEFIRE project include: 

x Cross-linked Polyethylene (XLPE)/CSPE, 16 AWG, 2/Conductor, Shielded RockbestosSurprenant Cable

x XLPE/CSPE, 18 AWG, 12/Conductor, Rockbestos-Surprenant Cable

x PVC/PVC, 16 AWG, 2/Conductor, Shielded General Cable

x PVC/PVC, 18 AWG, 12/Conductor General Cable

These cables were chosen to analyze the insulation and cable jacket material for a smaller cable, 

given that the bulk of CAROLFIRE tests were performed on 7-conductor 12 AWG cables. 

8 There were a number of USNRC-sponsored cable aging research efforts at Sandia National Laboratories in the 

1980’s associated with the Nuclear Plant Aging Research (NPAR) programs, and at EPRI and the U.S. Department 

of Energy relative to Plant Life Extension (PLEX) programs. The work cited here can be found in the reference 

SAND 96-0344, “Aging Management Guideline for Commercial Nuclear Power Plants – Electrical Cable and 

Terminations,” September 1996.
C-8

The CAROLFIRE report stated that the single most popular insulation material used in the US

nuclear power industry is the TS material XLPE. The most popular jacket with the XLPE insulation

type is CSPE, also known by the trade name Hypalon. The most common TP insulation material

in use at US NPPs is polyethylene (PE), however another very popular material is PVC. Given

the unavailability of the types of cables from the 2001 tests, instrumentation cables from

Rockbestos and General Cable manufacturers will be tested.

To meet the goals of the project, tests will be performed on a variety of instrumentation cable

types, sizes, and numbers of twisted pairs or conductors. This includes testing of both TS and TP

types of cable insulations. The goal is to make these tests as broadly applicable as possible while

establishing reasonable limits on the range of cables and configurations to be used in testing.

C.3 Test Apparatus and Experimental Setups

C.3.1 Heating Apparatus

C.3.1.1 General Description of Ceramic Fiber Heaters

A ceramic fiber heater will be used as the heating apparatus for this series of tests. Volume 2 of

the CAROLFIRE (NUREG/CR-6931) report provides a detailed description of the small-scale test

facilities and the general test protocols that will be utilized during this series of tests.

The ceramic fiber heater that will be used is constructed of ceramic fiber insulation which isolates

the heating chamber from the outside. The heater is lightweight, and its low-density properties

make it ideally suited for high temperature applications requiring low thermal mass. The heaters

can be customized provide the same cylindrical ring that the Penlight heating apparatus utilized in

previous testing. Penlight consisted of a cylindrical ring of 0.61 m (24”) long water-cooled quartz

lamps with a stainless cylindrical shroud 0.46 m (18”) in diameter and 0.6 m (24”) long. The 

ceramic fiber heater will have an inner diameter of 0.41 m (16”) and will be 0.6 m (24”) long. 

Similar to Penlight, the heat transfer will transfer heat radially onto the surface of the cables. This

creates a radiant heating environment analogous to that seen by an object enveloped in a fireinduced, hot-gas layer or in a fire plume outside the flame zone. The ceramic fiber heater will

simulate these conditions with the shroud temperature and shroud heat flux, assuming a constant

emissivity of 0.85, shown in Table C- 1. The heater will have a high emissivity coating which

provides it the constant emissivity, shown in Figure C-3.

The plan for this series of testing is to lay the cables on a ladder-back style cable tray suspended

through the center of the ceramic fiber heating shroud. The other physical test conditions are

effectively identical to those used in CAROLFIRE (NUREG/CR-6931).
C-9

Figure C-3 

Table C- 1 

Emissivity of Heat Surface for Watlow Ceramic Fiber Heater (9)

Relationship between the Ceramic Fiber Heater Shroud Temperature and 

Radiant Heat Flux Based on Measured Emissivity of 0.85. 

