NUREG/IA-0470 

Volume 1 

International 

 Agreement Report

Nuclear Regulatory Authority Experimental 

Program to Characterize and Understand 

High Energy Arcing Fault (HEAF) 

Phenomena

Prepared by: 

S. Tsuchino*, H. Kabashima*, S. Turner**, S. Mehta, D. Stroup, N. Melly, G. Taylor, F. Gonzalez

 *Regulatory Standard and Development Department 

Secretariat of Nuclear Regulatory Authority (S/NRA/R)

Tokyo, Japan 106-8450 

**Leidos, Inc.

301 Laboratory Road

Oak Ridge, TN 37830

M. H. Salley, NRC Project Manager 

 

Division of Risk Analysis

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

Manuscript Completed: August 2016

Date Published: August 2016

Prepared as part of 

the Agreement between NRC and NRA in the Area of Fire-Related Research

Published by

U.S. Nuclear Regulatory Commission

NUREG/IA-0470 

Volume 1 

International 

 Agreement Report

Nuclear Regulatory Authority Experimental 

Program to Characterize and Understand 

High Energy Arcing Fault (HEAF) 

Phenomena

Prepared by: 

S. Tsuchino*, H. Kabashima*, S. Turner**, S. Mehta, D. Stroup, N. Melly, G. Taylor, F. Gonzalez

 *Regulatory Standard and Development Department 

Secretariat of Nuclear Regulatory Authority (S/NRA/R)

Tokyo, Japan 106-8450 

**Leidos, Inc.

301 Laboratory Road

Oak Ridge, TN 37830

M. H. Salley, NRC Project Manager 

 

Division of Risk Analysis

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

Manuscript Completed: August 2016

Date Published: August 2016

Prepared as part of 

the Agreement between NRC and NRA in the Area of Fire-Related Research

Published by

U.S. Nuclear Regulatory Commission

iii

ABSTRACT

A High Energy Arcing Fault (HEAF) occurred in a high-voltage (6.9 kV) switchgear (SWGR) in

Unit 1 of the Onagawa Nuclear Power Plant of the Tohoku Electric Power Company on March 

11, 2011 during the Great East Earthquake in Japan. HEAF events are not common and have 

occurred in nuclear power plants (NPP) worldwide. The operating experience seen from the 

Onagawa event illustrate that HEAFs can present a potential threat to the safe operation of 

NPPs. As a result, the nuclear power industry has placed a new emphasis on understanding 

and developing evaluation methods for these events. 

To investigate the HEAF event sequence and to understand the phenomena, the Regulatory 

Standard and Research Department, Secretariat of the Nuclear Regulation Authority (S/NRA/R) 

(Japan) conducted HEAF tests by simulating the design and operating conditions of the SWGR

HEAF at Onagawa NPP in addition to simulating the HEAF energy effects using a “Rocket Fuel 

Arc Simulator” (RFAS). Tests of 480 V Motor Control Center (MCC) and Distribution Panel (DP) 

cabinets were also conducted to understand HEAF characteristics.

 

The results of the HEAF tests simulating the SWGR at Onagawa NPP showed similar damage 

to the actual HEAF with respect to the duration time, energy level, and ensuing cable fires. 

However, the overall structural damage and extent of the internal fire damage was much less 

severe than Onagawa. The tests for the MCC and the DP provide insight on HEAF behavior 

and ensuing fires in low voltage systems. Data such as temperature, heat flux, heat release 

rate during the arc and ensuing fires due to HEAF conditions were successfully simulated by the 

RFAS test.

The results were generally consistent with the previously observed behavior. However, the 

tests also provided a new appreciation for and recognition of the high thermal energy from the 

oxidation of aluminum bus bars, such as those used in the SWGR tests. Since aluminum is 

sometimes used in bus bars, the energetic effects of an arc involving this material should be

considered when analyzing HEAF effects. 

This report provides the results of the S/NRA/R tests that, in combination with operating 

experience and other HEAF test data, will be used by international teams to develop consensus 

conclusions on HEAF behavior, understand the potential for HEAF damage including ensuing 

fires, establish HEAF evaluation criteria to support Fire Hazards Analyses (FHA), and 

recommend protection measures. 

v 

FOREWARD

This work was completed under the “Implementing Agreement between the United States 

Nuclear Regulatory Commission and the Japan Nuclear Energy Safety Organization” in the

Area of Fire-Related Research,” as amended to change the Japan party to the Nuclear 

Regulation Authority (NRA).

The Regulatory Standard and Research Department, Secretariat of the Nuclear Regulation 

Authority (S/NRA/R) (Japan) was the lead organization for the tests and prepared the analysis 

and results. The Nuclear Regulatory Commission (NRC) attended all tests and provided 

support for specialized instrumentation, technical advice, and general testing support. The NRC 

also completed the final preparation of this report for publication. 

The contents of this report should not be viewed as an official NRC endorsement of the results 

or observations in this report. Nor should this report be viewed as binding the NRC in its 

rulemaking, licensing or adjudicatory process.

vii

TABLE OF CONTENTS

Page

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

FOREWARD............................................................................................................................... v

TABLE OF CONTENTS ...........................................................................................................vii

FIGURES...................................................................................................................................xi

TABLES ................................................................................................................................. xvii

EXECUTIVE SUMMARY .........................................................................................................xix

CITATIONS ............................................................................................................................xxv

ACKNOWLEDGMENTS.......................................................................................................xxvii

ACRONYMS AND ABBREVIATIONS...................................................................................xxix

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

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

1.2 Onagawa HEAF Event......................................................................................1-1

1.3 Test Approach and Electrical Test Conditions...................................................1-3

1.3.1 Arc Current .........................................................................................1-4

1.3.2 Arc Duration........................................................................................1-4

1.4 Measurements and Instrumentation..................................................................1-7

2 Distribution Panel HEAF TEST – KEMA (January 2014 and March 2015)...............2-1

2.1 DP Test Overview (2014 and 2015)..................................................................2-1

2.2 DP Tests Summary of Results ..........................................................................2-1

2.3 DP Test Configuration.......................................................................................2-2

2.4 DP Test Configuration.......................................................................................2-4

2.5 DP Test Cable Combustible Loading ................................................................2-5

2.5.1 Internal Combustible Loading..............................................................2-5

2.6 DP Test Temperature and Heat Flux Instrumentation .......................................2-6

2.6.1 Cable Tray Combustible Loading ........................................................2-9

2.7 DP Test Pressure Instrumentation ....................................................................2-9

2.8 DP Test 1 Key Observations (January 2013) .................................................. 2-10

2.8.1 DP Test 1 Calorimetry Data .............................................................. 2-14

2.8.2 DP Test 1 Temperature Data ............................................................ 2-15

2.8.3 DP Test 1 Pressure Data .................................................................. 2-16

2.8.4 DP Test 1 Arc Energy ....................................................................... 2-17

2.9 DP Test 2 Key Observations (January 2013) .................................................. 2-18

2.9.1 DP Test 2 Calorimetry Data .............................................................. 2-21

2.9.2 DP Test 2 Temperature Data ............................................................ 2-22

2.9.3 DP Test 2 Pressure Data .................................................................. 2-23

2.9.4 DP Test 2 Arc Energy ....................................................................... 2-24

2.10 DP Test 3 Key Observations (January 2013) .................................................. 2-25

2.10.1 DP Test 3 Calorimetry Data .............................................................. 2-29

2.10.2 DP Test 3 Temperature Data ............................................................ 2-30

2.10.3 DP Test 3 Pressure Data .................................................................. 2-31

2.10.4 DP Test 3 Arc Energy ....................................................................... 2-32

2.11 DP Test 4 Key Observations (March 2015)..................................................... 2-33

2.11.1 DP Test 4 Calorimetry Data .............................................................. 2-37

2.11.2 DP Test 4 Temperature Data ............................................................ 2-39

2.11.3 DP Test 4 Pressure Data .................................................................. 2-40

2.11.4 DP Test 4 Arc Energy ....................................................................... 2-41

2.12 DP Test 5 Key Observations (March 2015)..................................................... 2-42

2.12.1 DP Test 5 Calorimetry Data .............................................................. 2-47
viii

2.12.2 DP Test 5 Temperature Data ............................................................ 2-48

2.12.3 DP Test 5 Pressure Data .................................................................. 2-49

2.12.4 DP Test 5 Arc Energy ....................................................................... 2-50

2.13 DP Test 6 Key Observations (March 2015)..................................................... 2-51

2.13.1 DP Test 6 Calorimetry Data .............................................................. 2-55

2.13.2 DP Test 6 Temperature Data ............................................................ 2-56

2.13.3 DP Test 6 Pressure Data .................................................................. 2-58

2.13.4 DP Test 6 Arc Energy ....................................................................... 2-59

2.14 DP Tests 1 through 6: Summary of Electrical Conditions ............................... 2-60

2.15 DP Tests 1 through 6 Qualitative Summary .................................................... 2-61

3 Motor Control Center HEAF TEST – KEMA (May 2013)............................................3-1

3.1 MCC Test Overview..........................................................................................3-1

3.2 MCC Summary of Results.................................................................................3-1

3.3 MCC Test Configuration....................................................................................3-3

3.4 MCC Cable Combustible Loading .....................................................................3-5

3.5 MCC Temperature and Heat Flux Instrumentation............................................3-6

3.6 MCC Test Pressure Instrumentation .................................................................3-8

3.7 MCC Test 1 Key Observations..........................................................................3-9

3.7.1 MCC Test 1 Calorimetry Data ........................................................... 3-12

3.7.2 MCC Test 1 Temperature Data ......................................................... 3-13

3.7.3 MCC Test 1 Pressure Data ............................................................... 3-14

3.7.4 MCC Test 1 Arc Energy .................................................................... 3-15

3.8 MCC Test 2 Key Observations........................................................................ 3-16

3.8.1 MCC Test 2 Calorimetry Data ........................................................... 3-21

3.8.2 MCC Test 2 Temperature Data ......................................................... 3-22

3.8.3 MCC Test 2 Pressure Data ............................................................... 3-23

3.8.4 MCC Test 2 Arc Energy .................................................................... 3-24

3.9 MCC Test 3 Key Observations........................................................................ 3-25

3.9.1 MCC Test 3 Calorimetry Data ........................................................... 3-27

3.9.2 MCC Test 3 Temperature Data ......................................................... 3-28

3.9.3 MCC Test 3 Pressure Data ............................................................... 3-29

3.9.4 MCC Test 3 Arc Energy .................................................................... 3-30

3.10 MCC Test 4 Key Observations........................................................................ 3-31

3.10.1 MCC Test 4 Calorimetry Data ........................................................... 3-33

3.10.2 MCC Test 4 Temperature Data ......................................................... 3-34

3.10.3 MCC Test 4 Pressure Data ............................................................... 3-35

3.10.4 MCC Test 4 Arc Energy .................................................................... 3-36

3.11 MCC Tests 1 thorugh 4: Electrical Conditions ................................................ 3-37

3.12 MCC Tests 1 through 4 Qualitative Summary ................................................. 3-38

4 Switchgear HEAF Tests 1 through 3, Single Arc Tests – KEMA (June 2013).....4-1

4.1 SWGR Tests 1 through 3 Overview ..................................................................4-1

4.2 SWGR Tests 1 through 3 Summary of Results .................................................4-1

4.3 SWGR Tests 1 through 3 Cabinet Configuration...............................................4-2

4.4 SWGR Tests 1 through 3 Cable Combustible Loading......................................4-6

4.5 SWGR Tests 1 through 3 Temperature and Heat Flux Instrumentation.............4-9

4.6 SWGR Tests 1 through 3 Pressure Instrumentation........................................ 4-11

4.7 SWGR Test 1 Key Observations..................................................................... 4-11

4.7.1 SWGR Test 1 Calorimetry Data ........................................................ 4-17

4.7.2 SWGR Test 1 Temperature Data ...................................................... 4-18

4.7.3 SWGR Test 1 Pressure Data ............................................................ 4-19

4.7.4 SWGR Test 1 Arc Energy ................................................................. 4-20
ix

4.8 SWGR Test 2 Changes................................................................................... 4-21

4.9 SWGR Test 2 Key Observations..................................................................... 4-23

4.9.1 SWGR Test 2 Calorimetry Data ........................................................ 4-38

4.9.2 SWGR Test 2 Temperature Data ...................................................... 4-39

4.9.3 SWGR Test 2 Pressure Data ............................................................ 4-41

4.9.4 SWGR Test 2 Arc Energy ................................................................. 4-42

4.10 SWGR Test 3 Key Observations..................................................................... 4-43

4.10.1 SWGR Test 3 Calorimetry Data ........................................................ 4-48

4.10.2 SWGR Test 3 Temperature Data ...................................................... 4-49

4.10.3 SWGR Test 3 Pressure Data ............................................................ 4-50

4.10.4 SWGR Test 3 Arc Energy ................................................................. 4-51

4.11 SWGR Tests 1 thorugh 3: Summary of Electrical Conditions .......................... 4-52

4.12 SWGR Tests 1 through 3 Qualitative Summary .............................................. 4-52

5 Switchgear HEAF Tests 4 through 6, Two Arcs Tests - KEMA (March 2014, 

March 2015).................................................................................................................5-1

5.1 SWGR Tests 4 through 6 Overview ..................................................................5-1

5.2 SWGR Tests 4 through 6 Summary of Results .................................................5-1

5.3 SWGR Tests 4 through 6 Cabinet Lineup and Combustible Load.....................5-2

5.3.1 Internal Combustible Load ..................................................................5-6

5.3.2 External Combustible Load .................................................................5-6

5.4 SWGR Tests 4 through 6 Temperature, Heat Flux and Pressure 

Instrumentation .................................................................................................5-6

5.5 SWGR Test 4 Key Observations (March 2014)............................................... 5-10

5.5.1 SWGR Test 4 Calorimetry Data ........................................................ 5-17

5.5.2 SWGR Test 4 Temperature Data ...................................................... 5-19

5.5.3 SWGR Test 4 Pressure Data ............................................................ 5-21

5.5.4 SWGR Test 4 Arc Energy ................................................................. 5-23

5.6 SWGR Test 5 Key Observations (March 2014)............................................... 5-24

5.6.1 SWGR Test 5 Calorimetry Data ........................................................ 5-31

5.6.2 SWGR Test 5 Temperature Data ...................................................... 5-33

5.6.3 SWGR Test 5 Pressure Data ............................................................ 5-35

5.6.4 SWGR Test 5 Arc Energy ................................................................. 5-37

5.7 SWGR Test 6 Key Observations (March 2015)............................................... 5-38

5.7.1 SWGR Test 6 Calorimetry Data ........................................................ 5-48

5.7.2 SWGR Test 6 Temperature Data ...................................................... 5-49

5.7.3 SWGR Test 6 Pressure Data ............................................................ 5-51

5.7.4 SWGR Test 6 Arc Energy ................................................................. 5-53

5.8 SWGR Tests 4 through 6 Summary of Electrical Conditions ........................... 5-54

5.9 SWGR Tests 4 through 6 Qualitative Summary .............................................. 5-55

6 Switchgear with Rocket Fuel Arc Simulator Fire Test - SwRI (July 2013) ..............6-1

6.1 RFAS Test Overview ........................................................................................6-1

6.2 RFAS Test Summary of Results .......................................................................6-1

6.3 RFAS 5-Cabinet Test Configuration..................................................................6-3

6.4 RFAS Test Heat Flux Instrumentation...............................................................6-6

6.5 RFAS Test Temperature Instrumentation..........................................................6-6

6.6 RFAS Test Pressure Instrumentation................................................................6-8

6.7 RFAS Test Heat Release Rate and Smoke Production Instrumentation ...........6-8

6.8 RFAS Test Oxygen Measurement ....................................................................6-9

6.9 RFAS Test 1 Key Observations ........................................................................6-9

6.9.1 RFAS Heat Test 1 Flux Data............................................................. 6-12

6.9.2 Test 1 Temperature Data .................................................................. 6-13
x 

6.9.3 RFAS Test 1 Heat Release Rate/Smoke Production Data ................ 6-13

6.10 RFAS Test 2 Key Observations ...................................................................... 6-14

6.10.1 RFAS Test 2 Flux Data ..................................................................... 6-17

6.10.2 RFAS Test 2 Temperature Data........................................................ 6-19

6.10.3 RFAS Test 2 Heat Release Rate/Smoke Production Rate Data........ 6-21

6.10.4 RFAS Test 2 Oxygen Data................................................................ 6-22

6.10.5 RFAS Summary ................................................................................ 6-23

7 Switchgear Tests Results Discussion ......................................................................7-1

7.1 Onagawa Comparison ......................................................................................7-1

7.1.1 Exterior Damage .................................................................................7-1

7.1.2 Horizontal Bus Bar Arc........................................................................7-1

7.1.3 Secondary Side Arc and Damage .......................................................7-1

7.2 Aluminum Bus Bar Oxidation ............................................................................7-3

7.2.1 Case 1: Onagawa Bus Bar Oxidation in Cabinet 7 ..............................7-3

7.2.2 Case 2: KEMA 5-Cabinet Lineup June 2013 Test 3 ............................7-4

7.2.3 Case 3: KEMA 5-Cabinet Lineup March 2014 Test 4 ..........................7-4

7.2.4 Case 4: KEMA 5-Babinet Lineup March 2014 Test 5 ..........................7-5

7.2.5 Case 5: KEMA 3-Cabinet Lineup March 2015, Test 6 .........................7-6

7.2.6 Aluminum Oxidation Effects Summary ................................................7-7

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

APPENDIX A. MEASUREMENTS...................................................................................... A-1

APPENDIX B. KEMA TEST LABORATORY...................................................................... B-1

APPENDIX C. CABLE PROPERTIES ................................................................................ C-1

APPENDIX D. SHORT CIRCUIT CURRENT CALCULATIONS ......................................... D-1
xi

FIGURES

Page

Figure 1.2-1. Damage in Onagawa HEAF Event ................................................................1-2

Figure 1.2-2. Onagawa Arching Scenario...........................................................................1-3

Figure 2.3-1. DP Test Configuration...................................................................................2-3

Figure 2.4-1. DP Used in Tests ..........................................................................................2-4

Figure 2.5-1. DP Test Cable Combustible Load .................................................................2-5

Figure 2.6-1. DP Tests 1 through 3 Calorimeter Locations .................................................2-6

Figure 2.6-2. DP Tests 1 through 3 TC Locations...............................................................2-7

Figure 2.6-3. DP Tests 4 through 6 Calorimeter Hood and PT Locations ...........................2-8

Figure 2.7-1. DP Tests 1 through 6 Pressure Transducer and Locations (Rear View)........2-9

Figure 2.8-1. DP Test 1 Arc.............................................................................................. 2-10

Figure 2.8-2. DP Test 1 Ensuing Fire, 12 Minutes After Arc ............................................. 2-11

Figure 2.8-3. DP Test 1 Exterior Damage ........................................................................ 2-11

Figure 2.8-4. DP Test 1 HEAF and Fire Interior Damage ................................................. 2-13

Figure 2.8-5. DP Test 1 Slug Calorimeter Data: Temperature .......................................... 2-14

Figure 2.8-6. DP Test 1 Thermocouple Data.................................................................... 2-15

Figure 2.8-7. DP Test 1 Pressure..................................................................................... 2-16

Figure 2.8-8. DP Test 1 Arc Energy ................................................................................. 2-17

Figure 2.9-1. DP Test 2 Arc.............................................................................................. 2-18

Figure 2.9-2. DP Test 2 HEAF Exterior Damage .............................................................. 2-19

Figure 2.9-3. DP Test 2 Cabinet Top Deformation............................................................ 2-19

Figure 2.9-4. DP Test 2 Interior Cabinet Damage............................................................. 2-20

Figure 2.9-5. DP Test 2 Calorimetry Temperature Data: Temperature ............................. 2-21

Figure 2.9-6. DP Test 2 Thermocouple Data.................................................................... 2-22

Figure 2.9-7. DP Test 2 Pressure ..................................................................................... 2-23

Figure 2.9-8. DP Test 2 Arc Energy ................................................................................. 2-24

Figure 2.10-1. DP Test 3 Arc.............................................................................................. 2-25

Figure 2.10-2. DP Test 3 Ensuing Fire ............................................................................... 2-26

Figure 2.10-3. DP Test 3 Exterior Cabinet Damage ........................................................... 2-27

Figure 2.10-4. DP Test 3 Cabinet Top Deformation............................................................ 2-27

Figure 2.10-5. DP Test 3 Interior Damage.......................................................................... 2-28

Figure 2.10-6. DP Test 3 Calorimetry Data: Temperature .................................................. 2-29

Figure 2.10-7. DP Test 3 Thermocouple Data.................................................................... 2-30

Figure 2.10-8. DP Test 3 Pressure..................................................................................... 2-31

Figure 2.10-9. DP Test 3 Arc Energy ................................................................................. 2-32

Figure 2.11-1. DP Test 4 Arc.............................................................................................. 2-33

Figure 2.11-2. DP Test 4 Arc Flames ................................................................................. 2-34

Figure 2.11-3. DP Test 4 Thermal Images ......................................................................... 2-34

Figure 2.11-4. DP Test 4 Exterior Cabinet Damage ........................................................... 2-35

Figure 2.11-5. DP Test 4 External Cable Tray Damage ..................................................... 2-36

Figure 2.11-6. DP Test 4 Interior Cable Damage ............................................................... 2-36

Figure 2.11-7. DP Test 4 Ground Fault during the Arc ....................................................... 2-36

Figure 2.11-8. DP Test 4 Bus Bar Damage at Arc Location................................................ 2-36

Figure 2.11-9. DP Test 4 Calorimetry Data: Temperature .................................................. 2-37

Figure 2.11-10. DP Test 4 Cable Tray Plate Thermometer Data .......................................... 2-39

Figure 2.11-11. DP Test 4 Pressure..................................................................................... 2-40

Figure 2.11-12. DP Test 4 Arc Energy ................................................................................. 2-41

Figure 2.12-1. DP Test 5 Arc.............................................................................................. 2-42

Figure 2.12-2. DP Test 5 Arc Flames ................................................................................. 2-43
xii

Figure 2.12-3. DP Test 5 Thermal Images ......................................................................... 2-44

Figure 2.12-4. DP Test 5 Exterior Damage ........................................................................ 2-45

Figure 2.12-5. DP Test 5 Interior and Cable Damage......................................................... 2-46

Figure 2.12-6. DP Test 5 Bus Bar Damage at Arc Location................................................ 2-46

Figure 2.12-7. DP Test 5 Calorimetry Data: Temperature .................................................. 2-47

Figure 2.12-8. DP Test 5 Cable Tray Plate Thermometer Data .......................................... 2-48

Figure 2.12-9. DP Test 5 Pressure..................................................................................... 2-49

Figure 2.12-10. DP Test 5 Arc Energy ................................................................................. 2-50

Figure 2.13-1. DP Test 6 Arc.............................................................................................. 2-51

Figure 2.13-2. DP Test 6 Arc Flames ................................................................................. 2-52

Figure 2.13-3. DP Test 6 Thermal Images ......................................................................... 2-52

Figure 2.13-4. DP Test 6 Exterior Damage ........................................................................ 2-53

Figure 2.13-5. DP Test 6 Interior Cable Damage ............................................................... 2-54

Figure 2.13-6. DP Test 6 Bus Bar Damage at Arc Location................................................ 2-54

Figure 2.13-7. DP Test 6 Calorimetry Data: Temperature .................................................. 2-55

Figure 2.13-8. DP Test 6 Cable Tray Plate Thermometer Data .......................................... 2-56

Figure 2.13-9. DP Test 6 Pressure ..................................................................................... 2-58

Figure 2.13-10. DP Test 6 Arc Energy ................................................................................. 2-59

Figure 3.3-1. MCC Test Configuration................................................................................3-3

Figure 3.3-2. MCC for Test.................................................................................................3-4

Figure 3.4-1. MCC Cable Combustible Load......................................................................3-5

Figure 3.5-1. MCC Calorimeter and TC Location................................................................3-6

Figure 3.6-1. MCC Pressure Measurement Locations........................................................3-8

Figure 3.7-1. MCC Test 1 Arc.............................................................................................3-9

Figure 3.7-2. MCC Test 1 Thermal Image ..........................................................................3-9

Figure 3.7-3. MCC Test 1 Exterior Damage ..................................................................... 3-10

Figure 3.7-4. Test 1 Exterior and Interior Damage............................................................ 3-11

Figure 3.7-5. MCC Test 1 Calorimetry Temperature Data ................................................ 3-12

Figure 3.7-6. MCC Test 1 Thermocouple Data................................................................. 3-13

Figure 3.7-7. MCC Test 1 Pressure Data ......................................................................... 3-14

Figure 3.7-8. MCC Test 1 Arc Energy .............................................................................. 3-15

Figure 3.8-1. MCC Test 2 Arcs at Bottom and Top........................................................... 3-16

Figure 3.8-2. MCC Test 2 Sequence for 2 Arcs................................................................ 3-17

Figure 3.8-3. MCC Test 2 Thermal Images ...................................................................... 3-18

Figure 3.8-4. MCC Test 2 Exterior Damage ..................................................................... 3-19

Figure 3.8-5. MCC Test 2 Interior Damage....................................................................... 3-20

Figure 3.8-6. MCC Test 2 Calorimetry Temperature Data ................................................ 3-21

Figure 3.8-7. MCC Test 2 Thermocouple Data................................................................. 3-22

Figure 3.8-8. MCC Test 2 Pressure Data ......................................................................... 3-23

Figure 3.8-9. MCC Test 2 Arc Energy .............................................................................. 3-24

Figure 3.9-1. MCC Test 3 Arc........................................................................................... 3-25

Figure 3.9-2. MCC Test 3 Thermal Images (Rear View)................................................... 3-25

Figure 3.9-3. MCC Test 3 Exterior Damage. .................................................................... 3-26

Figure 3.9-4. MCC Test 3 Interior Damage....................................................................... 3-26

Figure 3.9-5. MCC Test 3 Calorimetry Data ..................................................................... 3-27

Figure 3.9-6. MCC Test 3 Thermocouple Data................................................................. 3-28

Figure 3.9-7. MCC Test 3 Pressure Data ......................................................................... 3-29

Figure 3.9-8. MCC Test 3 Arc Energy .............................................................................. 3-30

Figure 3.10-1. MCC Test 4 Arc........................................................................................... 3-31

Figure 3.10-2. MCC Test 4 Thermal Images (Rear View)................................................... 3-31

Figure 3.10-3. MCC Test 4 Exterior Damage ..................................................................... 3-32
xiii

Figure 3.10-4. MCC Test 4 Interior Damage....................................................................... 3-33

Figure 3.10-5. MCC Test 4 Calorimetry Data ..................................................................... 3-33

Figure 3.10-6. MCC Test 4 Thermocouple Data................................................................. 3-34

Figure 3.10-7. MCC Test 4 Pressure Data ......................................................................... 3-35

Figure 3.10-8. MCC Test 4 Arc Energy .............................................................................. 3-36

Figure 4.3-1. SWGR 5-Cabinet Test Configuration.............................................................4-3

Figure 4.3-2. Onagawa SWGR and GE Magneblast SWGR ..............................................4-4

Figure 4.3-3. Modified GE Magneblast Dimensions (in cm)................................................4-4

Figure 4.3-4. SWGR Cabinet Configuration Cabinets 7 and 8............................................4-5

Figure 4.3-5. SWGR Bus Bar Configuration .......................................................................4-5

Figure 4.4-1. SWGR Cabinet Combustible Load ................................................................4-6

Figure 4.4-2. SWGR Test Cable Combustible Load ...........................................................4-8

Figure 4.5-1. SWGR Tests 1 through 3 Instrument Locations .......................................... 4-10

Figure 4.7-1. SWGR Test 1 Arc........................................................................................ 4-11

Figure 4.7-2. SWGR Test 1 Thermal Image at Arc Extinction........................................... 4-12

Figure 4.7-3. SWGR Test 1 Exterior Damage .................................................................. 4-12

Figure 4.7-4. SWGR Test 1 Interior Damage.................................................................... 4-13

Figure 4.7-5. SWGR Test 1 Interior Damage, Detailed..................................................... 4-14

Figure 4.7-6. SWGR Test 1 Insulator and Bus Bar Damage............................................. 4-15

Figure 4.7-7. SWGR Test 1 Breaker Damage .................................................................. 4-16

Figure 4.7-8. SWGR Test 1 Calorimetry Temperature Data ............................................. 4-17

Figure 4.7-9. SWGR Test 1 Thermocouple Data.............................................................. 4-18

Figure 4.7-10. SWGR Test 1 Pressure Data ...................................................................... 4-19

Figure 4.7-11. SWGR Test 1 Arc Energy ........................................................................... 4-20

Figure 4.8-1. SWGR Test 2 Shorting Wire Changes ........................................................ 4-21

Figure 4.8-2. SWGR Test 2 Breaker Changes ................................................................. 4-22

Figure 4.8-3. SWGR Test 2 Wiring Changes.................................................................... 4-22

Figure 4.8-4. SWGR Test 2 Front Door Meter Changes................................................... 4-23

Figure 4.9-1. SWGR Test 2 Exterior Damage .................................................................. 4-35

Figure 4.9-2. SWGR Test 2 Interior Damage, Continued.................................................. 4-36

Figure 4.9-3. SWGR Test 2 Insulator and Bus Bar Damage............................................. 4-37

Figure 4.9-4. SWGR Test 2 Breaker 7 and 8 Damage ..................................................... 4-38

Figure 4.9-5. SWGR Test 2 Slug Calorimeter Temperature Data..................................... 4-39

Figure 4.9-6. SWGR Test 2 Thermocouple Data .............................................................. 4-40

Figure 4.9-7. SWGR Test 2 Pressure Data ...................................................................... 4-41

Figure 4.9-8. SWGR Test 2 Arc Energy ........................................................................... 4-42

Figure 4.10-1. SWGR Test 3 Arc........................................................................................ 4-43

Figure 4.10-2. SWGR Test 3 Ensuing Fire ......................................................................... 4-44

Figure 4.10-3. SWGR Test 3 Exterior Damage .................................................................. 4-45

Figure 4.10-4. SWGR Test 3 Interior Damage.................................................................... 4-45

Figure 4.10-5. SWGR Test 3 Interior Damage, Detailed..................................................... 4-46

Figure 4.10-6. SWGR Test 3 Insulator and Bus Bar Damage............................................. 4-47

Figure 4.10-7. SWGR Test 3 Breaker Damage .................................................................. 4-47

Figure 4.10-8. SWGR Test 3 Calorimetry Temperature Data ............................................. 4-48

Figure 4.10-9. SWGR Test 3 Thermocouple Data.............................................................. 4-49

Figure 4.10-10. SWGR Test 3 Pressure Data ...................................................................... 4-50

Figure 4.10-11. SWGR Test 3 Arc Energy ........................................................................... 4-51

Figure 5.3-1. SWGR Tests 4 through 6: Cabinet 7 .............................................................5-3

Figure 5.3-2. SWGR Tests 4 through 6: Cabinet 8 .............................................................5-4

Figure 5.3-3. SWGR Tests 4 through 6: Schematic of Cabinets 6, 9, and 10 .....................5-5

Figure 5.3-4. SWGR Tests 4 through 6 Cabinets 7 and 8 Shorting Wire Locations ............5-5
xiv

Figure 5.4-1. SWGR Tests 4 and 5, Instrument Locations..................................................5-7

Figure 5.4-2. SWGR Test 6 Instrument Locations ..............................................................5-9

Figure 5.5-1. SWGR Test 4 Arcs...................................................................................... 5-10

Figure 5.5-2. SWGR Test 4 Thermal Image Ensuing Fire ................................................ 5-11

Figure 5.5-3. SWGR Test 4 Exterior Damage .................................................................. 5-12

Figure 5.5-4. SWGR Test 4 Interior Damage.................................................................... 5-13

Figure 5.5-5. SWGR Test 4 Interior Damage, Detailed..................................................... 5-14

Figure 5.5-6. SWGR Test 4 Insulator and Bus Bar Damage............................................. 5-16

Figure 5.5-7. SWGR Test 4 Breaker Damage .................................................................. 5-17

Figure 5.5-8. SWGR Test 4 Calorimetry Data: Temperature ............................................ 5-18

Figure 5.5-9. SWGR Test 4 Thermocouple Data.............................................................. 5-20

Figure 5.5-10. SWGR Test 4 Pressure Data, Arc 1 ............................................................ 5-21

Figure 5.5-11. SWGR Test 4 Pressure Data, Arc 2 ............................................................ 5-22

Figure 5.5-12. SWGR Test 4 Arc Energy (both arcs).......................................................... 5-23

Figure 5.6-1. SWGR Test 5 Arcs...................................................................................... 5-24

Figure 5.6-2. SWGR Test 5 Thermal Image Ensuing Fire ................................................ 5-25

Figure 5.6-3. SWGR Test 5 Exterior Damage .................................................................. 5-26

Figure 5.6-4. SWGR Test 5 Interior Damage.................................................................... 5-27

Figure 5.6-5. SWGR Test 5 Interior Damage, Detailed..................................................... 5-28

Figure 5.6-6. SWGR Test 5 Insulator and Bus Bar Damage............................................. 5-29

Figure 5.6-7. SWGR Test 5 Breaker Damage .................................................................. 5-30

Figure 5.6-8. SWGR Test 5 Slug Calorimeter Temperature Data..................................... 5-31

Figure 5.6-9. SWGR Test 5 Thermocouple Data.............................................................. 5-33

Figure 5.6-10. SWGR Test 5 Pressure Data, Arc 1 ............................................................ 5-35

Figure 5.6-11. SWGR Test 5 Pressure Data, Arc 2 ............................................................ 5-36

Figure 5.6-12. SWGR Test 5 Arc Energy (both arcs).......................................................... 5-37

Figure 5.7-1. SWGR Test 6 Arc 1..................................................................................... 5-38

Figure 5.7-2. SWGR Test Arc 2........................................................................................ 5-39

Figure 5.7-3. SWGR Test 6 Thermal Image, Arc 1........................................................... 5-39

Figure 5.7-4. SWGR Test 6 Thermal Image, Arc 2........................................................... 5-40

Figure 5.7-5. SWGR Test 6 Breaker Opened in Arc 2 ...................................................... 5-41

Figure 5.7-6. SWGR Test 6 Cabinet Exterior Damage ..................................................... 5-42

Figure 5.7-7. SWGR Test 6 Cabinet Interior Damage ...................................................... 5-43

Figure 5.7-8. SWGR Test 6 Cabinet Interior Damage, Detailed........................................ 5-44

Figure 5.7-9. SWGR Test 6 Cabinet 8 Breaker Control Interior Wire Fire......................... 5-45

Figure 5.7-10. SWGR Test 6 Arc 1, Cabinet 7 Bus Bar Damage........................................ 5-45

Figure 5.7-11. SWGR Test 6 Arc 2 on Cabinet 8 Damage. ................................................ 5-46

Figure 5.7-12. SWGR Test 6 Arc 2, Breaker Secondary Side Damage .............................. 5-47

Figure 5.7-13. SWGR Test 6 Breaker 8 Damage ............................................................... 5-47

Figure 5.7-14. SWGR Test 6 Calorimetry Data: Temperature ............................................ 5-48

Figure 5.7-15. SWGR Test 6 Cable Tray Plate Thermometer Data .................................... 5-50

Figure 5.7-16. SWGR Test 6 Pressure Data, Arc 1 ............................................................ 5-51

Figure 5.7-17. SWGR Test 6 Pressure Data, Arc 2 ............................................................ 5-52

Figure 5.7-18. SWGR Test 6 Arc Energy (both arcs).......................................................... 5-53

Figure 6.3-1. SwRI 5-Cabinet RFAS Test Setup ................................................................6-3

Figure 6.3-2. RFAS Arrangement.......................................................................................6-5

Figure 6.5-1. Heat Flux and Pressure Sensors: Stations 1, 2, and 3 ..................................6-7

Figure 6.9-1. Test 1: RFAS Event ......................................................................................6-9

Figure 6.9-2. Test 1 Ensuing Fire..................................................................................... 6-10

Figure 6.9-3. Test 1 Interior Cabinet Damage .................................................................. 6-11

Figure 6.9-4. Test 1 Exterior Cabinet Damage ................................................................. 6-11
xv 

Figure 6.9-5. RFAS Test 1 Heat Flux ............................................................................... 6-12

Figure 6.9-6. RFAS Test 1 TC Measurements ................................................................. 6-13

Figure 6.9-7. Test 1 Heat Release Rates and Smoke Production..................................... 6-14

Figure 6.10-1. RFAS Test 2 Events.................................................................................... 6-14

Figure 6.10-2. RFAS Test 2 Ensuing Cable Fire ................................................................ 6-15

Figure 6.10-3. Test 2 Interior Cabinet Damage .................................................................. 6-16

Figure 6.10-4. Test 2 Exterior Cabinets Damage ............................................................... 6-17

Figure 6.10-5. RFAS Test 2 Heat Flux ............................................................................... 6-18

Figure 6.10-6. RFAS Test 1 TC Measurements, Cable Bundles for Cabinets 7 and 8........ 6-20

Figure 6.10-7. RFAS Test 1 TC Measurements, Cable Bundles for Cabinets 6, 9 and 10.. 6-20

Figure 6.10-8. Test 1 Heat Release Rates and Smoke Production..................................... 6-22

Figure 6.10-9. RFAS Test 2 Oxygen Concentration in Cabinet 8........................................ 6-22

Figure 7.1-1. SWGR Test Comparisons to Onagawa Damage...........................................7-2

Figure 7.2-1. Onagawa Cabinet 7 Bus Bar Damage...........................................................7-3

Figure 7.2-2. SWGR Test 3 Bus Bar Damage....................................................................7-4

Figure 7.2-3. SWGR Test 4 Arc 1, Cabinet 7 Bus Bar Damage..........................................7-4

Figure 7.2-4. SWGR Test 4 Arc 2, Cabinet 7 Bus Bar Damage..........................................7-5

Figure 7.2-5. SWGR Test 5 Arc 1, Cabinet 7 Bus Bar Damage..........................................7-5

Figure 7.2-6. SWGR Test 5 Arc 2, Cabinet 8 Rear Bus Bar Damage .................................7-6

Figure 7.2-7. SWGR Test 6 Arc 1, Cabinet 7 Bus Bar Damage..........................................7-6

Figure 7.2-8. SWGR Test 6 Arc 2, Cabinet 8 Bus Bar Damage..........................................7-7

Figure 7.2-9. SWGR Test and Onagawa Front Panel Damage ..........................................7-8

xvii

TABLES

Page

Table 1-1. Summary of NRA HEAF Tests. ............................................................................1-1

Table 1-2. Measurements and Instrumentation. ....................................................................1-7

Table 2-1. DP Test Summary of Results. ..............................................................................2-2

Table 2-2. DP Tests 1 through 3 Calorimeter and TC Locations............................................2-7

Table 2-3. DP Tests 4 through 6 Calorimeter Locations. .......................................................2-8

Table 2-4. DP Test 1 Flux Results....................................................................................... 2-14

Table 2-5. DP Test 1 TC Results......................................................................................... 2-15

Table 2-6. DP Test 2 Flux Results....................................................................................... 2-21

Table 2-7. DP Test 2 TC Results......................................................................................... 2-22

Table 2-8. DP Test 3 Flux Results....................................................................................... 2-29

Table 2-9. DP Test 3 TC Results......................................................................................... 2-30

Table 2-10. DP Test 4 Flux Results....................................................................................... 2-38

Table 2-11. DP Test 4 Plate Thermometer Results. .............................................................. 2-39

Table 2-12. DP Test 5 Flux Results....................................................................................... 2-48

Table 2-13. DP Test 5 Plate Thermometer Results. .............................................................. 2-49

Table 2-14. DP Test 6 Flux Results....................................................................................... 2-56

Table 2-15. DP Test 6 Plate Thermometer Results. .............................................................. 2-57

Table 2-15. DP Tests Electrical Results. ............................................................................... 2-60

Table 2-16. Acronyms and Abbreviations for Electrical Test Results..................................... 2-61

Table 3-1. MCC Test Summary of Results. ...........................................................................3-2

Table 3-2. MCC Calorimeter and TC Locations.....................................................................3-7

Table 3-3. MCC Test 1 Flux Results. .................................................................................. 3-12

Table 3-4. MCC Test 1 TC Results. .................................................................................... 3-13

Table 3-5. MCC Test 2 Flux Results. .................................................................................. 3-22

Table 3-6. MCC Test 2 TC Results. .................................................................................... 3-22

Table 3-7. MCC Test 3 Flux Results. .................................................................................. 3-27

Table 3-8. MCC Test 3 TC Results. .................................................................................... 3-28

Table 3-9. MCC Test 4 Flux Results. .................................................................................. 3-34

Table 3-10. MCC Test 4 TC Results. .................................................................................... 3-34

Table 3-11. MCC Test 1 through 4 Electrical Results (1)....................................................... 3-37

Table 4-1. SWGR Tests 1 through 3 Summary of Results.....................................................4-1

Table 4-2. Calorimeter and TC Locations SWGR Tests 1 through 3. ....................................4-9

Table 4-3. SWGR Test 1 Flux Results................................................................................. 4-17

Table 4-4. SWGR Test 1 TC Results. ................................................................................. 4-18

Table 4-5. Arc Sequence SWGR Test 2.............................................................................. 4-24

Table 4-6. Ensuing Fire Sequence SWGR Test 2. .............................................................. 4-28

Table 4-7. Thermal Image of Ensuing Fire SWGR Test 2.................................................... 4-31

Table 4-8. SWGR Test 2 Flux Results................................................................................. 4-39

Table 4-9. SWGR Test 2 TC Results. ................................................................................. 4-40

Table 4-10. SWGR Test 3 Flux Results................................................................................. 4-48

Table 4-11. SWGR Test 3 TC Results. ................................................................................. 4-49

Table 4-12. SWGR Tests 1 through 3 Electrical Results (1).................................................. 4-52

Table 5-1. SWGR Tests 4 through 6 Summary of Results.....................................................5-1

Table 5-2. SWGR Test 4 and 5 Calorimeter and TC Locations. ............................................5-8

Table 5-3. SWGR Test 6 Calorimeter Locations....................................................................5-8

Table 5-4. SWGR Test 4 Flux Results................................................................................. 5-19

Table 5-5. SWGR Test 4 TC Results. ................................................................................. 5-20

Table 5-6. SWGR Test 5 Flux Results................................................................................. 5-32
xviii

Table 5-7. SWGR Test 5 TC Results. ................................................................................. 5-34

Table 5-8. SWGR Test 6 Flux Results................................................................................. 5-49

Table 5-9. SWGR Test 6 Plate Thermometer Results......................................................... 5-50

Table 5-10. SWGR Test 4 through 6 Electrical Results (1).................................................... 5-54

Table 6-1. SWGR RFAS Summary of Results.......................................................................6-2

Table 7-1. Comparison of Arcs in Front Bus Bars of Cabinets...............................................7-9
xix

EXECUTIVE SUMMARY

A High Energy Arcing Fault (HEAF) occurred in a high-voltage (6.9 kV) switchgear (SWGR) at 

Unit 1 of the Onagawa Nuclear Power Plant of the Tohoku Electric Power Company on March 

11, 2011 during the Great East Earthquake in Japan. The Onagawa nuclear power plant (NPP) 

was the closest plant to the epicenter of the 2011 Great Eastern Earthquake. (To learn more 

about the effects of the earthquake and tsunami on the Onagawa NPP please see reference 

[1].) This type of HEAF event has occurred in electric equipment in NPPs worldwide and HEAF 

events have gained high interest in the safe operation of NPPs with an emphasis on developing 

evaluation methods. 

