NUREG/CR-2927

SAND82-0236

RP

Printed October 1982

Nuclear Power Plant Electrical Cable

Damageability Experiments

Larry L. Lukens

Prepared by

Sandia National Laboratories

Albuquerque, New Mexico 87185 and Livermore, California 94550

for the United States Department of Energy'

under Contract DE-AC04-76DP00789

- I

Prepared for

U. S. NUCLEAR REGULATORY COMMISSION

SF 2900-Q(6-82)
S

NOTICE

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United

States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any

legal liability or responsibility for any third party's use, or the

results of such use, of any information, apparatus product or process disclosed in this report, or represents that its use by such

third party would not infringe privately owned rights.

Available from

GPO Sales Program

Division of Technical Information and Document Control

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555

and

National Technical Information Service

Springfield, Virginia 22161

q
NUREG/CR-2927

SAND82-0236

RP

NUCLEAR POWER PLANT ELECTRICAL CABLE

DAMAGEABILITY EXPERIMENTS

L. L. Lukens

Printed: October 1982

Sandia National Laboratories

Albuquerque, New Mexico 87185

operated by

Sandia Corporation

for the

U.S. Department of Energy

Prepared for

Division of Engineering Technology

Office of Nuclear Regulatory Research

Washington, DC 20555

Under Memorandum of Understanding DOE 40-550-75

NRC FIN No. A1010-2
Id
ABSTRACT

Under the direction of the Nuclear Regulatory Commission,

Sandia National Laboratories has been conducting confirmatory research in fire protection for nuclear power plants.

As a part of this research, a program was developed to

determine the damageability of electrical cable insulation

to thermal radiation in a loaded cable tray. The critical

flux or threshold level at which cable damage occurs in

the form of electrical failure (short from conductor to

tray) and nonpiloted ignition was determined for two types

of electrical cable, one an IEEE-383 qualified cable and

the other an unqualified cable. The critical flux for

electrical failure was determined to be about 18 kW/m 2

for the IEEE-383 qualified cable and about 8 kW/m 2 for

the unqualified cable. The critical flux for nonpiloted

ignition was determined to be about 28 kW/m 2 for the

IEEE-383 qualified cable and about 22 kW/m 2 for the

unqualified cable.

A program was also developed to determine the damageability

of electrical cable insulation to constant temperature,

thermal exposure. Experimental results indicate that

exposure of the IEEE-383 qualified cable to temperatures

greater than 250 0 C (480 0 F) for periods of 60 minutes can

cause discoloration, blistering, smoking, loss of flexibility, and failure to pass a voltage withstand test as

described in the report. Experimental results indicate that

exposure of the unqualified cable to temperatures greater

than 130 0 C (265°F) for periods of 60 minutes can cause

electrical failure in the form of shorts between

conductors. In addition, the thermal forming temperature of

the unqualified cable jacket material was determined to be

between 170 0 C (340 0 F) and 200*C (390*F).

These results apply only to the two particular types of

electrical cables examined and described in this report, and

would need to be evaluated for any other type of electrical

cable. Thermal aging and radiation exposure efforts were

not included in the investigation.

iii
ACKNOWLEDGMENTS

The tests described in this report were ably performed by

L. D. Lambert and S. L. Ogan in conjunction with J. T.

Nakas and other Radiant Heat Facility personnel.

iv
CONTENTS

Page

Executive Summary 1

Radiant Heat Experiments 5

Apparatus 5

Procedure 6

Results 7

Oven Experiments 18

Apparatus 18

Procedure 19

Results 21

Conclusions 33

Recommendations 34

References 35

v
LIST OF FIGURES

Figure Page

1. Radiant Heat Facility Experimental Apparatua 13

2. Radiant Heat Experiment Instrumentation Placement 14

3. Reciprocal Time to Electrical Failure as a 15

Function of External Heat Flux

4. Reciprocal Time to Nonpiloted Ignition as a 16

Function of External Heat Flux

5. Maximum Temperature Reached During Experiment 17

as a Function of External Heat Flux

6. Oven Experiment Configuration B 24

7. Oven Experiment Configuration C 25

8. Oven Experiment Configuration D 26

LIST OF TABLES

Table Page

1. Radiant Heat Experiment Outline 9

2. Summary of Results for Radiant Heat Experiments 10

3. Critical Flux Levels for Electrical Cable Failures 11

4. Maximum Cable Temperatures for Radiant Heat 12

Experiments

5. Oven Experiments with Cables in Configuration A 27

6. Oven Experiments with Cables in Configuration B 28

7. Summary of Results for Oven Experiments with 29

Cables in Configuration B

8. Summary of Results for Oven Experiments with 30

Cables in Configuration C

9. Summary of Results for Oven Experiments with 31

Cables in Configuration D

10. Summary of Results for Oven Experiments on 32

Tensile Elongation of IEEE-383 Qualified Cable

Jacket and Insulation Material

vi
EXECUTIVE SUMMARY

Under the direction of the Nuclear Regulatory Commission,

Sandia National Laboratories has been conducting confirmatory research in fire protection for nuclear power plants.