Temperature (°C) Heat Flux (kW/m2)

200 2.42

225 2.97

250 3.61

275 4.35

300 5.20

325 6.17

350 7.27

375 8.51

400 9.90

425 11.45

450 13.18

475 15.10

Source: Performance Data for Ceramic Fiber Heaters, Watlow Heaters 

http://catalog.watlow.com/Asset/Performance-Data-for-Ceramic-Fiber-Heaters.pdf 

 9
C-10

Temperature (°C) Heat Flux (kW/m2)

500 17.22

525 19.56

C.3.1.2 Temperature Heating Profiles

For comparison purposes, the heat profile information for the 2001 tests is included here because 

this objective of this test plan is to confirm the circuit behavior demonstrated in the 2001 tests. The 

2001 testing took place in a 10’ x 10’ steel enclosure test chamber. Adiffusion flame burner was

used for all tests, with the radiant heat flux, shown in Table C- 2, calculated using the Oxygen 

Consumption Calorimetry principle described in ASTM E 1537. The cables were tested on a 

horizontal raceway in either a plume exposure where the burner is placed directly under the 

cables or a hot gas layer exposure where the burner is offset approximately two feet toward the 

center of the room. Tests 14 and 16 were in the plume exposure; tests 13, 15 and 18 are in the 

hot gas layer exposure. One instrumentation test, test 17, was tested vertically with a radiant 

exposure. More details on test exposures can be found EPRI TR-1003326.

The CAROLFIRE and DESIREE-fire series of tests used Penlight which has a maximum shroud 

temperature of about 900°C. Although one test was conducted at this temperature during the 

CAROLFIRE project, the rest of the tests used shroud temperatures ranging from 260-675°C to 

gauge when failure occurs. The instrumentation cables that were tested during the CAROLFIRE

project were tested with a shroud temperature of 325°C for the TP cables, and 470 and 475°C for

the two TS cables. The TP cables failed at around 205-225°C. The thermal response cable for the 

TS cables ignited prior to electrical failure. 

Table C- 2 Heat Fluxes and Temperatures from Previous Instrumentation Cable Testing 

Test Cable Description Radiant Heat 

Flux Tested 

(kW/m2) 

Shroud 

Temperatures 

(CAROLEFIRE) 

(°C) 

Cable 

Temperature 

at Failure

IRMS_13 EPR/CSPE 8/c Armored (TS/TS) 350 n/a unknown 

IRMS_14 PE/PVC 2/c Shielded (TP/TP) 145 n/a unknown 

IRMS_15 Thermoset Variable 

(350/200/450) n/a unknown

IRMS_16 PVC/PVC (TP/TP) 145 n/a unknown 

IRMS_17 EPDM/CSPE (TS/TS) 200 n/a unknown 

IRMS_18 EPR/CSPE (TS/TS) 250 n/a unknown 

CAROLFIRE_62 XLPE/CSPE 12/c 18 AWG (TS/TS) 14.5 475 n/a 

CAROLFIRE_63 PVC/PVC 12/c 18 AWG (TP/TP) 5.9 325 205 

CAROLFIRE_64 XLPE/CSPE 2/c 16 AWG (TS/TS) 14.1 470 n/a 

CAROLFIRE_65 PVC/PVC 2/c 16 AWG (TP/TP) 5.9 325 225 

Table C- 1 Relationship between the Ceramic Fiber Heater Shroud Temperature and 

Radiant Heat Flux Based on Measured Emissivity of 0.85 (Cont'd.) 
C-11

As in previous tests, it is desirable to monitor the degradation of cable integrity and behavior over 

relatively long times (nominally on the order of 10-30 minutes). This amount of time to failure was 

selected given the nature of typical NPP fires and the types of fire scenarios found to be important 

in risk analysis, according to the CAROLFIRE report. 