To investigate the HEAF event sequence and to understand the phenomena, the Regulatory 

Standard and Research Department, Secretariat of the Nuclear Regulation Authority (S/NRA/R)

(Japan) conducted HEAF tests by simulating the design and operating conditions of the SWGR 

HEAF at Onagawa in addition to simulating the HEAF energy effects using a Rocket Fuel Arc 

Simulator (RFAS). Tests of 480 V Motor Control Center (MCC) and Distribution Panel (DP) 

cabinets were also conducted to understand HEAF characteristics. 

The objectives were not only to understand the Onagawa event but also to obtain 

measurements of HEAF phenomenon such as pressures, temperatures, heat fluxes, electrical 

characteristics, and ability to cause ensuing (secondary) fires within the equipment and of 

external cables. The objectives also included making observations to assess current HEAF 

evaluation guidance, including the Zone of Influence (ZOI), in NUREG/CR-6850, “EPRI/NRCRES Fire PRA Methodology for Nuclear Power Facilities: Detailed Methodology, Appendix M for 

Chapter 11, High Energy Arcing Faults” (NUREG/CR 6850) [2].

Electrical arc tests were generally conducted per IEEE C37.20.7 “IEEE Guide for Testing MetalEnclosed Switchgear Rated Up to 38 kV for Internal Arcing Faults” that tests if SWGR cabinets 

remain intact and the HEAF cannot injure workers [3]. The key part of IEEE C37.20.7 for these 

tests is the initial arc was created by putting a wire between the bus bars to cause a direct short 

circuit at the desired position for the HEAF. Tests with electrical arcs were conducted at KEMA 

Laboratories Chalfont (KEMA), located in Chalfont, Pennsylvania between January 2013 and 

March 2015, using specialized large capacity electrical systems to create the arc and provide 

the high energy for the HEAF (usually 10-75 MJ over 2 or 3 seconds). The KEMA facilities are 

qualified to meet IEEE C37.30.7 requirements. 

Tests with Rocket Fuel Arc Simulators (RFAS) to simulate the arc heat were conducted at 

Southwest Research Institute (SwRI) using aluminum-based solid rocket fuel. The RFAS were 

used to investigate thermal effects and ensuing fires using a large, industrial calorimeter at 

SwRI. 

The 480 V tests on DP and MCC were the first tests performed to develop the test methods 

before the more important SWGR tests to simulate the Onagawa HEAF were performed. The 

test methods improved over the course of the tests with a key change to increase the number of 

arcs from one (1) to two (2) in the SWGR tests to be similar to the arcs at Onagawa. This 

confirmed that pre-heating of cable internal to the cabinet is important for rapid cable ignition in 

a second arc. The final SWGR and DP tests were completed in March 2015. 

DP tests 1 through 3 were completed in January 2013 and DP tests 4 through 6 were completed 

in March 2015 using General Electric (GE) APN-B cabinets. The DPs were tested at nominal 

480 V except Test 6 was conducted at nominal 400 V. The tests had target an arc duration of 2 
xx 

seconds and a target current of 53 kA. The results were arc durations varying between 0.8 to 2 

seconds, currents of 38 to 52 kA, and arc electrical energies ranging from 8.3 to 37.1 MJ. 

Cabinet pressures were 2.0 to 4.8 psi (13.8 to 33.1 kPa) and the maximum external measured

flux1 recorded was 158 kW/m2

, during the arc for a short duration (less than 1 second). There 

were ensuing internal cable fires in two tests. 

The key observations for the DP tests were: 

• It was difficult to repeat arc duration because the arcs could not be sustained. 

• The energy threshold for an ensuing internal cable fire was about 28 MJ. 

• The pressure was higher for the DP cabinet than the SWGR cabinet because there are 

fewer vents. The cabinet walls and roof had bending and deformation of several 

centimeters. 

Four MCC tests were completed in May 2013 using GE Series 7700 MCCs. The MCCs were 

tested at nominal 480 V with a target arc duration of 2 seconds and a target current of 63 kA. 

The resulting arc durations varied from 0.15 to 0.95 seconds, currents varied between 21 and

46 kA and arc electrical energies ranged from 1.7 to 17.6 MJ. Cabinet pressures were 4.4 to 

9.2 psi (30.3 to 63.4 kPa) and the maximum external flux recorded was 102 kW/m2 during the 

arc for a short duration (less than 1 second). There were no ensuing fires. 

The key observations for the MCC tests were: 

• Test 2 demonstrates the important observation that hot gases and plasma can travel 

from the initial arc point to other locations in the cabinet and cause a second and in this 

case higher energy arc. 

• Cabinets with few vents that are “tight” and have low ventilation like the MCC have 

higher pressures, as would be expected. The MCC tests had the maximum pressures of 

all tests including SWGR and DP. SWGR had the lowest pressures (most ventilated), 

DP had moderate pressure (less open than SWGR), and MCC had the highest (tight 

cabinets). 

• As shown with the DP tests, it is difficult to maintain a steady arc with 480 V. The bus 

bars were not very substantial in the MCC, which bent during testing and caused large 

arc gaps and the voltage could not sustain the arc. 

Three SWGR tests with single arcs were completed in June 2013 with a 5-cabinet lineup of GE 

Magneblast breakers modified to have geometry similar to the SWGR at Onagawa including 

aluminum bus bars. The SWGRs were tested at nominal 6.9 KV with a target arc duration of 2 

seconds and a target current of 23 kA. The results were arc durations of 2 to 3 seconds, 

currents between 30 and 31 kA and arc electrical energies ranging from 42.6 to 64.2 MJ. 

Cabinet pressures were 0.7 to 2.4 psi (4.8 to 16.5 kPa) and the maximum external flux recorded

was 107 kW/m2 during the arc for a short duration (less than 1 second). There were ensuing 

internal cable fires in two tests. 

Test 2 had a fully developed ensuing fire that completely burned the cables in Cabinets 7 and 8 

over approximately 20 minutes. Cables in Cabinets 6, 9, and 10 were only partially burned. 

 

1 The reported flux is the average over the arc duration based on the temperature change of slug 

calorimeters where the slug temperature is caused by an unknown combination of radiation and convection 

heat transfer but the flux analysis assumes that the flux is predominately radiation during the arc. See 

Appendix A for more detail.
xxi

Test 3 showed similar results and an ensuing fire but the ensuing fire was extinguished after 4

minutes for safety reasons at the laboratory. 

The key results from the SWGR 1-arc tests were: 

• The electrical arcing tests at KEMA did not duplicate the Onagawa damage conditions

because the damage was not as severe. 

• An electrical energy of about 60 MJ was needed for the ensuing fire in the KEMA SWGR 

tests. One observation on all the tests is that the ensuing fire usually required an energy 

of around 25 MJ or greater. The higher 60 MJ in this case is probably due to the heat 

lost through the vents. Cabinets with vents and the vent location may be an important 

consideration in determining the heat damage effects from HEAF. 

The 1-arc SWGR Tests 1 through 3 did not duplicate the assumed 2011 Onagawa HEAF event

that may have had two large arcs in two different cabinets several minutes apart. So, the 

SWGR test items were re-designed to include a working circuit breaker to provide two arcs. 

SWGR Tests 4 and 5 with two initiated arcs each were completed in March 2014 with 5-cabinet 

lineups of GE Magneblast breakers identical to SWGR Test 1 through 3. An additional Test 6

was completed in March 2015 with a 3-cabinet lineup. The SWGR were tested at nominal 6.9 

KV with Arc 1 target arc durations of 1.0 to 2.5 seconds and a target current of 23 kA. The Arc 

1 results were durations between 1.1 and 2.4 seconds, currents of 24 to 25 kA and arc electrical 

energies ranging from 26.5 to 64.6 MJ. The Arc 2 target arc durations were 2 to 3 seconds and 

a target current of 35 kA. The Arc 2 results were durations of 0.6 (there was a failure that 

shortened the duration) to 2.1 seconds, current of 33 – 34 kA and arc electrical energies ranging 

from 21.1 to 78.4 MJ. 

Cabinet pressures were 1.3 to 3.4 psi (19.0 to 23.4 kPa) and the maximum external flux was 

220 kW/m2 for a short duration (less than 1 second) during Test 4, Arc 2. This test also resulted 

in very large amount of aluminum oxidation from bus bar contact and shorting. There were 

ensuing internal cable fires in two tests. 

The key results from the SWGR 2-arc tests at KEMA were: 

• Test 4, Arc 2 had horizontal bus bar arcing that simulated the assumed second arc in the 

2011 Onagawa HEAF event scenario with severe bus bar arcing. The energy and fire 

were very large and the damage on the front of Cabinet 7 was similar to Onagawa but 

not as severe. This test confirms that the aluminum bus bar oxidation likely contributed 

to the large ensuing fire at Onagawa. 

• In Test 5 and Test 6 Arc 2, there were strong arcs in the secondary (rear) of Cabinet 8,

as planned. However, the damage to the circuit breaker was not as severe as at 

Onagawa because the arc did not travel down into to the breaker to cause the severe 

damage observed at Onagawa. In Test 5, Arc 2 the hot gas and plasma went up 

through the top of the cabinet and out the vent rather than down toward the breaker. In 

Test 6, Arc 2 the hot gas and plasma remained in the rear of the cabinet but the damage 

to the breaker was still minimal. 

• The energies for the arcs were greater than 60 MJ in SWGR Tests 4 and 5, and resulted 

in ensuing fires. This is similar to the results in SWGR Tests 1 through 3. The energies 

in Test 6 were not adequate for an ensuing fire because a shorter Arc 1 was planned (1 
xxii

second versus 2 seconds) and the second arc was extinguished by a hot short that 

opened the Cabinet 8 breaker carrying the arc current from the KEMA source. 

• Tests 4, 5 and 6 had higher total energies than Tests 2 and 3 because there were two 

electrical arcs and much more aluminum oxidation, especially in the case of Test 4, Arc 

2. The fire in Test 4 quickly spread to the other cabinets. The cables were pre-heated 

by Arc 1 so the cable burning was very rapid after Test 4, Arc 2. 

• Test 4, Arc 2 showed the highest external flux for any test in this report. None of the 

cables in the test cable trays 45.7 cm (18 in) above the top of the SWGR caught fire but 

there was some fire damage, such as charring and local burns where the cables were in 

contact with the tray rungs. 

• Test 6, Arc 2 demonstrated the important behavior that arcs can move from the initial 

ignition point because the arc ignited at the insulator but moved to the end of the bus 

bars along the path of the current. This also demonstrates that arc behavior is difficult to 

predict because in an identical test configuration in SWGR Test 5, Arc 2 stayed at the 

initial ignition point. 

Two RFAS tests in 5-cabinet lineups of GE Magneblast cabinets identical to SWGR Tests 1 

through 3 were tested in July 2013. RFAS energies of 140 MJ single RFAS burst (Test 1) to 

245 MJ in two bursts (like the two arcs assumed at Onagawa) were tested. 

RFAS Test 2 was one of the most interesting tests because there was a full ensuing fire that 

was allowed to burn to extinguishment 90 minutes after ignition. In Test 1 both RFAS charges 

ignited at the start of the test and there was no major ensuing fire even though the energy was 

more than 2 times the energy of KEMA SWGR Test 2 that had a major fire. The cables in Test 

1 reached a high temperature during the RFAS ignition but quickly cooled and there was no 

ensuing cable fire. 

The key results from the RFAS SWGR tests at SwRI were: 

• The RFAS is a good method to simulate the high energy of a HEAF and get more data 

about the ensuing fires. However, the energy required to get an ensuing fire is at least 2 

to 4 times higher for an RFAS than for an electrical arc. This suggests that the rapid 

aluminum oxidation (combustion) energy in addition to the electrical energy was needed 

to cause the ensuing fires in electrical SWGR HEAF tests. 

• The low pressure and rapid recovery of oxygen after the RFAS ignition show that the 

SWGR are well ventilated cabinets and much of the heat energy from a HEAF is lost. 

The KEMA tests suggest the energy is much higher to start an ensuing fire in a SWGR 

than for less-ventilated cabinets like the DP.

• Pre-heating from the first RFAS burst decreased the time needed to develop the ensuing 

fire and subsequently increased the growth of the ensuing fire to the peak temperature. 

However, cabinets without much pre-heat still can have an ensuing fire, but it took a 

longer time to ignite when the ramp up was slower. 

• Even at the very high energies (245 MJ) in RFAS Test 2, the damage was not as severe 

as occurred at Onagawa NPP in 2011. The exterior of the cabinet was not as charred 
xxiii

and there was no major damage in the secondary (rear) of the SWGR cabinet. This 

suggests a large thermal energy release from the bus bar oxidation at Onagawa. 

xxv 

CITATIONS

This report was prepared by the following:

Division of Research for Reactor System Safety 

Regulatory Standard and Research Department

Secretariat of Nuclear Regulation Authority 

(S/NRA/R)

1-9-9 Roppongi, Mianto-ku, Tokyo, Japan 106-8450

Division of Risk Analysis

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

S. Tsuchino, Senior Expert

H. Kabashima, Chief Researcher

S. Mehta

D. Stroup

N. Melly

G. Taylor

F. Gonzalez

Leidos, Inc.

301 Laboratory Road

Oak Ridge, TN 37830 

S. Turner 

Prepared as part of: 

The Agreement on Research Participation and Technical Exchange under the Fire-Related 

Research Program

xxvii 

ACKNOWLEDGMENTS

The authors acknowledge the dedicated team of individuals and international companies that 

contributed to the success of the HEAF tests. 

Dr. Fumio Kasahara of NRA provided senior management oversight and technical advice. 

Takeshi Saito and Masahiro Nagaki of Japan NUS Co, LTD (JANUS), Tokyo provided technical 

support and translation.

The NRC team observing and supporting the tests was led by Mark Henry Salley with support 

from Nicholas Melly, Gabriel Taylor, David Stroup, and Felix Gonzalez. Shivani Mehta was 

responsible for the final NUREG/IA preparation.

NRC was also supported by the National Institute of Standards and Technology (NIST) team 

that provided measurement support under the leadership of Anthony Putorti with test 

engineering support by Scott Bareham, Michael Selepak, Joseph Praydis Jr, and additional 

technical staff for test operations at NIST and KEMA. 

NRC was also supported by Carlos Lopez and other staff at Sandia National Laboratories (SNL) 

that tested some measurement methods. 

The tests were managed by Leidos, Inc. of Oak Ridge, Tennessee under the leadership of 

Stephen Turner and supported by various subcontractors. Jennie Henry was the Leidos 

Subcontract administrator. Karen Carpenter of Southwest Research Institute provided test 

management support and thermal imaging at KEMA and managed the tests at SwRI with 

support from the SwRI technical staff and oversight from Marc Janssens and Matt Blais.

Matthew Muthard, Kresimir Starcevic, Victor Savulak, Richard McLaughlin, Dennis Samuel, and 

George Khoury coordinated and managed the tests at KEMA Laboratories Chalfont. Robert 

Taylor of Brendan Stanton Incorporated (BSI) managed the assembly and installation of the test 

items with engineering support from Benny Lee and fabrication and technician support by other 

technical staff. David Muir of Advanced Motor Controls in cooperation with Paul Grein and Kyle 

Fincher at Circuit Breaker Sales provided the test items. James Phillips of Brainfiller, 

Incorporated provided Subject Matter Expert advice on arc flash hazards. 

xxix

ACRONYMS AND ABBREVIATIONS

AC Alternating Current

AL Aluminum

A Ampere

ASTM ASTM International

Bot Bottom

Cab Cabinet

cal calorie

CRIEPI Central Research Institute of the Electric Power Industry 

CT Cable Tray

CV A type of cable 

DFT Directional Flame Thermometers 

DP Distribution Panel

F Front

FS Front Side

FLIR Forward Looking Infrared, also a camera manufacturer

g gram

GE General Electric

HD High Definition

HEAF High Energy Arcing Fault 

HRR Heat Release Rate 

HS High Speed

HV High Voltage 

IEEE Institute of Electrical and Electronics Engineers 

in Inch

ISO International Organization for Standardization

JNES Japan Nuclear Energy Safety Organization (now NRA)

k 1,000

kA Kiloampere

KEMA KEMA Power Test, LLC 

kg Kilogram

kJ Kilojoule

KMS Knowledge Management System 

kPa Kilopascal

KPT KEMA Power Test (same as KEMA)

kV Kilovolt 

kVA Kilovolt Ampere

kW Kilowatt

LLC Limited Liability Corporation 

LV Low Voltage 

m meter

MBB MagneBlast Breaker

MC Mitsubishi Corporation
xxx 

MCC Motor Control Center 

MCCB Molded Case Circuit Breaker 

min minutes

MJ Megajoule

mol moles

MV Medium Voltage

MVA Megavolt Ampere

N/A Not Applicable 

NIST National Institute of Standards and Technology

NPP Nuclear Power Plant

NRA Nuclear Regulation Authority (Japan, also see S/NRA/R)

NRC Nuclear Regulatory Commission (United State of America)

OECD Organization for Economic Cooperation and Development 

Pa Pascal

PRA Probabilistic Risk Assessment

psi Pounds per Square Inch 

psig Pounds per Square Inch Gauge

PT Plate Thermometer

PRT Pressure Transducer

PVC Polyvinyl Chloride 

R Rear

RS Right Side

RFAS Rocket Fuel Arc Simulators 

s Second 

S Slug calorimeter

S/NRA/R Regulatory Standard and Research Department, Secretariat of the Nuclear 

Regulation Authority (S/NRA/R) (Japan)

SAIC Science Applications International Corporation (now Leidos)

SB Schmidt-Boelter (heat gauge)

SNL Sandia National Laboratories

SPR Smoke Production Rate 

SS Stainless Steel

SWGR Switchgear 

SwRI Southwest Research Institute

T Top

TC Thermocouples 

THR Total Heat Released 

US United States (of America)

V Volt

VAC Volts Alternating Current 

XLPE Cross-Linked Polyethylene 

ZOI Zone of Influence
1-1 

1 INTRODUCTION 

1.1 Background 

The High Energy Arcing Fault (HEAF) tests in this report were conducted to support research on 

a HEAF event that occurred during the 2011 Great East Earthquake at the Onagawa NPP that 

damaged a row of Switchgear (SWGR) panels [1]. 

HEAFs are a fast energy release that occurs in the form of heat, light, molten metal, and 

pressure rise from electrical shorts inside of electrical equipment cabinets. HEAFs are a hazard 

that can cause ensuing (or secondary) fires that destroy targets such as the power and control 

cables inside and outside the cabinet. Understanding HEAFs and their consequences is 

important, as demonstrated by a large HEAF in a high-voltage (HV)2 6.9 kV switchgear (SWGR) 

and ensuing fire that occurred at the Onagawa NPP during the March 11, 2011 Great East 

Japan Earthquake. 

In general, the electrical power industry refers to HEAF as an “arc-blast” or “arc-flash” and the 

basic behavior is documented in IEEE 1584 [4], which has a case history of arc-flash events. 

Industry has mainly been concerned about the effects of arc flash on workers and the protective 

equipment that is needed for workers to safely operate, maintain, and install electrical systems. 

The nuclear industry has focused more on evaluating the impact of ensuing fires as part of Fire 

Hazards Analysis (FHA). NRC Probabilistic Risk Assessment (PRA) guidance in NUREG/CR

6850 [2] specifically addresses analysis of HEAFs. The Organization for Economic Cooperation 

and Development (OECD), Nuclear Energy Agency (NEA) began an international activity to 

investigate HEAFs in 2009 and compiled information on 48 HEAF events [5]. 

The guidance in NUREG/CR 6850, Appendix M prescribes that the ensuing fire(s) typically 

includes ignition of combustible material within the HEAF Zone of Influence (ZOI). The resulting 

fire may be due to the ejection of hot particles or piloted ignition of combustibles. HEAF events 

are of concern due to their potential to impact adjacent items important to safety and current 

limitations in characterizing the ZOI. The ZOI was determined based on a review and 

characterization of the damage and detection/suppression behavior for the energetic phase of 

high-energy-arcing faults of 11 incidents that occurred in U.S. nuclear power industry between 

1979 and 2001. Specifically, the ZOI boundaries are at 1.5 m (5 ft) above the cabinet and 0.91 

m (3 ft) from the sides of the cabinet, in all directions.

The NRA test series focuses on HEAFs in a 6.9 kV SWGR with a similar configuration to the 

Onagawa event, and includes tests for 480 V Motor Control Centers (MCC) and Distribution 

Panel (DP) cabinets. The test objective included determining if ensuing fires occur and confirm 

the events in the Onagawa HEAF event. The tests performed are to better understand the 

HEAF phenomena and the ZOI for damage from the ensuing fires, as described in NUREG/CR 

6850, Appendix M. 

1.2 Onagawa HEAF Event 

The damaged Onagawa switchgear panels 7 through 10 are shown in Figure 1.2-1. The 

Onagawa arcing event is shown in Figure 1.2-2, in which the first arc occurred from a normal 

operating condition with “Common Use Power” in the Cabinet 7 SWGR from shaking during the 

 

2 Japan considers 6.9 kV as “High Voltage”, most other countries, including the US, consider 6.9 kV as 

“Medium Voltage”. 
1-2 

initial earthquake at 14:46, local time [1]. It appears that a second arc may have occurred from 

an abnormal operating condition, in which start up power was available at the Cabinet 8 SWGR 

through an unusual configuration of the startup power circuits. In both arcs, the heavy breakers 

hanging in the SWGR cabinets swung wildly, causing arcs where the SWGR bushings are 

mated with the insulation bushings. 

The circuit for Cabinet 7 had a reported impedance of 9.5% at 6.9 kV at the time of the Arc 1. 

The circuit for Cabinet 8 had an unknown impedance at the time of Arc 2 because the circuit 

was irregular and not covered in the design. 

The main goal of the SWGR tests in this report was to simulate these arcs. The initial SWGR 

Tests 1 through 3 attempted to simulate the Cabinet 7 arc only. However, based on the initial 

test results, the SWGR tests were redesigned to provide two arcs in Tests 4 through 6 to better 

simulate the Onagawa event. 

Figure 1.2-1. Damage in Onagawa HEAF Event

6 7 8 9 10
1-3 

Side View Front View, Door Open

Figure 1.2-2. Onagawa Arching Scenario

1.3 Test Approach and Electrical Test Conditions

Tests were generally conducted per IEEE C37.20.7 [3] that evaluates SWGR to determine if it 

meets the “arc proof” requirements in IEEE 1584 [4]. “Arc proof” testing ensures that SWGR 

cabinets remain intact and the HEAF cannot injure workers. The key part of IEEE C37.20.7 

used in these tests is the creation of the initial arc by putting a wire between the bus bars to 

cause a short at the desired position for the HEAF. The tests are intentionally creating an arc 

path at a specific location which will mimic event scenarios within cabinets. The cabinets are 

not connected to full electrical systems of breakers - this allows the arc to persist without safety 

mitigation strategies such as breaker trips. 

Tests with electrical arcs were performed at the KEMA Laboratories Chalfont (KEMA) using 

specialized large capacity electrical systems to create the arc and provide the high energy for 

the HEAF (usually 10-75 MJ over 2 or 3 seconds). Details of the KEMA facilities are discussed 

in Appendix B. HEAFs have the ability to cause severe, short duration, thermal insults that were 

characterized by heat flux measurements using slug calorimeters at KEMA. HEAF heat release 

rate (HRR) is another important parameter to assess thermal properties but HRR cannot be 

measured at KEMA. To measure and understand the HRR, tests with Rocket Fuel Arc 

Simulators (RFAS) were conducted at Southwest Research Institute (SwRI) with their largescale industrial calorimeter. The RFAS simulates the arc heat expected in a HEAF. 

Table 1-1 summarizes the tests. The test conditions listed in the table are the target test 

conditions (not the voltage and current achieved) but the arc duration and energy from the tests 

are reported. 

2. 

Connection 

contacts the 

surrounding 

structures and 

causes a 

ground fault 

4. Arc ignites cable 

insulation and causes 

a fire

1. There is a 30-cm 

space below the MBB 

and the earthquake 

causes the MBB to 

swing damaging the 

cabinet. 

3. Arc 

discharge
1-4 

The arc current and arc duration for the tests were much higher than properly designed circuits 

allow. Circuits are designed to limit the arc energy and duration during a fault so HEAFs do not 

occur. 

The bolted fault current that is the maximum feasible fault current for an electric circuit was used 

in the tests. KEMA used the bolted fault current as a target specified by NRA as a peak current 

target in no-load calibration runs with shorted busses before the current is applied to the test 

item. The actual symmetrical current in the tests is be slightly lower because of the impedance 

of the arc (it acts similar to a load). The peak current will be slightly higher than the symmetrical 

current but it only lasts for a few electrical cycles at the start of the arc. The calculations for the 

target test currents are provided in Appendix D. 

The planned target arc durations were nominally 2 seconds for most tests but were increased to 

3 seconds in some cases to increase the energy in attempts to ignite ensuing fires. The 2 

seconds was based on an assumption that older systems in Japan require long times for 

clearing a fault. This was a conservative duration to create very high energy. There are cases 

of reported HEAF events as long as 5 to 10 seconds [5]. 
Table 1-1. Summary of NRA HEAF Tests. 

Date/Location Test Tests/ Type of 

Test Test Conditions (1) Results 

January 2013

SwRI

1-cabinet 

SWGR

3 RFAS tests to 

understand 

ensuing fires

Simulate 1 70 MJ arc

2 RFAS slabs (35 MJ each), 2 

second burst time

No major ensuin

HRR very lo

RFAS work

July 2013

SwRI

5-cabinet 

SWGR 2 RFAS tests 

Test 1: Simulate 1 140 MJ arc, 

2 seconds

Test 2: Simulate 2 bursts, 70 

MJ + 175 MJ, 2 seconds

Test 1: No ensui

Test 2: Ensuing 90

fire with good H

measuremen

June 2013 KEMA 5-cabinet 

SWGR

3 electrical arc 

tests,

1 arc

Test 1-3: 6.91 KV, 23 kA, 2 - 3 

sec duration

Arc energy of 43 to 64 MJ

Test 1: No ensuing 

43 MJ

Test 2 and 3: Ensuin

cases with nomina

energy, fire damag

severe as Onag

March 2014

KEMA

5-cabinet 

SWGR

2 electrical arc 

tests,

2 arcs

6.9 KV, 23 kA, 2 - 3 sec 

duration

Test 4: Arc 1: 67 MJ (Cab 7); 

Arc 2: 78 MJ (Cab 7, bus bars)

Test 5: Arc 1: 57 MJ (Cab 7)

Arc 2: 62 MJ (Cab 8, rear)

Test 4: Large ens

and bus bar arcing 

Onagawa, highest 

fluxes and damage o

tests

Test 5: Ensuing fire 

2 on secondary s

Onagawa but dama

severe as Onag

1-5
Date/Location Test Tests/ Type of 

Test Test Conditions (1) Results 

March 2015

KEMA

5-cabinet 

SWGR

1 electrical arc 

test, 2 arcs

Test 6: 6.9 KV, 23 kA

Arc 1: 27 MJ (Cab 7), 1.1 sec

Arc 2: 21 MJ (Cab 8), 0.6 sec

Test 6: No ensuing 

energy), minor b

oxidation, breaker 

caused a short 

duration, Arc 2 mov

the secondary insula

end of the second

bars.

January 2013

KEMA DP 3 electrical arc 

tests

Tests 1 – 3: 1 arc 480 V, 53 kA, 

1.5- 2 seconds

Energy 30 – 37 MJ

Difficult for arc to s

Ensuing fires in 2 

March 2015

KEMA DP 3 electrical arc 

tests

Test 4 and 5: 480 V, 53 kA,

0.7 – 1.7 seconds

Energy 8 – 14 MJ

Test 6: 400 V, 53 kA, 0.8 

seconds

Energy 8.2 MJ

Difficult for arc to su

ensuing fires. All a

of the 2-second t

May 2013

KEMA MCC 4 electrical arc 

tests

Tests 1-4: 1 arc 480 V, 63 kA,

0.15 to 0.95 seconds, (2 

second target)

Energy 1.7 to 17.6 MJ

Difficult for arc to s

short arc tim

Proved that arcs co

inside the cab

No ensuing fires

penetrated the cab

tests.

(1) The energy is the electrical energy input only; no energy from bus bar oxidation is includ

1-6
1-7 

1.4 Measurements and Instrumentation 

The measurement items for the tests are shown in Table 1-2. The table includes the 

instruments used at SwRI and KEMA and additional instruments provided by Sandia National 

Laboratories (SNL) and the National Institute of Standards and Technology (NIST). SNL tested 

several instruments to potentially enhance the instruments available at KEMA. However the 

KEMA instruments were deemed adequate for the NRA testing [6]. NIST provided a portable 

oxygen-calorimetry hood and Plate Thermometers (PT) (described in Reference [7, 11]) for 

tests in March 2015. For this report, the results for plate thermocouples mounted on a cable 

tray above the cabinet are presented for DP Tests 4 through 6 and SWGR Test 6. Hood 

calorimetry results are not reported because, as noted in Reference [7, 11], the method was not 

effective during the arc but is useful for ensuing fires after the arc. However, none of the tests 

where the hood was used had ensuing fires. 

Table 1-2. Measurements and Instrumentation. 

Measurement Item Measurement Method

1. Current waveform 

measuring device

Voltage dividers, coaxial shunts, and other coils provided 

current and voltage waveforms to calculate energy. 

2. Pressure 

a. Internal

b. External 

a. Internal: Strain-gauge type pneumatic transducers were 

used by KEMA, SNL, and SwRI. 

b. External: Pencil-type gauges were used at the January 

2013 tests at KEMA by SNL and at SwRI. The 

measurements were not useful in the swirling air around the 

HEAF and fire. 

3. Temperatures Thermocouples (TC), passive temperature indicator labels 

and plate thermometers (PT). The TCs could not be placed 

directly on the cabinets in the electrical tests for safety. They

indicate local air temperatures 15.2 cm (6 in) from the 

cabinet. Results are reported but were not very useful. Not 

used in 2015 tests.

4. Heat Flux Slug calorimeters built to ASTM F1959 [8] were used at the 

ZOI positions in tests at KEMA (see Appendix A). SwRI 

used dual plate thermometers, Schmidt-Boelter (SB) gauges, 

Gardon Gauges and ASTM F1959 calorimeters for 

comparison and analysis. Other methods used by SNL were 

not effective, see Reference [6]. 

5. Oxygen calorimeter Industrial scale calorimeter used for ensuing fire HRR at 

SwRI. The NIST calorimetry hood was used in the March 

2015 tests but was not useful during the arcs [7, 11]. 

6. Infrared and visible light 

high-speed photography

FLIR T300 Thermal Imaging camera to see the HEAF 

ensuing fire effects and general thermal conditions, High 

speed camera at 500 – 1000 frames per second to study 

ignition and cabinet deformation. Various High Definition 

videos from many positions were used to see the HEAF 

effects and timing of key events like ensuing fire ignition. 

7. IEEE C37.20.7 indicators Used to study debris that escapes the cabinet at KEMA. The 

DP and MCC cabinets are not arc proof so debris escaped. 

The SWGR cabinets showed little debris. 
1-8 

Measurement Item Measurement Method

8. Oxygen monitor Used at SwRI to measure oxygen depletion in Cabinet 8 

caused by RFAS ignition in the SWGR tests. All oxygen 

calorimeter results include oxygen measurement. 

9. Cable Samples Short pieces of cable (less than 8 cm (3.15 in)) were placed 

at several internal and external positions and externally at 

the ZOI in DP Tests 1 through 3. Cable trays were placed 

above the DP and SWGR cabinets in the March 2015 tests. 
2-1 

2 Distribution Panel HEAF TEST – KEMA (January 2014 and March 

2015)

2.1 DP Test Overview (2014 and 2015)

The purpose of these tests was to obtain the basic HEAF data such as arc duration, energy, 

flux, temperature, pressure, and ensuing fire effects for six (6) Distribution Panels (DP). All 

tests were conducted at KEMA; Tests 1 through 3 were conducted on January 29-31, 2014 and 

Tests 4 through 6 were conducted on March 18-19, 2015. 

2.2 DP Tests Summary of Results 

Each test consisted of one 480 V General Electric (GE) APN-B DP that contained three (3) 

Molded Case Circuit Breakers (MCCBs). The DP is nominally 1.11 m wide by 2.29 m high and 

0.89 m deep (44 in by 90 in by 35 in). Japanese CV-2 cable that is typical of power cable was 

added as the combustible load. The key test parameters and results are in the Table 2-1. The 

target test voltage was nominally 480 V and the target test current was 53 kA bolted fault 

current. The final symmetrical current provided by the KEMA facility was nominally 38 to 43 kA

during the arc. 

The key results of the DP tests are: 

• Arc durations were difficult to repeat; the resultant arcs demonstrated random behavior 

after initiation and often could not be sustained, especially in Tests 4 through 6. 

• The energy threshold for the ensuing fire in these tests was about 28 MJ. 

• The cabinet walls and roof exhibited bending and deformation of several centimeters, 

potentially due to the use of thin materials for the walls and doors. 
2-2 

Table 2-1. DP Test Summary of Results. 

Test

Volt (V)

(1)

Current

(kA) (2)

Test 

Peak 

Current 

(kA) (3)

Arc

Duration

(sec) (4)

Arc 

Energy

(MJ)

Internal 

Max 

Press

(kPa/psi) 

(5)

Ext Max 

Flux (6) 

(kW/m2

) 

Ensuing fire?

Key 

Observations

1 484 / 404

43.3 / 30 71.2 2.01.574 29.6

14.5 ± 

2.8

2.1 ± 0.4

54 (7) Yes. After 7 

minutes.

2 

484/ 394

38.4 / 

31.6

66.9 2.0

1.446 26.2

18.6 ± 

2.1

2.7 ± 0.3

63 (7) No. Arc energy 

too low.

3 

484/ 416

41.4 / 

32.0

63.0 2.0

2.011 37.1

13.8 ± 

6.9

2.0 ± 0.3

27 (8) Yes. After 50 

seconds.

4 

484 / 403

50.3 / 

19.3

95.0 2.0

0.698 8.3

33.1 ±

1.4

4.8 ± 0.2

91 (9) No. Arc energy 

too low.

5 

484 / 363

44.7 / 

37.9

105 2.0

1.659 (10) 

14.3

(10) 

22.1 ±

2.1

3.2 ± 0.3

158 (9) No. Arc energy 

too low.

6 

400 / 305

51.8 / 

30.3

106 2.0

0.781 (11) 8.2 (11) 

16.5 ±

1.4

2.4 ± 0.2

73 (9) No. Arc energy 

too low.

Notes:

(1) The voltage is shown as the target voltage / arc Line-to- Line (L-L) voltage. 

(2) The symmetric arc current slowly drops during the test as the arc impedance increases. 

This shows the test start current/ test end current. These are average currents of all 3 

phases. 

(3) This is the peak current for any phase or time, usually the asymmetric current at the start. 

(4) The duration is shown as the target duration and the actual test duration is below it. 

(5) The uncertainty is described in Appendix A.

(6) The flux is reported for the outer boundary of the NUREG/CR 6850 ZOI at 0.91 m (3 ft) for 

the sides or 1.5 m (5 ft) at the top.

(7) The maximum flux was seen at 0.91 m (3 ft) at the rear of the cabinet at the height of the 

arc, 78.7 cm (31 in) from the floor (S8). 

(8) The maximum flux was seen at the top, 0.91 m (3 ft) to the left side of the cabinet (S5). A 

higher flux of 187 kW/m2 was seen at 30.48 cm (1 ft) from the cabinet (S8), not at the 0.91 

m (3 ft), as in other tests. 

(9) The highest flux during the arc was measured at the top left side of the cabinet (S8). 

(10) This includes the initial arc for 1.001 seconds and a re-strike. 

(11) This includes the initial arc for 0.550 seconds and several re-strikes. 

2.3 DP Test Configuration 

The GE APN-B DP has horizontal and vertical bus bars, as shown in Figure 2.3-1. The 

horizontal buses are extended outside the cabinet for KEMA to connect (gray). A wire to start 

the arc is connected to the buses inside (red lines). The breakers and components in the DP 

are the combustible load. An arc at the bottom below the combustibles should cause the largest

fire in the cabinet. DP Tests 1 through 3 used an arc at the bottom of the cabinet. DP Tests 4

through 6 used an arc at the top of the cabinet. 
2-3 

Figure 2.3-1. DP Test Configuration

Side Front

Location 

of bolted 

faults
2-4 

2.4 DP Test Configuration

This DP test item is a GE Spectra Series APN-B, shown in Figure 2.4-1. Small, medium, and 

large Molded Case Circuit Breakers (MCCB) were used in the cabinet. The MCCBs were 

evenly spaced to encourage an ensuing fire. The horizontal bus is rated for 3 kA and the 

busses are connected from the right side of the cabinet. 

Figure 2.4-1. DP Used in Tests

Horizontal 

buses Vertical 

buses 

Each breaker section has 

some combustibles like the 

plastic on the breaker. There 

are no wires.

Horizontal busses 

are connected from 

the right side.

Cables are placed in 

the left side areas for 

the combustible cable 

load.
2-5 

2.5 DP Test Cable Combustible Loading 

Japanese Type CV control cables with heat resistant PVC (Polyvinyl Chloride) sheath and 

XLPE (Cross-Linked Polyethylene) insulation were used for the combustible cable load in each 

test (see Appendix C for the properties). In actual use, power cables are used from the MCCB 

controllers to motors, and from the DP breakers to the loads. In these cases, typical large 4-

conductor cables are used (3 phases plus ground) but none were available for testing. Multiple 

2-conductor (CV-2) and 4-conductor (CV-4) cables were used to realistically model large power 

cables. 

The number of CV cables was changed for each breaker to represent larger power conductors 

for larger breakers. The cables loop over the top internal support bar and then to the floor as in 

a realistic cabinet where they exit the bottom of the cabinet, as seen in Figure 2.5-1. A total of

78 m (255 ft, about 9.4 kg of combustible load) of CV cable was included for Tests 1 through 6, 

with the following grouping: 

• Two (2) CV cables (like small power cables) 1.5 m (5 ft) long installed per phase to the 

small breaker (9.1 m (30 ft) total). 

• Three (3) CV cables (like medium power cables) 2.1 m (7 ft) long installed per phase to 

medium breaker (19.2 m (63 ft) total). 

• Six (6) CV cables (like large power cables) 2.7 m (9 ft) long installed per phase to large 

breaker (49.4 m (162 ft) total). 

Figure 2.5-1. DP Test Cable Combustible Load

Top

Middle

Bottom

Small

Medium

Large
2-6 

2.6 DP Test Temperature and Heat Flux Instrumentation

Slug calorimeter (slug, S) and thermocouple (TC) locations are in Figure 2.6-1 and Figure 2.6-2

for DP Tests 1 through 3 and Figure 2.6-3 for DP Tests 4 through 6. The TC and slug positions 

and names are in Table 2-2 and Table 2-3. 

For DP Tests 1 through 3 slugs are nominally 0.91 m (3 ft) from the cabinet sides (labeled as 

S5, S6, S7, S8, S10) and 1.5 m (5 ft) from the cabinet top (S9), as shown in the figures. These 

are located at the boundary of the postulated NUREG/CR 6850 ZOI distances. For DP Tests 1

through 3, external TCs, TC2, TC3, TC11, TC12, and TC13, are approximately 15.2 cm (6 in) 

from the cabinet in open air and not in contact with the cabinet. The air temperatures are likely 

much lower than the actual metal temperature. Therefore, the temperatures are only a 

qualitative measure of thermal behavior. See Appendix A for more information on the slug 

calorimeters and calculations. 

Front View Top View

Figure 2.6-1. DP Tests 1 through 3 Calorimeter Locations

S9

S5

S6

S7

S10

S9

S8

S5, S6, 

S7
2-7 

Figure 2.6-2. DP Tests 1 through 3 TC Locations

Table 2-2. DP Tests 1 through 3 Calorimeter and TC Locations. 

Slug or 

TC

From Floor

cm (in) Position Slug or TC Name

TC2 61 (24) Rear (R ) Bottom TC2-R-24-LS

TC3 61 (24) Rear Bottom TC3-R-24-RS

S5 198 (78) Left Side (LS) Top S5-LS-78-CL

S6 119 (47) Left side Middle S6-LS-47-CL

S7 89 (35) Left side Bottom S7-LS-35-CL

S8 78 (31) Rear Bottom S8-R-31-CL

S9 381 (150) Top (T) S9-T-150-CL

S10 78 (31) Front (F) Bottom S10-F-31-CL

TC11 61 (24) Left Side Bottom TC11-LS-24-R 

TC12 196 (77) Left Side top TC12-LS-77-CL

TC13 61 (24) Right Side (RS)

Bottom TC13-RS-24-CL

For DP Tests 4 through 6, slug calorimeters were located at 0.91 m (3 ft) and at the centerline

(CL) of the cabinet except Slugs 3 through 5 on the right side, which were closer to the front (F)

of the cabinet. The open air TCs were not used since useful data was not obtained in the 

previous tests. The tests also included a portable oxygen calorimeter and plate thermometers

(PT) provided by NIST [7]. A cable tray with PTs was added as an ignition test target on the top 

of the DP as described in Section 2.5.2. These tests were conducted in KEMA Test Cell 7 

rather than Test Cell 1 as in the previous DP tests to accommodate the hood. There was no 

slug calorimeter above the cabinet because of the hood. See Figure 2.6-3 for additional detail.

TC 13

TC 11

TC 12

TC 3

TC 2
2-8 

Cable Tray Detail Front View Top View

Figure 2.6-3. DP Tests 4 through 6 Calorimeter Hood and PT Locations 

Table 2-3. DP Tests 4 through 6 Calorimeter Locations. 

Slug From Floor

cm (in) Position Slug Name

S1 193 (76) Front (F) Top S1-F-76-CL

S2 41 (16) Front Bottom S2-F-16-CL

S3 193 (76) Right Side (RS) Top S3-RS-76-F 

S4 122 (48) Right Side Middle S4-RS-48-F 

S5 41 (16) Right Side Bottom S5-RS-16-F 

S6 193 (76) Rear (R ) Top S6-R-76-CL

S7 41 (16) Rear Bottom S7-R-16-CL

S8 193 (76) Left Side (LS) Top S8-LS-76-CL

S9 122 (48) Left Side Middle S9-LS-48-CL

S10 41 (16) Left Side Bottom S10-LS-16-CL
2-9 

In DP Tests 4 through 6, a cable tray, loaded with cable was installed 46 cm (18 in) above the 

cabinet. In each test, the tray was loaded with 30 CV-2 cables, each 1.05 m (41.3 in) long and

16 CV-4 cables, each 1.14 m (44.9 in) long. 

2.7 DP Test Pressure Instrumentation 

Two Dynisco Pressure Transducer PT150-50 strain gauge type pressure transducers (PRT) 

strain-gauge were used on the right side of the DP, at the top and bottom, as shown below in 

Figure 2.7-1. The gauges are in PVC pipe to protect them from fire. The measurement analysis 

method is discussed in Appendix A. 