On October 27, 1980, the Nuclear Regulatory Commission

(NRC) approved Appendix R to 10 CFR Part 50,1 which is a

new rule of fire protection. Section III.G.2.b, 'Fire

Protection of Safe Shutdown Capability,' in Appendix R to

10 CFR Part 50 allows the separation of cables/equipment

by a horizontal distance required to protect redundant

divisions exposed to a single transient exposure fire.

The 20-ft separation requirement represents the collective judgment of the NRC staff and its fire protection

consultants following onsite observation at operating

plants.

The Office of Nuclear Reactor Regulation requested that a

full-scale fire experiment program2 be developed and

implemented to determine the adequacy of the 20-ft

separation criterion. As a part of this program, experiments were performed at Sandia National Laboratories to

provide information on the damageability of electrical

cables exposed to a fire environment.

Two basic types of experiments were performed on

electrical cables, one in which cables were exposed to

thermal radiation at constant flux levels and one in which

cables were exposed to a constant temperature environment

with heating primarily by convection. These experiments

were designed to determine the radiant heat flux levels

and temperatures above which the physical and electrical

properties of electrical cables begin to degrade. The

experiments were performed on two particular types of

unaged electrical cables, an IEEE-383 2 qualified cable

and a PE/PVC unqualified cable.

This information is important for determination of an

acceptance criterion for electrical cables exposed to a

fire environment. The analytical determination of electrical cable damage for any given configuration of cable

trays and fuel packages also requires this type of

information.

The critical fluxes or threshold levels, at which

electrical cable damage occurs in the form of electrical

failure and nonpiloted ignition, have been determined for

the two types of cable examined. The critical flux for

electrical failure (short from conductor to tray) was
determined to be about 8 kW/m 2 for unqualified cable and

18 kW/m 2 for IEEE-383 qualified cable. These results,

along with the approximate time to electrical failure as a

function of heat flux, were determined. The critical flux

for nonpiloted ignition was determined to be about 22 kW/m 2

for unqualified cable and 28 kW/m 2 for IEEE-383 qualified

cable. These results, along with the approximate time to

nonpiloted ignition as a function of heat flux, were

determined.

The critical flux values for cable damage in the forms of

electrical failure and nonpiloted ignition determined for

the two cable types tested are based on a very limited

amount of test data. This limited amount of data and the

stochastic nature of the processes being investigated

introduce a margin of uncertainy in addition to that of

instrumentation accuracy to the results presented in this

report.The possible sources of error mentioned for these

results should be considered in their acceptability for

any particular application.

Experimental results indicate that exposure of the

particular IEEE-383 qualified cable examined in this study

to temperatures greater than 250°C (480 0 F) for periods of

60 minutes can cause discoloration, blistering, smoking,

loss of flexibility, and failure to pass a voltage withstand test as described in this report. Experimental

results indicate that exposure of the particular unqualified cable examined in this study to temperatures greater

than 130 0 C (265 0 F) for periods of 60 minutes can cause

electrical failure in the form of shorts between conductors. In addition, the thermal forming temperature of the

unqualified cable jacket material was determined to be

between 170 0 C (340 0 F) and 200 0 C (390 0 F).

The properties of electrical cables and threshold values

for electrical cable damage identified in this report

should not be interpreted as an acceptance criterion for

electrical cables exposed to a fire environment. They are

applicable to two particular types of unaged electrical

cable identified specifically in this report and would

need to be evaluated for any other type of electrical

cable.

2
INTRODUCTION

On October 27, 1980, the Nuclear Regulatory Commission

(NRC) approved Appendix R to 10 CFR Part 50,1 which is a

new rule of fire protection. Section III.G.2.b, 'Fire

Protection of Safe Shutdown Capability,' in Appendix R to

10 CFR Part 50 allows the separation of cables/equipment

by a horizontal distance of 20 ft (6.1 m). The purpose of

the 20-ft separation requirement is to provide a uniform

safe distance required to protect redundant safety

divisions exposed to a single transient exposure fire.

More specifically, the 20-ft separation of equipment must

be capable of limiting fire damage so that one train of

systems necessary to achieve and maintain hot shutdown

conditions from either the control room or emergency

control station(s) is free of fire damage. The 20-ft

separation requirement represents the collective judgment

of the NRC staff and its fire protection consultants

following onsite observation at operating plants.

The Office of Nuclear Reactor Regulation requested that a

full-scale fire experiment program2 be developed and

implemented to determine the adequacy of the 20-ft

separation criterion. As a part of this program, experiments were performed at Sandia National Laboratories to

provide information on the damageability of electrical

cables exposed to a fire environment.

Two basic types of experiments were performed on electrical

cables, one in which cables were exposed to thermal

radiation at constant flux levels and one in which cables

were exposed to a constant temperature environment with

heating primarily by convection. These experiments were

designed to determine the radiant heat flux levels and

temperatures above which the physical and electrical

properties of electrical cables begin to degrade. The

experiments were performed on two particular types of

unaged * electrical cables, an IEEE-383 2 qualified

cable and a PE/PVC unqualified cable.

