NUREG/CR-5546

SAND90-0696

An Investigation of the

Effects of Thermal Aging

on, the Fire Damageability

of Electric Cables

Prepared by

S. P. Nowlen

Sandia National Laboratories

Operated by

Sandia Corporation

Prepared for

U.S. Nuclear Regulatory Commission
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NUREG/CR-5546

SAND90-0696

RP

An Investigation of the

Effects of Thermal Aging

on the Fire Damageability

of Electric Cables

Manuscript Completed: May 1991

Date Published: May 1991

Prepared by

S. P. Nowlen

Sandia National Laboratories

Albuquerque, NM 87185

Prepared for

Division of Engineering

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

NRC FIN A1833
ABSTRACT

This report documents the findings of an experimental investigation of

the effects of thermal aging on the fire damageability of electric

cables. Two popular types of nuclear qualified cables were evaluated.

The two cables tested were (1) a neoprene jacketed, cross-linked

polyethylene (XFE) insulated, three conductor, 12AWG, 600V light power or

control cable produced by the Rockbestos Corporation and marketed under

the trade name Firewall III, and (2) an ethylene-propylene rubber (EPR)

insulated, chlorosulfonated polyethylene (CSPE or Hypalon) jacketed, two

conductor, 16AWG, twisted shield pair, 600V instrumentation and signal

cable produced by BIV Cable Systems, Incorporated, and marketed under the

trade name Bostrad 7E. For each cable type, both unaged (i.e., new off

the reel) and thermally aged samples were exposed to steady-state

elevated temperature environments until conductor-to-conductor electrical

shorting was observed. Plots of the time to electrical failure versus

the exposure temperature were developed and thermal damage thresholds

were determined.

Thermal aging had a different impact on the thermal damageability of each

of the two cable types tested. For the Rockbestos cable, the thermally

aged cables were less vulnerable to thermal damage than were the unaged

samples. This conclusion is supported by (1) an increase in the thermal

damage threshold for the aged samples, and (2) an increase in the time to

thermal damage for the aged cables at exposure temperatures above the

damage threshold. For the BIW cable, a mixed result was obtained. The

threshold of thermal damage was lowered somewhat by the aging process, an

indication of an increased vulnerability to thermal damage due to aging.

However, for the higher temperature exposures, no statistical difference

between the damage times for aged and unaged cable samples was noted.

For both cable types, the changes in the thermal damage threshold

observed were not considered large enough to result in a significant

impact on fire risk estimates because the changes in damage threshold

observed were not significant in comparison to other analysis

uncertainties including uncertainty in the current models used to assess

thermal damage times and uncertainties associated with other fire risk

assessment input values.

- iii-
TABLE OF CONTENTS

Section Pg

EXECUTIVE SUTMMARY ......................................... . .......... 1

1.0 INTRODUCTION AND OVERVIEW . ..................................... 4

2.0 OVERVIEW OF TEST APPARATUS AND PROCEDURES..... 5

2.1 Accelerated Thermal Aging ... .. 5

2.2 Thermal Damage Testing ...................... ............. 6

3.0 EXPERIMENTAL RESULTS FOR ROCKBESTOS FIREWALL III . . 10

3.1 Description of the Cable Product ........................ 10

3.2 Physical Effects of Accelerated Thermal Aging ............. 10

3.3 Measured Cable Response to Thermal Environment ............ 11

3.4 Thermal Damageability Observations.. 11

3.5 Thermal Damage Test Results ...... 12

3.6 Summary of Rockbestos Thermal Damage Results ......... 13

4.0 EXPERIHENTAL RESULTS FOR BIW BOSTRAD 7E.. . . 21

4.1 Description of the Cable Product .... 21

4.2 Physical Effects of Accelerated Thermal Aging . . 21

4.3 Measured Cable Response to Thermal Environment. . 22

4.4 Thermal Damageability Observations .. . 22

4.5 Thermal Damage Test Results . . . 23

4.6 Summary of BIW Thermal Damage.Results . . . 24

5.0 CONCLUSIONS .............................. 31

6.0 REFERENCES ......... ........................................... 33

APPENDIX A LEAKAGE CURRENT DATA . . ............. A-1
LIST OF FIGURES

Fig=r Title Pae

2.1: General View of the SCETCH Facility as Configured

for Use in These Tests .8

2.2: View of the Cable Support and Insertion Mechanism

Prior to Insertion of the Cable Samples. 8

2.3 Schematic Representation of the Cable Energizing

and Integrity Monitoring Circuitry. 9

3.1 Typical Cable Internal Temperature Response for an

Unaged Sample of the Rockbestos Cable. This Plot

was Taken from Test 20, and Also Illustrates the

Consistency of the Exposure Environment .................... 18

3.2: Typical Leakage Current Data for (a) an Unaged and

(b) an Aged Rockbestos Cable Sample ..................... ? ... 19

3.3: Cable Thermal Damage Data for both the Aged and

Unaged Samples of the Rockbestos Firewall III

Neoprene/XPE Cables ........................................ 20

4.1 Typical Cable Internal Temperature Response for an

Unaged Sample of the BIW Cable. This Plot was Taken

from Test 20, and Also Illustrates the Consistency

of the Exposure Environment ................................ 28

4.2: Typical Leakage Current Data for (a) an Unaged and

(b) an Aged BIW Cable Sample ............................... 29

4.3: Cable Thermal Damage Data for both the Aged and

Unaged Samples of the BIW Bostrad 7E EPR/Hypalon

Cables..................................................... 30

-vi-
LIST OF TABLES

Table Title Page

2.1: Equivalent Normal Life Exposure Conditions

Corresponding to the Accelerated Aging Conditions

Imposed Upon the Aged Cable Test Specimens. 5

3.1: Thermal Damageability Data for Unaged Rockbestos

Firewall III Cable Samples ................................. 15

3.2: Thermal Damageability Data for Aged Rockbestos

Firewall III Cable Samples ................................. 16

3.3: Average Failure Time Data for Rockbestos

Firewall III Cable Samples .. .. . 17

4.1: Thermal Damageability Data for Unaged BIW Bostrad

7E Cable Samples ........................................... 25

4.2: Thermal Damageability Data for Aged BIW Bostrad

7E Cable Samples ........................................... 26

4.3: Average Failure Time Data for B1W Bostrad 7E

Cable Samples ........... 27

5.1: Summary of Aging Effects on Cable Thermal Damage

Threshold.................................................. 31

-vii-
EXECUTIVE SUHHAkY

The objective of the Fire Vulnerability of Aged Electrical Equipment

Program is to identify and investigate fire safety issues for which plant

aging might lead to an increased level of risk. This report describes

the results of a series of tests performed to assess one fire aging

issue, that is, the effects of thermal aging on the vulnerability of

cables to fire induced thermal damage.

In the consideration of fire safety, cables represent the single most

important class of electrical equipment in a nuclear power plant. This

results from a number of factors. First, virtually every plant system

includes power, control, and/or instrumentation cables. Second, cable

*pinch' points (that is, locations where redundant train separation is

reduced by the merging of cable routings) often represent dominant

contributors to plant fire risk as determined by probabilistic risk

assessment (PRA) analyses. Third, cables represent the dominant

combustible fuel loading for most plant areas.

In the tests described here, the thermal damsgeability of two commonly

used types of IEEE-383 nuclear qualified, low-flame-spread electric

cables was examined. The two cable types tested were:

(1) A Neoprene jacketed, cross-linked polyethylene (XPE)

insulated, three conductor, 12AWG, 600V light power or control

cable produced by the Rockbestos Corporation and marketed

under the trade name Firewall III, and

(2) An ethylene-propylene rubber (EPR) insulated, chlorosulfonated

polyethylene (CSPE or Hypalon) jacketed, two conductor, 16AWG,

plus shield and drain, 600V instrumentation or signal cable

produced by BIV Cable Systems Incorporated and marketed under

the trade name Bostrad 7E.

For each of the two cable types tested, both unaged (i.e. new from the

cable reel) and thermally aged samples were tested. (No radiation aging

was employed in these tests.)

The exposure conditions simulated during testing were considered typical

of that expected during an enclosure fire when the subject cables are not

involved in the fire itself. The test exposure consisted of immersion of

the cable samples into a spatially uniform and optically thick

environment such as that which would be expected in the non-flaming

region of the fire plume, ceiling jet, or hot upper layer. The most

significant difference between the test exposures and anticipated actual

exposures was that the tests involved exposure at an elevated steadystate temperature while in actual exposures equipment would experience a

transient time/temperature exposure.

The test chamber used in these tests is the severe Combined Anvironment

lest chamber (SCETCH). This chamber was originally developed for use in

equipment fire environment vulnerability assessments under the USNRC-

-1-
sponsored Fire Protection Research Program. SCETCH has also been used in

the performance of realistic hydrogen burn environment simulations.

In these cable exposure tests, both the walls of and air within SCETCH

were maintained at a uniform steady-state exposure temperature.

Circulation of air through the chamber provided for a high level of air

movement and mixing within the chamber. Two energized cable samples were

exposed in each of the tests performed. The chamber was preheated to the

desired exposure temperature, and the cable samples then quickly inserted

through a small door in the cover of the chamber. This approach provided

a near step change in environment temperature for the cable samples.

In each test, two cable samples were energized using a three-phase, 208

volt power source. In the case of the Rockbestos cable, each of the

three conductors was connected to one phase of the power source. In the

case of the BIV cable, each of the two conductors and the drain conductor

were connected to one phase of the power source. Leakage currents

between power phases were monitored continuously. The time to ultimate

cable failure, as determined by the failure of a two ampere fuse in any

one of the three phase circuits, was also recorded. Two measures of

thermal damageability can be made based on these tests.