TP cables failed electrically when their inner (under the jacket) temperatures reached somewhere 

between 200°C and 250°C, according to the CAROLFIRE results (NUREG/CR-6931, Vol. 3). The 

failure temperature of 200°C is used in the NRC Thermally-Induced Electrical Failure (THIEF) 

Model (NUREG-1805) for TP instrumentation cables. In order to achieve this failure within the 

target time frame (of 10-30 minutes), a ramp-and-hold profile will be used. The intent of the rampand-hold profile is not to explicitly represent any particular fire profile but to generically represent 

typical fire behavior. The temperature of the heating shroud was 325°C for TP cables in the

DESIREE-Fire series of tests. This temperature provides a heat flux of 5.9 kW/m2

 and is expected 

to cause longer TP failure times. When this testing was done the heating apparatus was set to the 

desired temperature, which it achieved quickly, and held. Times to failure are expected to be 

longer than the CAROLFIRE and DESIRE-Fire results due to the gradual increase in temperature 

which is more representative of fire behavior. 

The ceramic fiber heater will start at ambient temperature, around 20°C (68°F). The first test for 

both TP and TS cables is intended to determine the appropriate temperature to achieve failure 

within the target time frame (10-30 minutes) and will be performed at lower temperature levels. 

The damage criteria for generic electrical cables in a fire probabilistic risk assessment is listed as 

205°C for TP cables and 330°C for TS cables, according to the EPRI/NRC-RES Fire PRA 

Methodology for Nuclear Power Facilities (NUREG/CR-6850). The heating profiles for these two 

temperatures are shown in Figure C-4 and Figure C-5. 

Figure C-4 Thermoplastic Cable Heating Profile- 205°C 

0

50

100

150

200

250

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440

Shroud Temperature (°C)

Time (s)
C-12

Figure C-5 Thermoset Cable Heating Profile- 330°C 

If ignition does not occur within an hour for either of these heating profiles, the temperature will 

increase until failure is observed. The next set heating profiles were based on the CAROLFIRE 

and DESIREE-Fire results, but will be altered based on results seen from the first tests. 

For TP cables, the primary exposure profile will then begin with a ramp from 20°C to 325°C at the 

rate of 45°C (113°F) per minute, reaching the maximum temperature at 410 seconds (6.8 

minutes). The temperature will be held constant at this temperature until failures are observed. 

Note that time t=0 is defined as the time when the primary ramp is initiated. 

Figure C-6 Thermoplastic Cable Heating Profile- 325°C

To test the TS cables, a similar heating profile was created. TS cables failed electrically when their

inner (under the jacket) temperatures reached somewhere between 400°C and 450°C

(NUREG/CR-6931, Vol. 3). The failure temperature of 400°C is used in the NRC ThermallyInduced Electrical Failure (THIEF) Model (NUREG-1805) for TP instrumentation cables. The 

temperature of the heating shroud was 470°C for TS cables in the DESIREE-Fire series of tests.

This temperature provides a heat flux of 14.1 kW/m2 and is expected to cause longer TP failure

0

50

100

150

200

250

300

350

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440

Shroud Temperature (°C)

Time (s)

0

50

100

150

200

250

300

350

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440

Shroud Temperature (°C)

Time (s)
C-13

times. TS cables will fail earlier than the desired time at a heat flux of 26.9 kW/m2 (600°C), 

according to the DESIREE-Fire report. 

The ceramic fiber heater will, again, start at ambient temperature, around 20°C (68°F). The ramp 

will begin from 20°C to 470°C at the rate of 45°C (113°F) per minute. The shroud should reach 

470°C at 600 seconds (10 minutes). The higher temperatures for TS cables correspond to the 

higher temperature failure rates observed in the CAROLFIRE series of tests. Again, time t=0 is 

defined as the time when the primary ramp was initiated and the maximum temperature (470°C) 

will be held until failures are observed. 

Figure C-7 Thermoset Cable Heating Profile- 470°C 

The maximum temperature values are intended to be flexible and will be updated based upon

results seen from testing. 