This information is important for determination of an

acceptance criterion for electrical cables exposed to a

fire environment. The analytical determination of electrical cable damage for any given configuration of cable

trays and fuel packages also requires this type of

information.

*Thermal aging and radiation exposure effects were not

included in the investigation

3
The two types of experiments performed will be described

separately in this report. The experiments in which

electrical cables were exposed to thermal radiation will

be referred to as "Radiant Heat" experiments and the

experiments in which electrical cables were exposed to a

constant temperature environment will be referred to as

"Ovenw experiments.

4
RADIANT HEAT EXPERIMENTS

Apparatus

A device was constructed at the Radiant Heat Facility3 to

expose a cable tray, 2.44 cm (8 ft) long by 30 cm (1 ft)

wide to thermal radiation at power levels of up to

60 kW/m 2 . The cable tray was mounted under a semicircular cylindrical steel shroud which was heated by three

banks of quartz infrared lamps. The ends of the shroud

were open to permit ventilation between the cable tray and

the shroud and to permit observation of the exposed cable

during the testing. The entire device was located in a

building which has a large bay door on the north side and

four ceiling fans for forced ventilation during the testing. The orientation of the device was with the long axis

of the cable tray running north/south and the north end of

the device just inside the bay door. A photograph of the

experimental apparatus showing the radiant heat device with

the cable tray covered by an insulated shutter and the

quartz lamps energized is shown in Figure 1.

The cable tray was filled with five bundles, eight loops

each, (approximately 244 m, (800 ft)) and three 2.44-m

(8-ft) lengths of cable for thermocouple placement. Two

types of unaged cable were used in these experiments. One

type was IEEE-383 qualified 3 conductor, no. 12 AWG tinned

copper, 30 mil Exane II insulation, silicon glass tape, 65

mil Exane II jacket, 600 volt. The other type was nonIEEE-383 qualified 3 conductor, no. 12 AWG copper, 20/10

PE/PVC insulation, 45 mil PVC jacket, 600 volt.

The cable was energized during experiments with 320 VDC and

5 amps AC. Cable currents, both AC and DC, were recorded

during testing and current from cable to cable tray was

recorded to detect electrical failure ( a short from cable

to cable tray) during experiments.

Cable temperatures during experiments were measured by a

set of 10 chromel/alumel thermocouples positioned in the

cable tray as shown in Figure 2. Thermocouples 102, 105,

106 and 107 were located inside the cable jacket, and

thermocouples 100, 101, 103, 104, 108 and 109 were located

around the cable.

Heat flux from the steel shroud to the cables was measured

with six water-cooled calorimeters positioned in the cable

tray as shown in Figure 2. Three of the calorimeters,

numbers HF7, HF8, and HF9, were monitored by the Radiant

5
Heat Facility personnel for control purposes and the other

three, numbers 113, 114, and 115, were monitored by Systems

Safety Technology Division personnel.

The experimental data, including electrical information,

temperatures, and heat fluxes, are recorded on magnetic

tape with a complete scan taken every 30 seconds. The

accuracy of the thermocouple is approximately + 30 C (5.5 0 F)

and the accuracy of the calorimeters is approximately + 5

percent. The weight measurements of the cable trays before

and after each experiment are accurate to about + 0.05 kg

(0.1 lbs).

Procedure

The first steps in this program were a series of calibration

tests on the radiant heat device. The purpose of the

initial calibration testing was to determine the approximate power level supplied to the quartz infrared lamps to

produce the desired power level of heat flux from the steel

shroud to the cables for the different heat flux levels to

be tested. These calibration tests were conducted with a

dummy load in the cable tray and also served to verify the

function of the radiant heat device both in terms of uniform flux distribution over the cable tray and structural

integrity over the range of heat flux levels anticipated.

The procedure followed for each of the ten experiments

performed with actual cable loading was as follows: The

cable tray was filled with cable, weighed, and photographed. The instrumentation was installed as shown in

Figure 2. The bay door on the building was opened to a

height just above that of the top of the radiant heat

device, approximately 2 m above the ground (see Figure 1).

An insulated shutter was placed between the shroud and the

cables to protect the cables until the shroud was heated to

the proper temperature for the experiment being conducted.

The power to the cables was turned on and the recording

device was started. The quartz lamps were energized to

heat the shroud to the proper temperature. When the shroud

was heated to the proper level the insulated shutter was

removed exposing the top of the cable tray to thermal

radiation. The three calorimeters monitored by the Radiant

Heat Facility personnel were used to control the heat flux

to the desired level throughout the experiment. The cable

was exposed for a period of 30 minutes or until ignition

(flames) occurred. If the cable started smoking, the

elapsed exposure time was recorded and the ventilation in

the building was started to remove excess smoke from the

test area. If flames developed, the power was cut to the

quartz lamps, the fire was extinguished using portable

6
CO 2 fire extinguishers, and the experiment terminated.

If no flames developed, power was cut to the quartz lamps

after 30 minutes and the experiment was terminated. After

the cable tray had cooled, it was removed from the radiant

heat device, weighed to determine cable weight loss, and

photographed.