One measure of fire damageability is the thermal damage threshold. In

the context of these tests, the thermal damage threshold is defined as a

derived temperature range. The upper limit of this temperature range is

defined by the lowest experimental exposure temperature at which

electrical failure was observed following exposures of up to 80 minutes.

The lower limit of the range was defined by the highest experimental

exposure temperature for which no electrical failures were noted

following exposures of no less than 80 minutes. These values were

determined directly for each cable type in both the aged and unaged

condition. (In three of the four cases the threshold temperature range

was narrowed to within 56C. In the case of the aged Rockbestos cable, a

shortage of aged samples allowed for narrowing of the threshold range to

15-C only.)

For the Rockbestos cable, the failure threshold of the unaged cable was

determined to be 325-330'C, whereas the thermal damage threshold for the

aged samples was 350-365-C. For the BIW cable, the unaged cable thermal

damage threshold is estimated at 365-370-C, while that of the aged

samples was estimated at 345-350-C. Thus, the aging process resulted in

the opposite effect on the thermal damage threshold for the two cable

products. For the Rockbestos cable, the damage threshold increased by

approximately 25-35-C due to aging, while for the BIW cable the threshold

decrease by approximately 20"C due to aging.

A second measure of thermal damageability is the relative time to failure

for exposure temperatures above the damage threshold. In the case of the

Rockbestos cables, the aged samples consistently displayed longer times

to failure at a given temperature than did the unaged samples, indicating

less vulnerability to thermal damage for the aged samples. In the case

of the BIW cable, the time to failure for the aged and unaged samples was

not significantly different for exposure temperatures at which failure

-2-
was observed in both'aged and unaged samples. Thus, in the case of the

BIW cable, aging had no effect on thermal vulnerability when the exposure

temperature was above- the threshold of unaged cable thermal damage. (As

was described above, aging did reduce the BIW failure threshold.)

It was also noted that in virtually every case, the failure of the cables

through conductor to conductor shorting resulted in the initiation of

intense, sustained, open flaming in the cable samples. As the cables

shorted, sparks ignited the gases being evolved from the cables. Thus,

the failure temperatures noted above are clearly above the piloted

ignition threshold of the cable samples. In no case was spontaneous

ignition of the cables observed prior to electrical failure. These

results also indicate that in the modeling of cable fire growth it would

be appropriate to include the failure of energized cables as a mechanism

for fire spread.

These tests have explored the effects of thermal aging on two of the most

common nuclear qualified'cables in use in the U. S. nuclear industry

today. For these two cable types, thermal aging did affect the thermal

damageability of the cables. In one case, aging increased the

susceptibility to thermal damage, while in the other case, the

susceptibility was reduced.

The thermal damage threshold changes observed in these tests are not

considered of a sufficient magnitude to significantly alter risk

estimates for scenarios involving cable thermal damage. The fact that

the thermal damage thresholds were altered by the aging process implies

the introduction of uncertainty in this fire risk assessment input

factor. However, the magnitude of the changes observed will not

significantly alter the risk perspective because fire risk assessments

typically include large uncertainties associated with fire modeling and

the estimation of equipment damage times, the inherent uncertainty in

fire behavior, and the uncertainty associated with other risk assessment

input values, particularly those associated with the use of engineering

judgment. These other sources of uncertainty will continue to dominate

overall fire risk estimate uncertainty.

It should also be noted that these tests have not explored the impact of

other fire environmental effects, such as suppressant application and

high humidity, on cable survival. The failure thresholds given above

indicate the threshold of gross electrical failure. In most cases,

significant levels of current leakage were noted prior to gross failure.

Specific applications must be examined to determine whether such leakage

could constitute the failure of a circuit to perform its design function.

Also, because a mixed result was obtained for the two cable types tested,

it can be assumed that for other cable types, the impact of thermal aging

on thermal damageability would display similar mixed results. Thus, no

direct conclusion regarding the impact of thermal aging on the fire

vulnerability of any other cable type can be drawn based on the results

of these tests.

-3-
1.0 INTRODUCTION

The tests described here were performed as a part of the USNRC-sponsored

Fire Vulnerability of Aged Electrical Components Program. It is the

objective of this program to identify and investigate fire safety issues

that might lead to an increased plant risk as a result of plant aging.

The tests described in this report investigated one of the identified

fire aging issues, namely, the potential that cable thermal aging might

result in an increased vulnerability to fire-induced thermal damage.

The issue of cable aging and fire vulnerability was chosen as the focus

of initial investigation under this program for a number of reasons. 1

First, cables represent the single most prevalent class of electrical

equipment in a nuclear power plant. Virtually every plant system

includes power, control, and instrumentation cables. Second, in the

analysis of fire risk, postulated cable damage scenarios often represent

dominant contributors to fire-induced core damage frequency estimates,

and often to overall plant core damage frequencies as well. In

particular, cable *pinch" points, that is points where the cabling for

multiple safety and support systems converge, are often identified as

risk important. Finally, cables represent the dominant combustible fuel

loading for most plant areas.

In the evaluation of fire risk, estimation of the thermal damageability

of electrical cables can play a critical role. Should the aging of

cables be determined to significantly change the vulnerability of cables

to fire-induced damage, then a significant change in fire risk estimates

for scenarios involving cable failure would result. It is this question

which the tests described here address. In these tests, the effects of

aging on the vulnerability of cables to thermal heating was investigated.

Two types of qualified nuclear grade cables were tested in these tests.

These two cable types represent two of the most commonly used nuclear

grade cables currently installed in U.S. commercial reactors 11]. The

two cable types tested were:

(1) A Neoprene jacketed, cross-linked polyethylene (XPE)

insulated, three conductor, 12AWG, 600V light power or control

cable produced by the Rockbestos Corporation and marketed

under the trade name Firewall III, and

(2) An ethylene-propylene rubber (EPR) insulated, chlorosulfonated

polyethylene (CSPE or Hypalon) jacketed, two conductor, 16AUG,

plus shield and drain, 600V instrumentation or signal cable

produced by BIW Cable Systems Incorporated and marketed under

the trade name Bostrad 7E.

As will be shown below, mixed results were obtained for the two cable

types tested. In one case aging reduced the vulnerability of the cables

to thermal damage while in the second case aging resulted in an increased

thermal damageability. However, in neither case were the differences

considered large enough to result in a significant change in fire risk

estimates. It should also be noted that these tests have not addressed

other damaging aspects of the fire environment such as suppressant

application and high humidity.

1. The identification and prioritization of issues is discussed further

in a draft NUREG/CR report currently under review (NUREG/CR-5464).

-4-
2.0 OVERVIEW OF TEST APPARATUS AND PROCEDURES

2.1 Accelerated Thermal Aging

The accelerated thermal aging protocol was based on use of the Arrhenius

theory of accelerated aging. For each of the two cable batches, a

thermal oven was used to provide a constant elevated temperature

environment for a period of approximately one month. The two cable types

were aged separately. No deviations from the anticipated aging protocol

were experienced for either of the two cable types utilized. For the

Rockbestos cables, an aging temperature of 150'C was utilized. For the

BIV cables, an aging temperature of 125'C was utilized. In the case of

thermal damageability, it was decided that the cable insulation, rather

than the jacket, would play the critical role. Therefore, the aging

conditions were aimed primarily at aging of the insulation to a

conservative end of life condition, and aging of the jackets was not a

primary consideration. Using the Arrhenius theory, these artificial

aging conditions correspond to normal life exposure conditions as

described in Table 2.1.

Table 2.1: Equivalent Normal Life Exposure Conditions

Corresponding-to the Accelerated Aging Conditions

Imposed Upon the Aged Cable Test Specimens

Accel. Aging'. Equivalent

Cable/Material: Conditions: 40 Year Life:

Rockbestos FIREWALL III:

Neoprene Jackets 28 days @ 150-C 59@C

XPE Insulator2 28 days 2 150-C 82"C

BIll BOSTRAD 7E:

Hypalon Jacket. 28 days @ 125-C 52"C

EPR Insulator. 28 days @ 125-C 60-C

1. Assumes an activation energy of 0.83 Electron Volts

2. Assumes an activation energy of 1.2 Electron Volts

3. Assumes an activation energy of 0.95 Electron Volts

4. Assumes an activation energy of 1.1 Electron Volts

Note that the Rockbestos cable product was aged to somewhat more severe

conditions than was the BIW cable product. The reason for this

difference is that the Rockbestos cable is utilized as a light power or

control cable whereas the BIW cable is primarily an instrumentation or

signal cable. Therefor, because the light power cable would be subject

to higher levels of self-heating, it was considered appropriate to

utilize a more severe aging end condition for the Rockbestos cable.

-5-
For the purpose of aging, cable sections were cut from the cable reel to

the desired length of 36 inches. The protective jacketing at each end of

these cable segments was trimmed back in anticipation of electrical

termination of the cables prior to the thermal damageability testing.

The cable specimens were then placed horizontally on metal mesh shelves

in the aging oven following pre-heating of the oven itself. The

environment at various points inside the aging oven was monitored

continuously.

2.2 Thermal Exposure Testing

For the performance of thermal exposure tests, the Severe combined

£nvironment _est chamber (SCETCH) was used. This chamber was originally

developed as a part of the USNRC-sponsored Fire Protection Research

Program (reference USNRC FIN A1010) for use in the evaluation of the

vulnerability of equipment to fire induced damage. SCETCH has also been

used for the performance of single and multiple pulse hydrogen burn

survival tests for electrical equipment [2].