C.3.2 Experimental Setups

C.3.2.1 Instrumentation Circuits

Instrument Loop: 4–20 mA Grounded and Ungrounded

A schematic representation that simulates a typical 4–20 mAcurrent loop is shown in Figure

C-8. Figure C-9 illustrates the same 4–20 mAcurrent loop, but not connected to a ground. The 

4–20 mA current loop is the most popular instrumentation circuit design in many industries given

its insensitivity to electrical noise. This is also the standard output signal, according to ANSI/

ISA-50.00.01-1975 (R2012), “Compatibility of Analog Signals for Electronic Industrial Process 

Instruments.” The instrument loop design in this test plan consists of a low-power current

source, two 10 Ω resistors to simulate a long run of instrument cable, in this case 610 m 

(2000 ft), as opposed to the short length exposed during the fire test, a 250 Ω load resistor, and 

a voltmeter to provide the simulated readout circuit. Note that the 250 Ω load resistor is analogous 

to a shunt resistor in an output meter that would convert the 4 to 20 mA signal into a 1 to 5 V

signal. Use of such a shunt resistor at the output device is typical of many instrumentation circuit

designs and 250 Ω is the maximum for a 4 to 20 mA standard current input (ANSI/

ISA-50.00.01-1975

(R2012)). Although not shown on the diagram, if the cable has a shield, it will be grounded at the 

meter consistent with common practice. The drain wire will also be grounded, which mirrors 

0

100

200

300

400

500

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440

Shroud Temperature (°C)

Time (s)
C-14

typical practice for a shielded cable which is to ground the shield/drain. If twisted pairs have a 

shield, it will be grounded at one end, and not both ends, based on discussions with the industry 

working group for the project who determined this was a common industry practice. 

The circuit will be driven by a constant current output from the current source of nominally 15 mA. 

In typical instrumentation circuits, a DC voltage would be converted to a current at the transmitter 

based on the signal from the sensor. In order to simulate this, a current source will be used 

instead of adding another variable to the fire test. A fire is assumed to only affect the 

instrumentation cable, not the transmitter or receiver which are assumed to be located in other 

rooms. Because of this, a constant current is expected from the transmitter, which is emulated by 

using a current source. 

As the fire degrades the instrument cable, some current can leak between the cable conductors 

resulting in an apparent drop in the instrument signal at the display device. That is, portions of the 

fixed 15 mA current signal may leak directly from conductor to conductor bypassing the load/shunt 

resistor. This behavior will be reflected as an inaccurate reading at the load resistor/voltmeter 

assembly. 

Note that in presenting the data from this device, the actual measured output voltage can be 

converted to an equivalent 0 to 100 percent process variable scale to ease the interpretation of 

the results. That is, an output reading of 1 V corresponds to 0 percent on the process variable 

scale, and an output reading of 5 V corresponds to 100 percent on the process variable scale. 

Given the 15 mA constant input current, a reading of about 68 percent on the process variable 

scale is expected. If the two conductors form a “hard” (or very low impedance) short, the reading 

would go off-scale low on the process variable scale (i.e., a zero voltage would be off-scale low 

because the minimum anticipated current load under normal circuit conditions is 4 mA). 

Since the circuit is of such a simplistic nature, robust circuit simulators that Sandia has used in the 

past, specifically Surrogate Circuit Diagnostic Unit (SCDU), are not necessary. Rather, the 

instrument loop will be implemented directly as shown. 

250 Ω Constant 

Current: 15mA

1 – 5 V 

(Expected 

3.75V)

+

-

Fire Test Cell

10 Ω

10 Ω

1/8 A

Figure C-8 4–20 mA Instrumentation Circuit for Fire Test, Grounded 
C-15

250 Ω Constant 

Current: 15mA

1 – 5 V 

(Expected 

3.75V)