Results

A total of ten experiments were conducted, five each on

IEEE-383 qualified cable and unqualified cable. The

experiment number, cable type, and nominal heat flux level

for each experiment are listed in Table 1.

A brief summary of the results of the experiments is listed

in Table 2, which includes a time-weighted average of the

heat flux level from calorimeters 113, 114, and 115, the

total exposure time, the elapsed time to electrical failure, the elapsed time to cable fire, and the cable weight

loss for each experiment. As noted in Table 2, the total

exposure time for experiment number 2 is 10 minutes longer

than the 30-minute period specified in the procedure. The

additional exposure time was added to test number 2 to

verify that the cable temperatures at the top of the tray

had reached their maximum for this heat flux level. The

additional exposure time had no significant effect on cable

damage, which was exhibited by only slight discoloration

and a weight loss of 0.05 kg (0.1 lb) which is on the order

of the accuracy of the weight measurement. The time to

electrical failure for experiment number 1 is listed as

greater than 30 minutes because the current from cable to

tray was nonzero but below the threshold value of 1 amp

used to describe electrical failure. The time to cable

fire for experiment number 7 is listed as greater than 30

minutes because the cable temperature was very close to

ignition temperature at the end of 30 minutes exposure

(Tmax = 5870C (10890F)) and it was assumed that ignition

would occur if the exposure were continued.

The threshold levels of heat flux for damage in the form of

electrical failure and nonpiloted ignition were calculated

for the IEEE-383 qualified cable and the unqualified cable

used in these experiments. These values are listed in

Table 3 and shown graphically in Figures 3 and 4. The

critical flux for electrical failure was determined to be

about 8 kW/m 2 for unqualified cable and 18 kW/m 2 for

IEEE-383 qualified cable. The critical flux for nonpiloted

ignition was determined to be about 22 kW/m 2 for unqualified cable and 28 kW/m 2 for IEEE-383 qualified cable.

These values were calculated using a linear least squares

7
analysis of the data summarized in Table 2. The data

points from experiments number 1 and number 7, in which the

time to electrical failure and the time to ignition are

listed as greater than 30 minutes, were included in the

least squares analyses, and are shown as a point with an

error bar in Figures 3 and 4.

The maximum temperatures reached during each experiment,

prior to ignition or termination of the test, are listed in

Table 4 along with the thermocouple number(s) which registered those temperatures. These maximum temperatures are

shown graphically in Figure 5. The lines in Figure 5

represent a linear least squares data fit of maximum

temperature vs. external heat flux for both types of

cable. Thermocouple locations can be determined from

Figure 2. In experiments 3, 9 and 10 the heating was very

rapid and probably uneven and the maximum temperature

recorded may not reflect the actual maximum temperature

reached in the cable tray. These data points were not

included in the least squares analyses. These temperatures

cannot be used for the determination of the temperature at

which electrical failure occurred because electrical failure may have taken place before the termination of the

experiment where the maximum temperature would have

occurred.

8
Table 1

Radiant Heat Experiment Outline

Radiant Heat

Experiment

Number

1

2

3

4

5

6

7

8

9

10

Cable Type

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Nominal Heat Flux

kW/m 2

20

10

40

30

5

10

20

5

30

30

9
Table 2

Summary of Results for

Radiant Heat Experiments

Radiant Heat

Experiment

Number

1

2

3

4

5

Measured

Heat Flux

kW/m 2

21

11

41

31

7

Time of

Exposure

min

30

Time to

Electrical

Failure

min

Time to

Ignition

min

Weight

Loss

lbs

t 30* 1.0

40 .1

6.5

26.5

6.0

9.5

6.5

26.5

6

7

8

9

11

23

30

30

30

30

22.5

3.0

7.4

0.0

0.2

5.1

0.2

2.3

1.2

7.5 t 30

6

30

29

7

6

4

4

7

10 6

* Partial electrical failure had developed at 30 minutes and it

is assumed that total failure would occur if the exposure

were continued.

Note that experiment number 2 was run 10 minutes longer than

normal.

Thermocouple readings indicate that the cables were very

close to ignition temperature (600°C) and it is assumed that

fire would develop if the exposure were continued.

10
Table 3

Critical Flux Levels for

Electrical Cable Failures

IEEE-383

Qualified Unqualified

Critical Flux 18 8

Electrical Failure

(kW/m 2 )

Critical Flux 28 22

Nonpiloted Ignition

(kW/m 2 )

11
Table 4

Maximum Cable Temperatures for

Radiant Heat Experiments

Radiant Heat

Experiment

Number

Maximum

Recorded

Temperature oC

Thermocouple

Location

1

2

3

4

5

6

409

301

607

667

167

285

587

186

510

362

106

104

104

104

106

105

106

106

103

7

8

9

10 101 & 105

12
* 'I. 

* /

653-~

LA

Figure 1. Radiant Heat Facility Experimental Apparatus
105

104/.

109

00

NORTH

SOUTH

HF7

115/.