SCETCH is comprised of a pressure vessel, designed to ASTM standards,

surrounded by quartz heating lamps. The power to these quartz lamps is

automatically controlled through a data logger and minicomputer

monitoring system. The chamber itself is a cylinder measuring

approximately 18 inches in diameter by 24 inches long. A small window

was installed in the front face of the test chamber so that direct

observation of the cables during exposure was possible. In a transient

mode the chamber temperature can be ramped at a rate of up to 600OF/min.

For the purposes of hydrogen burn simulations, an additional heat flux

simulation module capable of transients up to 2000'F/sec is also

available. This additional heat flux module was not utilized in the

tests described here.

For the purposes of these tests, lamp power was controlled to provide a

constant inner chamber wall temperature consistent with the desired

thermal exposure temperature. In addition, air was circulated through

the chamber in a flow-through system. The incoming air was heated by

circulation heaters. The power to these circulation heaters was also

automatically controlled to maintain a specified general chamber air

temperature. Because both the wall temperature and air temperature were

maintained at the same value, the environment simulated was that of a

spatially uniform and optically thick hot gas layer exposure. Because of

the rate and configuration of the air circulation within the chamber, a

highly convective environment resulted (i.e., the air inside the chamber

was very well mixed on a continuous basis). Figure 2.1 provides a

general view of the SCETCH facility as configured for these tests.

In the actual performance of testing, the cable samples were laid out,

two per test, on a cable support system outside the chamber. In each

test, both of the cable samples would be essentially the same (i.e., both

the same cable type, and either both aged or both unaged). The chamber

system was preheated to the desired temperature (both walls and air at

the same temperature) and the controller set to maintain that

temperature. The cable support mechanism was constructed such that very

fast insertion (on the order of 1-2 seconds) of the cable samples into

-6-
the exposure environment was possible. This quick insertion after oven

preheating resulted in a near step change in the cable thermal

environment from ambient to immersion in a uniform radiative and

convective environment at the desired temperature.

Once inserted, one end of each cable sample projected out of the chamber

for connection to the power source. The other end of the cable was

located inside the chamber. Special precautions were taken to insure

that the end of the cable inside the chamber was protected from direct

exposure in order to insure that cable end effects observed in other

tests 131 would not affect the test results. Figure 2.2 provides a view

of the cable insertion mechanism and general configuration of the cables

prior to insertion.

Each of the two cable samples was energized during testing. A threephase 208VAC power source was used. No base current load was imposed on

the cables. When testing the Rockbestos cable, each of the three

conductors was connected to one phase of the power source. When testing

the BIW cable, each of the two conductors, and the shield/drain conductor

were connected to one phase of the power source. For each conductor of

each cable, current limiting resistors were provided to limit fault

currents. Figure 2.3 provides a schematic representation of the cable

energizing circuit. Ultimate cable failure was determined by the failure

of 2 ampere fuses in a series/parallel circuit with the current limiting

resistors. Leakage currents were monitored continuously by monitoring

the voltage drop across each of the current limiting resistors.

The detection level of the leakage current measurement system is

estimated at approximately 3 mA. This estimate is based o.the

observation of poor AC voltage measurement accuracy at equivalent leakage

current levels of less than 3 mA. In the design of the AC voltage

measurement system, a compromise was required between the speed of the

measurements and the accuracy of the measurements at very low values.

Thus, a certain minimum detection level corresponding to this low voltage

inaccuracy was accepted as the price of higher measurement speed.

In each test, the time to initial electrical failure, as indicated by the

failure of any one of the three 2 ampere fuses for each cable sample, was

noted. Also noted was the time to ignition of the cable samples based on

visual observations. In order to determine the thermal failure

threshold, all tests were continued until either electrical failure was

observed or no less than 80 minutes of elapsed exposure time. (In some

cases, exposure times exceeded 90 minutes with no observed failures.)

Thus, the reported failure thresholds are generally for exposures of up

to 80 minutes.

-7-
OD

Figure 2.1: General View of the SCETCH

Facility as Configured for Use in

These Tests.

Figure 2.2: View of the Cable Support

and Insertion Mechanism Prior to

Insertion of the Cable Samples.

... I
cal Leakage Current

*toring Measurement Point

Figure 2.3: Schematic Representation of the Cable

Energizing and Integrity Monitoring Circuitry.

-9-
3.0 EXPERIMENTAL RESULTS FOR ROCKBESTOS FIREWALL III

3.1 Description of the Cable Product

The Rockbestos cable tested was a 3-conductor, 12 AVG, light power or

control cable. (Other sizes and configurations of this cable are also

available for higher power or instrumentation applications.) The

insulation was cross-linked polyethylene (XPE), and the jacket was

neoprene. (Rockbestos also markets this product with a chlorosulfonated

polyethylene (CSPE) jacket.) This cable is an IEEE-383 qualified nuclear

grade cable, and is marketed under the trade name Firewall III. This

cable was selected for use in these tests because it represents one of

the most commonly utilized cables in the commercial U.S. nuclear power

industry [lJ.

The Rockbestos cable product is a multi-conductor cable which is made up

of a number of individual constituents. The constituents of the

composite cable can be itemized as follows:

Constituent: Material: Weight per Length

of Cable (g/r)

Conductors Copper 87.9

Insulator XPE 36.1

Jacketing Neoprene 71.3

Interstitial Material (Assumed Nylon, 8.4

Paper, and Cellophane)

Total Cable Weight (grams/meter): 203.7

The final item, interstitial material, is made up of three separate

materials. The first, assumed to be a nylon-like material, is a thin,

rolled, expandable (i.e., extensively slitted) material which fills the

gaps between the individual insulated conductors below the jacketing.

The second is a paper material which is assumed to be a wrapping used to

bind the other materials together while the Jacketing is applied. The

third is a cellophane-like material in a small, thin, clear strip which

identifies the manufacturer.

3.2 Physical Effects of Accelerated Thermal Aging

Artificial aging of the Rockbestos Firewall III cables was performed at a

temperature of 150-C. The cable samples were aged at this temperature

for a total of 28 days. Assuming an activation energy of 1.2 eV, and

assuming Arrhenius behavior, the artificial aging would correspond to an

equivalent life of 40 years at 82'C.

Following the removal of the cable samples from the aging chamber it was

noted that the neoprene jacket had developed extensive cracks and had

become quite brittle. In several cases handling of the aged cable

samples resulted in small sections of the jacket falling away from the

cables. Visual inspection of the cable insulation revealed no such

-10-
cracking. Continuity and insulation resistance testing of the aged

samples prior to thermal exposure testing revealed no faults.

The cracking of the jacket observed following aging raised a concern that

the increased exposure of the inner insulation might result in more

efficient heat transfer directly to the insulation, and hence, might

reduce failure times. As will be discussed below, this turned out not to

be the case.

3.3 Neasured Cable Response to Thermal Environment

In certain tests on unaged cable samples, short sections of non-energized

"dummy" cable were included in the exposure. These dummy samples were

instrumented with two thermocouples; one located just below the jacket,

and one in the center of the cable between the three individual insulated

conductors. (Thermocouples could not be inserted into the aged samples

because the aging process sealed the small openings that were used to

feed thermocouples'into the cable.) None of the energized cable samples

were instrumented in this way.

Figure 3.1 illustrates the typical response of the dummy cable samples to

thermal exposure. This figure also provides an illustration of the

consistency of the exposure environment and the impact of cable insertion

on that exposure. Note that as the cables were inserted, at time-0

seconds on this figure, a drop in the exposure environment temperature is

experienced. This drop is caused by the insertion of cold thermal mass

and a limited amount of ambient air into the test chamber. The automatic

temperature control system would quickly compensate-for this effect and

typically within approximately 2 minutes the exposure environment had

fully recovered.

In many cases the thermocouple readings from these dummy samples

indicated that combustion of some parts of the cable was taking'place

prior to failure. This is indicated by the fact that the measured

internal cable temperatures often exceeded the exposure chamber

temperature. In Figure 3.1, this behavior is noted at approximately 650

seconds. An exothermic reaction, such as smoldering combustion, is the

only reasonable explanation for this behavior. It is assumed that this

reaction involved the interstitial materials used in the production of

the cables. It is also likely that smoldering of the jacketing material

occurred since cable samples removed after as much as 90 minutes of

exposure at temperatures just below the electrical damage threshold were

found to have severely charred jacketing. In these cases, the insulator

was intact, rather soft, and showed no signs of charring.

3.4 Thermal Damageability Observations

For the Rockbestos cable samples, the leakage current behavior observed

in each test sample followed a definite pattern. This pattern was

essentially the same for both the unaged and the aged samples. Figure

3.2 is typical of the leakage current data. Upon insertion into the test

chamber (time-0 in this plot) the cables experience an initial short-term

rise in conductor-to-conductor current leakage which falls off to near

-11-
zero leakage after approximately 120-200 seconds. This behavior is

attributed to thermal shock effects. The magnitude of the leakage

current during this period typically peaked at 5-10 mA. Beginning after

approximately 300-600 seconds of exposure, the cables would experience a

second increase in leakage current. Within an additional 300 seconds,

the leakage current would typically reach a level of approximately 15 mA.

This leakage rate would then remain essentially constant until the time

of ultimate failure when a precipitous increase in leakage would be

experienced.