Figure 2.7-1. DP Tests 1 through 6 Pressure Transducer and Locations (Rear View)

Top

Bottom
2-10

2.8 DP Test 1 Key Observations (January 2013) 

This cabinet test was initiated at 484 V and 43.3 kA, with a target duration of 2 seconds but the 

arc quenched at 1.6 seconds. It is theorized that the arc length from the bus bar to the cabinet 

increased as the arc connection points melted and vaporized and the voltage could not sustain 

the arc. The total energy was 29.6 MJ. Figure 2.8-1 shows the explosion after the arc at 0.012 

seconds, 0.052 seconds, 1 second, and 2 seconds after the arc was initiated. Note the whitehot lower panel at 2 seconds in Figure 2.8-1(d). A cable fire flame was visible out of the top 

vents about 7 minutes after the arc with a maximum flame about 5 minutes after that (12 

minutes from start of test) as seen in Figure 2.8-2 then the fire was visible for approximately 

another 12 minutes, for a total of 24 minutes. Post-test inspection showed the cable bundle was 

completely burned, demonstrating that the arc energy was enough to cause an ensuing cable 

fire. The fire self-extinguished. 

(a) (b)

(c) (d)

Figure 2.8-1. DP Test 1 Arc

0.012 seconds

0.052 seconds

1 second 2 seconds
2-11

Figure 2.8-2. DP Test 1 Ensuing Fire, 12 Minutes After Arc

The front was heavily damaged by the arc and ensuing fire. The top, sides and rear was also 

damaged, as seen in Figure 2.8-3. The top bulged out several centimeters. 

(a)

Figure 2.8-3. DP Test 1 Exterior Damage
2-12

(b) (c)

(d)

Figure 2.8-3. DP Test 1, Exterior Damage, Continued

The internal damage is shown in Figure 2.8-4. The arc moved downward to the bottom end of 

the vertical bus bars, melting several centimeters of the bus bars and burning through the 

horizontal support nearby. The cables were burned completely; the CV-2 cables burned like a 

typical thermoset (TS) with charring, flaking and no drips. Notice the burned insulation in the 

bottom of the cabinet, also indicating burning like a TS material. 
2-13

(a)

(b) (c)

Figure 2.8-4. DP Test 1 HEAF and Fire Interior Damage
2-14

Temperatures measured at the slug locations are shown in Figure 2.8-5. Data collection 

stopped at 4 minutes so some of the data for the ensuing fire was not recorded. Slug 10 is 

directly in front of the white-hot bottom panel at the bottom of the DP and shows the highest

response to the ensuing fire at 7 minutes. The internal cabinet fire had been burning since the 

arc occurred, based on the Slug 10 response. Slug 8 located at the rear had the strongest 

response to the initial arc. Slug 8 also showed some heating from heat escaping from the 

cabinet after the arc, probably from the ensuing fire. Slug 9 above the cabinet shows a small 

increase from the ensuing fire. The spikes during the arc indicate large variations in the slug 

temperature from noise and because the energy produced during the arc is not uniformly 

distributed external to the cabinet and varies during the arc. Venting conditions and cabinet 

integrity such as DP panel deformation and the associated plasma and flame leakage also 

affect the slug responses seen during the test series. 

(a) (b)

Figure 2.8-5. DP Test 1 Slug Calorimeter Data: Temperature

Table 2-4 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. A maximum flux of 54 kW/m2

is reported in the results 0.91 m (3 ft) from the rear, bottom of the cabinet (S8). As discussed in 

Section A.1, the maximum slug temperatures are also shown to indicate the maximum

temperature a metal object could reach. 

Table 2-4. DP Test 1 Flux Results. 

Slug ΔT ( ̊C) Flux (kW/m2

) Max T ( ̊C) 

S5-LS-78-CL 4.5 17 29

S6-LS-47-CL 5.7 21 36

S7-LS-35-CL 6.7 25 28

S8-R-31-CL 14.5 54 72

S9-T-150-CL 2.8 10 30

S10-F-31-CL 6.2 23 48
2-15

The temperatures measured by the TCs are seen in Figure 2.8-6 below. The strongest 

response was at the bottom rear panel (TC2, TC3) because this panel directly views the arc

through the vent openings. Table 2-5 shows the maximum temperature results. The 

thermocouple maximum temperature is a general indication of the air temperature 15.2 cm (6 in) 

from the cabinet and as expected TC2 and TC3 at the rear, lower panel near the arc had the 

highest temperatures. The thermocouples cannot be practically used to estimate flux. 

(a) (b)

Figure 2.8-6. DP Test 1 Thermocouple Data

Table 2-5. DP Test 1 TC Results.

TC Max T ( ̊C) 

TC2-R-24-LS 258

TC3-R-24-RS 310

TC11-LS-24-R 71

TC12-LS-77-CL 64

TC13-RS-24-CL 88
2-16

The pressures during the arc are depicted in Figure 2.8-7. Notice the higher level of noise in the 

measurements at the bottom location pressure near the arc. There are spikes near 2 seconds 

on the top pressure and at 2.1 seconds for the bottom pressure, both appear to be noise. The 

bottom pressure closer to the arc occurred earlier than the top pressure that was further from 

the arc. The maximum pressures are indicated by the arrows in Figure 2.8-7(c) and (d). The 

distinct sinusoidal responses on the bottom pressure transducer had a frequency of about 195 

Hz and could have been resonant pressure waves in the cabinet, as seen in other DP tests.

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc. 

(a) (b)

(c) (d)

Test 1 Pressure Transducer 1 Top

14.5 ± 2.1 kPa (2.1 ± 0.3 psi) 

@ 0.0171 s

Test 1 Pressure Transducer 2 Bottom

14.5 ± 2.8 kPa (2.1 ± 0.4 psi)

@ 0.0079 s

Figure 2.8-7. DP Test 1 Pressure
2-17

The total energy was 28.6 MJ, seen in Figure 2.8-8. The energy analysis methods are in 

Appendix A. The “Energy” is calculated as volts multiplied current multiplied by the time step 

and each time step is shown. “Energy Total” is the cumulative sum of the energy in each time 

step. The smooth increase of the cumulative energy, labeled as Energy Total shows a steady 

increase, indicating a stable arc (a smooth increase) in total energy during the arc.

Figure 2.8-8. DP Test 1 Arc Energy 

DP Test 1 resulted in an ensuing fire, which lasted about 24 minutes after the initial arc. 

The arc energy was sufficient to ignite the cables within the cabinet.

 
2-18

2.9 DP Test 2 Key Observations (January 2013)

This cabinet test was initiated at 484 V and 38.4 kA, with a target duration of 2 seconds but the 

arc quenched at 1.4 seconds probably because the arc length increased and the voltage could 

not sustain the arc. The total energy was 26.2 MJ. Figure 2.9-1 shows the explosion after the 

arc at 0.012 seconds, 0.052 seconds, 1 second, and 2 seconds after the arc. There was no 

ensuing cable fire but the cable damage showed this energy was almost enough to cause an 

ensuing fire. 

(a) (b)

(c) (d)

Figure 2.9-1. DP Test 2 Arc

0.012 

seconds

0.052

seconds

1 second 2 seconds
2-19

The cabinet front was heavily damaged by the arc. The sides and rear were damaged, as seen 

in Figure 2.9-2. The cabinet top had a deformation that occurred at about 0.022 seconds after 

the arc based on high speed images as shown in Figure 2.9-3. 

(a) (b)

Figure 2.9-2. DP Test 2 HEAF Exterior Damage

Figure 2.9-3. DP Test 2 Cabinet Top Deformation
2-20

The interior damage seen in Figure 2.9-4 shows that the arc moved downward to the bottom 

end of the vertical bus bars, where several centimeters of bus bar were melted. The cables did 

not ignite but showed damage indicating that they were pyrolizing. Notice the inside of the 

cabinet is coated with copper from the damaged bus bars.

(a)

(b) (c)

Figure 2.9-4. DP Test 2 Interior Cabinet Damage
2-21

Temperatures measured at the slug locations are shown Figure 2.9-5. Temperatures at the rear 

(S8) were higher than in the front (S10), indicating more heat escaped out the rear of the 

cabinet in this test. As expected, there are no heat increases in the later part of the test 

because there was no ensuing fire. The heating in the first few minutes after the arc was from 

heat escaping from the cabinet. 

(a) (b)

Figure 2.9-5. DP Test 2 Calorimetry Temperature Data: Temperature

Table 2-6 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux of 63

kW/m2 is reported at the rear of the cabinet (S8). The maximum slug temperatures are also 

shown to indicate the maximum temperature a metal object could reach. 

Table 2-6. DP Test 2 Flux Results.

Slug ΔT ( ̊C) Flux (kW/m2

) Max T ( ̊C) 

S5-LS-78-CL 5.9 23 50

S6-LS-47-CL 5.8 22 40

S7-LS-35-CL 6.3 24 39

S8-R-31-CL 16.5 63 84

S9-T-150-CL 3.1 12 49

S10-F-31-CL 3.4 13 57
2-22

The temperatures measured by the TCs are in the Figure 2.9-6. The highest response was at 

the rear bottom TCs (TC2, TC3), similar to all DP tests. Table 2-7 shows the maximum 

temperature results. The thermocouple maximum temperature is a general indication of the air 

temperature 15.24 cm (6 in) from the cabinet, and as expected TC2 and TC3 at the rear, lower 

panel near the arc had the highest temperatures. The thermocouples cannot be practically 

used to estimate flux. 

(a) (b)

Figure 2.9-6. DP Test 2 Thermocouple Data

Table 2-7. DP Test 2 TC Results.

TC Max T ( ̊C)

TC2-R-24-LS 340

TC3-R-24-RS 193

TC11-LS-24-R 132

TC12-LS-77-CL 163

TC13-RS-24-CL 114
2-23

The pressures during the arc are seen in Figure 2.9-7. Notice the result for the bottom 

pressure, near the arc has much more noise. There is a spike near 1.2 seconds on the top 

pressure and at 2.1 seconds for the bottom pressure, which both appear to be noise. The 

bottom pressure closer to the arc had a higher maximum and occurred earlier than the top 

pressure that was further from the arc. The maximum pressures are indicated by the arrows in 

Figure 2.9-7 (c) and (d). The distinct sinusoidal responses on both pressure transducers had a 

frequency of about 195 Hz and could have been resonant pressure waves in the cabinet. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc (using the middle charts below) then including a nominal uncertainty for the noise 

in the signal just before the arc.

(a) (b)

(c) (d)

Test 2 Pressure Transducer 1 Top

11.7 ± 2.1 kPa (1.7 ± 0.3 psi) 

@ 0.0194 s

Test 2 Pressure Transducer 2 Bottom

18.6 ± 2.1 kPa (2.7 ± 0.3 psi)

@ 0.0183 s

Figure 2.9-7. DP Test 2 Pressure
2-24

The total energy was 26.2 MJ, seen in Figure 2.9-8. The energy analysis methods are in 

Appendix A. The “Energy” is calculated as volts multiplied current multiplied by the time step 

and each time step is shown. “Energy Total” is the cumulative sum of the energy in each time 

step. The result shows a smooth increase in the total energy, indicated by the total energy 

showing that the energy provided by the KEMA power system was steady. 

Figure 2.9-8. DP Test 2 Arc Energy
2-25

2.10 DP Test 3 Key Observations (January 2013)

This cabinet test was initiated at 484 V and 41.4 kA, with a target duration of 2 seconds that was 

achieved with a total energy of 37.1 MJ. Figure 2.10-1 shows the explosion after the arc 

initiated at 0.012 seconds, 0.052 seconds, 1 second, and 2 seconds. One panel popped open 

based on the high speed images. A small fire was visible immediately after the arc but it selfextinguished in a few seconds (Figure 2.10-21(d)). An ensuing cable fire 50 seconds after the 

arc was visible at the bottom of the cabinet and half-way up the cabinets as shown in Figure

2.10-1(a). The fire reached the top of the cabinet in about 4 minutes (Figure 2.10-2(b)) then the 

fire self-extinguished after 14 minutes. The energy from the 2 second arc was enough energy 

to start a fire. 

(a) 0.2 seconds (b) 1 second

(c) 1.5 seconds (d) end of arc

Figure 2.10-1. DP Test 3 Arc
2-26

(a) 50 seconds after arc (b) 4 minutes after arc 

Figure 2.10-2. DP Test 3 Ensuing Fire

The front was heavily damaged by the arc and ensuing fire, as seen in Figure 2.10-3 through 

Figure 2.10-5. The sides and rear was also damaged. One panel opened from the high 

pressure at 0.024 seconds and roof deformation occurred at the same time, as seen in Figure 

2.10-3(c). The roof deformation was smaller than Tests 1 and 2, probably because the pressure 

was relieved by the panel coming off during the test. The pressures seen in Test 3 were 

between those in Tests 1 and 2. 
2-27

Figure 2.10-3. DP Test 3 Exterior Cabinet Damage

Figure 2.10-4. DP Test 3 Cabinet Top Deformation

0.024 

seconds; 

Panel 

openings

(a) (c)

(b)

0.024 

seconds
2-28

The arc moved downward to the bottom end of the vertical bus bars and where several 

centimeters of bus bar were melted, similar to Tests 1 and 2. More of the bus bars burned in 

Test 3 because of the higher energy and longer arc duration. The cables were burned 

completely, as in Test 1, and can be seen on the right side of the cabinet.

(a)

(b)

Figure 2.10-5. DP Test 3 Interior Damage
2-29

Temperatures measured at the slug locations are shown in Figure 2.10-6. Slug 8 showed the 

highest reading of all DP tests. Slug 8 responded strongly to the initial arc and the fire 

afterwards, and Slug 10 also had high response. There is an increase in temperatures due to 

the ensuing fire (between 2 and 8 minutes), and S10, located near the bottom of the cabinet, 

responded before S9, located near the top of the cabinet as expected since the cable fire 

started near the arc at the bottom.

NOTE: In this test, S8 was 0.31 m (1 ft) from the cabinet and S10 was 0.16 m (0.5 ft) from the 

cabinet, whereas in other tests, they were 0.91 m (3 ft) from the cabinet. This is indicated by 

the “*” in the series titles on the charts in Figure 2.10-6. The positions were changed to test the 

calorimeter sensitivity. The close distance for S8 contributed to its very high response. 

(a) (b)

Figure 2.10-6. DP Test 3 Calorimetry Data: Temperature

Table 2-8 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux of 187 

kW/m2 was at the rear (S8) and the maximum at a 0.91m (3 ft) on the left side (S5) was 27

kW/m2

. The maximum slug temperatures are also shown to indicate the maximum temperature 

a metal object could reach during or after the arc. 

Table 2-8. DP Test 3 Flux Results. 

Slug ΔT ( ̊C) Flux (kW/m2

) Max T ( ̊C) 

S5-LS-78-CL 9.2 27 62

S6-LS-47-CL 8.1 24 46

S7-LS-35-CL 7.6 22 36

S8-R-31-CL* 63.6 187* 137

S9-T-150-CL 4.5 13 54

S10-F-31-CL* 9.8 29 81

* S8 is 0.32 m (1 ft) from cabinet and S10 is 0.16 m (0.5 ft) from the cabinet. 
2-30

The temperatures measured by the TCs are seen in the Figure 2.10-7. As seen in previous 

tests, the highest temperatures were at the rear (TC2, TC3). However, it is not clear why TC2 

and TC3 are 100 to 140°C lower than in previous tests. At about 1.7 minutes, it appears that 

TC12 at the top of the cabinet is detecting the ensuing fire. All TCs show an unsteady 

response, indicating the turbulent nature of the ensuing fire. The thermocouples cannot 

practically be used to estimate flux. 

(a) (b)

Figure 2.10-7. DP Test 3 Thermocouple Data

Table 2-9. DP Test 3 TC Results.

TC Max T ( ̊C) 

TC2-R-24-LS 158

TC3-R-24-RS 198

TC11-LS-24-R 79

TC12-LS-77-CL 169

TC13-RS-24-CL 132
2-31

Figure 2.10-7 depicts the pressure measurement during the arc. Notice the result for the bottom

pressure, measured near the arc, has much more noise. There are spikes near 0.13 and 2.0

seconds at the top and several more around 2 seconds for the bottom pressure location. These 

appear to be noise. The bottom pressure closer to the arc had a slightly higher maximum and 

occurred earlier than the top that was further from the arc. The maximum pressures are

indicated by the arrows in Figure 2.10-8(c) and (d).The distinct sinusoidal responses on the 

bottom at the arc initiation had a frequency of about 195 Hz, similar to Test 2, and was probably 

caused by resonant pressure waves in the cabinet. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

(a) (b)

(c) (d)

Test 3 Pressure 1 Top

13.8 ± 2.1 kPa (2.0 ± 0.3 psi)

@ 0.0142 s

Test 3 Pressure 2 Bottom

13.8 ± 2.1 kPa (2.0 ± 0.3 psi)

@ 0.0072 s 

Figure 2.10-8. DP Test 3 Pressure
2-32

The total energy was 37.1 MJ, as shown in Figure 2.10-9. The energy analysis methods are in 

Appendix A. The “Energy” is calculated as volts multiplied current multiplied by the time step 

and each time step is shown. “Energy Total” is the cumulative sum of the energy in each time 

step. The result shows a smooth increase in the total energy, indicating that the energy 

provided by the KEMA power system was steady. 

Figure 2.10-9. DP Test 3 Arc Energy
2-33

2.11 DP Test 4 Key Observations (March 2015)

This cabinet test was initiated at 484 V and 50.3 kA, with a target duration of 2 seconds. The

arc quenched at 0.698 seconds due to a ground failure. The total energy was 8.3 MJ. Figures 

2.11-1 through 2.11-3 show the arc with High Speed (HS) camera, and High Definition (HD) 

camera, and Forward Looking Infrared (FLIR) camera. Note the arc flames extend to the 

postulated ZOI of 0.91m (3 ft) at 0.350 sec. There was no ensuing fire. 

(a) HS Start (b) HS 0.030 seconds

(c) HS 0.350 seconds (d) HS End 0.700 seconds

Figure 2.11-1. DP Test 4 Arc
2-34

Flames escaped the vents at the top and reached 0.91 m (3 ft), as shown in Figure 2.11-2. 

(a) Front (b) Rear

Figure 2.11-2. DP Test 4 Arc Flames

The FLIR camera indicated a maximum temperature of 350 ̊C at the top front “hot spot” that 

cooled 100 ̊C in 2 minutes, see Figure 2.11-3. The flux from this hot spot was detected by the 

slug calorimeter at the top front of the cabinet as discussed later. This hot spot on the panel 

near the arc was similar to previous DP tests in 2013. There was no ensuing fire. 

(a) 10 seconds after arc (b) 120 seconds after arc

Figure 2.11-3. DP Test 4 Thermal Images 
2-35

The damage is shown in Figure 2.11-4 through Figure 2.11-8. Figure 2.11-4 shows the exterior 

charring and discoloration on the top panel near the arc. There was minor deformation of the 

front and rear panels. The external cable tray showed no damage. The arc was shorter than 

planned because there was an external ground fault from a poor connection as shown in Figure 

2.11-7. Figure 2.11-6 shows the interior damage with charring and copper plated on the 

surfaces but no major fire. Figure 2.11-8 shows the interior bus bar damage. 

(a) (b)

(c) (d)

Figure 2.11-4. DP Test 4 Exterior Cabinet Damage
2-36

Figure 2.11-5. DP Test 4 External Cable 

Tray Damage

Figure 2.11-6. DP Test 4 Interior Cable 

Damage

(a) Before Failure (b) At failure

Figure 2.11-7. DP Test 4 Ground Fault during the Arc

(a) From Front (b) From Rear

Figure 2.11-8. DP Test 4 Bus Bar Damage at Arc Location

Ground attached to 

plate on cabinet to 

“neutral” on generator 

wye connection
2-37

Temperatures measured at the slug locations are shown in Figure 2.11-9. Slugs 3 to 5 had high 

noise during the arc probably due to electro-magnetic interference (EMI); the power supply was 

directly next to the slug calorimeters. The highest temperatures at the end of the arc were seen 

at the bottom of the cabinet (S7 and S8). These both showed cooling after the arc because 

there was no ensuing fire. After the arc the S1 calorimeter was the only calorimeter with 

increasing temperature caused by the hot spot on the front panel near the arc. 

(a) (b)

(c) (d)

Figure 2.11-9. DP Test 4 Calorimetry Data: Temperature
2-38

Table 2-10 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux of 91 

kW/m2 was at 0.91 m (3ft) at the top, left (S8). The maximum slug temperatures are also shown 

to indicate the maximum temperature a metal object would reach during the arc or after the arc. 

Table 2-10. DP Test 4 Flux Results.

Slug ΔT ( ̊C) Flux (kW/m2

) Max T ( ̊C) 

S1-F-76-CL 3.8 33 28

S2-F-16-CL 0.5 4 19

S3-RS-76-F 5.5 48 20* 

S4-RS-48-F 1.7 15 16* 

S5-RS-16-F 0.1 0.9 15* 

S6-R-76-CL 1.5 13 17

S7-R-16-CL 9.4 82 26

S8-LS-76-CL 10.4 91 27

S9-LS-48-CL 1.8 16 18

S10-LS-16-CL 0.8 7 16

* Maximums at the noise spikes in Figure 2.10-7 are excluded. 
2-39

PTs were used in this test to measure temperature; TCs were not used based on experience in 

previous DP tests. The temperatures measured by the PTs on the Cable Tray (CT) are seen in 

Figure 2.11-10. Table 2-11 shows the maximum PT temperature during the test. The PTs 

indicated the maximum temperature a metal object with gray surface emissivity of approximately 

0.85, 46 cm (18 in) above the cabinet in the rear could reach during the arc. 

As expected, the temperature in the center of the cable tray was the highest but all 

temperatures were low, indicating the heat released through the top rear vents below the cable 

tray were low. These low temperatures were consistent with no cable damage, as shown 

earlier. The maximum temperatures occurred at about 1.5 minutes after the arc, indicating that 

heat escaped from the cabinet after the arc heating the PT. 

Figure 2.11-10. DP Test 4 Cable Tray Plate Thermometer Data

Table 2-11. DP Test 4 Plate Thermometer Results.

PT Max T ( ̊C) 

PT-CT-1(RS) 32

PT-CT-2 33

PT-CT-3 35

PT-CT-4 30

PT-CT-5 (LS) 27
2-40

The pressures during the arc are seen in Figure 2.11-11. The top pressure, measured near the 

arc had a higher noise than at the bottom. The noise was significant towards the end of the 

arcing at the top; throughout the entire test, there was noise in the bottom measurement. A 

maximum pressure was indicated at the top of the cabinet, closer to the arc, before it was seen 

at the bottom of the cabinet. The maximum pressures are indicated by the arrows in Figure 

2.11-11(c) and (d).

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc. 

(a) (b)

(c) (d)

Test 4 Pressure 1 Top

33.1 ± 1.4 kPa (4.8 ± 0.2 psi)

@ 0.0105 sec

Test 4 Pressure 2 Bottom

23.4 ± 1.4 kPa (3.4 ± 0.2 psi)

@ 0.0139 sec

Figure 2.11-11. DP Test 4 Pressure
2-41

The total energy was 8.3 MJ, as shown in Figure 2.11-12. The energy analysis methods are in 

Appendix A. The “Energy” is calculated as volts multiplied current multiplied by the time step 

and each time step is shown. “Energy Total” is the cumulative sum of the energy in each time 

step. Note the arc quenched momentarily at about 0.3 seconds. 

Figure 2.11-12. DP Test 4 Arc Energy
2-42

2.12 DP Test 5 Key Observations (March 2015)

This cabinet test was initiated at 484 V and 44.7 kA with a target duration of 2 seconds. The arc 

quenched at 1.001 seconds with an additional restrike arc, 0.150 seconds in duration, and 0.55

seconds after the main arc. The total energy with the restrike was 14.3 MJ. Figure 2.12-1

shows the arc with High Speed (HS) camera, Figure 2.12-2 shows the HD camera images and 

Figure 2.12-3 shows the FLIR camera images. Note the arc flames extend to the NUREG/CR 

6850 specified ZOI of 0.9 m (3 ft) ZOI as in Figure 2.12-2. 

(a) HS Start (b) HS 0.030 seconds

(c) 0.5 seconds (d) HS Main Arc End

(e) Additional arc 0.4 seconds after main arc

Figure 2.12-1. DP Test 5 Arc
2-43

Flames escaped the vents at the top and reached the 0.91 m (3 ft), as seen in Figure 2.12-2. 

Some flames were visible inside the top vent on the left side of the cabinet immediately after the 

arc but these extinguished quickly, as seen in Figure 2.12-2(d). 

(a) Front start (b) Rear start

(c) Flame contact with calorimeter

(rear and side) (d) Flames in cabinet at end of arc

Figure 2.12-2. DP Test 5 Arc Flames
2-44

The FLIR camera was manually set at a fixed maximum of 150 ̊C. The flux from the hot spot is 

detected by the slug calorimeter at the top front of the cabinet. There was no ensuing fire.

(a) 10 seconds after arc

(b) 120 seconds after arc

Figure 2.12-3. DP Test 5 Thermal Images

The damage caused by the HEAF is shown in Figure 2.12-4 through Figure 2.12-6. Figure 

2.12-4 shows the exterior damage as char and discoloration on the top panel near the arc. 

There was minor deformation of the front and rear panels. The top front plate was dislodged 

during fire suppression. The external cable tray showed no damage. Figure 2.12-5 shows the 

interior damage with charring and copper plated on the surfaces but no major fire and no cable 

damage. Figure 2.12-6 shows the interior bus bar damage and the insulators that were 

dislodged when the arc reached that point. 
2-45

(a) Front in-situ (b) Front

(c) Rear cable tray (d) Rear

Figure 2.12-4. DP Test 5 Exterior Damage
2-46

(a) Plate on (b) Plate off

Figure 2.12-5. DP Test 5 Interior and Cable Damage

(a) With bus bar cover

(b) Without bus bar cover, insulator 

dislodged

(c) Top of bus bars with no cover

Figure 2.12-6. DP Test 5 Bus Bar Damage at Arc Location
2-47

Temperatures measured at the slug locations are shown Figure 2.12-7. The slug temperatures 

(in addition to the arc energy results shown in Section 2.12.4) show that the arc quenched at 

1.001 seconds then re-struck on its own and quenched at 1.659 seconds. Slugs 3 to 5 had high 

noise during the arc probably due to EMI; the power supply was directly next to the slug 

calorimeters. Note there were additional noise spikes at the restrike. The noise was very high 

in some places causing the data to go off scale, see Figure 2.12-7. The highest temperatures at 

the end of the arc were measured near the top of the cabinet (S8 and S7). S7 and S8 cooled 

after the arc because there was no ensuing fire. After the arc, the temperature was seen to 

increase at a hot spot on the front panel near the arc (S1). 

(a) (b)

(c) (d) (noise spikes off-scale)

Figure 2.12-7. DP Test 5 Calorimetry Data: Temperature

Table 2-12 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and the time the arc quenched. The maximum 

flux of 158 kW/m2 was at the top left side of the cabinet (S8). The maximum slug temperatures 

are also shown to indicate the maximum temperature a metal object could reach during or after 

the arc. 
2-48

Table 2-12. DP Test 5 Flux Results. 

Slug ΔT ( ̊C) Flux (kW/m2

) Max T ( ̊C) 

S1-F-76-CL 4.4 27 41

S2-F-16-CL 0.9 6 17*

S3-RS-76-F 5.8 36 23*

S4-RS-48-F 1.6 10 18*

S5-RS-16-F 0.1 0.6 16*

S6-R-76-CL 1.9 12 22

S7-R-16-CL 12.3 75 48

S8-LS-76-CL 25.7 158 51

S9-LS-48-CL 2.8 17 22

S10-LS-16-CL 1.3 8 20

*Maximums at the noise spikes in Figure 2.12-7 are excluded.

PTs were used in this test to measure temperature; TCs were not used based on experience in 

previous DP tests. The temperatures measured by the PTs on the CT are seen in Figure 

2.12-8. Table 2-13 shows the maximum PT temperature during the test. The PTs indicated the 

maximum temperature a metal object 46 cm (18 in) above the cabinet rear could reach during 

the arc. 

As expected, the temperature in the center of the cable tray was the highest but all 

temperatures were low indicating the heat released through the top rear vents below the cable 

tray was low. These low temperatures were consistent with no cable damage, as shown earlier. 

The maximum PT temperatures were higher than DP Test 4 because the duration was longer 

and there was more energy in Test 5. The maximum temperatures were about 1.5 minutes 

after the arc indicating that heat escaped from the cabinet after the arc heating the PT. 

Figure 2.12-8. DP Test 5 Cable Tray Plate Thermometer Data
2-49

Table 2-13. DP Test 5 Plate Thermometer Results.

PT Max T ( ̊C)

PT-CT-1(RS) 53

PT-CT-2 64

PT-CT-3 72

PT-CT-4 61

PT-CT-5 (LS) 52

The pressures during the arc are seen in Figure 2.12-9. There were noise spikes at 0.16, 0.24

seconds on the top and 0.365 seconds on the bottom. The top pressure, measured closer to 

the arc had a higher maximum and occurred earlier than the bottom pressure, which was 

measured further from the arc. The maximum pressures are indicated by the arrows in Figure 

2.12-9(c) and (d). There were additional pressure and noise spikes with the re-strike at 1.6 

seconds. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

(a) (b)

(c) (d)

Test 5 Pressure 1 Top

22.1 ± 2.1 kPa (3.2 ± 0.3 psi)

@ 0.0136 s 

Test 5 Pressure 2 Bottom

20.0 ± 1.4 kPa (2.9 ± 0.2 psi)

@ 0.0174 s 

Figure 2.12-9. DP Test 5 Pressure
2-50

The arc duration including the restrike was 1.659 seconds with total energy of 14.3 MJ, labeled 

as seen in Figure 2.12-10. The energy analysis methods are in Appendix A. The “Energy” is 

calculated as volts multiplied current multiplied by the time step and each time step is shown. 

“Energy Total” is the cumulative sum of the energy in each time step. There was a restrike of 

0.150 seconds that was 0.508 seconds after the main arc. 

Figure 2.12-10. DP Test 5 Arc Energy
2-51

2.13 DP Test 6 Key Observations (March 2015)

This cabinet test was initiated at 400 V and 51.8 kA with a target duration of 2 seconds. The arc 

quenched at 0.550 seconds and there were additional short duration arc restrikes at 0.60, 0.71, 

and 0.78 seconds after the arc initiation. The total energy including the restrikes was 8.2 MJ. 

Figure 2.13-1 through Figure 2.13-3 show the arc with the HS camera, the HD camera, and the 

FLIR camera. Note the arc flames extend to the NUREG/CR 6850 ZOI. There was no ensuing 

fire because the energy was too low.

For this test, a top steel plate cover was placed above the ends of the bus bars to act as a 

ground surface for the arc to attach in order to achieve the full 2-second arc duration but this did 

not work.

(a) HS Start (b) HS 0.030 seconds

(c) HS 0.350 seconds (d) HS End

Figure 2.13-1. DP Test 6 Arc
2-52

Flames escaped the vents at the top and reached the 0.91 m (3 ft), as shown in Figure 2.13-2. 

(a) Front Start (b) Rear Start – Note deformation of panels

(c) Right side

Figure 2.13-2. DP Test 6 Arc Flames

The FLIR camera indicated a maximum temperature of 360 °C at the top front “hot spot” that 

cooled by 140 °C in 2 minutes. The flux from this hot spot was detected by the slug calorimeter 

at the top front of the cabinet (see Figure 2.13-3). This hot spot was a little smaller than in Test 

4, with a similar arc. There was no ensuing fire. 

(a) 10 seconds after arc (b) 120 seconds after arc

Figure 2.13-3. DP Test 6 Thermal Images
2-53

Figure 2.13-4 shows the exterior charring and discoloration on the top panel near the arc. 

There was minor deformation of the front and rear panels. The external cable tray showed no 

damage. Figure 2.13-5 shows the interior damage with minor charring of the cables and copper 

plated onto the surfaces but no major fire. Figure 2.13-6 shows the interior bus bar damage 

was only burning at the top of the bus bars. 

(a) Left side (b) Front (c) Cable tray

(d) Rear and left bottom (e) Rear and right top

Figure 2.13-4. DP Test 6 Exterior Damage
2-54

Figure 2.13-5. DP Test 6 Interior Cable Damage

(a) Bus Bar Rear Cover (b) Without bus bar rear cover

(c) Top of bus bars with no cover plate

Figure 2.13-6. DP Test 6 Bus Bar Damage at Arc Location
2-55

Temperatures measured at the slug locations are shown in Figure 2.13-7. The slug 

temperatures (in addition to the arc energy results shown in Section 2.12.3) show that the arc 

quenched at 0.55 seconds then re-struck many times for short durations. Slugs 3 to 5 had high 

noise during the arc probably due to EMI; the power supply was located nearby. Note there 

were additional noise spikes at the restrike. The highest temperatures at the end of the arc 

were measured at the top of the cabinet (S1 and S8). Slug 8 cooled after the arc because there 

was no ensuing fire. After the arc, the temperature was seen to increase at a hot spot on the 

front panel near the arc (S1).

(a) (b)

(c) (d)

Figure 2.13-7. DP Test 6 Calorimetry Data: Temperature

Table 2-14 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and the time the arc quenched. The results

report a maximum flux of 73 kW/m2 at the left top of the cabinet (S8). The maximum slug 

temperatures are also shown to indicate the maximum temperature a metal object would obtain

during or after the arc. 
2-56

Table 2-14. DP Test 6 Flux Results.

Slug ΔT ( ̊C) Flux (kW/m2

) Max T ( ̊C) 

S1-F-76-CL 6.0 67 28

S2-F-16-CL 0.7 8 13*

S3-RS-76-F 4.2 47 11*

S4-RS-48-F 1.8 20 8*

S5-RS-16-F 0 0 8*

S6-R-76-CL 0.8 9 9 

S7-R-16-CL 3.2 35 17

S8-LS-76-CL 6.6 73 17

S9-LS-48-CL 1.9 21 14

S10-LS-16-CL 0.5 6 15

*Maximums at the noise spikes in Figure 2.13-7 are excluded.

PTs were used in this test to measure temperature; TCs were not used based on experience in 

previous DP tests. The temperatures measured by the PTs on the CT are seen in Figure 2.13-

9. Table 2.13-2 shows the maximum PT temperature during the test. The PTs indicated the 

maximum temperature a black-body, metal object 46 cm (18 in) above the cabinet rear could 

reach during the arc. 

Figure 2.13-8. DP Test 6 Cable Tray Plate Thermometer Data
2-57

As expected, the temperature in the center of the cable tray was the highest but all 

temperatures were low, indicating the heat released through the top rear vents below the cable 

tray was low. These low temperatures were consistent with no cable damage, as shown earlier. 

The temperature response was different than Tests DP-4 and DP-5 with the maximum occurring 

soon after the arc or in the case of the center temperature PT-CT-3 at the end of the arc. PTCT-3 also had a much higher temperature than test DP-4 even though the arc energies were 

nominally the same. It is theorized that flame/plasma escaped near the center rear of the 

cabinet in this test but this is not detectable on the videos and the discoloration and charring 

were similar in all tests. 

Table 2-15. DP Test 6 Plate Thermometer Results.

PT Max T ( ̊C)

PT-CT-1(RS) 21

PT-CT-2 35

PT-CT-3 61

PT-CT-4 33

PT-CT-5 (LS) 33
2-58

The pressures during the arc are shown in Figure 2.13-9. The top pressure, measured closer to 

the arc had a higher maximum and occurred earlier than the bottom pressure, which was 

measured further from the arc. At 0.67 and 0.77 seconds, there appears to be pressure spikes 

and noise related to the restrikes. The maximum pressures are indicated by the arrows in 

Figure 2.13-9 (c) and (d). 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

Test 6 Pressure 1 Top

16.5 ± 1.4 kPa (2.4 ± 0.2 psi)

@ 0.0111 s 

Test 6 Pressure 2 Bottom

13.1 ± 1.4 kPa (1.9 ± 0.2 psi)

@ 0.0142 s 

Figure 2.13-9. DP Test 6 Pressure
2-59

Figure 2.13-10 shows the initial arc was 0.55 seconds before the first extinction with a smooth 

and steady energy increase then there were several restrikes after the initial arc. The arc 

duration, including the restrikes was 0.781 seconds with total energy of 8.2 MJ. The energy 

analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied current 

multiplied by the time step and each time step is shown. “Energy Total” is the cumulative sum 

of the energy in each time step.

Figure 2.13-10. DP Test 6 Arc Energy
2-60 

2.14 DP Tests 1 through 6: Summary of Electrical Conditions 

The table shows the electrical conditions measured by KEMA. KEMA does not include any 

restrikes in their analysis so Tests 5 and 6 have shorter duration and lower energy than reported 

in the previous sections. 

Table 2-16. DP Tests Electrical Results. 

Test Arc 

Location

OCV

(V) Phase Sym

(kA)

Peak

(kA)

Sym 

@End 

(kA)

Curr. 

Dur.

(sec) 

(1)

Arc 

Energy

(MJ)

Freq 

@End 

(Hz)

Phase

Arc Volts

1 Bottom of 

bus bars 484

A 42.7 63.5 32.2

1.574

11

47.7 

A-N 248

B 40.0 66.3 28.1 8 B-N 220

C 47.2 71.2 29.7 9 C-N 231

AVG 43.3 67 30.0 Σ 28 AVG L-L 

404

2 Bottom of 

bus bars 484

A 40.7 60.8 33.6

1.446

10

47.7

A-N 246

B 35.9 60.5 25.6 8 B-N 211

C 38.6 66.9 35.5 9 C-N 225

AVG 38.4 62.73 31.6 Σ 27 AVG L-L 

394

3 Bottom of 

bus bars 484

A 41.9 60.7 33.6

2.011

14

46.6 

A-N 257

B 39.5 61.5 29.8 10 B-N 227

C 42.9 63.0 32.5 12 C-N 237

AVG 41.4 61.73 32.0 Σ 36 AVG L-L 

416

4 Top of bus 

bars 484

A 55.0 95.0 19.4

0.698

4

49.3

A-N 238

B 42.4 69.0 21.9 2 B-N 230

C 53.5 87.1 16.7 3 C-N 230

AVG 50.3 83.7 19.9 Σ9 (2) AVG L-L 

403

5 Top of bus 

bars 484

A 44.2 97.9 45.0

1.001

7

48.1

A-N 216

B 45.2 84.4 34.9 2 B-N 212

C 44.6 105.0 33.9 4 C-N 201

AVG 44.7 95.8 37.9 Σ13(2) AVG L-L 

363

6 Top of bus 

bars 400

A 51.1 100.9 30.5

0.550

4

50.0

A-N 177

B 52.9 93.7 32.7 1 B-N 176

C 51.3 105.8 27.8 2 C-N 176

AVG 51.8 100.1 30.3 Σ7(2) AVG L-L 

305

Notes:

(1) Does not include restrikes.

(2) As reported by KEMA instruments and results for the main arc. This does not include the 

restrike arcs after the main arc for Tests 5 (see section 2.12.4) and 6 (see section 2.13.4). 

Target energy was 35 MJ. 

(3) Target current duration was 2 seconds.
2-61

Table 2-17. Acronyms and Abbreviations for Electrical Test Results.

@End At the end of the test

AVG Average

Bot Bottom

Curr Current 

Dur Duration

Freq Frequency

L-L Line to Line

Max Maximum

N Neutral

OCV Open Circuit Voltage

Press Pressure

psi pounds per square inch

Sym Symmetrical

2.15 DP Tests 1 through 6 Qualitative Summary 

Although the tests in this series were planned to be similar, there were some differences in the 

results. Some important or interesting items to note are discussed below. 

1. Ensuing Fire: Only two of the tests (1, 3), with the arc at the bottom, resulted in ensuing 

fires in which all the internal combustibles were consumed. The damage to the internal 

combustibles in Test 2 suggests that an ensuing fire would be possible with a slightly 

more energetic arc; Test 2 was slightly less energetic than Test 1. The remaining three 

tests (4, 5, 6), with the arc at the top, showed little or no damage to the internal cables. 

Generally, the energy required for an ensuing fire was much less in the DP tests than 

what was required for the SWGR tests discussed later because the DP had less venting 

than the SWGR, so heat was better retained and lower electrical energy started the fire 

in the DP tests. 

2. Damage: All of the tests resulted in bus bar damage, as would be expected from 

oxidation during the arc. In Tests 1 and 3 several centimeters of the bus bar was 

consumed during the arc. Test 2 had bus bar losses which were not as severe as Tests 

1 or 3 because of the shorter arc duration. As expected Tests 4, 5 and 6 showed much 

less damage to the bus bars because of the very short arc durations.

Tests 1, 2 and 3 all showed heavy damage to the front of the cabinet, due to the high 

energy and ensuing fires. These tests also resulted in deformations of the panels. 

However, the deformation in Test 3 was smaller than Tests 1 and 2, probably because 

the pressure was relieved by the panel opening during the test. 

Tests 4, 5, 6 all resulted in minor deformation of the front and rear panels. These tests 

also included an external cable tray, which showed no damage in all tests. 
2-62

3. Calorimetry: The maximum measured flux varied between the tests. Tests 1, 2 and 3 

showed the maximum heat flux in the same location: at the bottom rear of the cabinet 

where the cabinet panel was directly exposed to the arc. The slug calorimeter located at 

the top left in Tests 4, 5 and 6 showed the maximum flux. Tests 4, 5 and 6 also showed 

high heat flux at the rear bottom (Tests 4 and 5 were particularly high), which was

unexpected because the arc was at the top, front of the cabinet. The flux at the top rear

was low for Tests 4, 5 and 6 that was also unexpected for the top arc location. 

In all the tests, there were spikes during the arc, which indicate large variations in the 

slug temperature from noise and because the energy produced during the arc is not 

uniformly distributed external to the cabinet and varies during the arc. Venting 

conditions and cabinet integrity such as DP panel deformation and the associated 

plasma and flame leakage also affect the slug responses seen during the test series

4. Temperature: Thermocouples to measure air temperature were only used in Tests 1, 2 

and 3. Since the arcs were in the rear of the cabinets, the highest temperatures 

occurred in this area for all three tests. However, the temperatures for Test 2 were less 

than Tests 1 and 3 because the energy was lower.

Plate thermometers were used for Tests 4, 5 and 6 in the external cable trays to 

measure temperature above the cabinet. The highest temperatures were seen in the 

center of the cable trays as expected. Tests 5 and 6 had similar maximum temperatures 

whereas Test 4 showed a lower temperature, probably related to the random nature of 

flames and plasma exiting the rear of the cabinet at the top just below the cable tray.