114

Figure 2. Radiant Heat Experiment Instrumentation Placement
€

m,

'00

4*

E-40

C',

I-'

0

'4

0

d

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0

External Heat Flux, kW/m 2

40.0 45.0 50.0

Figure 3. Reciprocal Time to Electrical Failure

as a Function of External Heat Flux
0 IEEE 383 Qualified Cable

q

D0 PE/PVC Unqualified Cable

.'-4

10

9 ~ Test 3

o9

4

7

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

External Heat Flux, kW/m 2

Figure 4. Reciprocal Time to Nonpiloted Ignition

as a Function of External Heat Flux
.I I i

0

0

Co

06

C30

E40)

C?

8

0Q

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

External Heat Flux, kW/m 2

Figure 5. Maximum Temperature Reached During Experiment

as a Function of External Heat Flux
OVEN EXPERIMENTS

Apparatus

Two convection type ovens at Sandia National Laboratories

Albuquerque (SNLA) were used for the exposure of electrical

cables to a constant temperature. One oven was capable of

producing temperatures up to 300 0 C (5701F), and one capable of producing temperatures up to 500 0 C (930 0 F). The

oven capable of producing temperatures up to 300 0 C was the

larger of the two ovens and was used for all except four

of the experiments (nos. 12 1 3 , 14 and 15). The large

oven is roughly 1 m(35 fti) in volume with all sides

roughly the same length. The smaller oven has approximately one-eighth the volume with the dimensions about

one-half those of the larger oven. The electrical cables

were exposed in the ovens in four basic configurations

which will be referred to as A, B, C, or D. The four

configurations are:

A. Segments of electrical cable were placed

directly on a mesh type shelf in the oven.

B. Segments of electrical cable were placed in a

segment of a cable tray with one end of the

cable bent at a 900 angle over a rung of the

cable tray and pulled down by a weight to

simulate additional cable length hanging down

(see Figure 6).

C. Segments of electrical cable were placed in a

segment of a cable tray supported by the

rungs of the tray and covered a with large

weight to simulate a distributed load of

electrical cables (see Figure 7).

D. Segments of electrical cable were wrapped

around an aluminum mandrel approximately 46

cm (18 in) in diameter (see Figure 8).

Two types of unaged cable were used in these experiments.

One type was IEEE-383 qualified 3 conductor, no. 12 AWG

tinned copper, 30 mil Exane II insulation, silicon glass

tape, 65 mil Exane II jacket, 600 volt. The other type

was non-IEEE-383 qualified 3 conductor, no. 12 AWG copper,

20/10 PE/PVC insulation, 45 mil PVC jacket, 600 volt.

Oven temperature was measured during experiments with a

chromel/alumel thermocouple positioned near the cables.

Cable temperatures during experiments were measured with

18
chromel/alumel thermocouples placed inside (under the

jacket) of cables. The accuracy of these thermocouples is

approximately ± 3PC (± 5.50F).

Procedure

A total of 30 experiments were conducted in which

electrical cable segments were exposed to a constant

temperature environment for periods of up to 60 minutes.

The experiments can be grouped into one of four categories

based on the basic configuration, previously described, of

the electrical cable segments during experiment.

There were 12 experiments conducted with the electrical

cable segments in configuration A (flat on the oven

shelf). The experiment number, type of cable, number of

cable segments, exposure temperature, and exposure period

are listed in Table 5, for these experiments. The procedure followed for these experiments was as follows. The

thermocouples were installed in the oven and in the cable

segments. The oven was turned on and allowed to stabilize

at the proper temperature for the experiment. For all

experiments in this configuration except 1 through 5, the

electrical cable segments were checked for internal shorts

or opens. The cable segments were placed in the oven and

exposed for the period of time shown in Table 5. In

experiments 2 through 5, one cable segment was removed at

the end of each interval. In the other experiments, all

of the cable segments were removed at the end of the

period shown in Table 5. The cable segments were allowed

to cool to room temperature and examined for physical

damage. For all experiments in this configuration except

1 through 5 the cable segments were checked for internal

shorts or opens.

There were 12 experiments conducted with the electrical

cable segments in configuration B (shown in Figure 6).

The experiment number, type of cable, number of cable

segments, exposure temperature, and exposure period are

listed in Table 6, for these experiments. The procedure

followed for these experiments was as follows: The

thermocouples were installed in the oven and in the cable

segments. The cable segments were positioned in the cable

tray, as shown in Figure 6, and a weight equivalent to

1.5 m (5 ft) of cable was attached to each cable segment.

For experiment number 21, the weights were equivalent to

3 m (10 ft) of cable. For experiment number 9, the rung

of the cable tray over which the cable was bent was

replaced with a piece of tubing 5.7 cm (2.25 in) in

diameter. The oven was turned on and allowed to stabilize

19
at the proper temperature for the experiment. The

electrical cable segments were checked for internal shorts

or opens. The cable tray and cable assembly were placed

in the oven and exposed for the period of time shown in

Table 6. The cable tray and cable assembly were removed

from the oven and allowed to cool until all cables were

below 90 0 C (195 0 F) in temperature. The electrical cable

segments were checked for internal shorts or opens.