Users of the failure/time data presented here should be careful to note

this behavior. The criteria used as the basis for the failure times

(presented in Tables 3.1-3.3) was a leakage current in excess of 2

amperes, as demonstrated by failure of a 2 ampere fuse. The test data

indicate that short sections of the cable can experience a long term

leakage rate on the order of 15 mA under elevated temperature conditions

before experiencing a precipitous short circuit. In some circuits, this

level of leakage may be unacceptable, and hence, may represent circuit

failure. One must also consider that exposure of longer sections of

cable to these elevated temperatures would increase the overall current

leakage. Each individual case must be examined for leakage current

sensitivity and the data applied accordingly.

3.5 Thermal Damage Test Results

One measure of thermal damageability is the threshold at which gross

electrical failure can be expected. Tables 3.1 and 3.2 provide the time

to electrical failure (based on failure of the two ampere. current

limiting fuse) as a function of exposure temperature for each individual

test of the unaged and aged Rockbestos cable samples, respectively.

Table 3.3 provides the average failure time for each of the exposure

temperatures for both the aged and unaged samples. Figure 3.3 provides a

graphic presentation of the data presented in these tables. Each of the

individual data points is shown, as well as simple linear splines

connecting the applicable average failure times as given in Table 3.3.

The actual leakage current data for each of the individual test samples

is presented in Appendix A.

For the unaged Rockbestos cable samples, the threshold of thermal damage

is estimated at approximately 325-330-C. For the aged samples the

threshold for thermal damage is estimated at 350-365'C. (Note that a

shortage of available cable samples prevented us from further narrowing

the failure threshold range for the aged samples.) In each case, these

failure ranges may be interpreted as follows:

- Cable failures were observed during exposure tests at the

temperature corresponding to the upper limit of the stated

range (i.e., 330"C and 365-C for the unaged and aged cables,

respectively).

- At a temperature corresponding to the lower limit of each

range, no failures were observed following cable exposures of

no less that 80 minutes in duration (i.e., 325-C and 350'C for

the aged and unaged cables, respectively).

-12-
These results indicate that for this cable type, extensive thermal aging

did not adversely impact the thermal damage threshold, and in fact,

raised the thermal damage limit.

A second measure of damageability is the relative time to gross

electrical failure at exposure temperatures above the threshold value.

As seen in Figure 3.3, at each of the temperatures at or above 365-C, the

lowest experimental temperature at which damage was observed in the aged

samples, the average time to failure, and in fact, the times to failure

for each of the individual samples, are greater for the aged cables than

for the unaged cables. This result again indicates that the aged cables

are less vulnerable to fire-induced thermal damage.

In observing the data one should also note the behavior of the time to

damage data, particularly at or near the estimated threshold temperature.

For temperatures on the order of lOC or more above the threshold, the

failure times are very consistent and well grouped. However, at or near

the damage threshold, the variation in failure times becomes quite large.

This can be attributed to two factors. First, slight variations in the

cable samples themselves are to be expected. Given the observed

behavior, even a small change in the actual damage threshold for a given

sample would result in a large change in the damage time when the

exposure is very near that threshold. Second, very slight variations in

the exposure environment could also result in significant changes in the

time to damage.

3.6 Summary of Rockbestos Thermal Damage Results

For each of the two measures of thermal damageability discussed, failure

threshold and failure time at temperature, the aged cables performed

bettor (i.e., displayed a lower damage vulnerability) than did the unaged

cables. However, the differences noted are not considered large enough

to result in a significant change in the estimation of fire risk for

scenarios involving fire-induced cable failure. The failure threshold

was raised by only 25-35-C, and "life expectancy' was generally extended

by only a few minutes. What is important, is that the aging process

clearly did not result in an increased fire vulnerability, the potential

concern being investigated here.

It was interesting to note that a possible concern raised upon

observation of the aged cable samples turned out to be unfounded.

Following thermal aging, the cable jacketing was observed to be

extensively cracked, and in some cases, small sections of the jacket had

fallen away. This was thought to represent a potential for increased

exposure of the inner insulation to heating, and thus, a potential

mechanism by which aged cables might be more vulnerable to thermal damage

than the unaged cables. However, in thermal exposure testing it was

found that with the unaged cable samples, the jacket would split open

almost immediately upon insertion, directly exposing the inner insulated

conductors. Thus, the cracking of the jacket through thermal aging

appeared to have no effect on the damageability of the cables.

-13-
It was also noted that during thermal exposure testing, in every case in

which failure of the energized cables was observed, the sparks which

resulted caused the ignition of intense, sustained, open flaming in the

cable sample. This observation indicates three things:

(1) the temperature threshold for piloted ignition of the cable

samples is lower than the damage thresholds identified here,

(2) in the modeling of cable fire growth, the failure of energized

cables should be considered as a mechanism for fire spread as

well, and

(3) in no case was spontaneous ignition of open flaming in the

cables prior to electrical failure observed indicating that

the spontaneous ignition (or non-piloted ignition, or autoignition) temperature is above the lower limit of thermal

damage for this cable.

The data presented provides an indication of the thermal damageability of

this cable product in a fire environment. Caution should be exercised in

the extrapolation of this data to other cable types and other cable

products utilizing similar materials.

-14-
Table 3.1: Thermal Damageability Data for Unaged Rockbestos

Firewall III Cable Samples.

Test No. Cable No. Exposure Temp. Failure Time*

(-C) (min:sec)

9 1 325 NF

9 2 325 NF

21 1 330 34:01

21 2 330 33:31

45 1 330 73:56

45 2 330 78:32

10 1 335 17:00

10 2 335 19:00

20 1 335 16:30

20 2 335 29:35

4 1 350 11:40

4 2 350 12:28

19 1 350 12:15

19 2 350 12:15

6 1 375 7:14

6 2 375 6:50

18 1 375 7:48

18 2 375 7:48

12 1 400 5:50

12 2 400 5:55

17 1 400 5:58

17 2 400 6:18

* NF indicates no failure observed following an exposure of

no less than 80 minutes.

-15-
Table 3.2: Thermal Damageability Data for Aged" Rockbestos

Firewall III Cable Samples.

Test No. Cable No. Exposure Temp. Failure Time

(C) (min:sec)

7

7

1

2

8

8

26

26

43

43

1

2

1

2

1

2

25

25

42

42

1

2

1

2

350

350

365

365

365

365

365

365

370

370

370

370

375

375

375

375

400

400

400

400

400

400

425

425

NF

NF

87:20

67:30

39:30

58:55

19:29

18:57

50:00

57:30

16:48

18:03

22:35

19:15

17:07

17:40

10:35

11:05

10:10

10:30

9:30

9:24

7:15

7:25

5

5

24

24

1

1

1

2

11

11

13

13

23

23

1

2

1

2

1

2

22

22

1

2

* NF indicates no failure observed following an exposure of

no less than 80 minutes.

** Cables aged to equivalent of 40 years at 82-C for the

insulator.

-16-
j

Table 3.3: Average Failure Time Data for

Rockbestos Firewall III Cable Samples.

Exposure Temp. Average Failure

IC) Time (min)

Unaged Samples:

325 NF

330 55.00

335 20.25

350 12.16

375 7.42

400 6.00

Aged Samples:

350 XF

365 48.61

370 35.59

375 19.15

400 10.21

425 7.33

* NE indicates no failure observed following an exposure of

no less than 80 minutes.

-17-
Wall Temperature Sub-Jacket Temp ...

Rir Temperature _ . ,-- - -- -- - -- - Cable Core Temp

400

300

Us

L)

In

E

Va

200

100 _

0I I

5 10 15 20 25 30

Time (min)

Figure 3.1: Typical Cable Internal

Rockbestos Cable. This Plot was

Consistency of the Exposure

Occurred at

Temperature Response for an Unaged Sample of the

Taken from Test 20, and Also Illustrates the

Environment. Note that Cable Insertion

(Time - 0) in this Plot.
Cable Conductor I1

Cable Conductor 42 Cable Conductor 13 --------------

C

a-

-

Si

-J

40

Time (min)

(a) Unaged Rockbestos Cable

Cable Conductor 41

Cable Conductor #2 Cable Conductor 13 --------------

M.)

C

A.

02

'U

-VJ

Time (min)

(b) Aged Rockbestos Cable

Figure 3.2: Typical Leakage Current Data

and (b) an Aged Rockbestos Cable Sample.

Insertion Occurred at (Time - 0) in

for (a) an Unaged

Note that Cable

these Plots.

-19-
450

L)

CD

a.

ro

a.,

a.,

a)

CD

0-

CDt

To

x

w

425

400

375

350

325

300

OO No Failure

(350 C)

o No Failure

(325 C)

90

Fai lure Time (min)

Figure 3.3: Cable Thermal Damage Data for

Both the Aged and Unaged Samples of the

Rockbestos Firewall III Neoprene/XPE Cables.

-20-
4.0 EXPERIMENTAL RESULTS FOR BIV BOSTRAD 7E

4.1 Description of the Cable Product

The second cable tested-in this effort was a Boston Insulated Wire (BIW),

2-conductor, 16 AVG cable with shield and drain. This cable is marketed

by BW under the trade name BOSTRAD 7E. The cable has a chlorosulfonated

polyethylene (CSPE or Hypalon) jacket, and an ethylene-propylene rubber

(EPR) insulator. The individual constituents of the cable can be

itemized as follows:

Constituent: Material: Weight per length

of Cable (g/m)

Conductors Copper 31.8

Insulator EPR 30.8

Jacket Hypalon 76.3

Interstitial Material (Foil, and 4.3

Cellophane Plastic)

Total Cable Weight (grams/meter): 143.2

The materials identified above as interstitial materials included two

different materials. First, a metal foil material was wrapped around the

individual conductors to act as the cable shield. The second material

was a thin clear plastic wrapping material, suspected to be cellophane,

used to identify the manufacturer and, presumably, to bind the

constituents while the jacket was applied. It should also be noted that

the weight of the conductors given above included the weight of the drain

wire and the two insulated conductors.