5. Pressure Data: In Tests 1 through 5, the highest pressures were measured near the 

arc; Tests 1 through 3 at the bottom, and Tests 4 through 6 at the top of the cabinets, as 

expected. Tests 4 through 6 had considerably higher pressures than Tests 1 through 3, 

perhaps because the top location had a different flow path from the initial arc shock to 

the PRT.

The pressure was, on average, higher for the DP cabinets than in the SWGR cabinets 

(Chapters 4 and 5) because there was less vent area in the DP and the SWGR vent was 

directly above the arc. Additionally, the SWGR had interior walls between the arc and 

the pressure measurement points. The cabinet walls and roof exhibited bending and 

deformation of several centimeters. The DP also had thinner materials for the walls and 

doors than the SWGR. 

6. Arc Energy: In all tests the total energy was proportional to the arc duration for the given

electrical testing conditions, as expected. Tests 1 through 3 showed a smooth increase 

of the total energy during the arc indicating stable arc conditions for the bottom bus bar 

and cabinet arrangement. Tests 4 through 6 showed severe decreases in the energy 

and restrikes indicating less stable arc conditions at the top of the cabinet. Based on the 

occurrence of ensuing fires, the electrical energy threshold for an ensuing internal cable 

fire was about 28 MJ. 
3-1 

3 Motor Control Center HEAF TEST – KEMA (May 2013) 

3.1 MCC Test Overview 

The purpose of these tests was to obtain the basic HEAF data such as duration, energy, flux, 

temperatures, pressures, and ensuing fire effects for three (3) Motor Control Centers (MCC) at 

KEMA on May 22-23, 2013. 

3.2 MCC Summary of Results 

Each test consisted of one GE Series 7700 MCC with a horizontal bus rating of 2.8 kA. 

Japanese CV-2 cable that is typical of power cable was added as the combustible load. 

The key test parameters and results are in Table 3-1. The target test values were nominally 

480 V and 63 kA bolted fault current and the symmetric current achieved was nominally 21 to 46 

kA. The target arc duration was 2 seconds. 

There were no ensuing fires in any of the tests. The resulting arc energies for the tests were 

low, and the cabinets panels bent or came off, allowing the heat to escape out of the cabinets. 

The small bus bars bent away from each other in every test and increased the distance between 

the bus bars so the arcs quenched quickly (all tests resulted in less than 1 second arc duration). 

The key results from the MCC tests at KEMA were: 

• Hot gases and plasma can travel from the initial arc point to other locations in the 

cabinet and cause a second and in this case higher energy arc (Test 2). 

• MCC cabinets have few vents and are “tight” and minimally ventilated, causing higher 

pressure increases, as to be expected. 

• It is difficult to maintain a steady arc with 480 V, which was also the case in the DP tests. 

The bus bars bent away from each other due to the strong magnetic fields from large 

current imbalances in the three phases during the arc causing large arc gaps, and

providing a condition under which the voltage could not sustain the arc. 
3-2 

Table 3-1. MCC Test Summary of Results.

Test

Volt (V)

(1)

Current

(kA) (2)

Test 

Peak 

Current 

(kA) (3)

Arc

duration 

(sec) (4)

Arc 

Energy

(MJ) 

Internal 

Max 

Press

(kPa/psi)

External 

Max Flux 

(9) 

(kW/m2)

Ensuing fire?

Key 

Observations

(10)

1 

484 / 432

21.4 / 

11.2

45.9 2.0

0.145 1.7 37.9 ± 1.45.5 ± 0.2 

38

(6) 

No. Low 

duration and low 

energy. Bottom 

arc.

2 

492 / 384

34.1 / 

25.2

80.3 2.0

0.952 (5) 17.4 30.3 ± 1.44.4 ± 0.2 

46

(7) (11) 

No. Two Arcsarc moved from 

bottom to top of 

MCC

3 

492 / 384

40.4 / 

26.8

67.7 2.0

0.256 4.2 31.0 ± 1.44.5 ± 0.2

102

(8) No. Bottom arc.

4 

492 / 374

46.4 / 

37.0

91.0 2.0

0.922 17.6 63.4 ± 1.49.2 ± 0.2

65

(9) 

No. Top arc was 

planned and 

occurred.

Notes: 

(1) The voltage is shown as the target voltage / arc Line-to- Line (L-L) voltage. 

(2) The symmetric arc current slowly drops during the test as the arc impedance increases. 

This shows the test start current/ test end current. These are average currents of all 3 

phases. 

(3) This is the peak current for any phase or time, usually the asymmetric current at the start.

(4) The duration is shown as the target duration and the actual test duration is below it. 

(5) This is for the total duration of the 2 arcs: one at the bottom then one at the top.

(6) The maximum flux was seen on the side at 0.91 m (3 ft), and 0.9 m (35.5 in) from the floor

(S1). 

(7) The maximum flux was seen on the rear at 1.5 m (5 ft), behind the cabinet, 79 cm (31 in) 

from the floor (S6). Flames reached and contacted the slug calorimeters on the left side of 

the cabinet (S1, S2, and S3). 

(8) The maximum flux was seen at the bottom, left side at 0.91 m (3 ft) (S1), which viewed the 

opening in the bottom left of the cabinet. The left side slug at 0.91 m (3ft) saw flames 

directly but was not contacted by the flame (S1). 

(9) The maximum valid flux was seen at the top, 1.5 m (5 ft) above the cabinet that could 

directly view the flames at the top of the cabinet (S4). The flux at the rear (S6) was greater 

but the slug calorimeter was closer than 0.91 meters to the cabinet. Three other slugs on 

the left side also had higher fluxes but flames made contact with these slugs and the flux 

measurements were not valid. 

(10) No ensuing fires so the maximum flux was during the arc or within 1 second after. Low flux 

in general. The arc caused large releases of hot gases and fire from the cabinet to the left 

toward the slug calorimeters. These gases and fire contacted the calorimeters increasing 

their temperature so they cannot measure the flux. As discussed in Appendix A, results 

from slugs contacted by flames are not reported. 
3-3 

3.3 MCC Test Configuration

GE Series 7700 equipment was used in the test because it is most similar to Japanese 

equipment. The MCC is nominally 0.51 m wide by 2.32 m high by 0.51 m deep (20 in wide by

91.5 in high and 20 in deep). The test configuration is shown in Figure 3.3-1 and Figure 3.3-2. 

The latter figure shows the three cabinets together in a line-up and each cabinet was tested 

individually. The combustible load consisted of plastics and wire in three motor starter sections, 

the two switch sections at the bottom and CV-2 cables. 

There were horizontal and vertical buses in each cabinet. The horizontal buses were extended 

outside the cabinet to the connection for the incoming KEMA power supply. Wire per IEEE 

C37.20.7 for low voltage tests was connected to the three phase of the buses to make the arc at 

the bottom of the MCC. This location was selected conservatively below the combustibles to 

provide the highest likelihood of causing a fire in the cabinet. The motor starter sections were 

not connected to the bus because the component could have arced at the connection rather 

than at the arc wire. The bottom 15.24 cm (6 in) of the bus covers (white) called “arc chutes” 

were removed to place the wire then the covers were put back in place in Test 1. In Tests 2 and 

3, the lower 61 cm (24 in) of the arc chute were removed to ensure the arc chutes did not 

extinguish the arc prematurely. Test 4 was at the top bus bars and the arc chutes were not 

involved. 

In Tests 2 through 4, the cabinets were wrapped with six (6) steel bands around the MCC, two 

vertically and three horizontally. This was done to prevent the panels from blowing off the MCC, 

as was seen in MCC Test 1.

Figure 3.3-1. MCC Test Configuration

Existing bus bar, 61 cm (24 in)

Bus bar extensions

Section A-A Test Cable Layout

Jumper wire 

#10AWG 

Fine Strand

Detail A
3-4 

Figure 3.3-2. MCC for Test

Each MCC section has 

some combustibles like the 

plastic on the breaker, the 

starter and some wires.

1.5 m (5ft)

 Cabinet A Cabinet B Cabinet C
3-5 

3.4 MCC Cable Combustible Loading 

Japanese CV-2 cable with heat resistant PVC sheath and XLPE insulation was used for the 

combustible cable load to simulate the power cables that are typically used from the MCC 

controllers to motors. The number of CV-2 cables was realistic for motor and control 

connections for a typical section/bucket. There were five (5) CV-2 cables in each of the top 

three (3) sections that dropped from each section to the bottom of the cabinet. Three (3) CV-2 

cables represented the power cable and two (2) CV-2 cables represented the control cables. 

For the bottom two sections, only power cable was needed and three (3) CV-2 cables were 

used. The total cable combustible load was 18.29 m (60 ft) of CV-2 or 5 kg. Cable properties 

are in Appendix C. 

Figure 3.4-1. MCC Cable Combustible Load
3-6 

3.5 MCC Temperature and Heat Flux Instrumentation

Slug calorimeters (slug, S) and thermocouples (TC) locations for these tests are shown in 

Figure 3.5-1. Slugs were nominally 0.91 m (3 ft) from the cabinet sides (S1, S2, S3, S5, S6) 

and 1.5 m (5 ft) from the cabinet top (S4). TCs were 15.2 cm (6 in) from the cabinet in open air 

and not in contact with the cabinet. The air temperatures are likely much lower than the actual 

metal temperature. Therefore, the temperatures are only a qualitative measure of thermal 

behavior. Table 3.5-1 shows the slug calorimeter and MCC locations. 

Figure 3.5-1. MCC Calorimeter and TC Location

S4

S3

S1

S2

S5

S6

S1, S2, S3

S4

TC 5

TC 4

TC 3

TC 1

TC 2
3-7 

Table 3-2. MCC Calorimeter and TC Locations. 

Slug or 

TC

From Floor

cm (in) Position Slug or TC Name

S1 90 (35.5) Left side (LS) S1-LS-36-LS

S2 119 (47) Left side S2-LS-47-CL

S3 198 (78) Left side S3-LS-78-CL

S4 381 (150) Top (T) S4-T-150-CL

S5 79 (31) Front (F) S5-F-31-CL

S6 79 (31) Rear (R) S6-R-31-CL

TC1 198 (78) Rear TC1-R-78-CL

TC2 61 (24) Rear TC2-R-24-CL

TC3 61 (24) Left Side TC3-LS-24-R 

TC4 61 (24) Left Side TC4-LS-24-F 

TC5 61 (24) Right Side (RS) TC5-RS-24-CL

*TC3, TC4, TC5 data was corrupted for all tests and no results are provided. 
3-8 

3.6 MCC Test Pressure Instrumentation 

Two Dynisco PT150-50 strain-gauge type pressure transducers were used. The pressure 

transducer was isolated from the cabinet with a fiber-reinforced rubber tube. The sensors are 

on the left side of the cabinet. The gauges were in PVC pipe to protect them from fire.

Figure 3.6-1. MCC Pressure Measurement Locations
3-9 

3.7 MCC Test 1 Key Observations

This cabinet test was initiated at 484 V and 21.4 kA with a target duration of 2 seconds. The arc 

quenched at 0.145 seconds with a total energy of 1.7 MJ. Figure 3.7-1 shows the explosion 

after the arc at about 0.050 seconds. 

(a) (b)

Figure 3.7-1. MCC Test 1 Arc

There was no ensuing fire and the thermal image in Figure 3.7-2 shows only a brief burst of 

heat from hot gas escaping at the bottom at the time of the arc. The FLIR camera was set at 

the maximum 750  ̊C and no residual heat was detected. The only visible response by the FLIR 

was during the arc. 

Figure 3.7-2. MCC Test 1 Thermal Image

(the yellow box represents the cabinet perimeter)
3-10

Damage was minor with only light charring and soot at the bottom of the cabinet and on a white 

external poster-board target, as seen in Figure 3.7-3(a). As shown in Figure 3.7-3(b) the top 

rear panel blew off during the arc; to avoid this in the future tests, steel bands were used to hold 

the cabinet panels in place. 

(a) No major exterior damage (b) Rear Panel Blew Off

Figure 3.7-3. MCC Test 1 Exterior Damage

Figure 3.7-4(a) shows only minor soot deposits on the interior, and no evidence of an ensuing 

cable fire (cables are on the right in the picture). Figure 3.7-4(b) shows no damage to the white 

plastic composite arc chutes covering the bus bars and only minor melting of the strut near the 

ends of the bus bars where the arc briefly attached. The bus bars burned upward and cannot 

be seen in the photo under the arc chutes. The bottom 15.24 cm (6 in) of bus duct had been 

removed before the test to expose the bus bars. Based on this result, it appeared that the arc 

chutes were obstructing the arc path, causing the arc to extinguish. In order to allow the arc to 

fully occur, the arc chutes were cut further from the end of the bus bars in Tests 2 and 3. 
3-11

(a) No cable fire

(b) No major damage to arc chutes (c) lower bus bar damage

Figure 3.7-4. Test 1 Exterior and Interior Damage
3-12

Temperatures measured at the slug locations are shown in Figure 3.7-5. The arc quenched at 

0.145 seconds. Slugs S5 and S6 recorded high noise during the arc, probably due to EMI; the 

power supply was directly next to the slug calorimeters. The highest temperature at the end of 

the arc was measured on the left side, 90 cm (35.5 in) from the floor (S1). After the arc these 

temperatures stopped increasing and there was no flux after that since there was no ensuing 

fire. Other slugs had a similar steady temperature response after the arc. 

(a) (b)

Figure 3.7-5. MCC Test 1 Calorimetry Temperature Data 

Table 3-3 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux of 38 

kW/m2 is reported at the bottom, left side (S1). The maximum slug temperatures are also 

shown to indicate the maximum temperature a metal object could reach during the arc.

Table 3-3. MCC Test 1 Flux Results. 

Slug ΔT ( ̊C) Flux (kW/m2

) Max T  ̊(C) 

S1-LS-36-LS 1.9 38 33

S2-LS-47-CL 0.8 16 32

S3-LS-78-CL 0.4 8 31

S4-T-150-CL 0.1 2 32

S5-F-31-CL 0.1 2 40

S6-R-35-CL 1.8 36 36
3-13

The temperatures measured by the TCs are shown in the Figure 3.7-6. Table 3-4 shows the 

maximum temperature results. The thermocouple maximum temperature is a general indication 

of the air temperature 15.2 cm (6 in) from the cabinet. The highest recorded temperature was 

seen at TC1, located at the rear top where the panel blew off. The TCs cannot be used to 

estimate flux. 

(a) (b)

Figure 3.7-6. MCC Test 1 Thermocouple Data

Table 3-4. MCC Test 1 TC Results. 

TC Max T ( ̊C) 

TC1-R-78-CL 38

TC2-R-24-CL 67

TC3-LS-24-R * 

TC4-LS-24-F * 

*Data was corrupt
3-14

The pressures during the arc are seen in Figure 3.7-7. The two pressure probes, top and 

bottom, exhibited similar noise. The maximum pressure at the bottom, measured closer to the 

arc was higher and occurred earlier than the pressure measurement at the top. The top 

pressure measurement probe was further from the arc location. The maximum pressures are 

indicated by the arrows in Figure 3.7-7(c) and (d). The pressure dropped quickly and the 

pressure after the peak was low when the back panel blew off. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

(a) (b)

(c) (d)

Test 1 Pressure 1 Top

27.6 ± 2.1 kPa (4.0 ± 0.3 psi)

@ 0.0080 s

Test 1 Pressure 2 Bottom

37.9 ± 1.4 kPa (15.5 ± 0.2 psi)

@ 0.0042 s

Figure 3.7-7. MCC Test 1 Pressure Data
3-15

The arc duration was 0.145 seconds with total energy of 1.7 MJ, seen in Figure 3.7-8. The 

energy analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied 

current multiplied by the time step and each time step is shown. “Energy Total” is the 

cumulative sum of the energy in each time step.

Figure 3.7-8. MCC Test 1 Arc Energy
3-16

3.8 MCC Test 2 Key Observations 

This cabinet test was initiated at 492 V and 34.1 kA with a target duration of 2 seconds. The arc 

quenched at 0.952 seconds with a total energy of 17.4 MJ. There was no ensuing internal cable 

fire, and only soot deposits on the cables. 

The Test 2 arc started at the bottom of the cabinet, as planned, but quenched at about 0.1 

seconds then the hot gases from the initial arc moved to the top of the cabinet and caused the 

horizontal bus bars at the top of the cabinet to arc to the left side of the cabinet at 0.141 

seconds as shown in Figure 3.8-1. This additional arc lasted until 0.952 seconds after arc 

initiation and caused significant damage to the cabinet. 

As discussed earlier, six steel bands were wrapped around the MCC to hold the cabinet panels 

in place. In addition, to prevent the arc chutes from interfering with the arc, the bottom 61 cm 

(24 in) of the arc chutes were cut and removed. 

(a) Arc start (b) Arc maximum

Figure 3.8-1. MCC Test 2 Arcs at Bottom and Top

The arc sequence is shown in Figure 3.8-2: (a) the initial arc at 0.018 seconds, (b) the initial arc 

almost quenches and is not visible, (c) the hot gases traveled up the right side of the cabinet 

and some escaped out of the panels (at this point the gases are about half way up the cabinet), 

and (d) the hot gases caused the arc at the top horizontal bus bars. This is the only test where 

the arc quenched at the ignition point at the arc wire followed by the hot gases causing a 

second arc in a separate location. 
3-17

(a) 0.018 seconds (b) 0.115 seconds

(c) 0.141 seconds (d) 0.192 seconds

Figure 3.8-2. MCC Test 2 Sequence for 2 Arcs

(the cabinet is outlined in yellow)

Figure 3.8-3 shows thermal images during the arc. Based on the poor sensitivity in the MCC 

Test 1 FLIR images, the FLIR was set to a fixed 350  ̊C (662  ̊F) maximum temperature. Figure 

3.8-3(a) shows a plume of plasma and hot gas coming out of the rectangular openings at the left 

bottom of the cabinet and gases escaping from the openings to the left. The heat was initially at 

the arc at the bottom then the heat progressed up the right side of the cabinet, as shown in 

Figure 3.8-3(b) and the second arc the top left occurred. Figure 3.8-3(c) shows there were large 

balls of hot gas and plasma on the left side of the cabinet, extending out 1 to 2 meters. 

However, 30 seconds after the arc shows there were no internal fires on the left rear even 

where the hot gas contacted the target cardboard poster boards (see Figure 3.8-3(d)). Some 

poster boards that were placed as targets near the front left out of view of the FLIR did ignite. 

After the arc extinguished, cooling was seen in the area at the top where the panels had burned 

through, as shown in Figure 3.8-3(e), indicating no sustained internal fire. The cabinet exterior 

showed no other hotspots that would indicate an internal fire as the top panels cooled. 
3-18

(a) Start of Arc (b) Arc Moving to Top

(c) Arc at Top (d) 30 Seconds after arc

(e) 3 minutes after arc

Figure 3.8-3. MCC Test 2 Thermal Images
3-19

Figure 3.8-4(a) shows there was heavy soot damage and copper coating on the exterior of the 

cabinets with heavy damage at the top. No panels were blown off but the front top panel 

opened about 5 cm (2 in). Figure 3.8-4(b) shows that the exterior top left panel was burned 

through by the strong arc at the top bus bars. About 5 cm (2 in) of the bus bars burned until the 

arc reached the vertical strut supporting the bus bars and the arc extinguished, as shown in 

Figure 3.8-4(c). 

(a) Exterior damage (b) Top Arc Burn Through

(c) Top Bus Bar Damage

Figure 3.8-4. MCC Test 2 Exterior Damage
3-20

Figure 3.8-5(a) shows that the thin bus bars at the bottom bent outward where the bottom arc 

quickly quenched. The arc appears to have attached to the bottom horizontal strut and when 

the bus bars bent they were too far from the bar to maintain the arc. Figure 3.8-5(b) shows 

interior soot deposits along the cables but the internal cables on the right did not ignite. 

(a) Bottom Arc Damage (b) No cable fire

Figure 3.8-5. MCC Test 2 Interior Damage
3-21

Temperatures measured at the slug locations are shown in Figure 3.8-6. The arc quenched at 

0.952 seconds. Several slugs had high noise during the arc, probably due to EMI; the power 

supply was directly next to the slug calorimeters. The highest temperature at the end of the arc 

was at top left side (S3), which was struck by flames. The highest slug response that was not 

struck by flames was at the rear of the cabinet (S6). 

All slugs except S2 showed cooling temperatures after the arc because there was no ensuing 

fire. The temperature is increasing after 0.2 minutes at the left side (S2) because the poster

board used to detect debris ignited and the slug was in the flames. Although Slug 5 was only 

12.7 cm (5 in) from the panel (rather than the usual 0.91 m (3 ft)), it had low response. 

The left side slugs (S1 through S3) had very high response from the arc breaking through the 

top left panel and the hot gases and plasma exiting directly to the slugs. 

(a) (b)

Figure 3.8-6. MCC Test 2 Calorimetry Temperature Data

Table 3-5 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum valid flux of 46 

kW/m2

, measured at the rear (S6) is reported. The maximum slug temperatures are also shown 

to indicate the maximum temperature a metal object would reach during the arc and after the 

arc. Except for at the left side, center (S2), all of these maximums were shortly after the arc

extinguished. At this location (S2), the maximum was during the external ensuing fire (the 

poster boards in front of the cabinet). 
3-22

Table 3-5. MCC Test 2 Flux Results. 

Slug ΔT ( ̊C) Flux (kW/m2

) Max T ( ̊C) 

S1-LS-36-LS 47.7 246 85

S2-LS-47-CL 54.6 282* 153

S3-LS-78-CL 140.6 736* 175

S4-T-150-CL 2.4 12 35

S5-F-31-CL 3.4 17 30

S6-R-35-CL 9.0 46 73

* Slugs in contact with flames, therefore calculated flux is not valid, see Appendix A, Section A.1 

The temperatures measured by the TCs are shown in Figure 3.8-7 and Table 3-6 shows the 

maximum temperature results. The thermocouple maximum temperature is a general indication 

of the air temperature 15.2 cm (6 in) from the cabinet and as expected TC1 at the rear top 

where near the final arc location had the highest temperature. TC1 was also near the point 

where the hot gases and plasma were released as shown in Figure 3.8-3(b). The TCs cannot 

be used to practically estimate flux. 

(a) (b)

Figure 3.8-7. MCC Test 2 Thermocouple Data

Table 3-6. MCC Test 2 TC Results. 

TC Max T ( ̊C) 

TC1-R-78-CL 970

TC2-R-24-CL 65

TC3-LS-24-R * 

TC4-LS-24-F * 

TC5-RS-24-CL * 

*Data was corrupt
3-23

The pressures during the arc are seen in Figure 3.8-8. The two pressure probes, top and 

bottom, exhibited similar noise. There were noise spikes at 0.87 seconds on the top and 0.64 

seconds on the bottom. The bottom pressure, measured closer to the arc, had a higher 

maximum and occurred earlier than the top pressure, which was measured further from the arc. 

The maximum pressures are indicated by the arrows in Figure 3.8-8(c) and (d). 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

(a) (b)

(c) (d)

Test 2 Pressure 1 Top

24.1 ± 1.4 kPa (3.5 ± 0.2 psi)

@ 0.0082 s

Test 2 Pressure 2 Bottom

30.3 ± 1.4 kPa (4.4 ± 0.2 psi)

@ 0.0048 s

Figure 3.8-8. MCC Test 2 Pressure Data
3-24

The arc duration including at the bottom and top positions was 0.952 seconds with total energy 

of 17.4 MJ, as shown in Figure 3.8-9. The energy analysis methods are in Appendix A. The 

“Energy” is calculated as volts multiplied current multiplied by the time step and each time step 

is shown. “Energy total” is the cumulative sum of the energy in each time step. The initial arc at 

the bottom almost quenched about 0.154 seconds then the arc re-struck in the top position 0.19 

seconds. 

Figure 3.8-9. MCC Test 2 Arc Energy
3-25

3.9 MCC Test 3 Key Observations 

This cabinet test was initiated at 484 V and 40.4 kA with a target duration of 2 seconds. The arc 

quenched at 0.256 seconds with a total energy of 4.2 MJ. For Test 3, the arc chutes were 

removed as in Test 2. Red board bands were placed across the bus bars at the bottom in an 

attempt to prevent the bus bar from bending, as observed in MCC Test 2. The arc broke the 

bands and the arc quenched. Figure 3.9-1 shows the arc at about 0.050 seconds. The arc was 

very short and the damage was minor. There was no ensuing cable fire. 

(a) Arc start (b) Arc maximum

Figure 3.9-1. MCC Test 3 Arc

Figure 3.9-2 shows FLIR images from the rear, left corner of the tests cell (other videos are from 

the front) to get a close view if the arc moved to the top of the MCC. In these views the right 

side of the cabinet is on the left side and the camera was turned upward to view more of the 

MCC. The FLIR was set at a constant 355  ̊C (671  ̊F) maximum. Arc plasma and hot gases 

escaped the lower part of the cabinet during the arc. After the arc, there was no detectable 

indication of high temperatures on the exterior of the cabinet or of internal fires. 

(a) Arc Start (b) Arc Maximum

Figure 3.9-2. MCC Test 3 Thermal Images (Rear View) 
3-26

Figure 3.9-3 shows the only major exterior damage; the rear top panel opened about a 1 

centimeter (0.5 in) but was held in place by steel bands and did not blow off. 

Figure 3.9-3. MCC Test 3 Exterior Damage.

Figure 3.9-4 shows the lower bus bar damage for the arc position in Test 3. Figure 3.9-4(a) 

shows the bus bar configuration before the test. The thin, copper bus bars were held in place 

by three red boards (fiber-reinforced composite) at approximately 20.3 cm (8 in), 35.6 cm (14

in), and 50.8 cm (20 in) from the bottom as shown in Figure 3.9-4(a). Figure 3.9-4(b) and (c)

shows that the bus bars bent despite the bands and caused the arc to quench. 

(a) Bus Bars Before Test (b) Bus bars bent (c) Bus Bar Damage

Figure 3.9-4. MCC Test 3 Interior Damage
3-27

Temperatures measured at the slug locations are shown in Figure 3.9-5. The arc quenched at 

0.256 seconds. All slugs had high noise during the test, probably due to EMI; the power supply 

was directly next to the slug calorimeters. The highest temperature at the end of the arc was 

measured at the bottom left side (S1) but this slug was contacted by flames when the arc 

initiated. S2 and S3 were also contacted by flames. All slugs had steady temperatures after the 

arc because there was no ensuing fire. 

(a) (b)

Figure 3.9-5. MCC Test 3 Calorimetry Data

Table 3-7 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux of 102 

kW/m2 was seen at the left side (S1). The maximum slug temperatures are also shown to 

indicate the maximum temperature a metal object could reach. 

Table 3-7. MCC Test 3 Flux Results. 

Slug ΔT ( ̊C) Flux (kW/m2

) Max T  ̊(C)

S1-LS-36-LS 5.0 102 20

S2-LS-47-CL 2.1 43 18

S3-LS-78-CL 0.3 6 16

S4-T-150-CL 0.2 4 17

S5-F-31-CL 1.2 24 18

S6-R-35-CL 2.2 45 18
3-28

The temperatures measured by the TCs are shown in the Figure 3.9-6. Table 3-8 shows the 

maximum temperature results. The thermocouple maximum temperature is a general indication 

of the air temperature 15.2 cm (6 in) from the cabinet and as expected TC2 at the rear bottom 

near the arc had the highest temperature. The TC2 temperatures were lower than expected 

because hot gas should have escaped from the panel opening shown in Figure 3.9-3. The TCs 

cannot be used to estimate flux. 

(a) (b)

Figure 3.9-6. MCC Test 3 Thermocouple Data

Table 3-8. MCC Test 3 TC Results.

TC Max T ( ̊C) 

TC1-R-78-CL 32

TC2-R-24-CL 42

TC3-LS-24-R * 

TC4-LS-24-F * 

TC5-RS-24-CL * 

*Data was corrupt
3-29

The pressures during the arc are seen in Figure 3.9-7. The two pressure probes, top and 

bottom, exhibited similar noise. There was a significant spike in noise at 0.24 seconds at the 

bottom pressure. The bottom pressure, measured closer to the arc, had a higher maximum and 

occurred earlier than the top pressure, which was measured further from the arc. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

(a) (b)

(c) (d)

Test 3 Pressure 1 Top

25.5 ± 1.4kPa (3.7 ± 0.3 psi)

@ 0.0088 s 

Test 3 Pressure 2 Bottom

31.0 ± 1.4 kPa (4.5 ± 0.2 psi)

@ 0.0149 s

Figure 3.9-7. MCC Test 3 Pressure Data
3-30

The arc duration was 0.256 seconds with total energy of 4.2 MJ, as seen in Figure 3.9-8. The 

energy analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied 

current multiplied by the time step and each time step is shown. “Energy total” is the cumulative 

sum of the energy in each time step. 

Figure 3.9-8. MCC Test 3 Arc Energy
3-31

3.10 MCC Test 4 Key Observations 

The cabinet from Test 3 was left in place and reused for Test 4 with the arc wire at the top bus 

bars to repeat the second arc that was observed in Test 2. This cabinet test was initiated at 492 

V and 46.4 kA and a target duration of 2 seconds. The arc quenched at 0.922 seconds with a 

total energy of 17.6 MJ. Figure 3.10-1 shows the explosion at 0.1 sec and 0.8 sec after the arc. 

There was a small metal fire at the top bus bars for a few minutes was but there was no major 

ensuing cable fire. The plasma escaped through the small cracks between the panels and 

burned through the steel bands. The top front panel was blown off and traveled about 3.66 m 

(12 ft) as shown in Figure 3.10-1(a). 

(a) 0.1 sec after arc (b) 0.8 sec after arc

Figure 3.10-1. MCC Test 4 Arc 

Figure 3.10-2 shows FLIR images (set at a constant 355  ̊C (671  ̊F) maximum) from the rear, 

left corner of the test cell. In these views the right side of the cabinet is on the left side of the 

view. Arc plasma and hot gases escaped the top part of the cabinet during the arc when the top 

and rear front panels blew off, and the top, left panel opened. After the arc, there was no 

detectable indication of high temperatures on the exterior of the cabinet or of internal fires. 

(a) Arc Start (b) Arc End

Figure 3.10-2. MCC Test 4 Thermal Images (Rear View) 
3-32

Figure 3.10-3(a) shows the damage caused by the arc was extensive at the top of the cabinet. 

The top rear panel blew off, as indicated by the white arrow, when the steel bands were burned 

through by plasma escaping the cabinet. Figure 3.10-3(b) shows that the arc burned through 

the top right panel, similar to MCC Test 2 and it almost detached from the cabinet. The exterior 

had charring, soot damage, and copper disposition and the MCCB panel on the front top also 

opened. The top front cover was blown off during the arc. The heat caused the metal in the 

area of the left top to glow for several minutes after the arc as seen from the front view in Figure 

3.10-3(c). 

(a) Top rear panel blew off (b) Top bus bars

(c) Glowing metal after arc

Figure 3.10-3. MCC Test 4 Exterior Damage 

Figure 3.10-4(a) shows that about 5 cm (2 in) of the copper bus bars burned during the arc 

before the arc progression ended at the vertical bus support; the yellow dashed lines show the 

initial length of the bus bars before oxidation. There was similar bus bar loss in MCC Test 2. 

Figure 3.10-4(b) shows that there was soot inside the cabinet but there were only small 

amounts inside the switch and motor starter sections that were protected by the doors on the 

bucket (the door is open in the photo). The cables were not charred, just coated with soot and 
3-33

there was no ensuing cable fire. Most of the energy escaped through the open panels and did 

not build up inside the cabinet. 

(a) Bus Bar Damage at Top (b) Interior Coated with copper

Figure 3.10-4. MCC Test 4 Interior Damage

Temperatures measured at the slug locations are shown in Figure 3.10-5. The arc quenched at 

0.922 seconds. Several slugs had high noise during the arc probably due to EMI; the power 

supply was directly next to the slug calorimeters. Similar to Test MCC 2, the highest 

temperature at the end of the arc was at the top left side (S3) where flames had contacted the 

slug; the highest response that was not contacted by flames was measured at the rear (S6). All 

slugs had steady temperatures after the arc because there was no ensuing fire. 

The left side slugs (S1 to S3) responded quickly due to the arc breaking through the top left 

panel causing hot gases and plasma to exit directly to the slugs. 

(a) (b)

Figure 3.10-5. MCC Test 4 Calorimetry Data

Table 3-9 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum valid flux of 65

kW/m2 was measured at 1.5 m (5 ft) above the cabinet (S4). The bottom rear (S6) had a higher 

flux but was closer to the cabinet than the 0.91 meters. The maximum slug temperatures are 

also shown to indicate the maximum temperature a metal object could reach. 
3-34

Table 3-9. MCC Test 4 Flux Results.

Slug ΔT ( ̊C) Flux (kW/m2) Max T  ̊(C)

S1-LS-36-LS 18.7 121* 36

S2-LS-47-CL 42.3 274* 61

S3-LS-78-CL 95.8 626* 124

S4-T-150-CL 10.0 65 28

S5-F-31-CL 2.5 16 17

S6-R-35-CL 12.5 81** 29

* Contacted by flames, result not valid, see Appendix A, Section A.1. 

** S6 was closer to the cabinet than the 0.91 meter ZOI

The temperatures measured by TC1 and TC2 are shown in the Figure 3.10-6. Table 3-10

shows the maximum temperature results. TC1 failed at 0.5 seconds, as indicated by the rapid 

temperature recovery from the maximum and by data that was intermittent thereafter; the TC1 

temperature reported is the maximum before the failure. The thermocouple maximum 

temperature is a general indication of the air temperature 15.2 cm (3 in) from the cabinet and as 

expected, TC1 at the rear top where near the final arc location measured the highest 

temperature. The TCs cannot practically be used to estimate flux. 

(a) (b)

Figure 3.10-6. MCC Test 4 Thermocouple Data

Table 3-10. MCC Test 4 TC Results. 

TC Max T ( ̊C) 

TC1-R-78-CL 1045*

TC2-R-24-CL 49

TC3-LS-24-R **

TC4-LS-24-F **

TC5-RS-24-CL **

*Maximum reading before TC failed

**Data was corrupt
3-35

The pressures during the arc are seen in Figure 3.10-7. The results for the top pressure near 

the arc has a little more noise than at the bottom. There was a noise spike near the end of the 

arc on the top. The top pressure, measured closer to the arc, had a higher maximum and 

occurred earlier than the bottom pressure, which was measured further from the arc. The 

maximum pressures are indicated by the arrows in Figure 3.10-7(c) and (d). These pressures 

are higher than the other MCC tests. The bus bar at the top is much thicker and larger than the

bus bars at the bottom. Perhaps this caused a strong initial arc pressure wave that caused 

higher pressures. The bus bars in Tests 1 through 3 were thin and bent quickly, causing a 

weaker arc that extinguished. The top left panel at the arc burned through very quickly and this 

caused a rapid drop in pressure. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

(a) (b)

(c) (d)

Test 4 Pressure 1 Top

63.4 ± 1.4 kPa (9.2 ± 0.2 psi)

@ 0.0078 s 

Test 4 Pressure 2 Bottom

45.5 ± 1.4 kPa (6.6 ± 0.2 psi)

@ 0.0105 s 

Figure 3.10-7. MCC Test 4 Pressure Data
3-36

The arc duration was 0.922 seconds with total energy of 17.6 MJ, as seen in Figure 3.10-10. 

The energy analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied 

current multiplied by the time step and each time step is shown. “Energy Total” is the 

cumulative sum of the energy in each time step. 

Figure 3.10-8. MCC Test 4 Arc Energy
3-37

3.11 MCC Tests 1 through 4: Electrical Conditions 

Table 3-11 shows the electrical conditions measured by KEMA. 

Table 3-11. MCC Test 1 through 4 Electrical Results (1). 

Test Arc\ 

Location

OCV

(V) Phase Sym

(kA)

Peak

(kA)

Sym 

@End 

(kA)

Curr. 

Dur.

(sec)

Arc 

Energy

(MJ)

Freq 

@End 

(Hz)

Phase

Arc Volts

1 Bottom of 

bus bars 484

A 22.7 34.3 10.5

0.145

0.7

50

A-N 260

B 19.2 37.3 14.9 0.5 B-N 256

C 22.2 45.9 10.1 0.5 C-N 233

AVG 21.4 39.17 11.2 Σ2 AVG L-L 432

2 Bottom of 

bus bars 492

A 42.5 80.3 34.9

0.952

6 

50

A-N 221

B 29.3 61.6 14.5 5 B-N 229

C 30.4 63.5 26.1 6 C-N215

34.1 68.47 25.2 Σ17 AVG L-L 384

3 Bottom of 

bus bars 492

A 43.1 65.3 27.9

0.256

2 

50

A-N 2209

B 38.5 67.7 33.0 1 B-N 218

C 39.6 67.5 19.6 1 C-N 215

AVG 40.4 66.83 26.8 Σ 4 AVG L-L 384

4 

Top 

horizontal 

bus bar 

neat left 

wall

492

A 47.6 87.6 22.4

0.922

6 

50

A-N 215

B 47.4 76.1 48.0 6 B-N 225

C 44.1 91.0 40.6 6 C-N 206

AVG 46.4 84.90 37.0 Σ18 AVG L-L 374

(1) See Table 2-16 for abbreviations and acronyms used in this table.
3-38

3.12 MCC Tests 1 through 4 Qualitative Summary

1. Ensuing Fire: There were no ensuing fires for any of the tests. The damage to the 

internal cables suggests that slightly more energy may have led to an ensuing fire in 

Test 2. In Test 4 there was a small fire metal fire at the top bus bars but is not 

considered an ensuing fire since none of the internal combustibles ignited. 

2. Damage: In all of the tests, part of the bus bar was consumed during the arc. In Tests 1 

the bus bars burned upwards but since the arc was obstructed by arc chutes, the bus 

bars were not consumed as much in the following tests. In Tests 2 and 4, the bus bars 

were consumed up to where the support strut is located. The bus bars bent away from 

each other in Tests 2 and 3.

Cabinet damage varied between the tests: Tests 1 and 3 resulted in minor damage to 

the cabinet. Tests 2 and 4 resulted in significant damage to the cabinet; the arc burned 

through the top panel. The internal cables were not significantly damaged in any MCC 

test. Test 4 also resulted in panels being blown off. There was no major deformation in 

these panels; the panels detached instead of deforming. 

3. Calorimetry: The maximum measured flux varied between the tests. Tests 1 and 3 

showed the maximum heat flux in the same location: at the bottom left side of the 

cabinet as expected for the arc position in the bottom of the cabinet. There was some 

impingement of flames on the slug calorimeters in Tests 2 and 4, reducing the number of 

valid flux results. The maximum valid flux for Test 2 was measured at the bottom rear as 

expected for an initial arc at the bottom of the cabinet that traveled to the top of the 

cabinet. In Test 4, the maximum flux was above the cabinet as expected because the 

arc was just below the top panel.

4. Temperature: The maximum air temperatures were measured in the same location, the 

top rear, in Tests 1, 2 and 4. The maximum for Test 3 was measured at the bottom rear. 

The thermocouples are indicative of the air temperature about 15.2 cm (3 in) from the 

cabinet. 

5. Pressure: As expected, the maximum pressure was measured near the arc location. In 

Tests 2 and 4, the arc burned through the panel or a panel detached, causing a quick 

drop in pressure. The pressures measured in Test 4 were higher than the other tests

possibly because the fraction of the initial energy burst related to the initial shock wave

on the large bus bars at the top was larger than at the small, thin bus bars at the bottom 

where some energy was lost to deformation.

6. Arc Energy: In all tests the total energy was proportional to the arc duration for the given 

electrical testing conditions. The arc durations for all tests were less than 1 second so 

energies were very low. Tests 1 and 4 showed a smooth increase of the total energy 

during the arc indicating stable but short lived arc conditions. Test 2 showed the energy 

stopped increasing during the time the arc moved from the bottom of the cabinet of the 

top of the cabinet but the arc was stable before and after the transition. Test 3 showed 

some rapid changes in energy and signs of instability during the last part of the arc 

probably caused by the severe bending and spreading of the bus bars as the arc 

progressed.
4-1 

4 Switchgear HEAF Tests 1 through 3, Single Arc Tests – KEMA 

(June 2013)

4.1 SWGR Tests 1 through 3 Overview 

The purpose of these tests is to obtain the basic HEAF data for Switchgear (SWGR) such as 

duration, energy, flux, temperatures, pressures, and ensuing fire effects. There were three (3) 

tests at KEMA conducted June 17-19, 2013. The tests were in a SWGR lineup of five cabinets 

(numbered 6-10 to match Onagawa) with the arc initiated in Cabinet 8 in the center. 

4.2 SWGR Tests 1 through 3 Summary of Results

The key test parameters and results are in the table below. The tests were single arc events; 

the target test voltage was nominally 6.9 kV and the target test current was 23 kA (symmetrical, 

sym.). The original plan was for a 2 second arc but this was increased to 3 seconds after Test 1 

to provide more energy to evaluate the impact of duration on the potential for ensuing fires. 

Table 4-1. SWGR Tests 1 through 3 Summary of Results.

Test

Volt (kV)

(1)

Curr (kA) 

(2)

Test 

Peak 

Current 

(kA) (3)

Arc

Duration

(sec) (4)

Arc 

Energy

(MJ) 

Internal 

Max 

Press

(kPa/psi)

Ext Max 

Flux (5)

(kW/m2

) 

Ensuing fire?

Key 

Observations

1 7.1 / 0.609

29.5 / 22.6 58.4 2.02.048 42.6

4.8 ± 1.4 

0.7 ± 0.2 

(6)

52

No. The energy 

was too low to 

cause the fire.

2 7.1/ 0.608

30.5 / 23.5 59.5 3.0

2.957

58.2 16.5 ± 1.4

2.4 ± 0.2 71

Yes. Full 

duration 

ensuing fire.

3 7.1 / 0.633

29.8 / 22.6 58.9 3.02.911 64.2 13.5 ± 1.42.0 ± 0.2 107

Yes. Ensuing 

fire 

extinguished 

after 4 minutes.

Notes: 

(1) The voltage is shown as the target voltage / arc Line-to- Line (L-L) voltage (L-L is the “arc 

voltage”)

(2) The symmetric arc current slowly drops during the test as the arc impedance increases. 

This shows the test start current / test end current. These are average currents of all 3 

phases. 

(3) This is the peak current for any phase or time, usually the asymmetric current at the start

(4) The duration is shown as the target duration and the actual test duration below it. 

(5) The maximum heat flux was at the slug calorimeter located at the 1.5 m (5 ft) above the 

cabinet. 