There were two experiments conducted with the electrical

cable segments in configuration C (shown in Figure 7),

experiments 8 and 10. The procedure followed for these

experiments was as follows: The thermocouples were

installed in the oven and in the cable segments. Four

segments of nonqualified cable were used in each experiment. The cable segments were positioned in the cable

tray, as shown in Figure 7, and a distributed load

equivalent to a layer of electrical cables 5 cables deep

was placed on the cables. The oven was turned on and

allowed to stabilize at a temperature of 170 0 C (340 0 F).

The electrical cable segments were checked for internal

shorts or opens. The cable tray and cable assembly were

placed in the oven and exposed for a period of 30 minutes

in experiment number 8 and 60 minutes in experiment 10.

The cable and cable assembly were removed from the oven

and allowed to cool until all cables were below 900C

(195 0 F) in temperature. The electrical cable segments

were checked for internal shorts or opens.

There were three experiments conducted with the electrical

cable segments in configuration D (shown in Figure 8),

experiments 28, 29, and 30. The procedure followed for

these experiments was as follows. The thermocouples were

installed in the oven and in the cable segments. Two

segments of IEEE-383 qualified cable approximately 3 m

(10 ft) long were used in each experiment. The cable

segments were wrapped around the mandrel shown in

Figure 8. The oven was turned on and allowed to stabilize

at a temperature of 2500C (480 0 F) for experiment 28 and a

temperature of 2750C (530 0 F) for experiments 29 and 30.

The electrical cable segments were checked for internal

shorts and opens. The mandrel and cable assembly were

placed in the oven and exposed for a period of 60

minutes. The mandrel and cable assembly were removed from

the oven and allowed to cool to room temperature. The

cable segments were removed from the mandrel, straightened

and rewrapped around the mandrel. The cable segments (on

the mandrel) were immersed in tap water at room temperature, 201C (68 0 F), and subjected to a voltage withstand

test at a potential of 2400 vac for a period of 5 minutes.

20
The leakage current which constitutes failure of the

voltage withstand test is not specified in the IEEE Std.

383-1974. The equipment available to SNLA for performing

similar voltage withstand tests utilized a 5 ma breaker to

indicate failure and that was the value for these tests.

The above procedure is based on IEEE Std. 383-1974,4

section 2.4, 'Testing for Operation During Design Basis

Event."

In addition to the experiments in which electrical cable

segments were exposed to constant temperature environments, two experiments were run in which pieces of cable

jacket and insulation materials were exposed to constant

temperature environments to examine the effect of thermal

exposure on the tensile elongation of the cable jacket and

insulation materials. The procedure followed for these

experiments was as follows: The jacket was stripped from

a segment of IEEE-383 qualified cable and test strips

5.6 mm (7/32 in) wide were prepared. The insulation from

the cable conductors was stripped off. Three strips of

cable jacket material and three pieces of cable insulation, one from each color of conductor insulation, were

tested for tensile elongation. A thermocouple was installed in the oven. The oven was turned on and allowed

to stabilize at a temperature of 250 0 C (480 0 F) for one

experiment and 275 0 C (530 0 F) for another. Two strips of

cable jacket material were placed in the oven and exposed

for a period of 60 minutes and three pieces of insulation

material were placed in the oven with their ends folded

over and clamped and exposed for a period of 45 minutes.

The cable material samples were removed from the oven and

allowed to cool to room temperature. The cable material

samples were tested for tensile elongation.

Results

A total of 29 experiments were completed in which

electrical cable segments were exposed to a constant

temperature environment, and two experiments were completed

in which pieces of cable jacket and insulation materials

were exposed to a constant temperature environment. The

results of these experiments will be reported in groups

according to the basic configuration of the electrical

cables during the experiments.

There were 12 experiments conducted with the electrical

cable segments in configuration A, (flat on the oven

shelf). In these experiments the exposure effects were

very uniform for cables of the same type exposed at the

same temperature for the same length of time. For all 12

21
experiments the electrical cable segments took about 15 to

20 minutes to heat up to the exposure temperature. The

cables from experiments 1 through 5 were not checked for

electrical shorts or opens and the other experiments in

this group showed no shorts or opens after exposure. The

effects of exposure on the IEEE-383 qualified cable jacket

material related to temperature and time of exposure were

as follow:

250-C (480-F), 10 to 60 minutes, slight discoloration.

275°C (5301F), 60 minutes, discoloration, blistering,

a decrease in flexibility, and smoking during exposure.

300 0 C (570 0 F), 10 minutes, slight discoloration with

light smoking during exposure.

300 0 C, 20 to 60 minutes, discoloration, blistering, a

decrease in flexibility, and smoking during exposure.

350 0 C (660 0 F), 60 minutes, discoloration, heavy

blistering, rough surface, very brittle, and smoking

during exposure.

400 0 C (750 0 F), 60 minutes, charred appearance, large

cracks, very brittle, and smoking during exposure.

450 0 C (840 0 F), 60 minutes, cable insulation and jacket

material underwent smoldering combustion reaching

temperatures of about 750°C (1380 0 F), and were reduced

to ash.

The effects of exposure on the unqualified cable jacket

material related to temperature and time of exposure were

as follow:

170°C (340 0 F), 10 to 60 minutes, slight shrinkage

(2-3 percent).