4.2 Physical Effects of Accelerated Thermal Aging

Artificial aging of the BIW Bostrad 7E cables was performed at a

temperature of 1250C. The cable samples were aged at this temperature

for a total of 28 days. For the EPR insulating material, assuming an

activation energy of 1.1 eV, and assuming Arrhenius behavior, the

accelerated aging protocol would correspond to an equivalent life of 40

years at 60'C.

Following the removal of the cable samples from the aging chamber it was

noted that the Hypalon jacket had changed in color from the original

bright orange, to a dull tan color. However, the Hypalon jacket retained

some flexibility and no cracking was observed. Visual inspection of the

cable insulation also revealed no cracking. Continuity and insulation

resistance testing of the aged samples prior to thermal exposure testing

revealed no faults.

-21-
4.3 Measured Cable Resgonse to Thermal Environment

In certain tests of the unaged cable samples, non-energized "dummy"

samples were included in the exposure. These dummys were instrumented

with a single thermocouple located just below the jacket and below the

foil shield wrapping material. Figure 4.1 illustrates the typical

response of the dummy cable samples to thermal exposure.

As noted above, it was observed that during exposure testing of the

unaged BIW cable samples, the jacketing material would swell

significantly. Thus the exact placement of the thermocouples during

exposure is uncertain. Because the thermocouples were located below the

foil shield wrap and because this foil material would typically be found

in essentially its original condition and location following testing, it

is assumed that the thermocouple remained in close contact with the

individual conductors during testing.

The thermocouple readings from these dummy samples did not indicate that

any combustion was taking place prior to electrical failure and the

resulting ignition. This may be due to the swelling which displaced the

jacket material from contact with the thermocouple. It was found that

the jacketing of cables removed from the oven with no observed failure or

flaming were heavily charred. Thus it is suspected that smoldering

combustion of the jacket did, in fact, occur, even though not indicated

directly by the temperature readings.

Note that this figure also provides an indication of the consistency of

the exposure environment. After insertion of the cable samples, a drop

in chamber temperature would be experienced (on the order of 50C).

Within approximately 2 minutes, this drop in temperature would have been

compensated for, and the desired exposure temperature reestablished.

4.4 Thermal Damageabilitv Observation

Figure 4.2 illustrates the typical leakage current response data for both

an aged and unaged BIW cable sample. For full presentation of the cable

leakage current data for each sample in each test, refer to Appendix A.

Note that the aged and unaged cables performed quite differently.

Leakage currents for the unaged cable samples would typically remain

below the threshold of instrumentation detection (estimated at 3 mA as

discussed in Chapter 2 above) until shortly before ultimate failure when

a precipitous rise in current leakage was experienced. For the aged

cable samples, the leakage currents would rise to a level of

approximately 10 mA within 2-3 minutes of insertion. Leakage currents

would remain relatively constant until within 2-4 minutes of ultimate

failure when the leakage current would again begin rising. Leakage

currents were observed to reach a level of 15-25 mA before a precipitous

jump and ultimate failure was observed. In some circuits, this level of

leakage current could represent the failure of the circuit to perform its

function [41. (The reported damage times described below are all based

on the failure of a 2 ampere fuse in any one current leg.) Each

application should be examined for sensitivity to leakage currents.

-22-
One other significant visual difference in the behavior of the aged and

unaged cable samples was noted during exposure testing. For the unaged

samples, the jacketing material was observed to swell significantly upon

heating. Thisvwelling gave the cable the appearance of a string of

blackened popcorn. For the aged cable samples, no such swelling was

observed. Upon heating, the aged samples would discolor further and

split open at various locations along the cable. This difference in

jacket behavior may be a result of the higher flexibility of the unaged

material. As the cables are heated, off-gassing takes place in the

materials below the jacket. In the case of the unaged cables, the jacket

is assumed to stretch and allow for expansion of these gases. In the

case of the aged cables, it is assumed that two factors reduce the

likelihood that such swelling would be observed. First, during the aging

process, certain of these-early release products would already have been

removed. Second, for the aged cable the jacket retains insufficient

flexibility to support such expansion, and hence, the jacket splits open

in order to relieve the buildup in pressure.

It was also noted that in every case in which failure of the energized

cables was observed, the sparks which resulted caused the ignition of

intense, sustained, open flaming in the cable sample. This observation

indicates that in the modeling of cable fire growth, the failure of

energized cables through heating should be considered a mechanism for

fire spread as well. It also indicates that the temperature threshold

for piloted ignition of the cable materials is lower than the observed

threshold of thermal damage. In no case was spontaneous ignition of the

cables prior to failure observed.

4.5 Thermal Damage Test Results

Tables 4.1 and 4.2 provide the time to electrical failure (based on

failure of the two ampere current limiting fuse) and exposure temperature

for each individual test of the unaged and aged BIW cable samples

respectively. Table 4.3 provides the average failure time for each of

the exposure temperatures for both the aged and unaged samples.

Figure 4.3 provides graphic presentation of the data presented in these

tables. Each of the individual data points is shown, as well as simple

linear splines connecting the applicable average failure times as given

in Table 4.3.

For the unaged cable samples the threshold of thermal damage was

determined to be 365-370C., For the aged samples the threshold for

thermal damage was determined to be 345-350sC. In each case these

threshold values may be interpreted as follows:

- Cable failures were observed during exposure tests at the

temperature corresponding to the upper limit of the stated

range (i.e., 370-C and 350-C for the unaged and aged cables,

respectively).

At a temperature corresponding to the lower limit of each

range, no failures were observed following cable exposures of

-23-
no less that 80 minutes in duration (i.e., 365*C and 3450C for

the aged and unaged cables, respectively).

These results indicate that thermal aging resulted in a reduction in the

thermal damage threshold of approximately 20C. This change is

relatively modest, and will not result in a significant change in

estimates of fire risk.

In observing the data, one should also note the relative time to damage

for the aged and unaged cables. For exposure temperatures at which both

the aged and unaged cable samples were observed to fail, that is

exposures greater than or equal to.370-C, the times to electrical failure

are essentially the same for the aged and unaged samples. This behavior

is quite different than that of the Rockbestos cable.

4.6 Summary of BIg Thermal Damage Results

For the BIV cable product tested, it was found that thermal aging reduced

the thermal damage threshold of the cable by approximately 20°C. This

result indicates an increased vulnerability to thermal damage due to

aging. However, the change is considered relatively modest, and is not

expected to result in a significant change in fire risk estimates. It

was also noted that for higher temperature exposures, no statistically

significant difference between the aged and unaged cables were noted.

One final insight gained was that in every case in which electrical

shorting of the cable samples was observed, an intense, self-sustaining

fire was initiated. In no case was spontaneous ignition of the cables

observed prior to cable failure. This indicates that:

(1) the temperature threshold for piloted ignition of the cable

samples is lower than the damage thresholds identified here,

(2) in the modeling of cable fire growth, the failure of energized

cables should be considered as a mechanism for fire spread,

and

(3) the spontaneous ignition (or non-piloted ignition, or autoignition) temperature is above the lower limit of thermal

damage for this cable.

The data presented provides an indication of the thermal damageability of

this cable product in a fire environment. Caution should be exercised in

the extrapolation of this data to other cable types and other cable

products utilizing similar materials.

-24-
Table 4.1: Thermal Damageability Data for Unaged BIV

Bostrad 7E Cable Samples.

Test No. Cable No. Exposure Temp. Failure Time*

(-C) (min:sec)

30 1 365 KE

30 2 365 NF

31 1 370 17:48

31 2 370 16:08

44 1 370 20:01

44 2 370 18:36

29 1 375 17:30

29 2 375 16:45

41 1 375 16:05

41 2 375 14:26

28 1 400 8:42

28 2 400 6:40

40 1 400 7:00

40 2 400 6:25

27 1 425 5:05

27 2 425 4:20

* HF indicates no failure observed following an exposure of

no less than 80 minutes.

-25-
Table 4.2: Thermal Damageability Data for Aged* BIW

Bostrad 78 Cable Samples.

Test No. Cable No. Exposure Temp. Failure Time*

(C) (min:sec)

49

49

48

48

50

50

47

47

46

46

51

51

37

37

38

38

36

36

39

39

33

33

34

34

32

32

35

35

345

345

350

350

350

350

355

355

360

360

360

360

365

365

365

365

375

375

375

375

400

400

400

400

425

425

425

425

N?

NF

59:12

47:11

72:59'

49:32

31:09

20:41

31:35

24:28

23:52

21:20

19:04

19:50

15:10

16:12

10:50

11:52

12:42

14:47

9:08

8:38

9:25

7:45

6:28

6:08

6:26

6:26

* NF indicates no failure observed following an exposure of

no less than 80 minutes.

** Cables aged to equivalent of 40 years at 601C for the

insulator.

***Loss of computer control resulted in drop in chamber

temperature to 330C for period of 2 minutes at time

equal to 68 minutes into the exposure. Cable #2 was not

affected as cable failure occurred prior to control failure.