+

-

Fire Test Cell

10 Ω

10 Ω

1/8 A

Figure C-9 4–20 mA Instrumentation Circuit for Fire Test, Ungrounded 

Instrumentation Loop: 10–50 mA

The 10–50 mA control signal circuit design began back in the days of vacuum tubes where high 

line voltages were required to power up the circuitry. Since transistor circuits have become more 

widely used (and are more stable and accurate) the 10–50 mAcurrent loop is not as prevalent in 

industry, however, these types of circuits may be present in older NPPs and is therefore 

considered in this test plan. The design is similar to the 4–20 mAin that there is no transmitter and

instead a constant current source is used. Two 10 Ω resistors are used again to simulate a long 

run of instrument cable, and a 100 Ω load resistor will act as a shunt resistor. A voltmeter will 

again be used to capture the voltage across the shunt resistor in the range of a 1 to 5 V signal. 

The constant current output from the current source will be 37.5 mA. The output was chosen to 

have the same expected output as the 4–20 mA circuit: 3.75 V. The rest of the setup will be the 

same as the ungrounded 4–20 mA instrumentation circuit. The fire behavior will be reflected as an 

inaccurate reading at the shunt resistor and voltmeter assembly. See Figure C-10 for the 10–50

mA current loop test setup. 

100 Ω Constant 

Current: 37.5 

mA

1 – 5 V 

(Expected 

3.75V)

+

-

Fire Test Cell

10 Ω

10 Ω

1/8 A

Figure C-10 10–50 mA Instrumentation Circuit for Fire Test 
C-16

Instrumentation Loop: 1–5 VDC

A 1 to 5 VDC instrumentation circuit will also be tested to see how a voltage loop acts reacts in 

response to a fire. Instead of a current source, a 24VDC power supply will be used. Instead of a 

transmitter, a resistor with a 600 Ω load, along with a line drop of 100 Ω and an intrinsic safety 

resistor of 250 Ω are included in the instrumentation circuit. The voltage drops across these loads 

equals the constant voltage, 24V. The load resistor is 250 Ω, which will provide a standard output 

of 5V, instead of the 3.75V in the previous two instrumentation circuits. This is the maximum load 

for the voltage source, and in the field the transmitter load drop would be less than 600 Ω, but for 

the purposes of this test we decided to test the loop at its maximum operating characteristics. A 

voltmeter will again be used to measure the expected voltage from the shunt resistor. 

250 Ω

Constant 

Voltage: 24V

1 – 5 V 

(Expected 5V)

Fire Test Cell

20 mA

100 Ω

(Line drop 2V)

250 Ω

(Intrinsic Safety 

Resistor 5V)

1/8 A

600 Ω

Figure C-11 1-5 VDC Instrumentation Circuit for Fire Test 

C.3.2.2 Cable Electrical Performance Monitoring 

Labview ® modules will be used to read current and voltage from the circuits described. These 

circuits are suitable for testing with typical twisted-pair instrument cables in particular. For testing, 

the cable shield wrap (typically present in such cables) will be connected to electrical ground as 

would be typical practice. As noted during the CAROLFIRE and DESIREE-Fire series of tests it is 

not appropriate to instrument any single cable for both thermal and electrical response since the 

instillation of a thermocouple on or within a cable could impact the electrical failure behavior. An 

additional cable will be included in the fire test cell to mirror the cable being monitored for 

electrical performance but will instead be monitored for thermal response. 

C.3.2.3 Thermal Response Monitoring

The cable’s temperature response will be measured using a thermocouple inserted below a 

cable’s outer jacket. This technique has been used in several prior test programs and has been 

shown to provide good correlation between cable temperature and electrical failure behaviors 

(e.g., see NUREG/CR-6931). That is, prior testing has shown that the cable insulation 

temperature is well correlated to electrical failure, and the subjacket thermocouples provide a 

reasonable measure of the cable insulation temperature. Insertion of a thermocouple does 

potentially compromise a cable’s electrical integrity, so temperature response cables are not 
C-17

monitored for electrical performance. The cable used for monitoring the temperature response will 

be the same instrumentation cable type as the cable used for determining electrical failure. 