200 0 C (390 0 F), 10 minutes, slight shrinkage

(2-3 percent).

200 0 C, 20 to 60 minutes, slight shrinkage

(2-3 percent), deformation of jacket where cable

rested on oven rack, a decrease in flexibility, and

smoking during exposure.

There were 12 experiments conducted with the electrical

cable segments in configuration B (shown in Figure 6). In

these experiments the electrical cable segments were

22
checked for electrical failure in the form of electrical

shorts or opens. For all 12 experiments the electrical

cable segments took about 15 to 20 minutes to heat up to

the exposure temperature. The results of the checks for

electrical failure are listed in Table 7 along with cable

type, exposure temperature, and exposure period.

There were two experiments conducted with the electrical

cable segments in configuration C (shown in Figure 7). In

these experiments the electrical cable segments were

checked for electrical failure in the form of internal

shorts or opens. For these two experiments the electrical

cable segments took about 25 to 30 minutes to heat up to

the exposure temperature. The increased heating time over

other experiments is probably caused by reduced convection

heat transfer due to shielding by the distributed load.

Of the four segments of unqualified cable exposed at 170 0C

(340 0 F) for 30 minutes, none showed electrical shorts or

opens. Of the four segments of unqualified cable exposed

at 170 0 C (340 0 F) for 60 minutes, one showed electrical

shorts and none showed opens. The results of these

experiments are summarized in Table 8.

There were three experiments conducted with the electrical

cable segments in configuration D (shown in Figure 8). In

these experiments the electrical cable segments were

checked for electrical failure with a voltage withstand

test. For these three experiments the electrical cable

segments took about 20 to 25 minutes to heat up to exposure temperature. Of the two segments of IEEE-383

qualified cable exposed at 250 0 C (480 0 F) for 60 minutes,

both passed the voltage withstand test. Of the four

segments of IEEE-383 qualified cable exposed at 275*C

(530 0 F) for 60 minutes, one segment passed and three

segments failed the voltage withstand test. The results

of these experiments are summarized in Table 9.

The experiments designed to examine the effects of thermal

exposure on the tensile elongation of the cable jacket and

insulation materials involved comparison of unexposed

samples and samples exposed to temperatures of 250 0C

(480 0F) and 2750C (530 0 F). The cable jacket material

samples were exposed for 60 minutes and the cable

insulation material samples were exposed for 45 minutes to

account for the thermal lag of the cable interior noticed

in earlier experiments. The results of these experiments

are summarized in Table 10.

23
90cm

10- l0cmI_

CABLE TRAY RUNG

CABLE 30cm

WEIGHT

Figure 6. Oven Experiment Configuration B
• e 0le

I 90cm

CABLE I

I11cm

TRAY -56cm

DISTRIBUTED-LOAD

\--CABLE TRAY CABLE-/ 23cm (typical)-

RUNG

Figure 7. Oven Experiment Configuration C
46cm

DIAMETER

CABLE

TC

46cm

Figure 8. Oven Experiment Configuration D
Table 5

Oven Experiments With Cables in

Configuration A

Oven

Experiment

Number

1

2

3

4

5

12

13

14

15

22

25

27

Cable

Type

Unqualified

Unqualified

Unqualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

IEEE-383

Qualified

Number of

Cables

Exposure

Temperature 0C

4

5

5

200

170

200

300

250

300

350

400

450

275

250

275

60

Exposure

Period

min

10, 20, 30,

40, 60*

10, 20, 30,

40, 60*

10, 20, 30,

40, 60*

10, 20, 30,

40, 60*

60

60

60

60

60

60

60

* One segment of cable removed from exposure at each interval.

These experiments utilized IEEE-383 qualified cable of the

same type described in this report, but from a different

lot. The cables from this lot were used in the 20-ft

separation experiments at UL.

27
Table 6

Oven Experiments With Cables in

Configuration B

Oven

Experiment

Number

6

7

9

11

16

17

18*

19

20

21

23

24

26

Cable

Type

Unqualified

IEEE-383

Qualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Number of

Cables

4

4

Exposure

Temperature

10°C

170 0 C

250 0 C

Exposure

Period

min

60

60

4

4

5

5

1700C

170 0C

1500 C

150 0 C

30

60

60

60

5

5

5

10

10

10

130 0C

1300 C

1300 C

1300 C

150 0C

170 0C

60

60

60

60

60

60

* Experiment number 18 was terminated with no data because the

weight dropped off three of the five cable segments.

These experiments utilized unqualified cable of the same type

described in this report, but supplied from a different

manufacturer. The cables supplied by this manufacturer were

used in the 20-ft separation experiments at UL.

28
Table 7

Summary of Results for Oven Experiments

With Cables in Configuration B

Cable

Type

IEEE-383

Qualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Unqualified

Exposure

Temperature CC

250

130

150

170

170

130

150

170

Exposure

Period

min

60

60

60

30

60

60

60

60

Number

of

Cables

4

15

10

4

8

10

10

10

Number*

Shorted

0

0

2

1

5

0

0

1

Number

Open

0

0

0

0

0

0

0

0

* Conductor-to-conductor internal shorts.