-26-
Table 4.3: Average Failure Time Data for.the

BIW Bostrad 7E Cable Samples

Exposure Temp. Average Failure

(C) Time (min)

Unaged Samples:

365 NF

370 17.98

375 16.11

400 7.20

425 4.70

Aged Samples:

345 NF

350 57.22

355 25.92

360 25.31

365 17.57

375 12.55

400 8.73

425 6.36

* NF indicates no failure observed in at least two samples

exposed for no less than 80 minutes.

-27-
Nal I Temperature

Air Temperature Cable Sub-Jacket Temp

400

. -... -- ... 

U

QJ

L.

ro

IE

a.,

-I 7

- .-

./

/I

I

/1

If

r

Li

*.1

J.,

01

rO01.

100 7

0

I I I I I I I I I I I I a a I

5 15 20

Time (min)

Figure 4.1: Typical Cable Internal Temperature Response for an Unaged Sample of the

BIW Cable. This Plot was Taken from Test 31, and Also Illustrates the

Consistency of the Exposure Environment. Note that Cable Insertion

Occurred at (Time - 0) in this Plot.
Shield Conductor

Cable Conductor 41 Cable Conductor 12 -------------- 30

25

2

4*

C

Li

e

-J

20 1

15 [

Test 31; Cable 12

A.. .

to li

5'.

a

.I 5 le

Time (min)

(a) Unaged BIW Cable

20

Shield Conductor

Cable Conductor 11 --- - Cable Conductor 42 --------------

Test 48; Cable 2

2

C

91

Li

25

20

15

Is

5

36

Time (min)

(b) Aged BIW Cable

Figure 4.2: Typical Leakage Current Data for (a) an Unaged

and (b) an Aged BIW Cable Sample. Note that Cable

Insertion Occurred at (Time - 0) in these Plots.

-29-
450-

425 - -o--Un aged BIW

--o-Aged BIW

CD

sro

C..

,

c2

a,

ci.,

Fi2

0

CD

400 -

375 -

350-

325 -

ooNo Failure

(365 C)

00 No Failure

(345 C)

0 :1-.

0

I I I I

10 20 30 40 I I l

50 60 70 80 90

Fai lure Time (min)

Figure 4.3: Cable Thermal Damage

Data for both the Aged and Unaged Samples of

the BIW Bostrad 7E EPR/Hypalon Cables.

-30-
5.0 CONCLUSIONS

In summary, the results of these tests demonstrated that thermal aging

can be expected to change the thermal damageability of electrical cables.

However, thermal aging had a quite different impact on the two cable

types tested. Table 5.1 presents a summary of the thermal damage

thresholds determined for both cable types in both the aged and unaged

condition.

In the case of the Rockbestos cable, the thermal damage threshold of the

aged cables was approximately 25-35"C higher than that of the unaged

cables. Also, the time to failure at any given exposure temperature was

consistently longer for the aged cables than for the unaged cables (See

Figure 3.3). Both of these results are indicative of a reduced

vulnerability to thermal damage for aged cables as compared to unaged

cables.

In the case of the BIV cable it was found that the threshold of thermal

damage for the aged cables was approximately 20-C lower than that of the

unaged cables. This result is indicative of an increased vulnerability

to thermal damage for the aged cables as compared to the unaged cables.

At higher exposure temperatures, no statistical difference between the

time to thermal damage for the aged and unaged cables was observed (see

Figure 4.3).

Table 5.1: Summary of Aging Effects on Cable

Thermal Damage Threshold.

Unaged Cable Aged Cable

Damage Thresholds Damage Threshold'

Cable (C SC) (Tye 

Rockbestos Firewall III

Neoprene/XPE 325-330 350-365

BIW Bostrad 7E

EPR/Hypalon 365-370 345-350

* Note that in each case, electrical failure was observed

during exposures at the upper end of the stated range,

while no failure was observed during exposures at the

lower limit of the stated range of no less than 80 minutes

in duration.

-31-
It should be recognized that for both cable types tested, significant

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

the onset of catastrophic failure. The damage thresholds and damage

times reported above are all based on the failure of a 2 ampere fuse in

any one leg of the energizing circuitry. Specific applications must be

examined to determine whether or not current leakage on the order of that

observed here could constitute failure of the circuit to perform its

function. In certain circuits, a current leakage of 15 mA may be

unacceptable. Also, if the length of cable exposed is longer than that

tested here, approximately 24 inches of exposed length, then a

corresponding increase in total current leakage should be anticipated.

It was also observed that for both cable types, in virtually every case

in which electrical failure occurred, the arcing caused the initiation of

intense, sustained, open flaming in the cable samples. This observation

leads to three conclusions:

- The temperature threshold for piloted ignition of the cable

materials is less than the thermal damage thresholds

identified in Table 5.1 above.

- The failure of energized cables during a fire should be

considered as a mechanism of further fire spread and secondary

fuel ignition.

- Because no cases of spontaneous ignition prior to cable

failure were noted, the spontaneous ignition temperature of

the cable materials is likely higher than the lower limit of

thermal damage identified above.

These tests have demonstrated that thermal aging can be expected to

affect the vulnerability of cables to thermal damage. The direction and

magnitude of that effect will be dependent on the composition of the

cable material, and most likely, on the composition of the insulation on

the individual conductors rather than the jacket. In the case of the two

cable types evaluated in this effort, the changes in thermal

damageability are not considered large enough to result in significant

changes in the estimated risk due to fire scenarios involving the failure

of these two cable types. Rather, the differences can be treated as

uncertainties in the cable damage threshold limits. No significant risk

impact is expected because the uncertainty in other fire risk assessment

input factors is much more significant than the uncertainties identified

here.

It should also be noted that these tests have investigated only one

damaging aspect of the fire environment, namely, direct thermal heating.

In particular, no examination of the vulnerability to fire suppressant

induced damage or the impact of aging on such vulnerability has been

undertaken.

-32-
6.0 REFERENCES

1. A.R. DuCharme and L.D. Bustard, "Characterization of In-Containment

Cables for Nuclear Power Plant Life Extension,m Presented at the

ASME/JSHE Pressure Vessel and Plping Conference, Honolulu, HI, July

1989.

2. D.B. King, V.F. Nicolette, and V.J. Dandini, Safety-Related

Equlpment Survlval In Hydrogen Burns In Large Dry PWR ContaInment

Buldfings NUREG/CR-4763, SAND86-2280, Sandia National Laboratories,

Albuquerque, NH, Harch 1988.

3. S.P. Nowlen, A Summary of Nuclear Power Plant Flre Safety Research

at Sandla Natlonal Laboratorles, 1975-1989, NUREG/CR-5384,

SAND89-1359, Sandia National Laboratories, Albuquerque, NH, December

1989.

4. C.M. Craft, ScreenIng Tests of Terminal Block Performance In a

Simulated LOCA EnvIronment, tUREG/CR-3418, SAND83-1617, Sandia

National Laboratories, Albuquerque, NH, August 1984.

.33-
APPENDIX A

LEAKAGE CURRENT DATA

The following figures provide the actual leakage current data for each of

the two cable specimens tested in each of Tests 4-51. (Tests 1-3 were

facility shakedown tests and the data is not reported here.) In each

plot, the leakage current for each of the individual conductors is given.

In the case of the three conductor Rockbestos cable, each of the three

conductors was connected to one phase of a 208VAC three-phase power

source as shown in Figure 2.3. The cable conductors were identical and

connected in random order. In the case of the two conductor BIW cable,

the two conductors and the shield drain conductor were each connected to

one phase of the power source. For the leakage current plots from the

BIW cable tests, the shield leakage current is consistently shown as the

solid line in each plot.

Each plot identifies the test number, the cable type, the aging

condition, and the exposure temperature. Any anomalous behavior noted

during testing (instrumentation or control failures) are also noted. In

some cases, leakage currents appear to return to zero following a

precipitous jump upwards (failure). This is due to the fact that the

power source was isolated to an individual cable after failure occurred.

In no cases was cable Shealings observed.
30

25

29

C

IaLi

-J

a5

e

gL5. gm2

Time (sec)

Test 4; Cable I

C.

C.3

-w

Time (beck

Test 4; Cable 2

Figure A-1: Leakage Current Data For Test 4 Involving an Unaged

Rockbestos Cable at an Exposure Temperature of 350-C.

-Al-
3a

Isep

LI 19

SI

aa

aa

-J 5

30

25.

2a9

c 15_

3I 1

LI 1

a A-2

3a

2I 5-

-jc1~~9 9u

FiueA2

Time (sec)

Test 5; Cable I

Time (sec)

Test 5; Cable 2

Leakage Current Data For Test 5 Involving an Aged Rockbestos

Cable at an Exposure Temperature of 3750C.

-A2 -
30

25

20

CE

V)

0, M

a0

a)0

is

t1

soo

Time (sec)

Test 6; Cable I

30

25

20

CE 15

S)-

U6

a)

a,

co

a0

a)

10

Time (sec)

Test 6; Cable 2

Figure A-3: Leakage Current Data For Test 6 Involving an Unaged

Rockbestos Cable at an Exposure Temperature of 375-C.

-A3-
3s

Ci

4-1

'I1

-j

25

20

I5

5

Time (sac)

Test 7; Cable I

I

39

13

I10

01

-j

Time (sec)

Test 7; Cable 2

Figure A-4: Leakage Current Data For Test 7 Involving an Aged Rockbestos

Cable at an Exposure Temperature of 350GC.