(6) Maximum pressure is one cabinet away from the cabinet with the arc, the pressure 

transducer failed in the cabinet with the arc. In other tests, the cabinet with the arc had the 

maximum pressure. 
4-2 

Test 1 did not have an ensuing fire with a 2 second arc. The arc duration was increased to 3 

seconds for Tests 2 and 3. Test 2 developed into a full ensuing fire that was allowed to 

completely burn the cables in the cabinet with the arc and one adjacent cabinet on each side in 

about 20 minutes. Cables in the end cabinets were only partially burned when the fire was 

extinguished. Test 3 showed similar results and had an ensuing fire but the ensuing fire was 

extinguished after 4 minutes for safety concerns. The arc and electrical results of Test 2 and 3 

are similar. The key results from the June 2013 SWGR tests at KEMA were: 

• The tests at KEMA did not duplicate the 2011 Onagawa damage conditions. It is 

believed the actual 2011 Onagawa event also was subjected to higher energy levels 

from possibly longer arc duration (the actual duration is unknown) and from the oxidation 

(burning) of the aluminum bus bars, as discussed in Chapter 7. It is also possible that 

there were two separate arcs in the Onagawa event. 

• The SWGR were well-ventilated cabinets, like the Onagawa cabinets. The highest 

external flux measured was a momentary 107 kW/m2 at 1.5 m (5 ft) above the cabinet, 

indicating that heat escaped through the vent on the top of the cabinet and flames 

spread over the roof of the cabinet. However, the high flux was a short duration, and did 

not damage the cable samples at the flux measurement point. 

• Based on all the SWGR tests, an energy of about 60 MJ was needed to ignite an 

ensuing fire in the KEMA SWGR tests. One observation on MCC and DP tests was that

the ensuing fire usually required an energy of around 25 MJ or greater to ignite. There is 

likely more heat loss through the vents in the SWGR, requiring a higher energy (60 MJ) 

to cause an ensuing fire within the cabinet. Cabinets with vents and the vent location 

will be an important consideration in heat damage effects from HEAF. 

• The resultant pressures in the SWGR tests were lower than the DP and MCC tests 

because the pressure escaped through the large vent above the arc in Cabinet 8. 

Cabinet 7 pressures are higher than Cabinet 8, as expected, because the pressure 

transducer is located closer to the arc.

4.3 SWGR Tests 1 through 3 Cabinet Configuration 

The test configuration is shown in Figure 4.3-1. Actual SWGR and cabinets from Onagawa 

were not available to test. GE Magneblast SWGRs built in the 1970’s are the closest U.S. 

SWGR to the Onagawa design. The SWGR was nominally 91.4 cm wide by 228.6 cm high by 

114 cm deep (36 in wide by 90 in high by 45 in deep). However, the GE SWGR and cabinets 

are not identical to Onagawa; Figure 4.3-2 that shows the differences in internal partition 

configuration and the bus bar configuration. The Onagawa cabinet also has a large vent on the 

top. 

The GE Magneblast SWGRs were modified, as shown in Figure 4.3-3 through Figure 4.3-5. 

The interior volume in the cabinets around the arc and any vents in the cabinets are very 

important. The bus bars, interior SWGR partitions, interior SWGR wire duct, and bus bar 

partitions between cabinets were relocated similarly to the Onagawa SWGR. The U.S. cabinet 

is 91.4 cm (36 in) wide, whereas the Onagawa cabinet is 100 cm (39 in) wide; this could not be 

changed. As shown in Figure 4.3-4, the volume formed by Plates A-B-C-D-E-F and the top is 

similar to the volume of the Onagawa SWGR where the arc occurred. The volume in the top 

front is similar to the 0.30 m by 0.41 m (11.8 in by 16.1 in) wire duct at the top front of the 
4-3 

Onagawa SWGR. A rectangular vent area was added on the top to match the Onagawa vent. 

Panel B in front of the primary insulators had vents to match Onagawa because these vents

were the postulated path for the arc plasma to ignite cables in the front of the cabinet during the 

Onagawa event. As shown in Figure 4.3-5, the aluminum bus bars were covered by a polymer 

coating which were considered a negligible part of the combustible load and were supported by 

phenolic panels, similar to the Onagawa design. 

In the June 2013 tests, “dummy” SWGR breakers were used to simulate the cabinet 

configuration and combustible load present at Onagawa in Cabinets 7 and 8. Cabinets 6, 9, 

and 10 did not have any breakers in them. Cabinets 6, 9, and 10 were included to provide the 

cable loads and cabinet configuration similar to Onagawa. 

(a) Front Views

(b) Side View showing arc on primary side of breaker

Figure 4.3-1. SWGR 5-Cabinet Test Configuration
4-4 

Onagawa GE Magneblast

Figure 4.3-2. Onagawa SWGR and GE Magneblast SWGR

Figure 4.3-3. Modified GE Magneblast Dimensions (in cm)
4-5 

Figure 4.3-4. SWGR Cabinet Configuration Cabinets 7 and 8

Figure 4.3-5. SWGR Bus Bar Configuration

Note: The 

horizontal 

bus bars 

are not 

shown for 

clarity

Perforated Steel Sheet 

30% flow through

0 cm73.1 cm91.6 cm110 cm
4-6 

4.4 SWGR Tests 1 through 3 Cable Combustible Loading 

Cables, wires, and wire ways were added to the cabinet to give a combustible load similar to the 

cabinets in Onagawa, as shown in Figure 4.4-1. Japanese CV-4 PVC/XLPE type cable and HIV 

PVC single wire instrument wires were used in the front of the cabinets as in Figure 4.4-1(b). 

Three, 1.5 m (5 ft) lengths of Japanese 6 kV-CHSVT single conductor, 28 mm (1.1 in) diameter, 

PVC, power cables were installed in the rear of Cabinets 7 and 8. 

(a) CV-4 in Top Horizontal Duct

HIV in top 

horizontal 

duct- 20 

pieces on 

lugs

CV-4 in top 

horizontal duct: 

Cabinet 7

1 bundle of 4

1 bundle of 5

HIV in top 

horizontal 

duct- 100 

pieces on 

cabinet; 

5 bundles 

of 20

CV-4 in top 

horizontal duct: 

Cabinet 7

to Cabinet 6; 

10 bundles of 5

1 bundle of 4

1 bundle of 2

(b) HIV in Cabinets (c) In Vertical Duct

Figure 4.4-1. SWGR Cabinet Combustible Load

92 CV-4 cables (after burning)

In vertical 

ducts

In horizontal 

ducts

Bare on 

cabinet
(d)

Figure 4.4-1. SWGR Cabinet Combustible Load, continued

6 8 9 

7

4-7
Figure 4.4-2. SWGR Test Cable Combustible Load

5 bundles of 20 5 bundles of 20 5 bundles of 20 5 bundles of 20 5 bundles of 

4-8
4-9 

4.5 SWGR Tests 1 through 3 Temperature and Heat Flux Instrumentation

Thermocouples (Type K) were used to measure the temperatures during each test. For 

electrical independence from the KEMA measurement systems and safety concerns, TCs are 

not in contact with the metal cabinet to prevent possible electrical shorting. The TCs are about

15 cm (6 in) from the cabinet to measure the air temperatures. The air temperatures are likely 

much lower than the actual metal temperature. Therefore, the temperatures are only a 

qualitative measure of thermal and fire behavior. 

ASTM F1959 slug calorimeters were also used for heat flux. The TC and slug locations are in 

Figure 4.5-1 and Table 4-3. Flux calculation methods are in Appendix A. 

Table 4-2. Calorimeter and TC Locations SWGR Tests 1 through 3. 

Slug or 

TC

From 

Floor

cm (in)

Position Slug or TC 

Name

S1 178 (70) Front (F) S1-F-70-Cab7

S2 178 (70) Front S2-F-70-Cab8

S3 91 (36) Front S3-F-36-Cab8

S4 178 (70) Rear (R) S4-R-70-Cab8

S5 381 (150) Top (T) S5-T-150-Cab8

TC1 178 (70) Front TC1-F-70-Cab6

TC2 178 (70) Front TC2-F-70-Cab7

TC3 178 (70) Front TC3-F-70-Cab8

TC4 178 (70) Front TC4-F-70-Cab9

TC5 422 (166)* Vertical Duct (V) TC5-V-Cab8

*TC5 is 7.62 cm (3 in) from the top of the vertical duct. 
4-10

Front View

Top View

Figure 4.5-1. SWGR Tests 1 through 3 Instrument Locations
4-11

4.6 SWGR Tests 1 through 3 Pressure Instrumentation 

Two Dynisco PT150-50 strain-gauge type pressure transducers (PRT) were used. See 

Appendix A for the analysis method. The pressure probe positions are in Figure 4.5-1. 

4.7 SWGR Test 1 Key Observations 

Test 1 was initiated at 7.1 kV and 29.5 kA with a target arc duration of 2 seconds that was 

achieved with a total energy of 42.6 MJ. The arc progression is seen in Figure 4.7-1. The 

energy was too low to start an ensuing cable fire. The maximum external cabinet temperature 

as indicated by the IR thermal image, seen in Figure 4.7-2(a) was much lower than 750 °C 

(1382 °F) immediately after the arc. At this time the FLIR was set to the maximum 750 °C so 

the video after the initial arc showed no colors. Ten minutes after the arc, the FLIR was set to 

auto scale as shown in Figure 4.7-2(b). The exterior cabinet temperatures were less than 90 °C 

(194 °F) indicating residual heat at the bottom of the vertical duct and no internal cable fire in 

the top front of the cabinets.

(a) 0 sec (b) 0.5 sec

(c) 1 sec (d) 2 sec

Figure 4.7-1. SWGR Test 1 Arc
4-12

(a) At end of arc (b) 10 minutes after arc 

Figure 4.7-2. SWGR Test 1 Thermal Image at Arc Extinction

The exteriors of the cabinets were not damaged since there was not a large fire, as seen in 

Figure 4.7-3. There is a little soot at the bottom of the vertical duct. The top had some soot 

deposits and minor scorching where the arc discharged through the top vent. 

(a) Front View Cabinets 6-10

Figure 4.7-3. SWGR Test 1 Exterior Damage
4-13

(b) Top of Cabinets 6-10

Figure 4.7-3. SWGR Test 1 Exterior Damage, continued

As shown in Figure 4.7-4, the cabinet interior damage was minor; details of the interiors are in 

Figure 4.7-5. Cabinet 7 and 8 had some scorching and orange discoloration from high heat on 

the interior panels at the arc level. Cabinets 6, 9, and 10 mainly had soot damage. The interior 

of the cabinet had some cable scorching in Cabinet 8. In Cabinet 7 and 9 there were some soot 

deposits on the cables. In Cabinets 6 and 10 the cables were virtually undisturbed. As shown 

in Figure 4.7-5(c), Cabinet 8 interior had some scorching in the front area but other areas only 

had very light soot deposits in the rear of the cabinet. 

Cabinets 6-10

Figure 4.7-4. SWGR Test 1 Interior Damage
4-14

(a) Cabinet 6 Cables (b) Cabinet 7 Cables

(c) Cabinet 8 cables (d) Cabinet 9 Cables

Figure 4.7-5. SWGR Test 1 Interior Damage, Detailed
4-15

(e) Cabinet 10 Cables (f) Cabinet 8 Interior

Figure 4.7-5. SWGR Test 1 Interior Damage, Detailed, continued

The vertical bus bars above the insulators were not heavily oxidized, as shown in Figure 4.7-6, 

because the arc was short. The orange bus bar insulation was not burned, indicating a low 

temperature and heat flux within the cabinet. The horizontal bus bars had some bending but 

much less than Onagawa where the bars bent and touched. The insulators were destroyed.

(a) Cabinet 7 (b) Cabinet 8

Figure 4.7-6. SWGR Test 1 Insulator and Bus Bar Damage
4-16

The Cabinet 8 breaker was not destroyed during the arc, however, the insulators were 

destroyed and the debris fell onto the top of the breaker. The Cabinet 7 breaker did not have 

any damage just some soot, as seen in Figure 4.7-7. 

(a) Cabinet 8 breaker with insulator debris (b) Cabinet 8 breaker with insulator debris

(c) Cabinet 7 breaker

Figure 4.7-7. SWGR Test 1 Breaker Damage

 Primary Secondary
4-17

Temperatures measured at the slug locations are shown in Figure 4.7-8. The arc quenched at 

2.048 seconds. Several slugs had high noise during the arc probably due to EMI; the power 

supply was directly next to the slug calorimeters. The highest temperature at the end of the arc 

was seen at the top of the cabinet (S5) above where the hot gases escaped through the roof 

vent. All slugs had steady temperatures after the arc because there was no ensuing fire. 

(a) (b)

Figure 4.7-8. SWGR Test 1 Calorimetry Temperature Data

Table 4-3 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux of 52 

kW/m2 was measured at the top (S5). The maximum slug temperatures are also shown to 

indicate the maximum temperature a metal object could reach. 

Table 4-3. SWGR Test 1 Flux Results. 

Slug ΔT ( ̊C) Flux (kW/m2

) Max T  ̊(C)

S1-F-70-Cab7 2.3 7 34

S2-F-70-Cab8 1.8 5 35

S3-F-70-Cab8 0.6 2 34

S4-R-70-Cab8 4.4 13 33

S5-T-150-Cab8 17.1 52 48
4-18

The temperatures measured by the TCs are shown in the Figure 4.7-9. Table 4-4 shows the 

maximum temperature results. The thermocouple maximum temperature is a general indication 

of the air temperature 7.62 cm (3 in) from the cabinet. The highest temperature was likely at the 

vertical duct (TC5), however, it appears the TC failed. The TCs cannot practically be used to 

estimate flux. Noise during the arc is from EMI. 

For TC3, the fluctuating response after the arc does not appear to be noise. TC3 was located in 

front of Cabinet 8 and is detecting the residual heat escaping from the cabinet. 

(a) (b)

Figure 4.7-9. SWGR Test 1 Thermocouple Data 

Table 4-4. SWGR Test 1 TC Results. 

TC Max T ( ̊C) 

TC1-F-70-Cab6 31

TC2-F-70-Cab7 32

TC3-F-70-Cab8 36

TC4-F-70-Cab9 31

TC5-V-Cab8 * 

*Data was corrupt
4-19

The pressure curves are shown in Figure 4.7-10. The data signal for Cabinet 7 showed noise 

during the arc that could not be treated with the method in Appendix A, so the data is not 

reported. The Cabinet 8 signal data showed the zero base line changed from 0.04 to 0.8 

seconds, recovered, and then had numerous negative spikes. There was considerable noise 

after 0.04 seconds but the data for the initial pressure spike looks reasonable, and is evaluated. 

The maximum pressure for Cabinet 8 is indicated by the arrows in Figure 4.7-10(d). 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc. 

(a) (b)

(c) (d)

Test 2 Pressure 1 Cab. 7

No data reported

Test 2 Pressure 2 Cab. 8

4.8 ± 1.4 kPa (0.7 ± 0.2 psi)

@ 0.0154 s 

Figure 4.7-10. SWGR Test 1 Pressure Data 
4-20

The arc duration was 2.048 seconds with total energy of 42.6 MJ, seen Figure 4.7-11. The 

energy analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied 

current multiplied by the time step and each time step is shown. “Energy total” is the cumulative 

sum of the energy in each time step. The energy was smooth and steady with no-restrikes that 

were typical of the medium voltage SWGR Tests 1 through 4. 

Figure 4.7-11. SWGR Test 1 Arc Energy
4-21

4.8 SWGR Test 2 Changes 

Based on the results of Test 1, the changes and key set up items for Test 2 and all future 

SWGR tests were: 

1. Increased the energy from Test 1 (no cable fire) by 50% by increasing the arc duration 

from 2 seconds to 3 seconds (results show an energy increase from 43 to 58 MJ). 

2. The shorting wire configuration was changed to use two wires toward the front of the 

cabinet to bring the arc forward in the cabinet in Tests 2 and 3, see Figure 4.8-1. In Test 

1 the arc was toward the back through Panel C and this did not happen at Onagawa. 

Moving the arc forward should increase the heat in the front of the cabinet and cause a 

cable fire. A sheet of red board was added on the front of panel C to protect it from the 

arc. However, this resulted in an arc in the front of the cabinet, causing the arc to leak 

into Cabinet 7 in Tests 2 and 3. 

Figure 4.8-1. SWGR Test 2 Shorting Wire Changes
4-22

3. Test 1 used a red board on the top of the breaker to direct the energy into the cabinet

but there was no damage on the breaker secondary side. In Test 2 this red board was 

removed to direct more energy to the breaker side. But there was still no major fire 

damage on the breaker secondary side. 

(a) Red board in Test 1 (b) Red board removed for Test 2

Figure 4.8-2. SWGR Test 2 Breaker Changes

4. More brackets and supports were added for the cables because they fell off in Test 1. 

Figure 4.8-3. SWGR Test 2 Wiring Changes

Secondary

Primary 
4-23

5. Two metering devices were removed from the front door to simulate the openings 

created during Onagawa event when some meters blew off. In all future SWGR tests, 

two rectangular openings were created by removing these meters on the front doors. 

Figure 4.8-4. SWGR Test 2 Front Door Meter Changes 

4.9 SWGR Test 2 Key Observations 

This test was initiated at 7.1 kV and 30.5kA with a target duration of 3 seconds with a total 

energy of 58.2 MJ. The target of 3 seconds was achieved. The arc flames died quickly and no 

flames were visible until the 7 minute mark where flames were seen in the vertical duct. Manual 

extinguishment was attempted at 12.5 minutes for two minutes but was unsuccessful. The fire

then returned to full intensity by 15.5 minutes with flames exiting at the top of the vertical duct. 

Finally, water was applied for about 5 minutes and the fire was extinguished, largely because 

the cables in the vertical duct were completely burned. 

The ensuing fire observed during Test 2 and associated cable damage was similar to the 

Onagawa event but the fire did not spread as far and cables were burned two cabinets away 

from the arc points at Onagawa. For Test 2, only the cables on the adjoining Cabinet 7 and 9 

were burned. 

The arc sequence and ensuing fire are shown in Table 4-5 and Table 4-6. The first 3 seconds 

is the actual arc. It appears that the arc in Cabinet 8 created a hole in the wall to Cabinet 7 and 

the hot gas and plasma entered Cabinet 7 causing ensuing fires and heavy damage in Cabinet 

7. 

2 rectangular 

meters removed
4-24

Table 4-5. Arc Sequence SWGR Test 2.

Image Time Description

0 Arc initiated.

0.2 

seconds

Fireball develops.

0.3 

seconds

Fireball expands; flame 

spreads across the top, 

see next figure. 
4-25

Table 4-5. Arc Sequence SWGR Test 2, Continued.

Image Time Description

1 second Flames emerge from 

top vents in Cabinets 7 

and 8, fire spreads 

down the wire duct and 

travels to Cabinet 10. 

1.5 

seconds

Fire continues in wire

duct and escapes from 

cabinets. 

2 

seconds

Fire continues to 

evolve, sparks 

escaping at the bottom 

of the cabinet. 
4-26

Table 4-5. Arc Sequence SWGR Test 2, Continued.

Image Time Description

2.5 

seconds

Flame and sparks 

between Cabinets 6 

and 7 indicate the arc 

plasma leaking from 

Cabinet 8 to Cabinet 7. 

2.8

seconds

The plasma leak into

Cabinet 7 continues 

with more flames 

between Cabinets 6 

and 7. There are

additional flames at the 

Cabinet 7 vent. 

3 

seconds

The arc quenches.
4-27

Table 4-5. Arc Sequence SWGR Test 2, Continued.

Image Time Description

4 

seconds

The fire ball quickly 

extinguishes at the top 

after the arc. Sparks 

and flames remain at 

the cabinet bottom. 

5 

seconds

Flames are mostly 

gone. 

6 

seconds

This is the last time 

small flames are visible 

until 7 minutes. These 

are around the 

Cabinets 7 and 8 top 

vent areas. 
4-28

Table 4-6. Ensuing Fire Sequence SWGR Test 2.

Image Time Description

3 minutes Still no flames visible, 

but smoke from 

cabinets increases.

7 minutes The flames from the 

vertical duct cables 

emerge.

11 

minutes

The fire was large 

because the duct acted 

like a stack pulling 

oxygen into all 

cabinets. Flames were 

1 to 2 meters high.
4-29

Table 4-6. Ensuing Fire Sequence SWGR Test 2, Continued.

Image Time Description

12.5 

minutes

Manual extinguishment 

with water/baking soda 

started. Later water 

was applied. 

15.5 

minutes

The water was not 

adequate to cool the 

fire and extinguishment 

stopped after 1.5 

minutes. Fire re-grew

to the oringial intenstiy.

21 

minutes

The cables in the 

vertical duct were 

mostly consumed and 

after 5 minutes of 

applying water, the fire 

was mostly out. 
4-30 

Table 4-6. Ensuing Fire Sequence SWGR Test 2, Continued.

Image Time Description

51 

minutes

Cabinet 7 was opened, 

some CV-4 cables 

were still on fire. 

Final 

State

Cabinets 7 and 8 are

heavily damaged. 

Propagation of fire into 

Cabinets 6 and 9. 

Cabinet 10 showed

less damage.

The fire was allowed to burn completely, providing the longest time-temperature data to study in 

the tests within this report. Table 4-7 shows the IR image sequence. The FLIR camera was set 

on “auto scale” to make the color spectrum distinct over the large range of temperatures and 

make it easy to see the fire spread. The fire visually apeared to reach its peak intensity at 

approximately 11 to 12 minutes. Although the HEAF was an intense ignition source, the fire 

behaved as expected for a typical cabinet fire. 
4-31

Table 4-7. Thermal Image of Ensuing Fire SWGR Test 2. 

Image Time Description

0 Arc Initiated.

0.38 

seconds

Fire expands.

2.8 

seconds

The flame between 

Cabinets 6 and 7 is 

from the plasma from 

Cabinet 8 leaking into 

Cabinet 7.
4-32

Table 4-7. Thermal Image of Ensuing Fire SWGR Test 2, Continued.

Image Time Description

30 

seconds

FLIR re-scaled for the 

much cooler fire. 

1 minute Fire intensified as 

indicated by the FLIR 

temperature

measurement. 

2 minutes Fire continues to 

expand and intensify 

across the top front of 

the cabinets and up the 

vertical duct. 
4-33

Table 4-7. Thermal Image of Ensuing Fire SWGR Test 2, Continued.

Image Time Description

3 minutes Fire continues to 

spread and intensify. 

4 minutes Fire continues to 

spread but maximum 

temperature decreases 

slightly. 

5 minutes Fire continues to 

spread and intensify.
4-34

Table 4-7. Thermal Image of Ensuing Fire SWGR Test 2, Continued.

Image Time Description

6 minutes Fire continues to 

spread and intensify.

7 minutes Just before flame was 

seen out of vertical 

duct. 

8 minutes Flame out of vertical 

duct. 

The SWGR cabinet outer walls did not have major deformation like the DP and MCC. The 

SWGR cabinet outer walls are thicker and the large vent allowed for pressure relief. The 

cabinet exteriors were slightly charred from the ensuing fire, but not as severely as at Onagawa

which was not extinguished for 7 hours (see Chapter 6.10.4 for more detail). The vertical stack 

was heavily scorched and discolored from the intense stack fire. The orange color was also 

observed in the Onagawa event. The cables in the vertical duct (shown with cover removed) 

were completely burned.
4-35

(a) (b)

Figure 4.9-1. SWGR Test 2 Exterior Damage

The interior primary side was heavily damaged from the large and ensuing fire. Some cables 

burned in all cabinets except cabinet 10 on the far right, which only showed soot damage. 

There was heavy soot damage in Cabinets 6 through 8 and lighter soot damge in Cabinets 9 

and 10. See Figure 4.9-2 for damage. 

In Cabinet 6, about 50 percent of the cables burned in place but in Cabinets 7 and 8, the cables 

detached from the cabinet, slumped down, and were completely burned. The pressure and 

violence of the arc and assoicated leaking plasma most likely contributed to the detachment and 

disarray. In Cabinet 9, about 80 percent of the cables burned and there was also detachment 

and slumping of the cable bundle that was attached to the ceiling. The cables in Cabinet 10 did 

not burn. 
4-36

(a) All cabinets

(b) Cabinet 6 Cables 

(c) Cabinet 7 Cables (d) Cabinet 8 Cables

Figure 4.9-2. SWGR Test 2 Interior Damage, Continued

Cabinet 6 Cabinet 7 Cabinet 8 Cabinet 9 Cabinet 10
4-37

(e) Cabinet 9 Cables (f) Cabinet 10 Cables

Figure 4.9-2, continued. SWGR Test 2 Interior Damage

Cabinet 7, Insulator 3 (on the right side of the cabinet) was damaged by the arc plasma coming 

from Cabinet 8, Insulator 1. The Cabinet 8 arc made a hole in the wall to Cabinet 7 as shown in 

the figure and the arc plasma spread. The vertical bus bars in Cabinet 8 were oxidized by the 

arc, as seen in Figure 4.9-3. The insulators in Cabinet 8 were destroyed, as expected and

similar to Onagawa.

(a) Cabinet 7 (b) Cabinet 8

Figure 4.9-3. SWGR Test 2 Insulator and Bus Bar Damage

Breaker 8 had damage at the top primary side under the arc position but the secondary side 

was not damaged- only some soot was observed. There was some front panel discoloration 

from the heat and the control cable bundle on the front left burned. Breaker 7 only had some 

soot covering as shown in Figure 4.9-4. 
4-38

(a) Breaker 7 (b) Breaker 7 (from rear)

(c) Breaker 8 (d) Breaker 8 (from front)

Figure 4.9-4. SWGR Test 2 Breaker 7 and 8 Damage

Temperatures measured at the slug locations are shown in Figure 4.9-5. The arc quenched at 

2.957 seconds. Several slugs had significant noise during the arc, probably due to EMI; the 

power supply was directly next to the slug calorimeters. As in Test 1 the highest temperature at 

the end of the arc was above the cabinet (S5), hot gases were escaping through the roof vent. 

The ensuing fire produced a smooth and linear slug temperature rise from about 3 minutes to 12 

minutes. At 12 minutes all of the slugs showed a temperature decrease as firefighting was 

started but subsequently all slugs showed when the firefighting efforts failed. The highest postarc temperature response as the heat from the fire rose up was measured at the top (S5). 
4-39

(a) (b)

(c)

Figure 4.9-5. SWGR Test 2 Slug Calorimeter Temperature Data 

Table 4-8 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. Like Test 1, the maximum 

flux of 71 kW/m2 is reported at the top (S5). The maximum slug temperatures are also shown to 

indicate the maximum temperature a metal object could reach during the arc. 

Table 4-8. SWGR Test 2 Flux Results.

Slug ΔT ( ̊C) Flux (kW/m2

) Max T  ̊(C)

S1-F-70-Cab7 6.8 14 48

S2-F-70-Cab8 6.9 14 58

S3-F-70-Cab8 2.6 5 40

S4-R-70-Cab8 8.9 18 35

S5-T-150-Cab8 34.7 71 122

The temperatures measured by the TCs are shown in the Figure 4.9-6. Table 4-9 shows the 

maximum temperature results. The only reliable data based on analysis was for TC1 and TC 2. 

The thermocouple maximum temperature is a general indication of the air temperature 15.2 cm 

(6 in) from the cabinet. Temperatures stayed low in the front of Cabinet 6 (TC1) and Cabinet 7 

(TC2). Temperatures slowly increased during the ensuing fire from 6 to 12 minutes then 

became erratic during firefighting efforts. The TCs cannot be used to estimate flux. 
4-40

(a) (b)

(c)

Figure 4.9-6. SWGR Test 2 Thermocouple Data

Table 4-9. SWGR Test 2 TC Results. 

TC Max T ( ̊C) 

TC1-F-70-Cab6 32

TC2-F-70-Cab7 41

TC3-F-70-Cab8 * 

TC4-F-70-Cab9 * 

TC5-V-Cab8 * 

*Data was corrupt
4-41

The pressures during the arc are shown in Figure 4.9-11. There were noise spikes in the data 

at 0.07 seconds for Cabinet 7 and several around 0.4 seconds and at 1.22 seconds for Cabinet 

8 (denoted by the red arrows in Figure 4.9-11(a) and (b)). Cabinet 8 also had numerous large 

negative spikes that do not have a known cause; it may be due to noise or sensor failure. The 

Cabinet 8 pressure closer to the arc had a higher maximum and occurred slightly earlier than 

the Cabinet 7 pressure that was further from the arc. The maximum pressures are indicated by 

the arrows in Figure 4.9-7(c) and (d). The pressures were low because the vents at the top of 

Cabinets 7 and 8 allowed the pressure to escape. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc. 

(a) (b)

(c) (d)

Test 2 Pressure 1 Cab. 7

8.3 ± 1.4 kPa (1.2 ± 0.2 psi)

@ 0.0135 s

Test 2 Pressure 2 Cab. 8

16.5 ± 1.4 kPa (2.4 ± 0.2 psi)

@ 0.0123 s

Figure 4.9-7. SWGR Test 2 Pressure Data
4-42

The arc duration was 2.957 seconds with total energy of 58.2 MJ, seen in Figure 4.9-8. The 

energy analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied 

current multiplied by the time step and each time step is shown. “Energy Total” is the 

cumulative sum of the energy in each time step. 

Figure 4.9-8. SWGR Test 2 Arc Energy 
4-43

4.10 SWGR Test 3 Key Observations 

This test was initiated at 7.1 kV and 29.8 kA and a target arc duration of 3 seconds with a total 

energy of 64.2 MJ. The arc duration of 3 seconds was achieved. The arc progression can be 

seen in Figure 4.10-1. Although there was an ensuing fire, it was manually extinguished quickly

for safety reasons. 

 

In this test, two 10.1 cm (4 in) circular openings were added at 30.5 cm (12 in) and 61 cm (24 

in), centered from the bottom of the vertical duct to provide a way to inject water for fire 

suppression. This was done as a precautionary measure for facility safety based on the fire 

intensity of Test 2. 

(a) 0 seconds (b) 0.5 second

(c) 1 second (d) 1.5 seconds

Figure 4.10-1. SWGR Test 3 Arc
4-44

(e) 2 seconds (f) 2.83 seconds

Figure 4.10-1. SWGR Test 3 Arc, continued

Figure 4.10-2 shows the ensuing internal fire (noted by the arrows). No large flames were 

visible; the only visible flames were through the holes in the vertical duct and in the front door of 

the cabinet shown by the arrows. The FLIR camera failed in this test so there are no IR thermal 

images. 

(a) 2:00; First flame in cabinet 8 (b) 4 minutes; Maximum fire

Figure 4.10-2. SWGR Test 3 Ensuing Fire

Exterior cabinet damage was small since the fire was extinguished quickly, as seen in Figure 

4.10-3. There was no major scorching or charring on the front of the cabinets. There was light 

soot that leaked from behind the instruments and at the door joints at the very top of Cabinets 6, 

7, and 8. The yellowish water streaks from the instruments to the bottom of the cabinet front 

doors were there before the tests (probably from long-term outdoor storage of the cabinets at 

the used electrical equipment vendor). 
4-45

(a) Cabinets 6, 7, and 8 (b) Cabinets 9, 10

Figure 4.10-3. SWGR Test 3 Exterior Damage

Figure 4.10-4 shows the interior damage; Figure 4.10-5 shows detailed damage. Cabinets 7 

and 8 showed heavy soot damage and orange discoloration from the high temperatures. Figure 

4.10-5(f) shows the soot was throughout the interior of Cabinet 8. 

Some cables burned in all cabinets except Cabinet 10, which only showed soot damage, in 

Figure 4.10-4. There was heavy soot damage in all cabinets. In Cabinet 6, only a few 

centimeters of the cables burned where they entered from Cabinet 7. The Cabinet 7 upper 

cables were completely burned, and had detached from the cabinet and slumped down. The 

Cabinet 8 upper cables were mostly burned and remained in place and attached. In Cabinet 9, 

a small amount of the upper cables burned where the cables entered from Cabinet 8, and the 

cables detached and slumped. This fire was quickly extinguished by KEMA personnel to avoid 

the large fire that occured during Test 2. 

Figure 4.10-4. SWGR Test 3 Interior Damage

Cabinet 6 Cabinet 7 Cabinet 8 Cabinet 9 Cabinet 10
4-46

(a) Cabinet 6 Cables (b) Cabinet 7 Cables

(c) Cabinet 8 Cables (d) Cabinet 9 Cables 

(e) Cabinet 10 Cables (f) Cabinet 8 Side View

Figure 4.10-5. SWGR Test 3 Interior Damage, Detailed
4-47

The bus bar damage was very similar to Test 2, and is shown in Figure 4.10-6. Cabinet 7, 

Insulator 3 (on the right side of the cabinet) was damaged by the arc plasma coming from 

Cabinet 8, Insulator 1. The Cabinet 8 arc made a hole in the wall to Cabinet 7 as shown in the 

figure and the arc plasma spread. The vertical bus bars in Cabinet 8 were oxidized by the arc. 

The insulators in Cabinet 8 were destroyed, as expected, similar to Onagawa. 

(a) Cabinet 7 (b) Cabinet 8

Figure 4.10-6. SWGR Test 3 Insulator and Bus Bar Damage

Figure 4.10-7 shows the breaker damage. Breaker 8 had damage at the top primary side under 

the arc position but the secondary side was not damaged - only some soot was observed. 

There was no front panel discoloration and the control cables on the front were not burned. 

Breaker 7 only had some minor soot at the top of the breaker. 

(a) Breakers 7 and 8 (b) Breaker 8

Figure 4.10-7. SWGR Test 3 Breaker Damage
4-48

Temperatures measured at the slug locations are shown in Figure 4.10-8. The arc quenched at 

2.911 seconds. Several slugs had high noise during the arc probably due to EMI; the power 

supply was nearby. The highest temperature at the end of the arc was at the top of Cabinet 8 

(S5), probably because hot gases escaped through the roof vent as in Tests 1 and 2. All of the 

slugs except S4 on the rear showed increasing temperature as the ensuing fire began to build. 

At 4.2 minutes all of the slugs showed temperature decreases as firefighting was started and 

the fire was extinguished. 

(a) (b)

Figure 4.10-8. SWGR Test 3 Calorimetry Temperature Data

Table 4.10-1 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux of 107 

kW/m2 was measured at the top (S5). The maximum slug temperatures are also shown to 

indicate the maximum temperature a metal object could reach. 

Table 4-10. SWGR Test 3 Flux Results.

Slug ΔT ( ̊C) Flux (kW/m2

) Max T ( ̊C)

S1-F-70-Cab7 7.6 16 33

S2-F-70-Cab8 5.1 11 34

S3-F-70-Cab8 1.9 4 37

S4-R-70-Cab8 29.7 62 55

S5-T-150-Cab8 51.2 107 85
4-49

The temperatures measured by the TCs are shown in the Figure 4.10-9. Table 4-11 shows the 

maximum temperature results. Only TC1 and TC 2 had valid data. The thermocouple 

maximum temperature is a general indication of the air temperature 15.2 cm (6 in) from the 

cabinet. Temperatures stayed low in the front of Cabinet 6 (TC1) and Cabinet 7 (TC2). 

Temperatures did not increase during the ensuing fire because the fire was extinguished 

quickly.

(a) (b)

Figure 4.10-9. SWGR Test 3 Thermocouple Data

Table 4-11. SWGR Test 3 TC Results.

TC Max T ( ̊C) 

TC1-F-70-Cab6 28

TC2-F-70-Cab7 49

TC3-F-70-Cab8 * 

TC4-F-70-Cab9 * 

TC5-V-Cab8 * 

*Data was corrupt
4-50

The pressures during the arc are shown in Figure 4.10-10. Cabinet 8 had positive noise spikes 

at 0.116 and 0.180 seconds and numerous negative noise after 0.04 seconds that do not have a 

known cause. The Cabinet 8 response also had a base line zero shift from 0.7 to 0.9 seconds 

(similar to SWGR Test 1) and at the start of the arc that was considered in the analysis. The 

Cabinet 8 pressure closer to the arc had a higher maximum and occurred earlier than the 

Cabinet 7 pressure that was further from the arc. The pressures were low because the vents at 

the top of Cabinets 7 and 8 allowed for significant pressure relief. The maximum pressures are 

indicated by the arrows in Figure 4.10-10(c) and (d). 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the arc 

(a) (b)

(c) (d)

Test 3 Pressure 1 Cab. 7

5.5 ± 2.1 kPa (0.8 ± 0.2 psi)

@ 0.016 s 

Test 3 Pressure 2 Cab. 8

13.8 ± 1.4 kPa (2.0 ± 0.2 psi)

@ 0.0155 s

Figure 4.10-10. SWGR Test 3 Pressure Data
4-51

The arc duration was 2.911 seconds with total energy of 64.2 MJ, seen in Figure 4.10-11. The 

energy analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied 

current multiplied by the time step and each time step is shown. “Energy Total” is the 

cumulative sum of the energy in each time step.

Figure 4.10-11. SWGR Test 3 Arc Energy
4-52

4.11 SWGR Tests 1 through 3: Summary of Electrical Conditions 

Table 4.11-1 shows the electrical conditions measured by KEMA. 

Table 4-12. SWGR Tests 1 through 3 Electrical Results (1). 

Test OCV

(KV) Phase Sym(kA)

Sym 

@End 

(kA)

Peak 

(kA)

Curr. 

Dur.

(sec)

Arc 

Energy

(MJ)

Freq 

@End 

(Hz)

Phase

Arc Volts

1 7.1

A 33.7 22.8 58.4

2.044

13

45

A-N 330

B 22.9 22.6 36.4 15 B-N 375

C 31.8 22.5 53.8 14 C-N 349

AVG 29.5 22.6 49.5 Σ42 AVG L-L 609

2 7.1

A 34.3 22.9 59.5

2.957

22

40.8

A-N 359

B 25.8 25.4 37.9 25 B-N 435

C 31.5 22.2 53.5 11 C-N 259

AVG 30.5 23.5 50.3 Σ58 AVG L-L 608

3 7.1

A 34.0 22.6 58.9

2.911

22

40.8

A-N 365

B 23.3 22.9 36.7 23 B-N 412

C 32.1 22.4 54.1 19 C-N 320

AVG 29.8 22.6 49.9 Σ64 AVG L-L 633

(1) See Table 2-16 for abbreviations and acronyms used in this table.

4.12 SWGR Tests 1 through 3 Qualitative Summary 

Although the configuration was slightly changed from Test 1 for Tests 2 and 3, there were many 

similarities in the test results. However, the increase in arc duration produced some differences 

in the tests, too.

1. Ensuing Fire: An ensuing fire occurred after the configuration and test conditions were 

changed between Test 1 and Test 2. The extra one second of arc duration in Tests 2 

and 3 provided enough heat to ignite the internal cables. The ensuing fire was allowed 

to burn in Test 2, providing new long-term data on the ensuing fire and showed fire 

spreading to all cabinets. In Test 3 (and future SWGR tests) the fire was extinguished 

after a few minutes. 

2. Damage: In all of the tests, there was oxidation of the aluminum bus bars and the 

associated heat release during the arc. The vertical bus bars in Cabinet 8 in Tests 2 and 

3 were oxidized and melted by the arc; Test 1 only resulted in minor bus bar oxidation. 

Bus bar oxidation in Test 2 and 3 likely contributed to the ignition of the ensuing fire. 

There was a variety of damage to the cabinets and internal cables. Since there was no 

internal or ensuing fire in Test 1, there was minor damage; mostly soot deposits, and 

discoloration, and no damage to the internal breakers. Tests 2 and 3 resulted in severe 

internal cable consumption but with minor external damage. 
4-53

The SWGR cabinet outer walls did not have major deformation like the DP and MCC 

cabinets. The cabinet outer walls are thicker and the large vent on the top directly above 

the arc kept the pressure low. Additionally, the arcs in SWGR Tests 1 through 3 were 

not directly inside an outer cabinet wall so external wall damage was minimal. There 

was significant bending, deformation, or burn-through of the internal walls directly 

exposed to the arc. 

3. Calorimetry: In all three tests, the resultant maximum heat flux occurred at 1.5 m (5 ft) 

above the cabinets because the flux from the arc travels through the single steel plate 

above the arc to the slug calorimeter. At other locations, the heat passes through an 

internal wall and external panels to reach the calorimeters. Also, the top slug 

calorimeter can view the flames and plasma that spread across the top of the cabinet as 

they exit the roof vent. 

4. Temperature: During these tests, many of the thermocouples failed for various reasons. 

Of the remaining valid measurements, it was evident that the temperatures increased in 

Tests 2 and 3, as compared to Test 1, as expected. 

5. Pressure: The measured pressures for Tests 1 through 3 were very low since there 

were vents at the top of the tested cabinets (Cabinets 7, 8). For Tests 2 and 3 the 

pressures were highest in Cabinet 8 where the arc occurred, as expected (there was no 

Cabinet 7 data to compare for Test 1). 

6. Arc Energy: In all tests the total energy was proportional to the arc duration for the given 

electrical testing conditions. All tests showed a smooth increase of the total energy 

during the arc indicating stable arc conditions and the target arc durations were achieved 

in all the tests. Based on the occurrence of ensuing fires, the electrical energy threshold 

for an ensuing internal cable fire was about 60 MJ. This is likely higher than what was 

sufficient to ignite an ensuing fire in the DP tests because heat was lost through the vent 

above the arc.

5-1 

5 Switchgear HEAF Tests 4 through 6, Two Arcs Tests - KEMA 

(March 2014, March 2015)

5.1 SWGR Tests 4 through 6 Overview

The purpose of these tests was to obtain the basic data for SWGR like the June 2013 tests. 

However, the tests presented in this section, conducted in March 2014 and March 2015, used

two arcs, one in Cabinet 7 and one in Cabinet 8, to be more like the assumed condition of the 

Onagawa event. 

5.2 SWGR Tests 4 through 6 Summary of Results

The key test parameters and results are in the table below; two arcs were initiated for each test. 

Tests 4 and 5 were conducted at the same parameters: Arc 1 target test voltage was nominally

6.9 kV and the target test current was 23 kA (symmetrical, sym) for 2.5 seconds, Arc 2 was also 

nominally 6.9 kV but with a test current of 35 kA for 3 seconds for Tests 4 and 5. Test 6 had 

target durations of 1 second for Arc 1 and 3 seconds for Arc 2. 

Table 5-1. SWGR Tests 4 through 6 Summary of Results. 

Test Arc

Volt (kV)

(1)

Curr (kA) 

(2)

Test 

Peak 

Current 

(kA) (3)

Arc

duration 

(sec) (4)

Arc 

Energy

(MJ) 

Internal 

Max 

Press

(kPa/psi)

Ext Max 

Flux

(kW/m2

) 

Ensuing fire?

Key 

Observations

4 

1 7.0/0.726

24.5/24.4 51.3 2.52.354 64.6 23.4 ± 0.73.4 ± 0.1 46 (5) Yes. Small fire 

after Arc 1 and 

large fire after 

Arc 2 from 

aluminum 

oxidation.

2 7.0/0.727

34.1/33.3 74.8 2.02.081 78.4 12.4 ± 0.61.8 ± 0.1 220 (6)

5 

1 7.0/0.639

24.4/25.7 50.1 2.52.316 57.2 17.9 ± 0.72.6 ± 0.1 37 (5) Yes. Small fire 

after Arc 1 and 

small fire after 

Arc 2. 2 7.0/0.603

33.9/33.3 60.3 2.02.071 62.0 13.1 ± 0.71.9 ± 0.1

113

(5,7)

6 

1 

7.0/0.882

24.6 / 

21.4

56.2 1.0

1.129 26.5 12.4 ± 1.41.8 ± 0.2 - (8) No. Energies 

including 

aluminum 

oxidation were 

too low. 2 

7.0/1.007

33.1 / 

33.5

75.5 3.0

0.568 21.1 9.0 ± 1.41.3 ± 0.2 53 (9)

Notes:

(1) The voltage is shown as the target voltage / arc Line-to- Line (L-L) voltage. 