These experiments utilized unqualified cable from the batch

used in the 20-ft separation experiments at UL.

29
Table 8

Summary of Results for Oven Experiments

With Cables in Configuration C

Cable

Type

Exposure

Temperature oC

Exposure

Period

min

Number

of

Cables

Number* Number

Shorted Open

Unqualified 170 30

Unqualified 170 60

* Conductor-to-conductor internal shorts.

4

4

0 0

1 0

30
Table 9

Summary of Results for Oven Experiments

With Cables in Configuration D

Exposure

Cable Temperature

Type 0 C

Exposure

Period

min

Number

of Cables

Tested*

Number

of Cables

Failed

IEEE-383 250 60 2

Qualified

IEEE-383 275 60 4

* Voltage withstand test described in report.

0

3

31
Table 10

Summary of Results for Oven Experiments on

Tensile Elongation of IEEE-383 Qualified

Cable Jacket and Insulation Material

Exposure

Temperature OC

Unexposed

Unexposed

Unexposed

250

250

250

275

275

275

Exposure

Period

min

Elongation

Sample of Jacket

Number

Elongation

of Insulation

60

60

60

60

60

60

1

2

3

1

2

3

1

2

3

168

215

165

205

162

208

100

118

81

92

No test

5

3

98

33

24

No test 23

* Cable insulation samples were exposed for 45 minutes.

32
CONCLUSIONS

The damageability of electrical cables, similar to those

found in some nuclear power plants, to radiant heat flux

and constant temperature thermal exposure have been

examined. Two particular types of unaged electrical

cables, one an IEEE-383 qualified cable similar to cables

currently used, and one an unqualified cable similar to

cables used in earlier power plants, were examined in this

study.

The critical fluxes or threshold levels at which

electrical cable damage occurs in the form of electrical

failure (short circuit) and nonpiloted ignition have been

determined for the two types of cable examined. The

critical flux for electrical failure was determined to be

about 8 kW/m 2 for unqualified cable and 18 kW/m 2 for

IEEE-383 qualified cable. These results along with the

approximate time to electrical failure as a function of

heat flux are shown graphically in Figure 3. The critical

flux for nonpiloted ignition was determined to be about

22 kW/m 2 for unqualified cable and 28 kW/m 2 for

IEEE-383 qualified cable. These results along with the

approximate time to nonpiloted ignition as a function of

heat flux are shown graphically in Figure 4.

The critical flux values for cable damage in the forms of

electrical failure and nonpiloted ignition determined for

the two cable types tested are based on a very limited

amount of test data. This limited amount of data and the

stochastic nature of the processes being investigated

introduces a margin of uncertainty in addition to that of

instrumentation accuracy to the results presented in this

report. The possible sources of error mentioned for these

results should be considered in their acceptability for

any particular application.

Experimental results indicate that exposure of the

particular IEEE-383 qualified cable examined in this study

to temperatures greater than 250 0C (480 0 F) and periods of

60 minutes can cause discoloration, blistering, smoking,

loss of flexibility, and failure to pass a voltage withstand test as described in this report. Experimental

results indicate that exposure of the particular unqualified cable examined in this study to temperatures greater

than 130 0 C (265 0 F) for periods of 60 minutes can cause

electrical failure in the form of shorts between conductors. In addition, the thermal forming temperature of the

unqualified cable jacket material was determined to be

between 1700C (340 0 F) and 200 0 C (3900F).

33
RECOMMENDATIONS

The properties of electrical cables and threshold values

for electrical cable damage identified in this report

should not be interpreted as an acceptance criterion for

electrical cables exposed to a fire environment. The

meaning of the term 'free of fire damage" 1 and, more

specifically, what properties should be used to determine

electrical cable functionability have not currently been

defined by the NRC. The identification of the properties

and their corresponding levels, which determine cable

functionability, should be the first step in the

establishment of an acceptance criterion. With the

properties and levels identified, the types of thermal or

fire environments which could cause cable damage can be

quantified. An acceptance criterion can then be

established in terms of both electrical cable properties

and thermal exposure levels. This information is

necessary for the proper design and interpretation of

tests and experiments such as those run on the adequacy of

20-ft separation, and is also necessary in the development

of analytical tools to predict electrical cable damage in

a potential fire environment. It is therefore recommended

that the NRC take steps to define the properties and their

respective levels, which will be used to determine cable

functionability after exposure to a fire environment.

34
REFERENCES

1. 10CFR Part 50, Nuclear Regulatory Commission "Appendix

R-Fire Protection Program for Nuclear Power Facilities

Operating Prior to January 1, 1979.w

2. Klamerus, L. J., et al., uEvaluation of Twenty-foot

Separation as a Fire Protection System," SAND82-1826,

to be published, January 1983.

3. Adams, Paul H., et al., "Sandia National Laboratories

Radiant Heat Facility,' SAND79-2182, November 1981,

Sandia National Laboratories, Albuquerque, NM.

4. IEEE Std. 383-1974, IEEE Standard for Type Test of

Class IE Electrical Cables, Field Splices, and

Connections for Nuclear Power Generating Stations,

1974.

35
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