-A4-
15

Co

30

a is

.C, M

.3 5 -h

B

I

30

25c

29-

15-

C

Ie is- a,

M-W

0

-j

A

Figure A-5:

Time (sec)

Test 8; Cable I

Time (secl

Test 8; Cable 2

Leakage Current Data For Test 8 Involving an Aged Rockbestos

Cable at an Exposure Temperature of 365-C.

-A5-
- -

38

i

1-'

S

w

A

SI

25

20

is

13

5

a

a 1Xxs 2M8 306 462

Time (sec)

Test 9; Cable I

I0

a.a

Eu

-J

Time (sec)

Test 9; Cable 2

Figure A-6: Leakage Current Data For Test 9 Involving an Unaged

Rockbestos Cable at an Exposure Temperature of 3250C.

-A6-
39

25

29

4.

6In

11..

I..

15

la

5

la

a

Time (zecd

Test 10; Cable I

32

25

2a

15

Is

ICI

IR

Time (secd

Test 18; Cable 2

Figure A-7: Leakage Current Data For Test 10 Involving an Unaged

Rockbestos Cable at an Exposure Temperature of 3350C.

-A7-
-

0C

L.)

*1M

-j

* * *0 08 * * * 0 

a 2U 481 6ea eaa

Time (sec)

Test 11; Cable I

39

25

29

a'

Ed

c

fa,

B3

-J

15

i1

5

Time (sec)

Test 11; Cable 2

Figure A-8: Leakage Current Data For Test 11 Involving an Aged

Rockbestos Cable at an Exposure Temperature of 400-C.

-A8-
30

=E

- IS c

In

G.2)

-

l 5

-J

7

3 0

38

25_

29

Is5

0

I- g A9

-J I/

Id I

Figure A-9:

Time (sec)

Test 12; Cable I

so

Time (sec)

Test 12; Cable 2

Leakage Current Data For Test 12 Involving an Unaged

Rockbestos Cable at an Exposure Temperature of 400C.
38

25 I

a 220 400 Gas see

Time (sec)

Test 13; Cable I

Co

is

aa 01

0 2 469 6se 623

Time (sec)

Test 13; Cable 2

Figure A-10: Leakage Current Data For Test 13 Inmvolving an Aged

Rockbastos Cable at an Exposure Temperature of 4008C.

-AlO-
30

25

28

i 5 Jill

e 280s0 600 sea 1000

Time (sec)

Test 14; Cable I

a , . I

20

s.1 IS.

3l X5

e 200 480 600 aw Ism0

Time (sec)

Test 14; Cable 2

Figure A-11: Leakage Current Data For Test 14 Involving an Unaged BTU

Cable at an Exposure Temperature of 3751C.

-All-
Is

WC

201 400 600 800 low0

Time {sec)

Test 15; Cable I

30

8 280423 Oes BO Ev 

Time (sac)

Test 15; Cable 2

Figure A-12: Leakage Current Data For Test 15 I mvolvng an Aged BIW Cable

at an Exposure Temperature of 375'C.

-A12-
Ai . 3---- 

25

20 F

c

0

za' 4-

le _7

5

.I . . . . . . I a 

5'I

U . . . . . . . . . . . . . ___

1Igo 2000 3000 4809

Time (sec)

Test 16; Cable I

39

2?5

28F

c

ED

9-

(-3

Si

en

do

.A

SI"

15 _

1 _-

5

wq4&V6QNf i- K% D 

°II 1000 3009

Time (sec)

Test 16; Cable 2

Figure A-13: Leakage Current Data For Test 16 Involving an Unaged B1W

Cable at an Exposure Temperature of 3500C.

-A13-
39

25

29

'5

a

* In9 299 389 429

Time (sec)

Test 17; Cable I

39

25 .

29

- 15 Iii

I0.

1 IO 280 38948

Time (secd

Test 17; Cable 2

Figure A-14: Leakage Current Data For Test 17 Involving an Unaged Rockbestos Cable at an Exposure Temperature of 400*C.

-A14-
20\ |

3Ig 26 300 402 50a

Time (sec)

Test 18; Cable I

25 '

15 Il

C

L

e 1a00 310 400 SW

Time (sac)

Test 1IB Cable 2

Figure A-15: Leakage Current Data For 'rest 18 Involving an Unaged

Rockbestos Cable at an Exposure Temperature of 375-C.

-A15-
Test 19; Cable I

30

25-

Q.3

.3 5

9 10a 209 399 409 509 60a 789

Time (sec)

Test 19; Cable 2

Figure A-16: Leakage Current Data For Test 19 I mvolving an Unaged

Rockbostos Cable at an Exposure Temperature of 3501C.

-A16-
lZ 5tl0 f320

25 /3

262

L

=

50 are0 1580 2MO0

Time (sec)

Test 20; Cable 2

Figure A-17: Leakage Current Data For Test 20 Involving an Unaged

Rockbestos Cable at an Exposure Temperature of 335'C.

-A17-
- - -

Ca

Time (sec)

Test 21; Cable I

3,

25

28

- 15 i'S

6 a

8 529 1201 1509 2022

Time (sec)

Test 21; Cable 2

Figure A-18: Leakage Current Data For Test 21 Involving an Unaged

Rockbestos Cable at an ExVosure Temperature of 3301C.

-A18-
25

I I1le 200 30a 480 Sao

Time tsec)

Test 22; Cable I

31102000 0 0

leec The 

Test 22; Cable 2

Figure A-19: Leakage Current Data For Test 22 Involving an Aged

Rockbestos Cable at an Exposure Temperature of 425IC.

-A19-
30

515

8 180 28a 380 408 see 600 800

Time (sec)

Test 23; Cabl1e I

a,

Iis 1

0 1[8 29 3NO 408 598 600 790

Time (sec)

Test 23; CabIe 2

Figure A-20: leakage Current Data For Test 23 Involving an Aged

Rockcbestos Cable at an Exposure Temperature of 4001C.

-A20-
CE 4..

r

4..

d3 is A

B 290 40d 603 So 1000

Time (sed

Test 24; Cable I

30

25-j

'5

e 200 40Z So 600ow0 Boo 

Timne {sec)

Test 24; Cable 2

Figure A-21: Leakage Current Data For Test 24 Imvolving an Aged

Rockbestos Cable at an Excposure Temperature of 375*C.

-A21-
39

25

29

log 2M0 a 3000

Time (sec)

Test 25; Cable I

25

20-

01

is

35

* 1000 280 3000

Time (sec)

Test 25; Cable 2

Figure A-22: Leakage Current Data For Test 25 Involving au Aged

Rockbestos Cable at an Exposure Temperature of 370-C.

-A22-
4.

C

S..

0)

m

-I"

lC

aI

I.

I.

Time (sac)

Test 26; Cable I

Time (sec)

Test 26; Cable 2

Figure A-23: Leakage Current Data For Test 26 Involving an Aged

Rockbestos Cable at an Exposure Temperature of 365-C.

-A23-
-

'5

Co

Li

00Joe 200 300 400

Time (secd

_ 19

25

2-a

3 1J 289 309 409

Time (sec)

Test 27; Cable 2

Figure A-24: Leakage Current Data For Test 27 Involving an Unaged BIW

Cable at an Exposure Temperature of 425-C.

-A24-
39

25

28

CE

0r

6.

-a

Is

Is

Time (sec)

Test 28; Cable I

38

0IA-I

-j

25

28

15

to

5

II

II

II

II

'I

II

II .. WE&a ---------------------------------- lee 209 39W 499 sea Eli

Time (icc)

Test 28; Cable 2

Figure A-25: Leakage Current Data For Test 28 Involving an Unaged BIW

Cable at an Exposure Temperature of 400'C.

-A25-
AI& 

.

25

a

P

*0

-I

29

is

5

V N

a 209 499 69o 999 1999 1290

Time (sec)

Test 29; Cable I

30

25 F

2a

aC

LI

a,

-J

15

It

5

'.V * a'I

a . . . .. . . . . . . . . . . . . . . . .

299 496 69e 899 1993 2096

Time (sec)

Test 29; Cable 2

Figure A-26: Leakage Current Data For Test 29 Involving an Unaged BIW

Cable at an Exposure Temperature of 375'C.

-A26 -
30

25

29

a

Li

LI

15

le

140et I . . I . . I bA, - logo 3000 4000 50

Time (sec)

Test 30; Cable I

30

25 _

20 _

SI

4-

'a

1i

15 _

e _-

s ~

I

5l'! v --- - - - - - - - - - - - - - - - - - - - - - - 100Z 28e9 3000 4800

Time (Czc)

Test 30; Cable 2

Figure A-27: Leakage Current Data For Test 30 Involving an Unaged BIW

Cable at an Exposure Temperature of 3651C.

-A27-
-

3a

25

29

'5

C

a200 4Ma see 82X IM 1200

Time (see)

Test 31; Cable I 0I

'a

61 5_

CD

a 29 420 sea an 1020 1222

Time (sec)

Test 31; Cable 2

Figure A-28: Leakage Current Data For Test 31 Involving an Unaged BIV

Cable at an Exposure Temperature of 3700C.

-A28-
3a

25 'V

28

C

'5 1 4.

INle 200 300 400

Timle (sec )

22 Test 32; Cable I

* S

-0

8 198 290 300 400

Time (sec)

Test 32; Cable 2

Figure A-29: Leakage-Current Data:For Test .32 Involving an Aged BIV Cable

at an Exposure Temperature of 425'C.