(2) The symmetric arc current slowly drops during the test as the arc impedance increases. 

This shows the test start current / test end current. These are average currents of all 3 

phases. 

(3) This is the peak current of for any phase or time, usually the asymmetric current at the start

(4) The duration is shown as the target duration and the actual test duration below it. 

(5) The maximum flux was measured at the top, 1.5 m (5 ft) above Cabinet 8 (S5). 

(6) The highest flux was measured 0.91 m (3 ft) in front of Cabinet 7 (S1), which had the large

horizontal bus bar arc and aluminum oxidation. This was the highest flux in all NRA tests. 

(7) A high flux of 67 kW/m2 was measured at 0.91 m (3 ft) from the rear of Cabinet 8, indicating

a strong arc in the secondary side of Cabinet 8, as planned. 
5-2 

(8) There was no slug calorimeter data for Arc 1 because the data trigger failed. 

(9) The maximum flux was measured at 0.91 m (3 ft) from the top rear of Cabinet 8 (S10). 

The key results from the SWGR 2-arc tests at KEMA were: 

• Test 4, Arc 2 had severe horizontal bus bar arcing, which was similar to the assumed 

second arc in the 2011 Onagawa event scenario. The arc energy progressed to a 

significant fire and extensive damage on the front of Cabinet 7, similar to Onagawa. 

This test confirms that the aluminum bus bar oxidation probably contributed to the large 

ensuing fire at Onagawa. 

• In Arc 2 of Tests 5 and 6, there were strong arcs in the secondary (rear) of Cabinet 8, as 

planned. However, the damage to the circuit breaker was not as severe as the event at 

Onagawa. In Test 5 Arc 2, the hot gas and plasma were expelled up through the roof 

and out the vent rather than down toward the breaker. In Test 6 Arc 2, the hot gas and 

plasma remained in the rear of the cabinet but the damage to the breaker was still minor. 

• The energies for the arcs were greater than 60 MJ in SWGR Tests 4 and 5, resulting in

ensuing fires. This is similar to the result in SWGR Tests 1 through 3. The energies in 

Test 6 were not adequate for an ensuing fire because a shorter Arc 1 was planned (1 

second versus 2 seconds) and the second arc was extinguished by a hot short that 

opened the Cabinet 8 breaker carrying the arc current from the KEMA source. 

• These tests had higher total energies than Tests 2 and 3 because there were two 

electrical arcs and much more aluminum oxidation, especially in the case of Test 4, Arc 

2. The fire in Test 4 quickly spread to the other cabinets. The cables were pre-heated 

by Arc 1 so the cable fire spread was very rapid in Test 4, Arc 2. 

• Test 4, Arc 2 showed the highest external flux in any NRA test. None of the cables in 

the test cable trays on the top of the SWGR ignited but there was some fire damage; 

there was localized burning where the cables were in contact with the tray rungs, and 

charring.

• Test 6, Arc 2 demonstrated the important behavior that arcs can move from the initial 

ignition point because the arc ignited at the insulator but moved to the end of the bus 

bars along the path of the current. This also demonstrates that arc behavior is difficult to 

predict because in an identical test configuration in SWGR Test 5, Arc 2 stayed at the 

initial ignition point. 

5.3 SWGR Tests 4 through 6 Cabinet Lineup and Combustible Load

The configuration was very similar to SWGR Test 1 through 3 tests except a working breaker 

was used in Cabinet 8 to allow two arcs. Arc 1 was initiated in the primary side of Cabinet 7

with the breaker open and Arc 2 was initiated in the secondary side of Cabinet 8 with the 

breaker closed. The bus bars were modified for the working breakers. The bus bars in Cabinet 

7 were moved up (this makes the vertical bus bars much longer than in the June 2014 tests), as 

seen in Figure 5.3-1. Insulator bushings were added to the secondary side of Cabinet 8 at the 

arc location. Cabinet 8 was modified for a working circuit breaker so the primary insulators were 

moved higher in the cabinet and secondary insulators were added, as seen in Figure 5.3-2. The 

shorting wires to start the arc were on the primary side of Cabinet 7 and seconday side of 

Cabinet 8, as seen in Figure 5.3-4. Cabinets 6, 7 and 10 were the same as in the previous 
5-3 

SWGR tests. Tests 4 and 5 were 5-cabinet line-ups and Test 6 was a 3-cabinet line-up without 

Cabinets 9 and 10 to enable a fit under a hood calorimeter. 

Figure 5.3-1. SWGR Tests 4 through 6: Cabinet 7

Bus bars

0.056.473.992.2110.7121.4

236.7

228.1

214.4

117.3

0.0

0.0

55.491.9

128.5218 7

All dimensions 

in cm
5-4 

 

Figure 5.3-2. SWGR Tests 4 through 6: Cabinet 8

Breaker

All dimensions 

in cm

0.0

73.992.5110.7154.7

236.7

228.3

214.4

147.6

0.0

0.06.6

47.254.6

128.5218.7
5-5 

Figure 5.3-3. SWGR Tests 4 through 6: Schematic of Cabinets 6, 9, and 10

 

Figure 5.3-4. SWGR Tests 4 through 6 Cabinets 7 and 8 Shorting Wire Locations

Primary Secondary 

Shorting Wires

(in red)
5-6 

The combustible loads were the same as Tests SWGR Tests 1 through 3 except the cables in 

Cabinets 9 and 10 were not needed for Test 6, 3-cabinet test. 

In SWGR Tests 4 through 6, a cable tray, loaded with cable was installed 46 cm (18 in) above 

the cabinet. In each test, the tray was loaded with 44 CV-2 cables, each 1.02 m long plus 16 

CV-4 cables, each 1.02 m long. 

5.4 SWGR Tests 4 through 6 Temperature, Heat Flux and Pressure 

Instrumentation 

The SWGR Tests 4 and 5 had instrumentation similar to SWGR Tests 1 through 3. The 

instrumentation locations are in Figure 5.4-1. SWGR Test 6 had similar instrumentation but also 

included a portable oxygen calorimeter and PTs provided by NIST as shown in Figure 5.4-2

(see References [7, 11] for more information on the NIST instruments). A cable tray was added 

as an ignition test target on the top of the SWGR. 

Slugs 1, 2, 3, 4, and 7 are 0.91 m (3 ft) from the cabinet. Slug 5 is 1.5 m (5 ft) above the 

cabinet. The bare TCs were 15.2 cm (6 in) in front of the cabinets in Tests 4 and 5 only. PTs 

were added to the cable tray only in Test 6. Left side slug calorimeters are not used because 

the left side is far away from the arcs and heat. 
5-7 

Front View

Top View

Figure 5.4-1. SWGR Tests 4 and 5, Instrument Locations 
5-8 

Table 5-2. SWGR Test 4 and 5 Calorimeter and TC Locations. 

Slug or 

TC

From Floor 

(cm/in) Position Slug or TC Name

S1 178 (70) Front (F) S1-F-70-Cab7

S2 178 (70) Front S2-F-70-Cab8

S3 91 (36) Front S3-F-36-Cab8

S4 178 (70) Rear (R) S4-R-70-Cab8

S5 381 (150) Top (T) S5-T-150-Cab8

S6 91 (36) Front (F) S6-F-36-Cab7

S7 91 (36) Rear (R) S7-R-36-Cab8

TC1 178 (70) Front TC1-F-70-Cab6

TC2 178 (70) Front TC2-F-70-Cab7

TC3 178 (70) Front TC3-F-70-Cab8

TC4 178 (70) Front TC4-F-70-Cab9

TC5 422 (166)* Vertical Duct TC5-V-Cab8

TC6 178 (70) Front TC6-F-70-

Cab10

* Located near the top of the duct on the side 6 inches from the duct. 

Table 5-3. SWGR Test 6 Calorimeter Locations. 

Slug or 

TC

From 

Floor

cm (in)

Position Slug Name

S1 178 (70) Front (F) 7 S1-F-70-Cab7

S2 91 (36) Front 7 S2-F-36-Cab 7

S3 41 (16) Front 7 S3-F-16-Cab7

S4 178 (70) Front 8 S4-F-70-Cab8

S5 91 (36) Front 8 S5-F-36-Cab8

S6 41 (16) Front 8 S6-F-16-Cab8

S7 178 (70) Right Side (RS) S7-RS-70-Cab8

S8 91 (36) Right Side S8-RS-36-Cab8

S9 178 (70) Rear (R )7 S9-R-70-Cab7

S10 178 (70) Rear 8 S10-R-70-Cab8
5-9 

Top view

Figure 5.4-2. SWGR Test 6 Instrument Locations 

Cable Tray Detail 

Front View
5-10

5.5 SWGR Test 4 Key Observations (March 2014) 

Two arcs were initiated in this test; the first at 7 kV at 24.5 kA with a target duration of 2.5 

seconds, and the second arc was initiated 3.7 minutes later at 7 kV and 34.1 kA with a target 

duration of 2.0 seconds, see Figure 5.5-1. The target arc durations were nominally achieved; 

Arc 1 had an energy of 64.6 MJ and Arc 2 had an energy of 78.5 MJ. Although the second arc 

was initiated in Cabinet 8, the resultant arc was at the Cabinet 7 top horizontal bus bar (as in the 

assumed Onagawa event) because the current drawn by the second arc on the secondary side 

of Cabinet 8 was very large. The high current caused the horizontal bus bars in Cabinet 7 to 

flex and contact each other, causing a very large arc and disrupting additional current to Cabinet 

8, quickly extinguishing the initial arc in Cabinet 8. Therefore, the Cabinet 8 breaker secondary 

side had little damage. The first arc in Cabinet 7 resulted in high energy because there was 

high aluminum bus bar oxidation, causing an ensuing fire after Arc 1. The arrow in Figure 

5.5-1(c) shows the direction that the Cabinet 8 door opened at about 0.037 seconds when the 

arc moved from Cabinet 8 to Cabinet 7.

(a) Test 4 Arc 1 (in Cabinet 7)

(b) Test 4 Arc 2 (initiated in Cabinet 8 and moved to 7), 3:40 after Arc 1

(c) Test 4 Arc 2 Cabinet 8 Door opening at 0.037 sec

Figure 5.5-1. SWGR Test 4 Arcs
5-11

An ensuing fire occurred after Arc 1, and remained in Cabinet 7 and at the bottom of the vertical 

duct before Arc 2 was initiated. Figure 5.5-2(a) shows thermal images of the SWGR before the 

second arc. Figure 5.5-2(b) shows the ensuing fires after the Arc 2, just before the fire was 

manually extinguished. At the time the fire was extinguished the fire had spread into Cabinets 6 

and 8 but Cabinets 9 and 10 had no fire. 

(a) Before Second Arc at 3:40 after Arc 1

(b) Maximum after Second Arc at 2:33 after Arc 2

Figure 5.5-2. SWGR Test 4 Thermal Image Ensuing Fire

There was heavy damage at the top of Cabinet 7 from the ensuing fires and aluminum bus bar 

oxidation as shown in Figure 5.5-3. As shown in Figure 5.5-3(a) the front of Cabinet 7 had 

showed charring like Onagawa from high heat from aluminum bus bar oxidation. Some of the 

soot was washed off by firefighting.

As shown in Figure 5.5-3(b) the cable tray 45.72 cm (18 in) above the cabinet had some 

scorching on the side but the cables did not ignite and only had some minor scorching. SWGR 

Test 4 had the largest amount of fire and plasma that escaped the top vent that was deflected 

toward the cable tray by the vent cover plate. Yet, in these harsh conditions, the cables did not 

ignite. The cables did scorch where they crossed the bus bars as shown in Figure 5.5-3(c). 

Figure 5.5-3(d) shows the cables in the vertical duct were completely burned.
5-12

(a) Cabinets 6-10 

(b) Cabinet 7 top (c) Cable Tray (from bottom) (d) Vertical Duct

Figure 5.5-3. SWGR Test 4 Exterior Damage

Figure 5.5-4 shows the interior damage, the heavy soot damage, and orange discoloration from 

high temperatures. Figure 5.5-5 (a) through (f) shows cable fire damage in all the cabinets. 

Some cables burned in all cabinets except Cabinet 10. In Cabinet 6, a few centimeters of the 

cables burned where they entered from Cabinet 7. The Cabinet 7 upper cables were 

completely burned and had detached from the cabinet and slumped down. The Cabinet 8 upper 

cables were mostly burned and remained in place and attached. In Cabinet 9 about 10 percent 

of the upper cables burned where the cables entered from Cabinet 8 and the cables detached 

and slumped. The cables in Cabinet 10 did not burn. Figure 5.5-5 (d) shows the soot was 

throughout the interior of Cabinet 8. 
5-13

Figure 5.5-4. SWGR Test 4 Interior Damage 
5-14

(a) Cabinet 6 Cables (b) Cabinet 7 Cables

.5

(c) Cabinet 8 Front Cables (d) Cabinet 8 Rear Cables

(e) Cabinet 9 Cables (f) Cabinet 10 Cables

Figure 5.5-5. SWGR Test 4 Interior Damage, Detailed
5-15

Figure 5.5-6 shows the insulator and bus bar damage. Figure 5.5-6(a) and (b) show that the 

front horizontal aluminum bus bar was completely destroyed as were the vertical bus bars; the 

white dashed lines show the initial location of the front bus bar. The middle, horizontal 

aluminum bus bar was bent from the strong arcing current contacted the front bus bar, shorted, 

and the front bus bar oxidized. 

Figure 5.5-6(c) shows that most of the vertical bus bars were destroyed, caused by energy

released from the aluminum exothermic reaction and electrical energy in Arc 1 and Arc 2. This 

almost complete destruction did not happen in SWGR Tests 1 through 3 (only partial oxidation) 

or in Tests 5 and 6. Only part of the vertical bus bars burned in Test 5 even though the planned 

test conditions were the same. 

Figure 5.5-6(d) shows light to moderate damage on the Cabinet 8 insulators. Figure 5.5-6(e) 

shows the Cabinet 8 front (primary) insulators stayed fairly intact but did crack and have some 

damage. There is a small hole burned in the left wall probably from Arc 1 on the right 

connection in Cabinet 7 that burned through the wall toward Cabinet 8 and the plasma exiting 

this hole caused most of the damage. 

Figure 5.5-6(f) shows that the Cabinet 8 secondary insulators had minor damage (less than 5 

mm was oxidized) from the short duration arc that occurred because the shorting current was 

stopped by the Cabinet 7 horizontal bus bar short and the Cabinet 8 arc extinguished.
5-16

(a) Cabinet 7 Horizontal Bus Bars (b) Cabinet 7 Horizontal Bus Bars

(c) Cabinet 7 Vertical Bus Bar 

Location (d) Cabinet 8 Bus Bars (Front and Rear)

(e) Cabinet 8 Bus Bars (Front) (f) Cabinet 8 Bus Bars (Rear) 

Figure 5.5-6. SWGR Test 4 Insulator and Bus Bar Damage 
5-17

Breaker 8 only had some soot covering as shown in Figure 5.5-7(b) with some minor debris on 

the primary side from the damage to the primary insulators. Breaker 7 had damage at the top 

primary side under the arc position but the secondary side was not damaged - only some soot 

was observed. There was some front panel discoloration of Circuit Breaker 7 from the heat and 

the control cable bundle on the front left burned. This damage was much less severe than the 

damage observed in the Onagawa event.

(a) Cabinet 7 Breaker (b) Cabinet 8 Breaker

Figure 5.5-7. SWGR Test 4 Breaker Damage

Temperatures measured at the slug locations are shown in Figure 5.5-8. Arc 1 was intentionally 

extinguished at 2.354 seconds and Arc 2, occurring 3 minutes 40 seconds minutes later, was 

intentionally extinguished at 2.081 seconds, as planned. Most of the slugs had high noise 

during the arc, probably due to EMI. The highest temperature at the end of Arc 1 was at the top 

(S5) that was detecting the hot gas and flames escaping from the top vent. Slug 1, in front of 

Cabinet 7 where the arc was located also measured a high temperature. 

Slug 5 fell from position at the end of Arc 1 (the supporting line burned and broke; the line 

supporting the TC in the front of the cabinets also burned and fell as discussed later) so the S5 

temperature data after 3 seconds is taken with the slug calorimeter laying top of Cabinet 8 with 

the copper disk facing the top of the cabinet. S5 data cannot be analyzed for flux after Arc 1. 

The highest temperature at the end of Arc 2 was at the top front of Cabinet 7 (S1), probably

because the high heat from the horizontal bus bar oxidation in Cabinet 7. 

Decreasing temperatures between Arc 1 and Arc 2 show that all slug calorimeters were cooling. 

For S1 and S6 in the front of Cabinet 7, the temperatures were increasing slightly after 2 

minutes indicating some heat was probably escaping a small fire in Cabinet 7 or residual heat 

from Arc 1. After Arc 2, Slugs 1, 2, 6, and 3 showed slightly increasing temperatures after 5 

minutes probably from the ensuing fire. The large ensuing fire observed in Test 2 was not 

allowed to grow in Test 4 and the fire was manually extinguished at 7.5 minutes. 
5-18

(a)

(b) (c)

Figure 5.5-8. SWGR Test 4 Calorimetry Data: Temperature

Table 5-4 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux was 

measured to be 46 kW/m2 at 1.5m (5 ft) from the top of the cabinet (S5), similar to Tests 1

through 3. For Arc 2, the maximum flux of 220 kW/m2 was measured at the front of Cabinet 7 

near the height of the oxidizing horizontal bus bar (S1). This was the highest flux reported in 

any of the HEAF tests in this report. High fluxes were also measured in front of the cabinet (S2, 

S3, and S6). Arc 2, which was a very short duration, was initiated in the rear of Cabinet 8

resulting in very low fluxes at that location (S4, S7). The maximum slug temperatures are also 

shown to indicate the maximum temperature a metal object could obtain during the arc. 
5-19

Table 5-4. SWGR Test 4 Flux Results.

Slug

Arc 1 Arc 2

ΔT ( ̊C) Flux 

(kW/m2) Max T ( ̊C) ΔT ( ̊C) Flux (kW/m2)

Max T 

( ̊C)

S1-F-70-Cab7 10.6 28 116 73.8 220 116

S2-F-70-Cab8 6.4 17 59 36.3 107 59

S3-F-70-Cab8 2.0 5 47 27.2 80 47

S4-R-70-Cab8 2.5 6 22 2.3 7 22

S5-T-150-Cab8 17.6 46* 61* 35.9 * * 

S6-F-36-Cab7 3.4 9 71 45.0 133 71

S7-R-36-Cab8 1.7 4 19 2.8 8 19

*For first 2 seconds of Arc 1 only.

** S5 fell and was not measuring flux after 2 seconds of Arc 1.

The temperatures measured by the TCs are shown in Figure 5.5-9. Table 5.5-2 shows the 

maximum temperature results. Thermocouples T1 through TC4 and TC6, in the front of the 

cabinets fell to the floor during Arc 1, consequently, the TC measurements were of the floor and 

the exact positions are not known so the data is not useful after Arc 1. For Arc 1, the highest 

temperature, 59  ̊C (138  ̊F), was measured at the front of Cabinet 7 (TC2) where the arc 

occurred. The only valid data after Arc 1 was for in the vertical duct (TC5), which showed 

increasing temperatures during the arcs and in the ensuing fire as expected with a maximum 

temperature of 160  ̊C (320  ̊F). The TCs cannot practically be used to estimate flux. 
5-20

(a)

(b) (c)

Figure 5.5-9. SWGR Test 4 Thermocouple Data

Table 5-5. SWGR Test 4 TC Results.

TC Arc 1*

Max T ( ̊C)

Post Arc 1

Max T ( ̊C)

Arc 2*

Max T ( ̊C)

Post Arc 2

Max T ( ̊C)

TC1-F-70-Cab6 28 **  

TC2-F-70-Cab7 59 **  * **

TC3-F-70-Cab8 34   ** 

TC4-F-70-Cab9 14 **  

TC5-V-Cab8 31 33 55 159

TC6-F-70-Cab10 13 **  ** **

*To allow for noise, the maximum temperature is the measured value at the end of the arc.

**The TC support burned and fell during Arc 1 so data is not valid. 
5-21

The pressures during the arc are shown in Figure 5.5-10 and Figure 5.5-11. The pressures for 

both arcs were higher than SWGR Tests 1 through 3 but lower than the MCC and DP tests low 

because the vents at the top of Cabinets 7 and 8 allowed the pressure to escape. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc, then including a nominal uncertainty for the noise in the signal just before the 

arc. 

For Arc 1, there were numerous noise spikes for Cabinet 7 and Cabinet 8 and both had a noise 

spike at 0.005 seconds before the maximum pressures and at the end. Both cabinet pressures 

had a zero shift at the start of the arc that has been considered in the reported results. The 

Cabinet 7 pressure closer to the arc had a higher maximum and occurred earlier than the 

Cabinet 8 pressure that was further from the arc. The maximum pressures are indicated by the 

arrows in Figure 5.5-10(c) and (d).

(a) (b)

(c) (d)

Test 4 Pressure 1 Cab. 7 Arc 1

23.4 ± 0.7 kPa (3.4 ± 0.1 psi)

@ 0.0129 s

Test 4 Pressure 2 Cab. 8 Arc 1

12.4 ± 0.7kPa (1.8 ± 0.1 psi)

@ 0.0126 s

Figure 5.5-10. SWGR Test 4 Pressure Data, Arc 1
5-22

For Arc 2, there were numerous noise spikes for Cabinet 7 and Cabinet 8 and both had noise 

spikes at 0.005 seconds before the pressure maximums, another at 0.5 seconds, and numerous 

spikes as the arc terminated probably because the arc in the top horizontal bus bars in Cabinet 

7 became unstable and caused high noise. Both cabinet pressures had a zero shift at the start 

of the arc that is considered in the reported results. 

The Cabinet 8 pressure closer to the arc had a higher maximum that occurred earlier than the 

Cabinet 7 pressure that was further from the arc. The pressure in Cabinet 8 had some small 

pressure spikes from 0.04 to 0.055 seconds after the door on Cabinet 8 opened when the arc 

moved from the back of Cabinet 8 to Cabinet 7 about 0.037 seconds after the arc initiation 

based on high speed film analysis. 

The Arc 2, Cabinet 7 pressure had a distinct sinusoidal response for the next four peaks 

immediately after the maximum peak at 0.0267 seconds that had a frequency of about 140 Hz. 

The amplitudes of these peaks were about the same as the initial peak. The maximum 

pressures are indicated by the arrows in Figure 5.5-11(c) and (d). This may have been from 

pressure waves reflecting within the cabinet. 

(a) (b)

(c) (d)

Test 4 Pressure 1 Cab. 7 Arc 2

6.9 ± 0.6 kPa (1.0 ± 0.1 psi)

@ 0.0267 s

Test 4 Pressure 2 Cab. 8 Arc2

12.4 ± 0.6 kPa (1.8 ± 0.1 psi)

@ 0.0215 s

Figure 5.5-11. SWGR Test 4 Pressure Data, Arc 2 
5-23

The Arc 1 duration was 2.35 seconds with total energy of 64.6 MJ, seen in Figure 5.5-12. Arc 2 

was 2.081 seconds with a total energy of 78.4 MJ. The energy analysis methods are in 

Appendix A. The “Energy” is calculated as volts multiplied current multiplied by the time step 

and each time step is shown. “Energy Total” is the cumulative sum of the energy in each time 

step. 

SWGR Test 4, Arc 2 showed the highest energy of any arc in the NRA tests in this report 

probably because the shorted horizontal bus bars provided a longer arc gap at the arc point 

than the gap in other tests and the arc voltage was nominally 730 V versus 600 V for SWGR 

Tests 1 through 3.

(a)

(b)

Figure 5.5-12. SWGR Test 4 Arc Energy (both arcs)
5-24

5.6 SWGR Test 5 Key Observations (March 2014) 

Two arcs were initiated in this test; the first at 7 kV at 24.4 kA with a target duration of 2.5 

seconds, and the second arc was initiated 2 minutes and 55 seconds later at 7 kV and 33.9 kA 

with a target duration of 2.0 seconds (see Figure 5.6-1). The target arc durations were 

nominally achieved and Arc 1 had an energy of 57.2 MJ and Arc 2 had an energy of 62.0 MJ. 

The arc conditions and arc wires were very similar to Test 4 but the ensuing fire was smaller 

and the arcing was different. As in Test 4, two arcs occurred and Arc 1 had adequate energy to 

ignite an ensuing fire. However, Arc 2 showed the random nature of arc events because the 

bus bars in Cabinet 7 did not flex and make contact as in Test 1 and instead Arc 2 occurred in 

the secondary side of Cabinet 8 and remained there as planned. 

Figure 5.6-1 shows the arcs at the start and end of each arc. The flames in Arc 2 were much 

smaller than in Test 4 because the horizontal bus bars in Cabinet 7 did not arc. 

(a) Test 5 Arc 1 (initiated in Cabinet 7)

(b) Test 5 Arc 2 (initiated in Cabinet 8); 2:56 after Arc 1

Figure 5.6-1. SWGR Test 5 Arcs
5-25

As shown in the thermal images in Figure 5.6-2, an ensuing fire occurred after Arc 1, and before 

Arc 2. The additional energy from Arc 2 accelerated the ensuing fire as seen in the thermal 

images before and after the arc. 

(a) Arc 1 (b) Before Arc 2 (2:56 after Arc 1)

(b) Arc 2 (d) Maximum After Arc (2 :06 after Arc 2)

Figure 5.6-2. SWGR Test 5 Thermal Image Ensuing Fire

The fire was manually extinguished in about 3 minutes after Arc 2 and the fire was not allowed 

to fully spread as in Test 2. There was no charring of the exterior and very little exterior 

damage, as seen in Figure 5.6-3(a). There was charring on the exterior of the cable tray. The 

vertical duct was charred but the same duct was used in Test 4 so this charring is primarily from 

Test 4. The cables in the vertical duct did not burn. Test 5 had the longest duration of Arc 2 in 

the rear part of the cabinet for all SWGR tests and this caused the roof to deform as shown in in 

Figure 5.6-3(d). Figure 5.6-3(c) and (e) show that the exterior cables in the tray did not burn but 

had slight charring where the cables crossed the support rails of the cable tray. 
5-26

(a) Front Cabinet 6-10

(b) Top of Cabinets (from Cabinet 8 side) (c) Cable Tray (from top)

(d) Cabinet Top (from rear) (e) Cables (removed from tray)

Figure 5.6-3. SWGR Test 5 Exterior Damage
5-27

As shown in Figure 5.6-4, there was less internal damage than in Test 4 because there was less 

aluminum bus bar oxidation. The Cabinet 7 internal panels in front of the vertical bus bars bent 

but did not fall off like in Test 4. Figure 5.6-5(a) through (e) show the cable damage in the 

cabinet interiors before the fire was extinguished. In Cabinet 6, the first 15.24 cm (6 in) 

approximately of cable from Cabinet 7 was burned. In Cabinet 7, the cables were completely

burned. In Cabinet 8, approximately the first 15.24 cm (6 in) of cable from Cabinet 7 was 

burned. In Cabinet 9, there was no cable burning but the cover on the plastic wire duct on the 

internal panel was blown off. In Cabinet 10 there was no burning and little damage 

Figure 5.6-5(f) shows the damage at the top inside rear of Cabinet 8 above the Arc 2 location 

that caused the damage to the roof shown in Figure 5.6-3(d). 

Figure 5.6-4. SWGR Test 5 Interior Damage
5-28

(a) Cabinet 6 Cables (b) Cabinet 7 Cables

(c) Cabinet 8 Cables (d) Cabinet 9 Cables

(e) Cabinet 10 cables (f) Cabinet 8 Interior

Figure 5.6-5. SWGR Test 5 Interior Damage, Detailed
5-29

Figure 5.6-6 shows the damage to the bus bars in Cabinet 7 from Arc 1 and Cabinet 8 from Arc 

2. In Cabinet 7, the vertical bus bars did not burn completely in Arc 1 like in Test 4. So, there 

was less aluminum oxidation energy in Arc 1 for Test 5. The fire was not as big and rapid as 

Test 4, based on the video and thermal images. The insulators were completely destroyed. 

In Cabinet 8, the arc broke through the horizontal panel just above the secondary insulators and 

arc plasma entered the bus bar compartment then from there went directly up to the vent 

opening and plate on top of the cabinet. There was also a hole burned through the rear, vertical 

panel of the bus bar compartment and some damage to the cabinet roof directly behind the bus 

bar compartment. One of the insulators was partially intact, the other two were destroyed. The 

damage in the secondary side of the cabinet was much less than at Onagawa. 

(a) Cabinet 7 Vertical Bus Bars

(b) Cabinet 7 Insulators 1, 2 and 3

(destroyed)

(c) Cabinet 8 Primary Insulators

(d) Cab. 8 Primary and Secondary 

Insulators

Figure 5.6-6. SWGR Test 5 Insulator and Bus Bar Damage 

Figure 5.6-7 shows the damage to the breakers. Breaker 7 only had some soot covering and no 

major damage. This was the second test where this particular Breaker 7 was used as a 

“dummy” so the damage in Figure 5.6-7(a) is in addition to the damage shown in Figure 5.5-7(a) 

for SWGR Test 4. Breaker 8 had damage at the top secondary side under the arc position but 

the primary side was not damaged - only some soot was observed. There was some front 

panel discoloration from the heat. The bushings were not damaged like the bushings at 

Onagawa that completely shattered. 
5-30

In Test 5, the hot gas and plasma went up to the cabinet vent. In Onagawa, the hot gas and 

plasma possibly went into the breaker because the arc may have been inside the insulators. In 

any case, the breaker damage at Onagawa was much more severe. 

(a) Breaker 7 (b) Breaker 8

(c) Breaker 7, side (d) Breaker 8

Figure 5.6-7. SWGR Test 5 Breaker Damage
5-31

Temperatures measured at the slug locations are shown in Figure 5.6-8. Arc 1 was intentionally 

extinguished after 2.316 seconds and Arc 2, approximately 3 minutes later, was intentionally 

extinguished after 2.071 seconds, as planned. Most of the slugs had high noise during the arc, 

probably due to EMI from the nearby power supply. The highest temperature at the end of Arc 

1 was measured at 1.5 m (5 ft) above the cabinet (S5), probably because hot gases, flames and 

plasma escaped through the roof vent as in SWGR Tests 1 through 4. 

The highest temperature at the end of Arc 2 was also at the top (S5) but had some unknown 

malfunction approximately 0.5 seconds after the arc. After that, the response was erratic and 

decreasing, as if from an unsteady but shrinking fire. Averaging of the data to remove noise 

showed that the erratic behavior was not noise. As expected, the next highest temperature was 

measured at the rear of Cabinet 8 where Arc 2 was located (S7). This was the first SWGR test 

where significantly higher slug temperatures were seen in the rear of the cabinets as expected 

because previous tests had arcs in the front, primary side compartments. 

Decreasing temperatures between Arc 1 and Arc 2 show that all slug calorimeters were cooling 

except S6 in the front of Cabinet 7. This slug showed a slow increase during the time between 

the arcs probably from heat escaping a small fire in Cabinet 7 or residual heat from Arc 1. Slug 

S5, above Cabinet 8 showed the temperatures were increasing slightly after 1.5 minutes. After 

Arc 2, Slugs 1, 2, 6, and 3 showed slightly increasing temperatures in the first few seconds, then 

decreasing temperatures until the fire was extinguished at about 10 minutes. The large ensuing 

fire observed in Test 4 did not appear to be developing based on the decreasing trend and the 

fire was manually extinguished beginning at about 6 minutes. 

(a)

(b) (c)

Figure 5.6-8. SWGR Test 5 Slug Calorimeter Temperature Data
5-32

Table 5-6 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. For Arc 1, similar to the 

previous SWGR tests, a maximum flux of 37 kW/m2 was measured at 1.5 m (5 ft) from the top of 

the cabinet (S5). For Arc 2, the maximum was measured to be 113 kW/m2 at the same location

(S5). This high flux is from the arc plasma entering the bus bar compartment that is directly 

below the vent and steel plate on top of the cabinet and in direct view of S5. The maximum slug 

temperatures are also shown to indicate the maximum temperature a metal object could reach. 

There was also a high flux of 67 kW/m2 (S7) as expected for Arc 2 in the rear, secondary side of 

Cabinet 8. 

Table 5-6. SWGR Test 5 Flux Results. 

Slug

Arc 1 Arc 2

ΔT ( ̊C) Flux 

(kW/m2) Max T ( ̊C) ΔT ( ̊C) Flux (kW/m2) Max T ( ̊C) 

S1-F-70-Cab7 8.0 21 28 3.2 9 36

S2-F-70-Cab8 4.6 12 32 10.4 31 38

S3-F-70-Cab8 1.5 4 26 0.9 3 29

S4-R-70-Cab8 1.3 3 18 12.9 38 31

S5-T-150-Cab8 13.9 37 34 46.0 113 79*

S6-F-36-Cab7 2.1 6 32 5.8 17 37

S7-R-36-Cab8 0.4 1 16 22.5 67 39

*Approximately 0.5 seconds after the arc, there was a temperature spike to 439 ̊C (822  ̊F). 
5-33

The temperatures measured by the TCs are shown in Figure 5.6-9. Table 5-7 shows the 

maximum temperature results. The thermocouple maximum temperature is a general indication 

of the air temperature 15.2 cm (6 in) from the cabinet and, as expected, the highest 

temperatures were at measured in the Cabinet 8 vertical duct (TC5) as hot gases from residual 

heat and fires exhausted up the vertical duct. 

(b) (c)

Figure 5.6-9. SWGR Test 5 Thermocouple Data

All TC data were very noisy during the arc, with some major spikes at the start of Arc 2. TC6 

appeared to have an additional unidentified instrumentation problem since the temperature 

dropped to almost zero after Arc 1 and the data after Arc 1 should not be used. The TCs cannot 

practically be used to estimate flux. 

At the end of Arc 1, the maximum temperature of 38  ̊C (100 °F) was measured in the duct 

(TC5). TC2 in front of Cabinet 7 where the arc was located, measured 27  ̊C (81  ̊F), much 

lower than the same location in Test 4 (59  ̊C (138  ̊F)). This could be because in Test 4, TC2 

fell near the end of the arc and may have been subjected to flame and heat escaping from the 

bottom of the cabinet. 

Between the arcs, all TCs were initially measuring cooling similar to the slug calorimeters but 

TC2 showed increasing temperatures at 1.5 minutes after Arc 1 substantiating there was a 

small fire in Cabinet 7 after Arc 1. TC1, TC3, and TC5 also indicated some small increases in 

temperature after 2 minutes. 

For Arc 2, the spikes for TC2, TC3, TC4 and TC 5 at the arc start are noise. The highest 

temperature of 51  ̊C (124  ̊F) was measured in the vent (TC5). At the end of Arc 2, TC5 did not 
5-34

show a large temperature spike like the one observed on S5, which was nearby. This makes 

the S5 response suspect and perhaps the S5 spike and subsequent erratic signal indicate an 

instrument problem or some realignment or change in position of S5. 

After Arc 2, TC5 on the vertical stack showed an increase for the first minute to a maximum of 

58  ̊C (136 °F; as residual heat and heat from a small fire were exhausting the stack). But 1 

minute after Arc 2, TC5 showed a decrease in temperature like the other TCs. This indicates 

that there was not a major ensuing fire as in Test 4 but there was some fire as indicated by the 

IR images and the cable damage. 

Table 5-7. SWGR Test 5 TC Results. 

TC Arc 1*

Max T ( ̊C)

Post Arc 1

Max T ( ̊C)

Arc 2*

Max T ( ̊C)

Post Arc 2

Max T ( ̊C)

TC1-F-70-Cab6 22 23 25 32

TC2-F-70-Cab7 27 29 39 45

TC3-F-70-Cab8 23 24 40 42

TC4-F-70-Cab9 20 22 31 34

TC5-V-Cab8 38 39 51 58

TC6-F-70-Cab10 **   ** 

*To allow for noise, the maximum temperature is the measured value at the end of the arc.

**TC failed during Arc 1.
5-35

The pressures during the arc are shown in Figure 5.6-10 and Figure 5.6-11. The pressures 

were low because the vents at the top of Cabinets 7 and 8 allowed the pressure to escape. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

For Arc 1, there were numerous noise spikes for Cabinet 7 and Cabinet 8 and both had noise 

spikes at 0.005 seconds, 0.038 seconds, 1.43 seconds and at the end. During the arc, pressure 

spikes were virtually continuous and larger magnitude than in previous tests. Both cabinet 

pressures had a zero shift at the start of the arc that was considered in the analysis. For Arc 1, 

the Cabinet 7 pressure closer to the arc had a higher maximum and occurred earlier than the 

Cabinet 8 pressure that was further from the arc. The maximum pressures are indicated by the 

arrows in Figure 5.6-10(c) and (d).

(a) (b)

(c) (d)

Test 5 Pressure 1 Cab. 7 Arc 1

17.9 ± 0.7 kPa (2.6 ± 0.1 psi)

@ 0.0150 s

Test 5 Pressure 2 Cab. 8 Arc 1

8.3 ± 0.7 kPa (1.2 ± 0.1 psi)

@ 0.0167 s

Figure 5.6-10. SWGR Test 5 Pressure Data, Arc 1
5-36

For Arc 2, there were numerous noise spikes for Cabinet 7 and Cabinet 8, and both had a large 

noise spike at 0.001 seconds and several other spikes before the pressure maximums. During 

the arc, pressure spikes were virtually continuous as in Arc 1. Both cabinet pressures had a 

zero shift at the start of the arc. The maximum pressures are indicated by the arrows in Figure 

5.6-11(c) and (d).

The Arc 2, Cabinet 7 and Cabinet 8 pressures had sinusoidal responses for the next 10 peaks 

immediately after the maximum peak that had a frequency of about 180-190 Hz. The 

amplitudes of these peaks were about the same as the initial peak. The noise spikes were 

superimposed on these sinusoids. This may have been from pressure waves reflecting within 

the cabinet. However, the frequency is different than the 140 Hz observed in Test 4, which may 

indicate some other cause. The temperature differences between the runs do not significantly

explain the difference on changes in the sonic velocity. 

(a) (b)

(c) (d)

Test 5 Pressure 1 Cab. 7 Arc 2

6.9 ± 0.7 kPa (1.0 ± 0.1 psi)

@ 0.0266 s 

Test 5 Pressure 2 Cab. 8 Arc 2

13.1 ± 0.7 kPa (1.9 ± 0.1 psi)

@ 0.0216 s 

Figure 5.6-11. SWGR Test 5 Pressure Data, Arc 2
5-37

The Arc 1 duration was 2.316 seconds with total energy of 57.2 MJ, seen in Figure 5.6-12. Arc 

2 was 2.071 seconds with a total energy of 62.0 MJ. The power of Arcs 1 and 2 began to 

slightly increase after 1.5 seconds as indicated by the rise in the Energy and the increasing 

slope of Energy Total. The cause is not known but is likely from the arc length from the end of 

the bus bars to the cabinet increasing as the buses melted causing an increase in the arc 

voltage. 

The energy analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied 

current multiplied by the time step and each time step is shown. “Energy Total” is the 

cumulative sum of the energy in each time step.

(a)

(b)

Figure 5.6-12. SWGR Test 5 Arc Energy (both arcs)
5-38

5.7 SWGR Test 6 Key Observations (March 2015) 

Two arcs were initiated in this test; the first at 7 kV at 24.6 kA with a target duration of 1 second, 

and the second arc was initiated 4 minutes and 50 seconds later at 7 kV and 33.1 kA with a 

target duration of 3.0 seconds. These arc durations were recommended by NRA to evaluate 

effects at lower Arc 1 energies. Arc 1 had a duration of 1.129 seconds and a total energy of 

26.5 MJ. Arc 2 in the test was only 0.922 second because of a hot short caused by accidental 

burning of the control cable to the breaker that caused the breaker to open. Arc 2 had an 

energy of 21.1 MJ. Although there was some vertical aluminum bus bar oxidation in Cabinet 7, 

it was not as much as in Tests 4 and 5 because of the shorter Arc 1 duration. There was no 

ensuing fire and all slug calorimeter locations indicated decreasing temperatures within 5 

minutes after Arc 2 so the test was stopped at that time.

Figure 5.7-1 and Figure 5.7-2 shows the high-speed camera images. Flames escaped the rear 

and right-side panels and reached 0.91 m (3 ft). It appeared there may have been contact with 

slug calorimeters at the Right Side (RS) top and Rear (R) top but there were no temperature 

spikes in the temperature data. 

There was no major ensuing fire and no visible flames, as seen in the IR thermal images of 

Figure 5.7-3 and Figure 5.7-4. The temperatures after the arcs were low as indicated by the 

temperature scale that was set to auto scale. At 5 minutes (300 seconds) after each arc, heat 

escaped the top vent on Cabinet 8 and the exterior cabinet temperatures were in the 50 ̊C 

range. 

(a) Arc 1 start (b) Arc 1 maximum

Figure 5.7-1. SWGR Test 6 Arc 1
5-39

(a) Arc 2 start (b) Arc 2 maximum

Figure 5.7-2. SWGR Test Arc 2

(a) Arc 1 (b) 10 seconds after Arc 1

(c) 120 seconds after Arc 1 (d) 300 seconds after Arc 1 (just before Arc 2)

Figure 5.7-3. SWGR Test 6 Thermal Image, Arc 1
5-40

(a) Arc 2 (auto scale failed) (b) 10 seconds after Arc 2

(c) 120 seconds after Arc 2 (d) 300 seconds after Arc 2

Figure 5.7-4. SWGR Test 6 Thermal Image, Arc 2

Arc 2 caused the control wire for the breaker to hot short within Cabinet 8 and the breaker 

opened as shown in Figure 5.7-6(a). Additionally, it appears that the internal pressure wave 

and shock caused the connector for the control cable to unplug as in Figure 5.7-6(b). The wires 

for AC power to the breaker did not fail so when the hot short occurred AC power was available 

and the breaker opened resulting in a shorter than planned Arc 2.
5-41

(a) Breaker opened during Arc 2

(b) Control cable un-plugged during Arc 2

Figure 5.7-5. SWGR Test 6 Breaker Opened in Arc 2

Because there was no ensuing fire, there was no charring of the front exterior as seen in Figure 

5.7-6(a). The panels on the sides and rear of Cabinet 8 were bent and opened by Arc 2 as 

shown in Figure 5.7-6 (b) and (c). Figure 5.7-6 (d) and (e) show that the cable tray had no soot 

or charring and the exterior cables in the tray did not char or burn indicating low flux in the cable 

tray area. 
5-42

(a) Cabinets 6-8

(b) Side of Cabinet 8 (c) Rear

(d) Cable Tray (e) Cable Tray Cables

Figure 5.7-6. SWGR Test 6 Cabinet Exterior Damage
5-43

The interior damage in all cabinets, shown in Figure 5.7-7(a), was much less than Tests 4 and 5 

because of the shorter Arc 1 duration. There was minor discoloration of the front interior panel 

and light soot on the panel in front to the bus bars in Cabinet 7 where Arc 1 was located. As 

shown in Figure 5.7-8, none of the cables burned and only had a light soot coating. This was 

the first SWGR test where all of the cable bundles and cable trays remained intact; the low 

energy caused little damage. Figure 5.7-8(d) shows heavy soot and some discoloration in the 

rear of Cabinet 8 where Arc 2 occurred. There was only minor damage in the initial arc location 

just above the insulators because the arc moved to the end of the bus bars and attached to the 

ceiling of cabinet, causing discoloration of the top and side panels. 