The thermocouples will be of Type K and will be placed just below the cable jacket. A small slit in 

the cable jacket allows for the insertion of the thermocouple bead. The bead itself will be inserted 

into a distance of approximately 2.5 – 10 cm (1-4 inches) along the length of the cable placing it 

well away from the cut in the outer jacket. The slit will then be closed and secured with a single 

layer of fiberglass tape. Figure C-12 demonstrates the placement of the thermocouple under the 

jacket and also shows the relation of the temperature monitored cable to the electrically monitored 

cable. The thermocouples will be electrically isolated from the conductors. 

Figure C-12 Example Thermocouple Arrangement for Monitoring of 7-Conductor Cable 

Located Near the Electrically Monitored Cable in Tray 

C.3.2.4 Placement of Cables 

The two cable manufacturers chosen for this test matrix are General Cable and Rockbestos 

Firewall III. The instrumentation cables from these manufacturers were analyzed during the 

CAROLFIRE tests and are intended to have representative properties of cables across industry. 

There are two sizes of conductors for both manufactures: 16 and 18 AWG. The current test plan 

includes both sizes for testing but focuses on 16 AWG as it is understood to be the most common 

size cable for instrumentation circuits. For this series of testing the lowest number of twisted pairs 

available (1-pair for General Cable TP-insulated cable and 2-pair for Rockbestos TS-insulated 

cable) and a 7-pair conductor cables were selected. The plan is also to test cables with an overall 

shield, shielded pairs, or both shields, depending on what the manufacturer offers. An armored 

cable (preferably with an EPR insulation and CSPE jacket to correspond to the test in the 2001

test where signal degradation was found) has not yet been identified as available. If one is 

located, it will be included it in the tests. Finally, the plan is to route the cables in cable trays as 

individual cables and not cable bundles. 

The cables will be tested in a horizontal position and run through the heating apparatus on a cable 

tray. The CAROLFIRE and DESIREE-Fire tested straight lengths of cable rather than cables with 

a radial bend section. This choice was made because a radial bend is expected to maximize the 

likelihood that a cable will fail, but it might also more likely that failure will lead to a fuse blow 

TC

~25mm.

Electrically Monitored 

Cable

Temperature Monitored 

Cable
C-18

rather than a spurious action. For example, if the failure occurs fairly abruptly, the bent section 

might drive all conductors together more quickly leading to more fuse blow failures and fewer 

spurious actuation failures. With a straight section, the cable failure would be driven primarily by 

the internal cable geometry and any residual internal stresses normal within a multi-conductor or 

twisted pair cable. This could lead to more failures that involve a subset of the conductors present 

and therefore more failures that involve hot shorts and spurious actuation. For this reason, the 

cables for this test will also be straight rather than in a radial bend. 

The cable tray will be 300 mm (12-inch) wide standard ladder-back configuration, which are 

identical to those used in CAROLFIRE and DESIREE-Fire. For this series of tests, the open ends 

of the ceramic fiber heater will be closed off using a 24 mm (1 in) thick, low-density, solid 

refractory insulating board material. These boards will be cut around the raceways. It is not 

intended for the heating apparatus to be well sealed. The primary purpose of these end covers is 

to minimize air circulation into and out of the exposure chamber, as demonstrated in the 

CAROLFIRE Tests (NUREG/CR-6931). Figure C-13 shows the planned test setup. 

Figure C-13 Ceramic Fiber Heater Testing Apparatus (Shown with Cable Tray) 

C.4 Test Matrix

This text matrix is intended to focus the test planning for instrumentation cables. The tests are 

designed to measure the temperature and time at failure, and electrical failure behavior, 

particularly focusing on the behavior differences between TP and TS instrumentation cables. Our 

goals are to confirm previous tests indicating that a fire affecting a TP cable would likely cause an 

abrupt failure and to better characterize the failure of a TS cable. This draft test matrix is based on 

data available during the literature search and Sandia assumptions. It can be modified based on 

information received during the public comment period as no direct operations experience data 

was made available during the test plan preparation process. 