(a) Cabinet Interior Damage - Cabinets 6, 7, 8

Figure 5.7-7. SWGR Test 6 Cabinet Interior Damage
5-44

(a) Cabinet 6 Cables (b) Cabinet 7 Cables

(c) Cabinet 8 Cables (d) Cabinet 8 Rear

Figure 5.7-8. SWGR Test 6 Cabinet Interior Damage, Detailed

Figure 5.7-9 shows the deformation of the panel on the right side of Cabinet 8 looking toward 

the rear. This was about 10 minutes after Arc 2 and there were still small flames from the 

control wire burning. The wire was well insulated but the insulation blew off. This appears to be 

the only fire resulting from either of the arcs. 
5-45

Figure 5.7-9. SWGR Test 6 Cabinet 8 Breaker Control Interior Wire Fire

As shown in Figure 5.7-10(a), there was minor bus bar melting (see additional information in 

Section 7.2). The arc burned a hole in the right wall of the bus bar compartment toward Cabinet 

8 as shown in Figure 5.7-10(b), but the hole was much smaller than observed in other tests 

because of the short Arc 1 duration. 

(a) Cabinet 7 (b) Cabinet 7 Holes

Figure 5.7-10. SWGR Test 6 Arc 1, Cabinet 7 Bus Bar Damage

For Arc 2, the arc moved from the breaker secondary side to the end of the bus bars as shown 

in Figure 5.7-11. This demonstrated that arcs can move because the arc ignited at the insulator 

but moved to the end of the bus bars along the path of the current. This also demonstrated that 

arc behavior is difficult to predict because in an identical test configuration in SWGR Test 4, the 

arc at this point was interrupted by the short in Cabinet 7 horizontal bus bars and in SWGR Test 

5, the arc stayed at the insulators. So, there were three outcomes for the final arc position for 

the same initial arc position and conditions.
5-46

Figure 5.7-11(a) shows only soot damage to the primary side bus bars and insulators that 

successfully carried the current to the breaker to feed Arc 2. Arc plasma leaking from Cabinet 7 

through the wall did not have time to cause major damage in the primary side of Cabinet 8. The 

side view of the secondary side, rear compartment of Cabinet 8 showed the bus bars remained 

intact when the arc moved to the final position at the top of the bus bars. Notice that the arc gap 

between the end of the bus bars and the roof is quite long and this is reflected in the Arc 2 arc 

voltage that was 1,007 V, much higher than the 603 V observed in SWGR Tests 5. 

(a) Cabinet 8 Primary Side

(b) Cabinet 8 Secondary Side

Figure 5.7-11. SWGR Test 6 Arc 2 on Cabinet 8 Damage.

Figure 5.7-12 is a view from the rear showing the damage to the top of the bus bars and the 

interior roof panel. About 7 cm (2.8 in) were burned off the top of the bus bars (see Section 

7.2.5) while the arc was attached from the bus bars to the roof panel. It is likely that if the arc 

had been the full duration of 2 seconds, the roof panel would have burned through and the 

damage to the exterior cable tray would have been much worse. 

Arc moved
5-47

Figure 5.7-12. SWGR Test 6 Arc 2, Breaker Secondary Side Damage

Figure 5.7-13 shows the damage to the breakers. Breaker 7 only had some soot coating. 

There was no major damage to the Cabinet 8 breaker and the bushings were intact. The full 

shorting current passed through Breaker 8 but did not cause damage. In the Onagawa event,

Breaker 8 was heavily damaged with the bushings almost completely melted and the arc chute 

covers in the rear were heavily deformed and detached. The test results indicate some other 

high-energy phenomenon (it could be postulated that the arc passed through the breaker or the 

arc was very long duration) must have occurred at Onagawa.

(a) Breaker 7 (b) Breaker 8

Figure 5.7-13. SWGR Test 6 Breaker 8 Damage
5-48

Temperatures measured at the slug locations are shown in Figure 5.7-14 (note the scale 

change from Tests 4 and 5 results). The Arc 1 slug calorimeter data was not available because 

the data trigger failed. 

For Arc 2, the arc extinguished at 0.568 seconds because the breaker opened. All of the slugs 

had noise during the arc, probably due to EMI. All the slugs except S6 and S8 have a similar 

rise in the signal at approximately 0.5 seconds that could be an actual temperature rise when 

the arc changed positions. However, based on the negligible damage at the original arc point, 

the arc must have moved much earlier than 0.5 seconds and the rise at 0.5 seconds was 

attributable to noise common to most of the slugs. 

The highest temperature at the end of Arc 2 was measured in the rear of Cabinet 8 near the Arc 

2 location (S10). In Cabinet 7, high temperatures were also measured at the rear (S9) and the 

at right side top position (S7). Both of these locations were exposed to the hot gas and plasma 

escaping from the openings from the dislodged panels on Cabinet 8. The temperature 

increases in the slugs in the front of the cabinets were very small because the arc was in the 

rear of Cabinet 8. 

After the arc, slugs on the rear and right side showed increasing temperatures as the heat 

escaped from the cabinets. All of the slugs showed steady or decreasing temperatures after 2 

to 3 minutes, indicating that there was no major ensuing fire. 

(a) (b)

(c) (d)

Figure 5.7-14. SWGR Test 6 Calorimetry Data: Temperature
5-49

Table 5-8 shows the flux results based on the ASTM F1959 method in Appendix A using the 

change in temperature (ΔT) between the start and end of the arc. The maximum flux was 

measured to be 53 kW/m2 at the rear of Cabinet 8 (S10). The maximum slug temperatures are 

also shown to indicate the maximum temperature a metal object could reach. 

Table 5-8. SWGR Test 6 Flux Results.

Slug Arc 1

Arc 2

ΔT ( ̊C) Flux 

(kW/m2) Max T ( ̊C) 

S1-F-70-Cab7 * 0.0 0 9 

S2-F-36-Cab 7 * 0.0 0 7 

S3-F-16-Cab7 * 0.1 1 6 

S4-F-70-Cab8 * 0.2 2 8 

S5-F-36-Cab8 * 0.1 1 7 

S6-F-16-Cab8 * 0.1 1 7 

S7-RS-70-Cab8 * 3.6 39 15

S8-RS-36-Cab8 * 1.6 17 9 

S9-R-70-Cab7 * 3.7 40 12

S10-R-70-Cab8 * 4.9 53 19

* No data available

TCs were not used in SWGR Test 6. The temperatures measured by the PTs on the Cable 

Tray (CT) are seen in Figure 5.7-15. Table 5-9 shows the maximum PT temperatures during 

the entire 2-arc test and in more detail around the arcs. The PTs indicated the approximate 

maximum temperature a metal object, with gray surface emissivity of approximately 0.85, 

located approximately 0.46 m (18 in) above the cabinet rear, could reach. 

 

As expected, for Arc 1 in the center, Cabinet 7, the temperatures in the center of the cable tray 

were the highest. During Arc 2 in the rear of the right side Cabinet 8, the temperatures on the 

right side of the cable tray were the highest. For both arcs, the behavior was similar to the DP 

Tests 4 and 5 where the maximum temperature was about 2 minutes after the arc because the 

heat escaped from the cabinet. After Arc 1, the heat was in the front of the cabinet and primarily 

escaped from the top vent about 22 cm (8.7 in) in front of the cable tray. After Arc 2, the heat 

was in the rear of the cabinet and primarily escaped through the dislocated side panel just 

below the cable tray right side PTs and also by heating the top panel directly below the right 

side PTs. Subsequently, the right side PT reached the highest PT temperature in the tests with 

the cable tray PTs. 

Notice that the left side PTs above Cabinet 6 that did not have an arc measured very low 

temperature increases, as would be expected. Although the temperatures were higher in Arc 2 

than other tests, there was still no cable damage as shown earlier. 
5-50

(a)

(b) (c)

Figure 5.7-15. SWGR Test 6 Cable Tray Plate Thermometer Data

Table 5-9. SWGR Test 6 Plate Thermometer Results.

PT

Arc 1 to Arc 2

Max T ( ̊C)

After Arc 2

Max T ( ̊C)

PT-CT-1(RS) 16 172

PT-CT-2 21 188

PT-CT-3 24 177

PT-CT-4 26 146

PT-CT-5 31 94

PT-CT-6 30 61

PT-CT-7 23 36

PT-CT-8 18 24

PT-CT-9(LS) 14 15
5-51

The pressures during the arc are shown in Figure 5.7-16 and Figure 5.7-17. The pressures 

were low because the vents at the top of Cabinets 7 and 8 allowed the pressure to escape. 

The pressure analysis methods are in Appendix A and involved picking the maximum near the 

start of the arc then including a nominal uncertainty for the noise in the signal just before the 

arc.

For Arc 1, there were numerous noise spikes for Cabinet 7 and Cabinet 8 and both had noise 

spikes at 0.007, 0.014 and 0.017 seconds. During the arc, pressure spikes were virtually 

continuous as in Test 5 but at slightly lower magnitude. Both cabinet pressures had a zero shift 

at the start of the arc that is considered in the analysis. 

For Arc 1, the Cabinet 7 pressure closer to the arc had a higher maximum and occurred earlier 

than the Cabinet 8 pressure that was further from the arc. The Arc 1, Cabinet 7 and Cabinet 8 

pressures had rough sinusoidal responses for the next 4 to 5 peaks immediately after the 

maximum peak that had a frequency of about 180 Hz. The maximum pressures are indicated 

by the arrows in Figure 5.7-16(c) and (d).

(a) (b)

(c) (d)

Test 6 Pressure 1 Cab. 7

12.4 ± 1.4 kPa (1.8 ± 0.2 psi)

@ 0.0145 s

Test 6 Pressure 2 Cab. 8

6.9 ± 1.4 kPa (1.0 ± 0.2 psi)

@ 0.0172 s

Figure 5.7-16. SWGR Test 6 Pressure Data, Arc 1

For Arc 2, there were numerous noise spikes for Cabinet 7 and Cabinet 8 and both gauges had 

several spikes before the pressure maximums. During the arc, pressure spikes were virtually 
5-52

continuous as in Test 5 but at slightly lower magnitude. Both cabinets had very high noise at 

the end of the arc around 1 second possibly because the arc from the bus bar to the cabinet 

roof was unstable and EMI increased. Both cabinet pressures had a zero shift at the start of the 

arc that was considered in the analysis and Cabinet 8 had a large zero shift at the end of the 

arc. The maximum pressures are indicated by the arrows in Figure 5.7-17(c) and (d).

The Arc 2 Cabinet 7 pressures had sinusoidal responses for the next 10 peaks immediately 

after the maximum peak that had a frequency of about 190 Hz. The amplitudes of these peaks 

were about the same as the initial peak. The noise spikes were superimposed on the sinusoids 

that may have been from pressure waves reflecting within the cabinet. 

(a) (b)

(c) (d)

Test 6 Pressure 1 Cab. 7

6.9 ± 1.4 kPa (1.0 ± 0.2 psi)

@0.0261 s

Test 6 Pressure 2 Cab. 8

9.0 ± 1.4 kPa (1.3 ± 0.2 psi)

@0.0228 s 

Figure 5.7-17. SWGR Test 6 Pressure Data, Arc 2
5-53

The Arc 1 duration was 1.129 seconds with total energy of 26.5 MJ, seen in Figure 5.7-18. Arc 

2 was 0.568 seconds with a total energy of 21.1 MJ. The power of Arc 2 increased during the 

arc as indicated by the rise in the energy, as seen in Test 5. The cause is not known but is 

likely from the arc length from the end of the secondary bus bars to the cabinet roof increasing 

as the buses melted causing an increase in the arc voltage. As mentioned previously, the Arc 2 

arc voltage was much higher than in SWGR Tests 4 and 5. 

The energy analysis methods are in Appendix A. The “Energy” is calculated as volts multiplied 

current multiplied by the time step and each time step is shown. “Energy Total” is the 

cumulative sum of the energy in each time step. 

(a)

(b)

Figure 5.7-18. SWGR Test 6 Arc Energy (both arcs)
5-54

5.8 SWGR Tests 4 through 6 Summary of Electrical Conditions

Electrical conditions reported by KEMA are below. For several tests, the KEMA energy results 

are slightly lower than the results in the previous section and reported as the correct result. The 

KEMA analyst manually selects the beginning and end of the arc voltage and current waveforms 

using two cursors on the screen. In this case the cursors were not properly set causing some 

current and voltage data to be missed, and the energy to be underestimated. 

Table 5-10. SWGR Test 4 through 6 Electrical Results (1). 

Test Arc OCV

(KV) Phase Sym

(kA)

Sym 

@End 

(kA)

Peak 

(kA)

Curr. 

Dur.

(sec)

Arc 

Energy 

(2)

Freq 

@End

(Hz) (3)

Phase

Arc Volts

4

Arc 1 7.0

A 24.1 24.2 59.6

2.354

21.3

30.7

A-N 410

B 26.0 24.7 37.8 19.7 B-N 401

C 23.3 24.4 56.5 23.6 C-N 447

AVG 24.5 24.4 51.3 Σ64.6 AVG L-L 726

Arc 2 7.0

A 34.0 34.3 88.2

2.081

24.9

50.5

A-N 404

B 34.8 33.2 67.1 20.5 B-N 363

C 33.4 32.5 69.2 30.4 C-N 493

AVG 34.1 33.3 74.8 Σ75.8 AVG L-L 727

5

Arc 1 7.0

A 24.4 25.3 58.6

2.316

20.0

32.9

A-N 396

B 25.2 26.2 36.2 17.4 B-N 354

C 23.8 25.5 55.6 17.5 C-N 354

AVG 24.4 25.7 50.1 Σ54.9 AVG L-L 639

Arc 2 7.0

A 34.1 31.8 85.7

2.071

21.1

52.1

A-N 367

B 34.4 34.8 65.9 24.0 B-N 396

C 33.2 33.4 67.9 15.2 C-N 282

AVG 33.9 33.3 73.2 Σ60.3 AVG L-L 603

6 

Arc 1 7.0

A 24.5 21.7 51.6

1.129

11.0

49.5

A-N 524

B 25.0 21.6 51.3 6.9 B-N 480

C 24.2 20.8 65.7 8.4 C-N 523

AVG 24.6 21.4 56.2 Σ26.3 AVG L-L 882

Arc 2 7.0

A 32.8 33.6 71.3

0.568

8.46

57.5

A-N 882

B 34.4 34.0 68.0 6.09 B-N 626

C 32.0 32.9 87.2 5.39 C-N 579

AVG 33.1 33.5 75.5 Σ19.9 AVG L-L 1007

Notes:

(1) See Table 2-16 for abbreviations and acronyms used in this table.

(2) As reported by KEMA instruments and results. 

(3) Arc 1 was 50 Hz, Arc 2 was 60 Hz at start of current. 
5-55

5.9 SWGR Tests 4 through 6 Qualitative Summary

1. Ensuing Fire: Ensuing fires occurred in Tests 4 and 5 and it appears that with an initial 

arc to preheat the cabinets, that ensuing fires after the second are easier to achieve than 

with just a single arc. In Test 4, the ensuing fire spread was also accelerated by very 

high aluminum bus bar oxidation energy caused by an arc on the horizontal bus bars of 

Cabinet 7. The ensuing fires were extinguished after a few minutes. The electrical 

energy in Test 6 was too low to initiate an ensuing fire. 

2. Damage: The bus bar damage varied widely because the arcs occurred at various 

locations and various energies. In most tests, several centimeters of bus bars were 

oxidized greatly increasing the total energy during the arc and causing internal cable 

fires in Tests 4 and 5. Unlike all the other SWGR tests, the vertical bus bars were 

mostly destroyed in Test 4 with heavy damage to the horizontal bus bar; only part of the 

vertical bus bars burned in Tests 2, 3 and 5 even though the conditions were the same. 

Test 6 resulted in less bus bar damage because the energies were lower from shorter

duration arcs but there was still bus bar oxidation from both arcs.

Only Tests 4 and 5 showed internal cable damage; Test 4 had more serve damage due 

to the high energy from the horizontal bus bar aluminum oxidation that did not occur in 

Test 5. There was no external cable tray damage in any of the tests. 

In Tests 4 and 5 as in SWGR tests 1 through 3 the SWGR cabinet outer walls did not 

have major deformation like the DP and MCC cabinets. The cabinet outer walls are 

thicker and the large vent on the top kept the pressure low. Additionally, the arcs in 

SWGR Tests 1 through 5 were not directly inside an outer cabinet wall so external wall 

damage was minimal. There was significant bending, deformation, or burn-through of 

the internal walls directly exposed to the arc. However, in Test 6, because it was a 3-

cabinet configuration, the right side wall of Cabinet 8 with Arc 2 was an exterior wall and 

was directly exposed to Arc 2. So, there was deformation and displacement of the 

exterior panel in the rear of Cabinet 8 where the arc occurred.

3. Calorimetry: Similar to the previous SWGR tests, Tests 4 and 5 showed the highest 

resultant heat flux from the first arc at 1.5 m (5 ft) above the cabinets. Test 6 did not 

have measurements during the first arc. The second arc in these tests resulted in 

maximum fluxes in different locations, because the arc in Test 6 was in the rear of the 

cabinet and not under the top vent and the path of the escaping heat to the slug 

calorimeter was different. As expected, the maximum flux was at the top rear for Test 6. 

4. Temperature: In these tests, thermocouples to measure air temperature were only used 

in Tests 4 and 5, however, almost all of the data for Test 4 is invalid due to the 

thermocouple support falling during the first arc. Plate thermometers (PT) were used in 

Test 6 on the cable tray and showed low temperatures (30  ̊C (86 °F)) for Arc 1 and 

higher temperatures for Arc 2 (180  ̊C (356 °F)) because the PTs were directly above the 

cabinet roof where the arc was attached. 

5. Pressure: As with SWGR Tests 1 through 3, the measured pressures for Arc 1 were 

very low since there were vents at the top Cabinets 7 where the arc occurred. The 

exception is Test 4, Arc 1, where the pressure was 40 to 50 percent higher than other 

SWGR tests; the reason is not known. For Arc 2, the pressures were lower because 

Cabinet 8, where the arc occurred, does not have a direct line of sight to the top vent. 
5-56

The pressures were higher in the cabinet where the arc occurred (Cabinet 7 for Arc 1 

and Cabinet 8 for Arc 2), as expected. 

6. Arc Energy: In all tests for both Arc 1 and Arc 2 the total energy was proportional to the 

arc duration for the given electrical testing conditions. All tests showed a smooth 

increase of the total energy during the arcs indicating stable arc conditions and the 

target arc durations were nominally achieved in all the tests except Arc 2, Test 6 where 

there was an equipment failure. The smooth increases were a little surprising for Test 4, 

Arc 2 considering that the arc initiated on the secondary side of Cabinet 8 then 

progressed to the bus bars in Cabinet 7. 

 
 6-1 

6 Switchgear with Rocket Fuel Arc Simulator Fire Test - SwRI

(July 2013)

6.1 RFAS Test Overview 

The key objective of these tests was to measure the Heat Release Rate (HRR) and other key 

ensuing fire parameters that could not be measured during the electrical arc tests at KEMA. 

Specifically, this effort was undertaken to try to achieve temperatures and heat fluxes that would 

cause cables outside of the cabinet to ignite. The tests used a number of 4 kg (8 lb) Rocket 

Fuel Arc Simulator (RFAS) slabs to vary the total available energy. The RFAS are slabs consist 

of aluminum and ammonium-perchlorate based rocket fuel, and were developed to provide 

short-time high energy bursts similar to electrical arcs. 

The initial RFAS tests in SWGR cabinets in January 2013 were in a 1-cabinet configuration and 

only one RFAS ignition slab was used. These proof-of-concept tests were conducted to show 

that the RFAS could reliably simulate arc energy in a cabinet configuration with repeatable 

results. The RFAS tests in July 2013 used two RFAS explosions in Cabinets 7 and 8 of a 5-

cabinet SWGR line-up to simulate the two arcs that are assumed to have occurred in Cabinets 7 

and 8 in the Onagawa event. 

6.2 RFAS Test Summary of Results 

The RFAS tests in July 2013 simulated two arcs in the assumed Onagawa event. The plan was 

to first ignite an RFAS in Cabinet 7, and then ignite a second RFAS in Cabinet 8, nominally 8

minutes later. In Test 1, the 8 minute delay did not occur because RFAS1 also ignited RFAS2. 

Changes were made for Test 2 to add additional insulation and barriers between Cabinets 7 and 

8 to ensure the initial ignition in Cabinet 7 did not ignite the RFAS in Cabinet 8. In Test 2 the 

delay between RFAS ignitions was successful (7.8 minutes) and the ensuing fire was similar to 

the KEMA SWGR Test 2. The results are shown in the table below. No useful pressure 

measurements were made and therefore are not reported. 

There was a full ensuing fire in Test 2 that was allowed to burn to self-extinguishment, 90 

minutes after ignition. In Test 1 both RFAS charges ignited at the start of the test and there was 

no major ensuing fire even though the RFAS energy was more than two times the arc energy of 

KEMA SWGR Test 2 (58 MJ). The cables in Test 1 reached a high temperature during the 

RFAS ignition but quickly cooled and there was no ensuing cable fire. 
 6-2 

Table 6-1. SWGR RFAS Summary of Results.

Test

RFAS 

Used

(#Slabs) 

(1)

RFAS 

ignition 

time

(sec)

RFAS 

Energy

(MJ) 

Maximum 

Flux

(kW/m2) 

(2)

Max 

Temp.

( ̊C) 

Max 

HRR

(kW) 

Ensuing 

Fire?

Key 

Observations

1 RFAS1: 2

RFAS2: 2

RFAS1: 

0 

RFAS2: 

0 

140 Front: 3

Top: 14

Door: 97

Cables: 

500

RFAS: 3

Fire:

N/A

Small. Both 

RFAS ignited 

at the same 

time. High 

cable 

temperature 

was short 

time

2 RFAS1: 2

RFAS2: 5

RFAS1: 

0 

RFAS2: 

465

RFAS1: 

70

RFAS2: 

175

Total: 

245

Front: 11

Top: 11

Door: 

680

Cables: 

812

RFAS: 4

Fire:

0.4

Large. 

Burned for 90 

minutes.

Notes:

(1) RFAS1 slabs were in Cabinet 7 and RFAS2 slabs were in Cabinet 8. 

(2) The flux is measured at the boundaries of the NUREG/CR 6850 ZOI: 1.5 m (5 ft) above the 

cabinet and 0.91 m (3 ft) from the sides of the cabinet. 

The key observations from the July 2013 RFAS SWGR tests at SwRI were: 

• The RFAS is a reasonable surrogate to simulate the high energy of a HEAF and obtain

more data for the ensuing fires. It was observed that the energy to ignite an ensuing 

cable fire was 140 to 245 MJ from the RFAS tested at SwRI as compared to 50 to 60 MJ 

from the electrical test, KEMA SWGR Test 2. Thus, it appears that three to four times 

more energy is required for ignition using an RFAS heat source than from an electrical 

arc source. The oxidation of the aluminum bus bars was a candidate source for the 

additional energy and based on the basic oxidation reaction (see Section 7.2.1) it 

became the likely additional energy source. The eventual conclusion was aluminum 

oxidation in addition to the electrical energy was needed to cause the ensuing fires 

observed in KEMA SWGR Test 2. 

• The low pressure and rapid recovery of oxygen in the cabinets after the RFAS ignition 

indicate that the well-ventilated SWGR cabinets likely quickly lose much of the energy 

created by a HEAF. The KEMA electrical arc tests also show that the energy to start an 

ensuing fire is much higher for the SWGR cabinets than for less-ventilated cabinets like 

the DP, as discussed in other sections of this report.

• In RFAS Test 2, pre-heating from the first RFAS decreased the time to the start of the 

ensuing fire and accelerated the growth of the ensuing fire to peak temperature. 

Cabinets without long pre-heating still had an ensuing fire but it took more time to ignite 

the cables and the fire growth was slower. 

• Cabinets isolated from the initial preheat and two cabinets away from the RFAS heat 
 6-3 

source like Cabinet 10 did not ignite. 

• Even at the higher RFAS Test 2 energies, the damage was not as severe as at 

Onagawa. The exterior of the cabinet was not as charred and there was no major 

damage on the secondary side of the SWGR cabinet. 

6.3 RFAS 5-Cabinet Test Configuration 

Testing was conducted under the 10-MW large scale calorimeter located in Building 222 at 

SwRI’s Fire Technology Department. Each test consisted of five GE Magneblast Switchgear 

cabinets that contained varying numbers of RFAS slabs, three aluminum bus bars, lengths of 6 

kV-CHSVT cable, and bundles of HIV and CV-4 cable, both in the cabinets and horizontal and 

vertical cableways. 

The cabinets and combustible loads were identical to the June 2013 KEMA 5-cabinet tests. 

Figure 6.3-1 shows the test setup for Test 1; Cabinet 7 is on the left. The cabinets and 

combustible loads are identical to the June 2013 KEMA SWGR tests (Section 4). 

To prevent the RFAS in Cabinet 7 from igniting the RFAS in Cabinet 8 in Test 2, the interior of 

the RFAS area in Cabinet 7 was insulated with ceramic fiber blanket. Gaps in the cabinets and 

around the bus bar penetrations were filled with fire-proof materials. Ceramic fiber blanket was 

also added to the top vent of Cabinet 7 to block any sparks from entering the vent of Cabinet 8 

during the first RFAS event. A phenolic composite panel (referred to as “red board”) was placed 

between Cabinet 7 and 8 at the top. 

Figure 6.3-1. SwRI 5-Cabinet RFAS Test Setup

Each test used varying amounts of 4 kg (8.82 lb) slabs of aluminum and ammoniumperchlorate-based solid rocket fuel. The RFAS slabs have a 70% Ammonium perchlorate 

(APCP-oxidizer), 14% aluminum powder (Al-fuel) and 16% binder (common yellow glue). This 

produces an energy density of 8.72 MJ/kg and a temperature in the range of 7500 °C (13,532 

°F). Each set of fuel slabs was arranged so that the sides with the igniters faced each other in 

pairs to ensure even ignition. The slabs were designed to each release 35 MJ of thermal 

energy in 2.0 ± 0.5 seconds. The energy content of each fuel batch to make the RFAS slabs 

was measured and confirmed by bomb calorimetry per International Organization for 
 6-4 

Standardization ISO 1716 [9]. The duration of the burn was governed by the thickness of the 

slabs. Slab thickness was controlled during the fabrication process. Figure 6.3-2 shows two 4 

kg (8.82 lb) RFAS slabs with the igniters installed. Several igniters were within each slab to 

make it burn for approximately 2 seconds. Slabs were 9 mm (0.35 in) thick and had an 

aluminum foil back that was used in manufacture. The slabs were supported by a stainless 

steel frame that was reused for all tests. 

Figure 6.3-2 also shows the cabinet configuration that was virtually identical to the KEMA 

SWGR Tests 1 through 3, 5-cabinet configuration. The RFAS slabs were located just below the 

horizontal bus bars in the cabinet compartment with a vent opening on the top of the cabinet as 

in the Onagawa cabinets. This location was chosen to simulate the position of the ends of the 

bus bars and the arcs in the KEMA electrical tests. The top vent was covered with a thin steel 

plate about 15.2 cm (6 in) above the vent; during RFAS events, the flames exiting the top 

deflected from this plate and spread over the top of the cabinets in view of the flux 

measurement instrumentation at 1.5 m (5 ft) above the cabinet. 

In this configuration much of the heat was released upwards. The heat also propagated through 

an interior wall to the right of the RFAS and then through the front door to expose the heat flux 

meter in front of the cabinet at 0.91 m (3 ft). The wall to the right of the RFAS had some vent 

louvers which allowed the heat to escape from the RFAS cabinet compartment to the front 

compartment and ignite the cables at the top of the front compartment. “Dummy” circuit 

breakers with the same shape and configuration as the breakers in the KEMA SWGR tests were 

in place just below the RFAS compartment to provide a similar flow path, cabinet volume and 

thermal mass as in the electrical arc HEAF tests. 
 6-5 

Figure 6.3-2. RFAS Arrangement

Front

RFAS 

slabs

Bus 

Stainless 

steel holder

Stainless steel 

holder with 

RFAS in place 

– top view

Stainless steel 

holder with 

RFAS in place
 6-6 

6.4 RFAS Test Heat Flux Instrumentation 

Heat flux was measured at the NUREG/CR 6850 ZOI locations: 

• 0.91 m (3 ft) in front of Cabinets 7 and 8 (locations referred to as Stations 1 and 2, 

respectively) and approximately 1.98 m (6.5 ft) above the floor; 

• 1.5 m (5 ft) above Cabinet 8 (location referred to as Station 3). 

The heat flux meters were:

• Schmidt-Boelter (SB) gauge, Medtherm 64-5SB, 50 kW/m2 (Station 1 and 2) 

• Gardon gauge, Medtherm 64-10, 100 kW/m2 (Station 3)

• ASTM F1959 slug calorimeter (like KEMA slug calorimeters) 

• Dual Plate Thermometer

• Directional Flame Thermometer

Analyses of the heat flux data indicated that the commercial SB and Gardon gauges had the 

fastest response times. Consequently, only data from these gauges are presented in this 

report. 

6.5 RFAS Test Temperature Instrumentation 

A total of 12, 24-AWG type K thermocouples (TCs) were used to measure the temperatures 

during each test. Thermocouples 1 through 5 were located on the interior of each cabinet door. 

The TCs were peened into the door, centered 1.8 m (70 in) from the floor. T6 was centrally 

located 15.2 cm (6 in) in front of the exterior of the door of Cabinet 8 and TC7 was located 15.2

cm (6 in) in front of the vertical duct near the top. T7 was not attached to the vertical duct to 

replicate the TC locations for the five cabinet tests performed at KEMA where the TC could not 

contact the cabinets for safety purposes. T8 to T12 were located in the cable bundle at the top, 

front portion of each cabinet approximately at the center of the cabinet in order to track the 

horizontal flame spread along the row of cabinets. The thermocouples were not embedded in 

the cables.
 6-7 

(a) Station 1 at Cabinet 7 is on the right, Station 2 at Cabinet 8 is on the left

(b) Station 3 at the 1.5 m (5 ft) ZOI above Cabinet 8

Figure 6.5-1. Heat Flux and Pressure Sensors: Stations 1, 2, and 3
 6-8 

6.6 RFAS Test Pressure Instrumentation

Pressure was measured with a PCB Piezotronic 137B23B “pencil probe”, which is a high speed 

blast probe with a quartz sensor sampling pressures up to 35 psi (31 kPa) at a rate of 1 kHz. 

The blast pencil probe was located in front of Cabinet 7 during Test 1 and in front of Cabinet 8 

for Test 2 (see Figure 6.5-1, Station 2) because the latter had the larger amount of fuel. There

was no useful data from the pencil probe because the pressures were too low and spikes and 

other transient responses did not make physical sense. No pencil probe data is therefore 

reported. 

A Honeywell Pressure Transducer Model TJE, 50 psi, was used to measure internal cabinet

pressure. It was a strain-gauge type pressure transducer, which was connected by 1.83 m (6 ft) 

of Inconel tube to protect it from heat. There was no useful data from the pressure gauge

because the pressures were low and there were apparent temperature effects in the tests. 

Some data indicate large negative pressures that were not physically possible. No internal 

pressure data is therefore reported. 

6.7 RFAS Test Heat Release Rate and Smoke Production Instrumentation

To measure the HRR during the RFAS event and post-RFAS combustion, the products of 

combustion and entrained air were collected in a hood and extracted through an exhaust duct 

by a fan. A gas sample was drawn from the exhaust duct and analyzed for oxygen, carbon 

dioxide, and carbon monoxide concentrations. The gas temperature and differential pressure 

across a bi-directional probe were measured for calculating the mass flow rate of the exhaust 

gases. The HRR measurement generally follows ASTM E2067 [12].

The HRR is usually measured based on oxygen consumption calorimetry. However, the 

standard method, which relies on the observation for a wide range of fuels that approximately 

13.1 MJ of heat is released per kg of oxygen consumed in complete combustion, does not work 

for the RFAS. This is because rocket fuel combustion is an exothermic reaction that consumes 

the chemically bound oxygen in the perchlorate molecules (although for the rocket fuel used in 

the RFAS tests some external oxygen is needed to burn part of the aluminum foil backing and 

the binder). Therefore, the HRR was calculated two ways, based on oxygen consumption and 

based on carbon dioxide generation. 

The heat of combustion of the rocket fuel as measured in an oxygen bomb calorimeter is 8.72 

MJ/kg. Based on the chemical composition of the rocket fuel, 0.24 kg of carbon dioxide is 

generated per kg of fuel burned. These HRR calculation based on carbon dioxide generation

uses these values. That is, 36.3 MJ of heat is released per kg of carbon dioxide generated 

(8.72 MJ of heat released per kg of fuel consumed divided by 0.24 kg of CO2 generated per kg 

of fuel consumed). This measurement assumes that all of the CO2 evolved from the RFAS, 

which is reasonable given that there is little or no combustion occurring elsewhere in the test 

during the RFAS ignition.

The HRR calculation via oxygen consumption is based on the standard method, which assumes 

that 13.1 MJ ± 5% of heat is released per unit mass of oxygen consumed. As discussed earlier, 

the standard oxygen consumption technique is not valid for determining the HRR from RFAS 

combustion and was only used to estimate the post-RFAS HRR from the ensuing cable fire.
 6-9 

The Smoke Production Rate (SPR) is determined by the measured light obscuration in the 

exhaust duct using a vertically-oriented, white-light extinction photometer located close to the 

gas sampling port, and the flow rate measured in the exhaust duct. 

6.8 RFAS Test Oxygen Measurement 

For Test 2, a sampling line was run from the interior of Cabinet 8, through the door, and 

connected to a paramagnetic oxygen analyzer. This was used to measure the oxygen 

concentration in the area of the cable bundles throughout the test. The oxygen is a combination 

of ambient oxygen and any excess oxygen generated as a result of the rocket fuel 

decomposition. 

6.9 RFAS Test 1 Key Observations

The attempt to delay the RFAS2 event during Test 1 was unsuccessful and all four slabs of fuel 

contained in Cabinets 7 and 8 ignited within 5 seconds. Figure 6.9-1 shows the RFAS event, 

this test resulted in a total energy release of approximately 140 MJ. A sustained ensuing fire in 

the cableways was not achieved during Test 1 and the test was terminated at 10 min. Figure 

6.9-2 shows the ensuing fire, in which there was only a fire of the bus bar insulation, following 

the RFAS ignition. 

Figure 6.9-1. Test 1: RFAS Event
 6-10 

(a) Small ensuing fire of bus bar insulation

(b) 5 minutes after RFAS1. Note the low 

maximum temperature- there is residual 

heat, but no fire

(c) 15 minutes after RFAS1. Note the low 

maximum temperature- no fire

Figure 6.9-2. Test 1 Ensuing Fire
 6-11 

The damage to the exterior of the cabinets was insignificant. Figure 6.9-3 shows the interior

damage to each cabinet and Figure 6.9-4 shows the exterior damage. 

Cabinet 6 Cabinet 7 Cabinet 8

Cabinet 9 Cabinet 10

Figure 6.9-3. Test 1 Interior Cabinet Damage

Figure 6.9-4. Test 1 Exterior Cabinet Damage
 6-12 

Figure 6.9-5 shows data from the SB gauge for Stations 1 and 2 and the Gardon gauge for 

Station 3. The data includes 140 seconds of baseline data at the beginning before the RFAS1 

ignition indicated by the spike. The maximum heat flux was at the top of Cabinet 8 where the 

SB gauge had a view of the flames exiting the top vent spread over the top of the cabinet. The 

heat fluxes in front of Cabinets 7 and 8 were lower even though the gauges were closer to the 

cabinet (0.91 m (3 ft) versus 1.5 m (5 ft)) because (1) the heat was transferred through an 

internal vented wall plus the front door, and (2) these gauges have an oblique view of the flames 

on top of the cabinet. All heat fluxes were lower than recorded in SWGR Test 2 at KEMA (58 

MJ) even though the RFAS released more energy.

(a) (b)

(c)

Figure 6.9-5. RFAS Test 1 Heat Flux
 6-13 

Temperature data for Test 1 is shown in Figure 6.9-6. The temperatures quickly peaked at the 

time of ignition of the RFAS then decreased because there was no major ensuing fire. 

However, the increasing temperatures on the Cabinet 7 and 8 doors from 3 to 5 minutes 

indicate some minor combustion. The maximum temperatures were in Cabinet 7 and 8 where 

the RFAS heat sources were located. The peak external temperature was 98  ̊C (208  ̊F) for the 

Cabinet 7 door and the peak internal cable bundle temperature was 509  ̊C (948  ̊F) for Cabinet 

7. 

(a) (b)

Figure 6.9-6. RFAS Test 1 TC Measurements

During the RFAS ignition, the peak HRR measured in the hood using CO2 calorimetry was 

approximately 3.1 MW. The oxygen calorimetry is valid after about 3 minutes and showed very 

low HRR since there was no ensuing fire. The Total Heat Released (THR) 2 minutes after 

ignition was 114 MJ, about 82% of the 140 MJ released by the RFAS was actually measured. 

There were probably some hood losses and the response time of the instrumentation may have 

been slow to capture the spike of the RFAS HRR. 

The peak SPR was about 24.4 m2

/sec, which was similar to the Test 2 RFAS SPR discussed in 

the next section. 
 6-14 

(a) (b)

(c) (d)

Figure 6.9-7. Test 1 Heat Release Rates and Smoke Production

6.10 RFAS Test 2 Key Observations 

The energy released in the first RFAS was 70 MJ, which did not ignite an ensuing fire, but it 

preheated the cabinets/cables for the next part of the test. The second RFAS released 175 MJ, 

which resulted in an ensuing fire with an initial intensity and spread similar to that observed in 

KEMA SWGR Test 2. Figure 6.10-1 shows both RFAS events. The ensuing fire was allowed to 

burn to completion, which included consumption of the cables inside the vertical duct. The HRR 

data measured at SwRI is likely representative of the HRR from the fire in KEMA SWGR Test 2. 

(a) Cabinet 7 (b) Cabinet 8 (8 min after Cabinet 7)

Figure 6.10-1. RFAS Test 2 Events
 6-15 

Figure 6.10-2 shows the ensuing cable fire. A sustained fire of the cables was visible within 1 

minute after the second RFAS event, and was allowed to propagate, unimpeded to selfextinguishment. Approximately 8 minutes after the second RFAS event, flames were visible at 

the top of the vertical duct. The test was continued for 90 minutes, until the burning had slowed 

to the point that there was virtually no measurable HRR. 

(a) 15 minutes after RFAS event

(b) 5 minutes after RFAS1 (c) 15 minutes after RFAS1

Figure 6.10-2. RFAS Test 2 Ensuing Cable Fire

The RFAS events and ensuing fire resulted in minor internal and exterior damage to the 

cabinets. The damage to the exterior of the cabinets was greater than in Test 1 due to the long 

ensuing fire. Figure 6.10-3 shows the internal damage to each cabinet, and Figure 6.10-4

shows the exterior damage. The latter was primarily charring at the top front of the cabinets 

caused by the internal cable fire, and melting of the instruments on the top front of Cabinet 7. 

Although the discoloration and charring had a similar pattern to KEMA SWGR Test 2, it was not 

as severe. 
 6-16 

(a) Cabinet 6 (b) Cabinet 7 (c) Cabinet 8

(d) Cabinet 9 (e) Cabinet 10

Figure 6.10-3. Test 2 Interior Cabinet Damage
 6-17 

Figure 6.10-4. Test 2 Exterior Cabinets Damage

Data from the SB gauge for Stations 1 and 2 and the Gardon gauge for Station 3 are shown in 

Figure 6.10-5. The data includes 225 seconds (3 minutes 45 seconds) of baseline data at the 

beginning before the RFAS1 ignition. The RFAS2 ignition was at 690 seconds (11 minutes 30 

seconds). 

For the RFAS1, the maximum heat flux was recorded at Station 3 viewing the top of Cabinet 8 

as in Test 1. However, the heat flux was lower than in Test 1 (5 versus 14 kW/m2

) because the 

RFAS1 energy in Test 2 was much lower than the combined RFAS1 and RFAS2 energy in Test 

1 (70 MJ versus 140 MJ). 

Unlike Test 1 and Test 2 RFAS1, the maximum heat flux as a result of Test 2 RFAS2 was not at 

Station 3 above Cabinet 8; the maximum heat flux was at Station 2 viewing the front of Cabinet 

8. Additionally, the heat flux at Station 3 was lower in Test 2 (11 versus 14 kW/m2

) even though 

the RFAS energy was higher (175 versus 140 MJ). This is possibly because in Test 1 both 

RFAS ignited at the same time and the flame area on the top of the cabinets viewed by the 

Station 3 heat flux gauge was larger than the flame area in Test 2. 

The maximum heat flux of 11.4 kW/m2 was measured with an SB at 0.91 m (3 ft) in front of 

Cabinet 8 (Station 2). The maximum heat flux in Test 1 at the same location was 2.5 kW/m2

. 

The increase is consistent with the fact that in Test 1 only 70 MJ was released in Cabinet 8 

compared to 175 MJ in Test 2, although the energy ratio (175/70=2.5) is significantly lower than 
 6-18 

the heat flux ratio (11.4/2.5≈4.5). The discrepancy between the two ratios can be partly 

explained by the added ceramic fiber insulation which was added between Cabinets 7 and 8 

before Test 2, between Cabinets 7 and 8, which may have reduced the heat losses from 

Cabinet 8 during combustion of RFAS2 in Test 2.

The Test 2 Station 1 results for RFAS1 show a heat flux of 3.5 kW/m2 that is similar to the 3.3 

kW/m2 in Test 1. 

The Test 2 Station 1 results for RFAS2 show a heat flux of 5.6 kW/m2 that is higher than the 3.3

kW/m2 in Test 1 by a factor of about 1.7. 

The ensuing fire caused a maximum heat flux of about 1.6 kW/m2 at Station 1 (Cabinet 7) and 

Station 2 (Cabinet 8) at 1,900 seconds (about 32 minutes). Station 3 at 1.5 m (5 ft) above 

Cabinet 8 showed negligible heat flux from the ensuing fire. 

(a) (b)

(c)

Figure 6.10-5. RFAS Test 2 Heat Flux
 6-19 

The temperature data for Test 2 are grouped by the time to ignition of the ensuing fire in Figure 

6.10-6. In Cabinets 7 and 8 the ensuing fires ignite quickly, and in Cabinets 6, 9, and 10 the 

ignition is delayed. 

The temperatures quickly peaked then recovered at the RFAS1 ignition as in Test 1. However, 

the peak temperatures were lower than in Test 1 as expected because the RFAS1 energy in 

Test 2 was lower than the combined RFAS1 and RFAS2 energy in Test 1 by a factor of two. 

The peak external temperature was 63 ̊C (145  ̊F) (versus 98 ̊C (208  ̊F) for Test 1) and the 

peak internal cable bundle temperature was 371  ̊C (700  ̊F) (versus 509 ̊C (948  ̊F) for Test 1). 

In this test, the 70 MJ released from RFAS1 was not adequate to cause an ensuing cable fire in 

Cabinet 7 or 8. This is inconsistent with the KEMA test results which showed that 50 to 60 MJ

of electrical input is adequate ignition energy for an ensuing cable fire. The electrical energy 

was supplemented by the energy associated with aluminum bus bar oxidation within the cabinet 

in the KEMA SWGR tests. It is postulated that this additional oxidation energy provided the 

necessary energy to ignite an ensuing cable fire. This is additional evidence that the aluminum 

bus bar oxidation in addition to the electrical energy (50 to 60 MJ) in the KEMA tests led to 

ensuing cable fire ignitions. 

The temperatures quickly peaked then decreased after the RFAS2 ignition. The peak external 

temperatures were higher than in Test 1, as expected, because the cabinets and cables were 

preheated and the RFAS2 energy in Test 2 was higher than the combined RFAS1 and RFAS2 

energy by a factor of 1.75. The peak external temperature was 439  ̊C (822  ̊F) (versus 98  ̊C 

(208  ̊F) for Test 1) and the peak internal cable bundle temperature was 812  ̊C (1494  ̊F)

(versus 509  ̊C (948  ̊F) for Test 1). 

Cabinets 7 and 8 showed a decrease of the initial high temperature for a few minutes after 

RFAS2 (about 5 minutes in Cabinet 7 and 6 minutes in Cabinet 8). The ensuing internal cable 

fire then caused a rapid temperature increase with a peak of about 780  ̊C (1436  ̊F). The 

cabinet exterior temperatures increases lagged in time and reached a maximum temperature of 

about 680  ̊C (1256  ̊F). These temperature behaviors were as expected. 

Based on the cable temperatures, a stable cable fire in Cabinet 7 began at minute 17 and 

steadily persisted for an additional 45 minutes with a slight increase at the end, which is not

completely understood but could be attributed to the burning of the instruments mounted in the 

front door near the cables. The ensuing fire in Cabinet 8 appears to decay between minute 19 

and minute 32, and temporarily becomes more intense between minute 32 and minute 40. 

As expected for an ensuing cable fire, the cable fires in Cabinets 6 and 9 lagged in time behind 

the fires in Cabinet 7 and 8. The Cabinet 6 ensuing fire lagged the Cabinet 7 fire by about 6 

minutes, resulted in temperatures exceeding 600  ̊C (1112  ̊F) from minute 24 to minute 41, and 

remained relatively steady with temperatures between 400 ̊C (752  ̊F) and 500 ̊C (752 to 932

 ̊F) from minute 41 to minute 71. The cause for the abrupt change is not known. 

The Cabinet 9 ensuing fire lagged the Cabinet 7 internal fire by about 18 minutes during which 

time, the cable was pre-heated from a temperature of about 70  ̊C to 140  ̊C (158 to 284  ̊F) at 

minute 32. The Cabinet 9 cables then fluctuated between 215  ̊C and 465  ̊C (419 to 869  ̊F)

from minute 32 to minute 65 in a slow burn based on the low temperature. 
 6-20 

The Cabinet 10 cable bundle temperature slowly increased to about 143  ̊C (289  ̊F) but did not 

burn as confirmed by post-test observation. 

The external vertical duct temperature (TC7) increased similarly to the Cabinet 7 and 8 doors 

reaching a maximum of 485  ̊C (905  ̊F). The TC at this location was not attached to the duct; 

the temperature was lower than the attached door TCs. The high temperature of TC7 persisted

longer than the Cabinet 7 and 8 door temperatures because the cable fire in the vertical duct 

was the main fire still burning for the last 30 minutes of the test. The unsteady behavior of TC7 

at minute 60 was from the cable fire existing the duct and burning down the 0.91 m (3 ft) extra 

cable dangling outside the duct. 

(a) (b)

Figure 6.10-6. RFAS Test 1 TC Measurements, Cable Bundles for Cabinets 7 and 8

(a) (b)

Figure 6.10-7. RFAS Test 1 TC Measurements, Cable Bundles for Cabinets 6, 9 and 10
 6-21 

During the RFAS ignitions, the peak HRRs measured in the hood using CO2 calorimetry were

about 1,634 kW for RFAS1 and 3,512 kW for RFAS2. The HRR quickly decreased to less than 

one tenth of the peak at about 1.5 minutes after the RFAS ignitions. The measured HRR 

correlates with the RFAS energy in Test 1: 

• RFAS1: HRR was a factor of 0.53 lower than Test 1 (1.63 MW versus 3.12 MW) where 

the RFAS energy was a factor of 0.50 lower (70 MJ vs. 140 MJ). 

• RFAS2: HRR was a factor of 1.12 higher than Test 1 (3.51 MW versus 3.12 MW) where

the RFAS energy was a factor of 1.24 higher (175 MJ vs. 140 MJ). 

Based on the O2 calorimetry response, the ensuing fire HRR time evolution was similar to that of 

the cable bundle temperatures shown previously. The HRR was low (150 to 180 kW) 

immediately after RFAS2 (this was likely only the bus bar insulation burning plus residual 

combustion products) and remained low until the steady cable burning HRR reached a peak of 

432 kW at 21 minutes. The HRR then steadily decreased as the combustibles were consumed. 

The SPR peaks were about 7 m2

/sec from RFAS1 and 24.5 m2/sec from RFAS2. The RFAS2 

peak SPR was about the same as the Test 1 RFAS SPR even though the energy was 1.24

times higher. Immediately after the RFAS2 the SPR decreased to about 6 m2

/sec, and 

subsequently then increased to 10 to 14 m2

/sec from minute 15 to 19. The increase was likely

caused by smoldering combustion before the cable fire was established. The Cabinet 7 cabinet 

fire was established at minute 18 and the SPR decreased to 5 m2

/sec. During the steady cable 

fires after 21 minutes, the SPR correlated to the HRR time evolution, as expected. 

The THR 2 minutes after ignition was 57 MJ for RFAS 1 indicating that about 81% of the 70 MJ 

from the RFAS1 ignition was measured. The THR for RFAS2 increased from 62 MJ to 205 MJ 

(2 minutes after ignition) for a net increase of 143 MJ from RFAS2 indicating that the hood 

measured about 81 percent of the 175 MJ from the RFAS2 ignition. As in Test 1, hood losses 

and slow instrumentation response times probably caused the low measurements versus the 

RFAS energy. The hood calorimetry losses were surprisingly similar for all RFAS ignitions (Test 

1 was 82 percent). 
 6-22 

(a) (b)

(c) (d)

Figure 6.10-8. Test 1 Heat Release Rates and Smoke Production

As shown in Figure 6.10-9, there are two spikes of reduced oxygen at the time of the RFAS 

ignitions that quickly recover. During the ensuing fire, oxygen decreased to 20 percent at about 

16 minutes, which indicates the fire was well-ventilated. 

Figure 6.10-9. RFAS Test 2 Oxygen Concentration in Cabinet 8
 6-23 

As discussed in Section 6.1, RFAS tests required three to four times more heat energy than the 

electrical energy in the KEMA electrical arc tests to cause an ensuing fire in similar SWGR 

configurations. One hypothesis to explain the additional energy required for ignition is that the 

RFAS oxidation was lowering the oxygen levels in the cabinets, causing under-ventilated 

combustion conditions. However, the oxygen measurements in Figure 6.10-9 indicate that the 

oxygen recovered quickly so there was adequate oxygen for combustion. The reason for the 

higher energy, as discussed in the next chapter was the aluminum bus bar oxidation increased 

the energy in the KEMA tests. 

 7-1 

7 Switchgear Tests Results Discussion

7.1 Onagawa Comparison

The results of the KEMA tests are compared with the 2011 Onagawa event conditions in Figure 

7.1-1. The Onagawa external charring damage had a V-shape with Cabinet 7 showing the most 

damage based on the burned paint on the outside of the doors. As shown in the KEMA posttest photos, some paint burning and charring was observed in the KEMA 5-cabinet SWGR Test 

2. But the damage and charring was not as severe as Onagawa. The burning and charring 

was more severe in the KEMA 5-cabinet SWGR Test 4, where there was large aluminum 

oxidation and large ensuing fire but the damage was still not as severe as Onagawa. 

SWGR Test 4, Arc 2 had horizontal bus bar arcing in Cabinet 7 that was like the second arc in 

the assumed Onagawa event scenario. The initial Arc 2 arc in Cabinet 8 drew high current that 

caused the horizontal bus bars in Cabinet 7 to bend and touch and the arc in Cabinet 7 became 

the main arc location at that time. Therefore Arc 8 was very short duration and low energy 

because the electrical current stopped at the Cabinet 7 arc. The energy and ensuing fire was 

very large and the damage on the front of Cabinet 7 was similar to Onagawa, as discussed in 

Section 7.2. This test shows that the aluminum bus bar oxidation was probably a main 

contributor of such a large fire event at Onagawa.

In SWGR Test 5, Arc 2, there was a strong arc in the secondary (rear) of Cabinet 8, as planned. 

However, the damage to the circuit breaker and rear of the cabinet was not as severe as at 

Onagawa. Perhaps the arc needed to be inside the insulator and travel down into the breaker 

to cause the severe damage seen at Onagawa. In SWGR Test 5, Arc 2, the hot gas and 

plasma went up through the roof and out the vent rather than down toward the breaker. 

In SWGR Test 6, Arc 2 in the rear of Cabinet 8 traveled along the bus bar, similar to the 

suspected travel of the second arc at Onagawa. However, the damage in the rear of the 

cabinet was still much less than observed at Onagawa. In the Onagawa event, the cables were 

completely burned and the rear part of the breaker was completely destroyed. 

The overall observations are (1) some of the severe conditions at Onagawa like the bus bar 

oxidation were seen, and (2) the additional energy of aluminum oxidation led to the severe 

conditions and ensuing fires. 
 7-2 

(a) Onagawa Post Fire Damage

Note: This photo shows the test configuration with Cabinet 6 on the left, the Onagawa configuration is 

Cabinet 6 on the right.

(b) Maximum, SWGR Tests 1 to 3 (c) Maximum, SWGR Tests 4 to 6

(d) Post-Test Charring

SWGR Test 2 SWGR Test 4

Figure 7.1-1. SWGR Test Comparisons to Onagawa Damage
 7-3 

7.2 Aluminum Bus Bar Oxidation

This section discusses the high energy of oxidation (burning) of the aluminum bus bars at 

Onagawa and in the SWGR tests. The high energy of aluminum bus bar oxidation is a 

recognized phenomenon and should be considered in HEAF analyses [9]. The energy is from 

the aluminum that burns in the arc that forms aluminum oxide (Al2O3); the main reaction that 

occurs is 2Al(s) + 3/2O2(g) → Al2O3(s). The heat of formation (ΔHf) for Al2O3 is used to 

determine the amount of energy that is released during this reaction. Using the Born-Haber 

cycle for the heat of formation of Al2O3, ΔHf, is calculated to be -1669.79 kJ/mol (g) (16.37 kJ/g). 

The oxidation of 1 gram of Al yields 1.89 grams of Al2O3 (based on the ratio of molecular 

weights of Al to Al2O3, 54/102). Thus, 30.9 kJ is released for 1.89 grams of Al2O3, which can 

also be expressed as 30.9 kJ/g of aluminum burned. 

The bus bar oxidation energy during an arc is based on the amount of bus bar destroyed and an

energy release of 30.9 kJ/g. Direct measurements of bus bar mass before and after the tests 

were not recorded; photographic analysis was conducted to determine the length of bus bar that 

remained after the tests and the associated mass that was lost. The mass loss of the bus bars 

is therefore an estimate. This is a conservative, bounding analysis because it assumes that all 

the melted aluminum is converted to Al2O3. Some aluminum may have been ejected as melted 

aluminum so the actual energy may be lower than reported. Also, in typical situations, 

aluminum oxidization is limited by condensation of the Al2O3 and coating of the aluminum at the 

reaction point [13] but in the case of the high energy arc, the aluminum and Al2O3 are effectively 

flash melted and vaporized and the coating is probably negligible. That being said, even if only 

50% of the aluminum is converted to Al2O3, the Onagawa event would still have had as more 

than 300 MJ of heat generated from aluminum oxidation based on the results in this section. 

Results from Onagawa and the SWGR tests are in the following sections. 

The aluminum burned for the three (3) horizontal bus bars in Cabinet 7 is shown in Figure 7.2-1. 

In this case, the aluminum oxidation is estimated as:

• Bus Bar T: 0 % burned; 

• Bus Bar S: 65% burned - a little was left on both sides, 

• Bus Bar R: 86% burned, and

• The estimated total horizontal bus bar mass burned was 9.2 kg with a net energy of 284

MJ. 

Figure 7.2-1. Onagawa Cabinet 7 Bus Bar Damage

Horizontal bus bar 

pieces not burned

R

S

T

R

S

T
 7-4 

• The vertical bus bars on the primary side of Cabinets 7 and 8 were partially destroyed. 

Only a small part of the vertical bus bar in Cabinet 8 remained. 

o The estimated total vertical mass burned was 10.8 kg with a net energy of 333 MJ. 

o The total energy from all aluminum bus bars burned at Onagawa was 618 MJ.

The burned aluminum bus bars are shown in Figure 7.2-2. The estimated total mass burned 

was 1 kg with an energy of 31 MJ.

Figure 7.2-2. SWGR Test 3 Bus Bar Damage

7.2.3.1 Test 4, Arc 1 

The burned vertical aluminum bus bars are shown in Figure 7.2-3. 

• Arc 1 destroyed the vertical bus bars in Cabinet 7. 

• The estimated total mass burned was 5.4 kg with an energy of 167 MJ.

Figure 7.2-3. SWGR Test 4 Arc 1, Cabinet 7 Bus Bar Damage
 7-5 

7.2.3.2 Test 4, Arc 2 

The burned horizontal aluminum bus bars in Cabinet 7 are shown in Figure 7.2-4. 

• Arc 2 which was initiated about 3.6 minutes after Arc 1, destroyed the front horizontal 

bus bar in Cabinet 7. 

• The estimated total mass burned was 3.7 kg with an energy of 114 MJ. 

Figure 7.2-4. SWGR Test 4 Arc 2, Cabinet 7 Bus Bar Damage

7.2.4.1 Test 5, Arc 1 

The burned vertical aluminum bus bars are shown Figure 7.2-5. 

• Arc 1 destroyed part of the vertical bus bars in Cabinet 7. 

• Much less damage than Test 4, Arc 1 so the energy is lower. 

• The estimated total mass burned was 1.6 kg with an energy of 49 MJ.

Figure 7.2-5. SWGR Test 5 Arc 1, Cabinet 7 Bus Bar Damage
 7-6 

7.2.4.2 Test 5, Arc 2 

The burned vertical aluminum bus bars in the rear of Cabinet 8 are shown in Figure 7.2-6. 

• Arc 2 occurred about 2.9 minutes after Arc 1 and destroyed part of the vertical bus bars 

in Cabinet 8 rear. About 8 cm of each bus bar was lost. 

• The estimated total mass burned was 0.5 kg with an energy of 15 MJ. 

Figure 7.2-6. SWGR Test 5 Arc 2, Cabinet 8 Rear Bus Bar Damage

7.2.5.1 Test 6, Arc 1

The burned vertical aluminum bus bars are shown in Figure 7.2-7. 

• Arc 1 destroyed part of the vertical bus bars in Cabinet 7. 

• The damage was much less than other tests because the arc energy was lower. 

• Two bus bars did not burn through; the right bus bar burned through then the connector 

on top of the insulator fell down. 

• The estimated total mass burned was 0.3 kg with an energy of 9 MJ.

Figure 7.2-7. SWGR Test 6 Arc 1, Cabinet 7 Bus Bar Damage
 7-7 

7.2.5.2 Test 6, Arc 2 

The aluminum bus bars in the rear of Cabinet 8 are shown in Figure 7.2-8. 

• Arc 2 was about 4 minutes after Arc 1 and the arc was between the top of the bus bar 

and the roof. About 7 cm at the top of each bus bar was lost. There were two holes in 

the lost bus bar that reduced the mass lost 

• The estimated total mass burned was 0.3 kg with an energy of 9 MJ. 

Figure 7.2-8. SWGR Test 6 Arc 2, Cabinet 8 Bus Bar Damage

Table 7-1 compares the explosions in the bus bars in the front of the cabinets for various tests. 

The higher energy explosions have larger fire balls, as expected. Arcs in the horizontal bars 

located near the top vent have the largest external fireballs.

The aluminum oxidation of vertical and horizontal bus bars at Onagawa resulted in 618 MJ, 

which was much greater than the 281 MJ resulting from the highest energy KEMA test (167 MJ

+ 114 MJ in March 2014, Test 4). This is an additional 337 MJ of energy from aluminum 

oxidation in the Onagawa incident. 

The much higher energy for Onagawa could be the reason that the char on the front of the 

cabinets in the KEMA test is less than Onagawa. The KEMA March 2014 Test 1 total energy 

including the electrical energy was about 424 MJ (281 MJ + 64.6 MJ + 78.4 MJ). Onagawa was 

about 658 MJ assuming a minimum of 40 MJ Qarc (the electrical energy at Onagawa is not 

known) plus 618 MJ for aluminum oxidation. The total energy difference is about 234 MJ and 

the lower energy resulted in less damage in the KEMA tests as shown, in Figure 7.2-9. If the 

Onagawa electrical energy was greater than 40 MJ (and it probably was), the difference would 

be higher. 

The higher heat fluxes in the tests with aluminum oxidation indicate that the aluminum oxidation 

is very important in HEAF events. The large arc explosion and rapid fire in March 2014 Test 4 

Arc 1 showed this and the very large arc explosion in March 2014 Test 4 Arc 2 (when the 

horizontal bus bar burned) are strong proof of the high energy of aluminum oxidation in actual 

HEAFs. 

The energy from the aluminum oxidation was probably the main reason that the SwRI tests 

using RFAS require more RFAS energy (140 MJ) than the electrical energy at KEMA (nominal 

60 MJ) to ignite an ensuing fire. There was no aluminum bus bar oxidation in the SwRI tests.
 7-8 

KEMA March 2014 Test 4

Onagawa

Figure 7.2-9. SWGR Test and Onagawa Front Panel Damage

Table 7.2-1 shows the energies and the fire ball at the time of the arc. Test 4 the arc wire was 

in the rear but the horizontal bus bars in the front of cabinet 7 arced. The March 2015 tests had 

much lower total energy and there were no ensuing cable fires. 

Additional 

234 MJ of 

Energy
 

Table 7-1. Comparison of Arcs in Front Bus Bars of Cabinets. 

Tests/Arc

June 2013

Test 3

Vert. Bus 

Bars

March 2014

Test 4

Arc 1

Vert. Bus 

Bars

March 2014

Test 4

Arc 2

Hor. Bus 

Bars

March 2014

Test 5

Arc 1

Vert. Bus 

Bars

March 2014

Test 5 

Arc 2

Rear Bus 

Bars

March 20

Test 6

Arc 1

Vert. Bu

Bars

Electrical 

Energy

(MJ)

64 65 78 57 62 27 

Aluminum 

Oxidation 

(MJ)

31 167 114 49 15 9 

Total 

Energy

(MJ)

95 232 192 106 77 36 

Photo

7-9
8-1 

8 REFERENCES

1. “The Situation of Onagawa Following the Tohoku Region Pacific Ocean Earthquake and 

Tsunami”, Tohoku Electric Power Co., Ltd, May 2011. Japanese only, available at 

https://www.nsr.go.jp/archive/nisa/earthquake/files/houkoku230530-2.pdf (as of 2015-08-

19).

2. NUREG/CR-6850 and EPRI 1011989, “EPRI/NRC-RES Fire PRA Methodology for Nuclear 

Power Facilities,” Volume 1: Summary and Overview and Volume 2: Detailed Methodology.” 

Electric Power Research Institute, Palo Alto, CA and U.S. Nuclear Regulatory Commission, 

Office of Nuclear Regulatory Research (RES) Rockville, MD, September 2005.

3. IEEE C.37.20.7, “IEEE Guide for Testing Metal-Enclosed Switchgear Rated Up to 38 kV for 

Internal Arcing Faults,” 2007 Edition, Institute of Electrical and Electronics Engineers, New 

York, New York.

4. IEEE 1584, “IEEE Guide for Performing Arc-Flash Hazard Calculations”, 2002 Edition, 

Institute of Electrical and Electronics Engineers, New York, New York.

5. “OECD Fire Project – Topical Report No. 1, Analysis of High Energy Arcing Fault (HEAF) 

Fire Events”, NEA/CSNI/R(2013)6, Organization for Economic Cooperation and 

Development, June 2013. 

6. Lopez, C., Wente, W.B., Figueroa, V.G., “Evaluation of Select Heat and Pressure 

Measurement Gauges for Potential Use in the NRC/OECD High Energy Arc Fault (HEAF) 

Test Program”, Sandia National Laboratories, Albuquerque, New Mexico, January 2014.

7. Putorti. A., Melly, N.B., Bareham, S., Praydis Jr, J., “Characterizing the Thermal Effects of 

High Energy Arc Faults.” 23rd International Conference on Structural Mechanics in Reactor 

Technology (SMiRT 23) – 14th International Post-Conference Seminar on Fire Safety In 

Nuclear Power Plants and Installations, September, 2015.

8. ASTM F1959, “Standard Test Method for Determining the Arc Rating of Materials for 

Clothing”, 2012 Edition, ASTM International, West Conshohocken, Pennsylvania. 

9. ISO 1716, “Reaction to Fire Tests for Products - Determination of the Gross Heat of 

Combustion (Calorific Value),” 2010 Edition, International Organization for Standardization, 

Geneva Switzerland.

10. Iwata, M., Anantavanich, K., Pietsch, G.J., “Influence of Current and Electrode Material on 

Fraction of Electric Arc Energy Leading to Pressure Rise in a Closed Container During 

Internal Arcing.” IEEE Transactions on Power Delivery, Vol. 25, No. 3, July 2010. 

11. Ingason, H., Wickstrom, U., “Measuring Incident Radiant Heat Flux Using the Plate 

Thermometer.” Fire Safety Journal, Volume 42, p 161-166, 2007.

12. ASTM E2067, “Standard Practice for Full-Scale Oxygen Consumption Calorimetry Fire 

Tests”, 2008 Edition, ASTM International, West Conshohocken, Pennsylvania.

13. Beckstead, M. W., “A Summary of Aluminum Combustion,” in Internal Aerodynamics in 

Solid Rocket Propulsion. 2004 (Chapter 5). RTO-EN-023.
A-1 

APPENDIX A. MEASUREMENTS 

A.1 Thermocouples and Slug Calorimeter Measurements

Type K thermocouples (TC) were used to measure the temperatures during each test prior to 

2015. For safety reasons from possible electrical shorting, the TCs are not in contact with the 

metal cabinet. The TCs are measuring the air temperature since they are located about 15.2

cm (6 in) from the front of the cabinet, in air. The TCs also detect radiation heat transfer from 

the cabinet. The temperatures are probably much lower than the actual metal temperature. 

Therefore, the temperatures are just a qualitative measure of thermal and fire behavior. TCs

located in the air were not used in the 2015 tests.

Heat flux is measured using slug calorimeters (slugs) built to ASTM F1959 [8]. ASTM F1959 is 

used to test protective clothing materials where the arc energy is measured by slug calorimeters 

that are directly exposed to the arc. The slug calorimeters are placed on metal mesh instrument 

stands and are placed at the 0.91 m (3 ft) ZOI from NUREG/CR 6850 to measure the heat flux, 

as seen Figure A.1-1. ASTM F1959 has the procedure to convert the temperature of the slug 

measurement to a heat flux. 

Figure A.1-1. ASTM F1959 Slug Calorimeters3

The method in ASTM F1959, Section 11.10.5 calculates the total energy: 

 

3 Note that ASTM F1959 specifies insulation board however the slug calorimeters in the tests used plywood 

that should provide suitable insulation to reduce conduction losses.
A-2 

Total heat Energy, 

area

mass pC Temp Temp Q final initial ×× ( − ) = (1)

Where: 

Q = Total Heat energy per unit area4

; 

mass = Mass of the copper slug; listed as “mass” in ASTM F1959, kg (nominal 18 g); 

c p = Specific heat capacity specified in ASTM F1959 (kJ/kg·K) 5

; 

Temp = Temperature (K); 

area = Exposed Area of the slug (12.57 cm2

);

ASTM F1959 does not prescribe a method to evaluate heat flux. For the heat flux analysis of 

the HEAF tests, the energy is divided by the time between Tempfinal and Tempinitial: 

t

Q Q ∆

 =

Q

 = heat flux (W/m2); 

Δt = Time associated with ΔTslug (s) 

For the analysis of the NRA HEAF tests, the reported flux is the average over the arc duration

(Δt is approximately the arc duration) based on the ΔTslug caused by an unknown combination of 

radiation and convection heat transfer. The flux analysis assumes the flux is predominantly 

radiation during the arc because the convection would be low during the short time of the arc at 

the ZOI distances (results where the arcs are impacted by flames and convection may be 

significant, and are not included in the analysis as discussed in this section). Radiation sources 

viewed by the slug calorimeters include the flames and plasma that are escaping the cabinet 

and in some cases, the arc itself if a panel is lost or the arc burns though a cabinet wall. The 

effects of re-radiation or convection from the back of the slug, conduction to the slug mount and 

other effects are assumed to be negligible. With the assumption that the dominant flux is via 

radiation heat transfer, the 1/ε factor is included to account for the emissivity:

ε

1

tA

Tcm

t

Q Q p slug

c ∆

∆ = ∆

 = (2) 

Where:

Q

c = Incident heat flux (W/m2) corrected for absorptivity;

m = Mass of the copper slug; listed as “mass” in ASTM F1959, kg (nominal 18 g); 

c p = Specific heat capacity specified in ASTM F1959 (kJ/kg·K); 

ΔTslug = Slug Temperature difference over time (K); 

A = Exposed Area of the slug (12.566 cm2

);

Δt = Time associated with ΔTslug (s); 

 

4 This is ASTM F1959 nomenclature; the total heat energy received at the surface of the panel as a direct 

result of an electric arc. 

5 This is the average specific heat, cp, over the temperature range using formula specified by ASTM 

F1959 that is included in the calculations but the effect is small over the observed temperature ranges in 

the tests.
A-3 

ε = Emissivity/absorptivity of the coating/paint (~0.9)

An emissivity of 0.9 is assumed in accordance with the paint specified in ASTM F1959. 

However, the slug calorimeters did not appear to be maintained and re-painted, and the copper 

surface appeared greyish in some cases and this creates uncertainty in the measurements 

because the emissivity is not known. The heat energy and the heat flux are indirectly 

proportional to the emissivity. That is, if the actual emissivity is assumed to be 0.85 to 0.95 the 

assumption of 0.90 has an uncertainty of ± 5.5%. 

For ASTM F1959 formula (1), the slug calorimeters are 30.5 cm (12 in) from a completely 

exposed high energy arc, and the slugs are engulfed in flames and convection heat transfer 

effects are significant and ASTM does not include emissivity explicitly in the formula. Note that 

for cases where convection is negligible that heat fluxes analyzed using ASTM F1959 formula 

(1) without the 1/ε would be lower by a factor of 1.11 so including the emissivity in (2) above is 

conservative relative to the ASTM method.

For this method, the Tempfinal is just after the arc extinguished and the Tempinitial was just before 

the arc initiated. This method is not impacted by electrical noise and temperature spikes during 

the arc. The results of the slug calorimeter temperature are shown with a straight line that 

indicates the start and end of the arc and represents the time, Δt, and temperature ΔT used for 

the flux calculation as shown for DP Test 1 in Figure A.1-2. The ASTM F1959 results are 

reported for flux in the various results tables in this report. Usually the flux reported is the 

maximum flux which for Figure A.1-2 was Slug S8. 

Figure A.1-2. Typical Slug Calorimeter Temperature Results

Most of the results have large variations of the indicated temperature with time. Some of these 

variations are from EMI/RFI noise that is evident in Figure A.1-2 because negative temperatures 

are not physically possible. Noise is usually worse if the slug is near the power supply and the 

noise was usually different for all the slug calorimeters. Other variations are from rapidly 

varying arc flux or flames escaping the cabinet intermittently through vents or loss of cabinet 

integrity such as cabinet burn-through, or dislodged and bent cabinet panels that cause the slug 

to heat and cool. 
A-4 

In some cases, the temperature spikes were very large where the flames contacted the slug 

calorimeter. If the calorimeter was contacted by flames as indicated by a large spike and review 

of videos, the data was not used to calculate the flux and this is noted in the results. These 

cases indicate that radiation may not be the dominant heat transfer mode. Some of the spikes 

in the calorimeter temperatures are noise but these do no effect the start and end temperatures 

over the arc interval used for the Formula (2) ASTM F1959 flux calculation because the Δt is 

between the arc start and arc end. 

The flux values that are reported are only for the time during the arc. After the arc quenches, 

the flux from the arc and residual heat in the cabinet is very small and the decreasing 

temperature of the slug indicates a negative flux using Formula (2). However, this flux is a 

measure of the slug calorimeter cooling; not of the cabinet conditions. If an ensuing fire occurs, 

the slug will eventually heat up, but at this point the slug response is some complicated mix of 

low radiation heat transfer from the warm cabinet wall the slug is viewing, convective heat 

transfer from the cabinet to the local air, and the convective heat transfer from the air to the 

slug. Therefore, it can be assumed that the results are valid during the arc itself because the 

arc duration is short and the temperature response at the slug is primarily related to heat 

conditions caused by the arc and the associated escaping flames and plasma.

In cases where the flux measurements using Formula (2) are not valid (for example if there is 

flame contact), the slug temperature measurements provide a qualitative indication of the 

temperature that a small metal object at the NUREG/CR 6850 ZOI boundary could attain during 

the test. The slug’s small copper disk with high emissivity provides a conservative estimate of a 

typical metal object that would typically have much lower thermal inertia and lower emissivity. 

This is true during the arc, after the arc, and also in cases where the slug calorimeter is 

contacted by flames. Therefore, the slug temperatures as well as the flux results are presented 

in this report. For example, an increasing slug temperature response after the arc is a 

qualitative indicator of an ensuing fire. The reported maximum slug temperatures are 

immediately after the arc to avoid noise spikes and indicate the maximum temperature a copper 

object could achieve from the arc heat.
A-5 

A.2 Pressure Measurements 

The Dynisco PT150-50 strain-gauge type Pressure Transducers (PRT) were connected to the 

cabinets by a reinforced rubber tube and then placed inside a PVC pipe for protection, as shown 

in various figures in the main text. The PRTs were not attached to the cabinet and moved and

flexed the tube during some tests and this may have caused some very small pressure effects 

in the tubing and electrical effects in the cable. However, such effects were not specifically 

identified. Since the tubing was not filled with incompressible fluid, the compression of the air 

may have some effect on the time constant of the pressure response but this is not considered 

in the analysis. 

Figure A.2-1 shows a typical pressure history for SWGR Test 4 in March 2014, Arc 1 where

PRT1 was on Cabinet 7 and PRT2 was on Cabinet 8. Moving point averages were used to 

show the general trend of the response and remove some the noise and pressure effects. The

data acquisition frequency was 20 kHz so 50 point averaging covers 0.0025 seconds and is an 

effective filter. The pressure transducers use strain gauges in bridge circuits that have high 

frequency response but the frequency response is limited by the mechanical limitations of the 

internal components and the manufacturer reports a minimum frequency response of 2 kHz but 

a typical response of 7 kHz depending on the connection to the item being measured. The 

minimum should allow measurements every 0.0005 seconds and this is adequate to measure 

the peaks that typically occur in the range of 0.010 to 0.025 seconds. The reported peak 

pressures were from the un-averaged data because the averaging artificially reduces the 

amplitudes of the highest peak pressure.

(a) (b)

Figure A.2-1. Typical Pressure Results with Noise

The pressure often had spikes as the arc first forms and later quenches. The spikes were 

probably caused by rapidly changing magnetic field effects as the start and stop of the arc 

causes unstable and unbalanced current in the 3-phase power in the nearby bus bars and 

conductors. The maximum pressures for all tests were typically 0.010-0.025 sec after the arc. 

There were usually one or two noise spikes before the maximum pressure in most tests, as 

seen in Figure A.2-1. Noise spikes could be distinguished from pressure by expanding the timescale and observing the response width because noise spikes are extremely narrow as shown 

in Figure A.2-2 for SWGR Test 4 in March 2014, Arc 1. The noise spike at 0.005 seconds is 

very narrow compared to the peak pressure at 0.0129 seconds. The initial negative spike down 

also indicates this is a noise spike. The manufacturer reports that the gauges should not be 

used to measure negative pressure so any negative pressures are noise. 
A-6 

Note that the pressures are typically very low so electrical noise in the result was estimated and 

included as a pressure uncertainty. Figure A.2-2 shows a typical pressure analysis to 

understand the electrical noise in the circuits. The plus/minus (±) uncertainty is based on the 

peak-to-peak un-averaged noise before the arc. The results before the arc initiated were 

reviewed to manually select the peak to peak noise level including the higher frequency noise 

that is filtered by the 50-point moving average. This peak-to-peak value was used as a 

conservative uncertainty. 

The high frequency noise is considered when evaluating the maximum pressure as shown in 

Figure A.2-3. This example shows there is a high frequency noise (around 3.7 kHz) that occurs 

on many of the pressure results. The origin is not known. The noise is filtered by the 50-point 

average but the averaging reduces the indicated maximum pressure and delays the time of the 

maximum pressure as shown in the figure. The maximum pressure that is reported is selected 

as the mid-point of the peak-to-peak values in the cycle that includes the maximum measured 

pressure. As shown in the figure, the maximum measured pressure in MCC Test 1 was 4.8 psi 

but 4.1 psi is reported; this is about a 20% reduction. So, it is important to consider the high 

frequency noise using this manual method. The maximum pressure and the time are manually 

recorded directly from the EXCEL® chart. 

The pressure gauge measurement uncertainty is not included because the only measurements 

that are reported are the peak pressure relative to the pressure at the start of the arc and the 

peak pressure that occurs within about 0.025 seconds after the start of the arc. It is assumed 

that the gauge accuracy that applies to absolute measurements did not change during this short 

interval and accuracy is not included in the uncertainty. The manufacturer lists the accuracy as 

±0.5% of the full scale range which is ±0.25 psi for the 50 psi full scale range for the PT150-50 

and includes linearity, hysteresis, and repeatability. There are other factors that could affect the 

results such as movement of the PRT and flexing of the tube that connects the PRT to the 

cabinet but these also occur after the peak pressure and are not considered. The entire 

pressure data history is shown in the charts for interest, but only the peak pressure is reported. 
A-7 

SWGR Test 4 

Arc 1 

Pressure 1 

(Cab 7)

3.4 ± 0.1 psi

23.4 ± 0.7 kPa

@0.0129 sec 

(12.9 ms) 

SWGR Test 4 

Arc 1 

Pressure 2 

(Cab 8)

1.8 ± 0.1 psi

12.4 ± 0.7 kPa

@0.0126 sec 

(12.6 ms)

Figure A.2-2. Typical Pressure Results and Uncertainty Estimate

Figure A.2-3. High Frequency Noise Analysis

Maximum measured: 4.8 psi Maximum reported: 4.1 psi
A-8 

A.3 Energy Measurements

Total arc energy, Qtot, is a key parameter that characterizes the strength of the arc and the 

potential for damage and ability to cause an ensuing fire in the cabinet or externally at the ZOI. 

An EXCEL worksheet is used to calculate the energy for the June 2013 SWGR Test 2, shown in 

Figure A.3-1. The currents and voltages for each phase, a, b, and c (Columns C-H) are 

multiplied to give the power in each phase (Columns J-K). The powers from each phase are 

added and then multiplied by the time step (0.00005 seconds) to give energy in Column M. The 

energy for each step is added to a cumulative total (referred to as “Qtot” or “Energy Total” in this 

report) in Column N. The resulting graph, as shown in Figure A.3-2, is just for the time of the 

arc. 

The cumulative energy should be a smooth line, linear with time that shows the KEMA power 

system provided a steady energy for the test. Discontinuities or spikes in the Qtot line indicates 

the arc was not steady and also could indicate re-strikes. A rise in the Energy or a change in 

slope of the Energy Total indicate that the electric power is changing and this is observed when 

the voltage increases as the arc gap increases because the metal at the arc connection points 

oxidizes or melt and the arc length increases (voltage increase with arc gap). 

Figure A.3-1. Test 2 Arc Energy Calculation 
A-9 

Figure A.3-2. Test 2 Arc Energy Result

B-1 

APPENDIX B. KEMA TEST LABORATORY

KEMA Laboratories Chalfont (“KEMA”) performed the NRA HEAF tests at their lab facilities in 

Chalfont, Pennsylvania shown in Figure B.1-1. Both the large KEMA G2 - 2250 MVA, 16 kV, 

Variable frequency generator and KEMA G1 - 1000 MVA, 16 kV, 60 Hz were used. Note that 

G1 is fixed at 60 Hz only so the SWGR tests with two arcs were performed at 60 Hz. G2 at 50 

Hz was used for all other tests 

Test Cell 7 in Figure B.1-2 has a US “Medium Voltage” supply bus for the SWGR 6.9 kV arc (on 

the left) and a low voltage supply bus for the 480 V DP tests 4 through 6. DP Tests 1 through 3 

and MCC Tests 1 through 4 were in Test Cell 1 with a low voltage supply only. 

Figure B.1-1. KEMA Powertest Facility

Customer 

Assembly

Building

Motor 

Generator 

Hall

Tests are observed in the control 

room through windows with impact 

resistant glazing. The doors to the 

tests cells are open during tests.

Control 

Room
B-2 

Figure B.1-2. KEMA Test Cell 7 Arrangement

KEMA Test Cells
C-1 

APPENDIX C. CABLE PROPERTIES

This appendix shows the properties of the cables used as the combustible loads in the NRA 

tests. 

Table C-1. Cable Materials. 

CV-4 or CV-2

Jacket/Sheath: JIS Flame Retardant Vinyl 

(Polyvinylchloride PVC)

First Wrapping: No

Shield: None

Fill: Yes

Insulation: Cross-Linked Polyethylene (XLPE) 

Conductor: Stranded 

6KV-CSHVT

Sheath: JIS Flame Retardant Vinyl (Polyvinylchloride 

PVC)

First Wrapping: None

Shield: None

Second Wrapping: None 

Fill: No, one conductor 

Insulation: Cross-Linked Polyethylene (XLPE)

Conductor: Stranded

HIV 

Sheath: Fire Retardant Low Hydrochloric Vinyl 

First Wrapping: None 

Shield: None

Second Wrapping: None 

Fill: None 

Insulation: Sheath is insulation
C-2 

Table C-2. Cable Properties. 

Item CV-2 CV-4 HIV 6KV-CSHVT

Number of Conductors 2 4 1 1 

Conductor area mm2 2 2 2 250

Outer Diameter mm 10.5 12 3.6 28

Mass per length kg/km 120 180 28 2500

Combustible % 69 61 35 37
D-1 

APPENDIX D. SHORT CIRCUIT CURRENT CALCULATIONS 

As discussed in Section 1.3.1 the bolted fault current that is the maximum feasible fault current 

for an electric circuit was used as the short circuit current in the tests. The bolted fault current 

was based on the well-known “infinite bus” short circuit calculation (or “bolted short”) from text 

books as described below. 

D.1. DP and MCC Test Current

The feed circuit in Japan is not specified. The schematic assumed for the DP and MCC in a 

typical NPP plant is in Figure D.1-1. A 480 V, 3 kA, bus feeds the DP. A 480 V, 600 A, DP 

MCCB feeds the MCC. 

Figure D.1-1. Circuit Assumed for DP and MCC Tests

The calculated maximum, bolted, three phase short circuit current that could occur for a 480 V 

secondary bus of a 2,500 KVA transformer with a percent impedance of 5.75% is:

SCA2 = (FLA2 * 100%) / Z%

FLA2 = kVA three-phase / (Sqrt(3) * kVLL)

FLA2 = 2,500 kVA / (1.732 * 0.480 kVLL)

FLA2 = 3.007 kA

SCA2 = (3007 * 100%) / 5.75%

SCA2 = 52.296 kA (nominal 53 kA was specified for the tests)

Where:

SCA2 = bolted short circuit amperes on the secondary bus (short circuit amps)

FLA2 = transformer secondary full load current rating (full load amps)

kVLL = line-to-line voltage in kV 

Sqrt(3) = square root of three which is 1.732

Z% = transformer nameplate percent impedance, 5.75% is a conservative lowest value in 

typical industrial circuits 

DP

MCC

2,500 KVA 

13.8 kV/480 V 

3 kA Secondary

480 V 600 A
D-2 

Figure D.1-2 shows the basis of determining the available short-circuit current to include the 

current from the motors that are connected to the MCC. The current includes shorting current 

from the DP (Is) and the motors (Im). 

Figure D.1-2. Short Circuit Current for MCC Test

Is is the short-circuit current available from the system at the point where the MCC is connected 

in Figure D.1-1. That current (Is) is nominally 52 kA from the DP above. 

Im is the short circuit current contribution of the motors connected to the MCC. GE and ANSI 

C37.001 say that if the actual motors are not known, use four times (4X) the continuous-current 

rating of the main horizontal bus in the MCC. In this case, the continuous rating is 2.8 kA and 

Im= 4 X 2.8 = 11.2 kA. 

Isc is the available short-circuit current to be used for the test. Isc = Is + Im. So the test current is 

52 + 11.2 = 63.2 kA. The tests here were conducted at 63 kA. 

D.2. SWGR Test Current

The calculated maximum, bolted, three phase short circuit current that could occur at the 6.9 kV 

secondary bus of a 26 MVA transformer with a percent impedance of 9.5 percent is nominally 

23 kA.

SCA2 = (FLA2 * 100%) / Z%

FLA2 = kVA three-phase / (Sqrt(3) * kVLL)

FLA2 = 26,000 kVA / (1.732 * 6.9 kVLL)

FLA2 = 2.176 kA 

SCA2 = (2.176 * 100%) / 9.5%

SCA2 = 22.9 kA; a nominal 23 kA was specified as the symmetric current

To get higher energy for an ensuing fire the bolted fault current was about 31 kA. 




 

 

NUREG/IA-0470

Volume 1

Nuclear Regulatory Authority Experimental Program to Characterize and 

Understand High Energy Arcing Fault (HEAF) Phenomena