The test matrix is shown in Table C-3 . These tests are characterized by the following parameters 

where either a value or an “X” in a given column indicates the active choice for each experimental 

variable:

x Cable Manufacturer. General Cable and Rockbestos Firewall III instrumentation cables will

Penlight Shroud

Cable Tray & Test Cables

Cable Tray Supports

A

A

A-A 0.81 m (2'-8") 0.51 m (1'-8 1/4")

be tested. 

Cable Type. Specifies the cable insulation and jacket material for the cables being 

tested. These are either TP or TS, as described in Section C.2.4 . 

•
C-19

x Number of Twisted Pairs. Specifies the number of twisted pairs in each cable. For this

series of testing the lowest number of twisted pairs available (1-pair or 2-pair) and a 7-pair

conductor cables were selected.

x Conductor Size. Identifies the AWG size of the copper conductors within the cable. Typical

conductor sizes range from AWG 16 – 22 for instrument circuits. The manufacturers only

listed cables with 16 and 18 AWG conductor sizes. The majority of the tests will analyze

16 AWG conductors.

 

x Overall Shield. Specifies whether or not the cable has a shield system in-between the

insulated conductors and the cable jacket. 

x Shielded Pairs. Specifies whether or not the twisted pairs have a shield.

x Exposure Temperature. Defines the initial set-point temperature of the heating apparatus.

The final set point is either 325oC or 470oC (617oF or 878oF), for the TP and TS samples,

respectively. At least two tests will be done on a lower heating setting of 205 °C or 330 °C

or (401oF or 626oF) for TP and TS samples to analyze the failure in a less severe, but still

damaging condition.

Table C-3 Test Matrix for Instrumentation Cable Tests 

Cable Type Cable Characteristics

Manufacturer Insulation & 

Jacket Materials TS TP Number of Twisted 

Pairs

Conductor 

Size (AWG)

Overall 

Shield

Shielded 

Pairs

Rockbestos Firewall III XLPE/CSPE x 2/c 16 x

Rockbestos Firewall III XLPE/CSPE x 4/c 16 x

Rockbestos Firewall III XLPE/CSPE x 2 16 x

Rockbestos Firewall III XLPE/CSPE x 4 16 x

Belden PVC/PVC-Nylon x 2 16 x

Belden PVC/PVC Nylon x 8 16 x

Belden FR-EP/CPE x 2 16 x x

Belden FR-EP/CPE x 8 16 x x

Belden XLP/LSZH x 1 16 x x

Belden XLP/LSZH x 8 16 x x

All of the cables in the matrix will be tested for the following three circuits: 

x 4–20 mA instrumentation circuit, ungrounded

x 10–50 mA instrumentation circuit

x 1–5 VDC instrumentation circuit

A limited number of tests will be performed on the 4–20 mA grounded instrumentation circuit. The 

initial test will be performed on a 16 AWG, 2-twisted pair Rockbestos cable with an overall shield 

and shielded pairs. Depending on the outcome, more tests could be conducted on grounded 

circuits. 

The total number of tests, not including multiple iterations of the same test, will equal 38. The 

equipment and physical test configurations used for these tests are similar to the CAROLFIRE 

and DESIREE-Fire small-scale series of tests. 
C-20

C.5 References

[1] NUREG-1805: Stroup, D., Taylor, G., Hausman, G., Fire Dynamics Tools (FDTs)

Quantitative Fire Hazard Analysis Methods for the U.S. Nuclear Regulatory Commission

Fire Protection Inspection Program, Volume 1, Supplement 1, June 2013.

[2] NUREG/CR-6776: Wyant, F.J., Nowlen, S.P., Cable Insulation Resistance Measurements

Made During Cable Fire Tests, SAND2002-0447P, US NRC, Washington DC, June 2002.

[3] NUREG/CR-6834: LaChance, J.L., Nowlen, S.P., Wyant, F.J., Dandini, V.J., Circuit

Analysis-Failure Mode and Likelihood Analysis, SAND2002-1942P, US NRC, Washington

DC, September 2002.

[4] NUREG/CR-6850:EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities,

Volume 2: Detailed Methodology, a joint publication of the US NRC, Washington DC, and

the Electric Power Research Institute (EPRI), Palo Alto, CA, September 2005.

[5] NUREG/CR-6931: Nowlen, S. P., Wyant, F. J (Vols. 1 and 2), and McGrattan, K. (Vol. 3)

Cable Response to Live Fire (CAROLFIRE) Volume 1-3, April 2008.

[6] NUREG/CR-7010: McGrattan, K., et al, Cable Heat Release, Ignition, and Spread in Tray

Installations During Fire (CHRISTIFIRE) Volumes 1 and 2, July 2012.

[7] NUREG/CR-7100: Nowlen, S. P., Brown, J. W., Olivier, T. J., Wyant, F. J., Direct Current

Electrical Shorting in Response to Exposure Fire (DESIREE-Fire), April 2012.

[8] NUREG/CR-7150: Joint Assessment of Cable Damage and Quantification of Effects from

Fire (JACQUE-Fire), Volume 1: Phenomena Identification and Ranking Table (PIRT)

Exercise for Nuclear Power Plant Fire-Induced Electrical Circuit Failure, October 2012.

[9] Regulatory Guide (RG) 1.189:Fire Protection for Nuclear Power Plants, October 2009.

[10] Rockwell Automation: Documentation for Dynamix 1444 Series Monitoring System

Specifications

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/1444-td001_-enp.pdf

[11] SAND 89-2369, “Aging of Cables, Connections, and Electrical Penetration Assemblies Used

in Nuclear Power Plants,” July 1990.

[12] SAND 96-0344, “Aging Management Guideline for Commercial Nuclear Power Plants –

Electrical Cable and Terminations,” September 1996.

[13] TR-1003326, Characterization of Fire-Induced Circuit Faults – Results of Cable Fire Testing,

EPRI, Palo Alto, CA, Dec. 2002.


NUREG/CR-7244

This report presents the results of instrumentation cable tests sponsored by the US Nuclear Regulatory 

Commission (NRC) Office of Nuclear Regulatory Research and performed at Sandia National Laboratories 

(SNL). The goal of the tests was to assess thermal and electrical response behavior under fire-exposure 

conditions for instrumentation cables and circuits. The test objective was to assess how severe radiant 

heating conditions surrounding an instrumentation cable affect current or voltage signals in an 

instrumentation circuit. 

A total of thirty-nine small-scale tests were conducted. Ten different instrumentation cables were tested, 

ranging from one conductor to eight-twisted pairs. Because the focus of the tests was thermoset (TS) cables, 

only two of the ten cables had thermoplastic (TP) insulation and jacket material and the remaining eight 

cables were one of three different TS insulation and jacket material. Two instrumentation cables from 

previous cable fire testing were included, one TS and one TP. Three test circuits were used to simulate 

instrumentation circuits present in nuclear power plants: a 4–20 mA current loop, a 10–50 mA current loop 

and a 1–5 VDC voltage loop. A regression analysis was conducted to determine key variables affecting 

signal leakage time.

Electrical cables, cables, fire, cable failure, fire risk, fire PRA, post-fire safe shutdown, 

spurious operation, spurious actuation, hot short, leakage current, instrumentation 

circuit, instrument cable 

January 2019

Technical

Response of Nuclear Power Plant Instrumentation Cables Exposed to Fire

Conditions

A. Muna, C. Lafleur, D. Brooks

Sandia National Laboratories

Risk and Reliability Analysis, Department 8851

P.O. Box 5800

Albuquerque, NM 87185-0748

Division of Risk Analysis

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555-0001

G. Taylor, NRC Project Manager



NUREG/CR-7244 Response of Nuclear Power Plant Instrumentation Cables Exposed to Fire Conditions January 2019