-A29-
30

C5

a in 20a Ma 4Qa sea EN

T i me (sec )

Test 33; Cable I

LI 9

20

* 5

6-

a too 208 368 488 so8 goo

Time (secd

Test 33; Cable 2

Figure A-30: Leakage Current Data For Test 33 Involving an Aged BIV Cable

at an Exposure Temperature of 400-C.

-A30-
il 1 _

25

208

0C

S.

'I15 i

!i

'I

I

I

*...- Z-14d I

. . . I . . -2 . I . . -A , I I . . . I I . - t I . . . .

19I

5

dI 1 - 202 392 4fe

Time (sec)

Test 34; Cable I

592 6s9 792

3a

25

20

15

c

V

21

.a

10

Time (&ec)

Test 34; Cable 2

Figure A-31: Leakage Current Data For Test 34 Involving an Aged BIV Cable

at an Exposure Temperature of 40O'C.

-A31-
- -

39

25

20

i

Ia)

CGa

-J

15

5 A -,\ ve

B

I 102 209 309 400 520

Time (sec)

Test 35; Cable I

32

25

29

I

C

S3

en

a

'I

a.!

Is

5

a

I l98 299 308 428 529

Time (sec)

Test 35; Cable 2

Figure A-32: Leakage Current Data For Test 35 Involving an Aged BI Cable

at an Exposure Temperature of 425-C.

-A32-
30

25

20

C

c

6)

A.

Oa

15

I

I III

10I

5

I 409 699 Sao

Time (sec)

Test 36; Cable I

4.-

OD

6'

C,

sea

Time (sec)

Test 36; Cable 2

Figure A-33: Leakage Current Data For Test 36 Involving an Aged BIW Cable

at an Exposure Temperature of 375'C.

-A33-
30

P 5

0 200 400 Goa 803 120Q 1200 14Q0

T ime (sec)

Test 37; Cable I

C

a,

a 200 400 GOB 880 low 1220 14Q0

T ime (sec

Test 37; Cable 2

Figure A-34: Leakage Current Data For Test 37 Involving an Aged BIW Cable

at an Exposure Temperature of 365-C.

-A34-
30

25

15

qi

a _o

a _

Time (sec)

Test 38; Cable 1

36

25

28

! e d

e2M0 400 silo Boo

Time (secI

Test 38;: Cable 2

Figure A-35: Leakage Current Data For Test 38 Involving an Aged BIW Cable

at an Exposure Temperature of 365'C. Note that a failure in

the data logging system occurred prior to the observed cable

failures.

-A35-
Ca'

132

GI

0 220 490 69a ON9 '999

Time (esc)

Test 39; Cable I

a

I13

LI

CD

01

U

86

Time (sac)

Test 39; Cable 2

Figure A-36: Leakage Current Data For Test 39 Involving an Aged BIW Cable

at an Exposure Temperature of 375*C.

-A36-
39

25

282

'E . 15

0C

L.

- la

a) 5

-j

I

/

I I

I . . -I g ~ ~~~~ ~ . .5 ~ ,. 

I 100 298 390 4.9 SO9

Time (sccl

Test 40; Cable I

25

29

loI

Ie

If

C

a,

4-

A3

arC

-8 - I0S 390 400 590

Time (sec)

Test 40; Cable 2

Figure A-37: Leakage Current Data For Test 40 Involving an Unaged BIW

Cable at an Exposure Temperature of 400'C.

-A37-
5_51

C

0 200 400 Gas see logo 1200

Time (sec)

Test 41; CablIe I

15

I

a 289 400 600 800 1808 1228

Time (seci

Test 41; Cable 2

Figure A-38: Leakage Current Data For Test 41 Involving an Unaged BIV

Cable at an Exposure Temperature of 375-C.

-A38-
30

25 I

20

CE

Z1

4-

200 400 see sea 1000 120

Time (sec)

Test 42; Cable I

Li NE19 j

3e

i5 -. .. -.

61

61

* 5

a 200 400 see GM 1992 1200

Time (sec)

Test 42; Cable 2

Figure A-39: Leakage Current Data For Test 42 Involving an Aged

Rockbestos Cable at an Exposure Temperature of 370'C.

-A39-
. ..-

25 ;

20

C

rIn

-W

15 j

A. . I . . . . . . I . . . I

1of

S

-- - - I 209 400 6co s9e logo 120a

Time (see)

Test 43; Cable I

C

0)

-a

Tise (sec)

Test 43; Cable 2

Figure A-40: Leakage Current Data For Test 43 Involving an Aged

Rockbestos Cable at an Exposure Temperature of 3650C.

-A40-
30

E fill

9 200 409 600 19e 19 1299 1499

Time (sec)

Test 44; Cable I

30

29

CE

to.

C,

:

0 209 490 69o 99o 1900 1290 1490

Time (sac)

Test 44; Cable 2

Figure A-41: Leakage Current Data For Test 44 Involving an Unaged BIW

Cable at an Exposure Temperature of 3701C.

-A41-
15 Z-; 41

a0

a 200 409 6se 8se l0o9 1200

Time (see)

Test 45; Cable I

39

29 / )

25 0 8

WC

L is2

e1

0)

a 208 409 see sea I0n9 1209

Time (sec)

Test 45; Cable 2

Figure A-42: Leakage Current Data For Test 45 Involving an Unaged

Rockbestos Cable at an Exposure Temperature of 330-C.

-A42-
38

se - low5 150 220

Time (sec)

Test 46; Cable I

4. .

CE

15-

to

e 589 1wo 1500 2826

Time (ccc)

Test 46; Cable 2

Figure A-43: Leakage Current Data -For Test 46 Involving an Aged BIW Cable

at an Exposure Temperature of 360"C.

-A43-
39

25

28

-

a

-j

i5

to

5

9 -

I 500 low 1569 260

Time (sec)

Test 47; Cable I

30

25

29

I

63

-J

I1

S

QlL

a

Time (sec)

Test 47; Cable 2

Figure A-44: Leakage Current Data For Test 47 Involving an Aged BIW Cable

at an Exposure Temperature of 355-C.

-A44-
30

43 a

6)

100 - 2800 .300

Time (sec)

Test ;4B; Cable I

25-

29

I

- 15-

. 1000 2000 - 3000s

Time (Sec)

Test.48; Cable 2

Figure A-45: Leakage Current Data For Test 48 Involving an Aged BIW Cable

at an Exposure Temperature of 350'C.

-A45-
38

3

C

31

01

0I

-W

Time (see)

Test 49; Cable I

I?

3

01

ft

-j

Tie (sec

Test 49; Cable 2

Figure A-46: Leakage Curran Data For Test 49 Involving an Aged 31W Cable

at am Exposurae TemPerature of 345*c.yI a gdBI al

-A46-
30

C

i6

B,

.- j

25

209

15_

5

0

I.

Time (sec)

Test 50; Cable I

C

F

I1.)

B,

Arc

30

25

20

15

to

5

a

Il

Time (sec)

Test 50; Cable 2

Figure A-47: Leakage Current Data For Test 50 Involving an Aged BIW Cable

at an Exposure Temperature of 3506C. Note that a failure in

the data logging system occurred prior to the failure of

Cable 1.

-A47-
ce

a

06

310

-J

r * * * . * I*p U * . * . . . U . . . X . * U * . La 293 400 69a ogo 13 I29a 3 140a

Time (sec)

Test 51; Cable I

3a

25

28

10to

II

6..

L1I

61

4

a

30 201 43 6N s0ilo low 1291 1420

Time (sec)

Test 51; Cable 2

Figure A-48: Leakage Current Data For Test 51 Involving an Aged BIW Cable

at an Exposure Temperature of 360@C.

-A48-
DISTRIBUTION:

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Office of Nuclear Regulatory Research

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Mail Stop L-442

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Attn: Kenneth Dungan

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Attn: Jean-Pierre Sursock

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Attn: Leon Przybyla

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Attn: Richard Patton

5316 Roseville Rd., Suite P

North Highlands, CA 95660

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Attn: Jeff Newman

1151 Boston-Providence Hwy.

Norwood, MA 02062

American Electric Power Service Corp.

Attn: Jack Grier

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PO Box 16631

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Attn: Joe Priest

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Attn: Jin Evans

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Attn: Michael S. Kaminski

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Attn: Ulrich Heinzs Schneider

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-Dist. -2-
Internal SNL:

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-Dist. -3-
WRC P ORm 335 US. NUCLEAR REGULATORYCOMMISSION I. REPORTNUMBEt

2.3= BIBLIOGRAPHIC DATA SHEET VUREG/CR-5546

an Uwmai en me œnmJ SAND90- 0696

2.TITLEAND SUTITLE

An Investi Ration of the Effects of Thermal Aging on S DATE REPORT PUBLISHED

the Fire bamageability of Electric Cables MONUTH j EAR

May 1991

4.FINORGRANTNUMBER

F FIN A-1833

6. AUTHORCSI L TYPE OF REPORT

Steven P. Nowlen Technical

7. PERIOD COVERED Uacthwie Da

8. PERFORMING ORGANIZATION - NAME AND ADDRESS WNRIAv a. UI Faiamar "iub. odium reknO4.OiB i O t1W#utDtvW.

*41*4 *da1IftWl

Sandia National Laboratories

Albuquerque, WM 87185

G. SPONSORING ORGANIZATION -NAME AND ADDRESS (If MRc- NRC0lv. OII*N AJ Ihe 4u*. UK f x*,joWv CnIbn.

Division of Engineering

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commissibn

Washington, DC 20555

10. SUPPLEMENTARY NOTES

II. ABSTRACT a2WO*or~wrb

This report documents the findings of an experimental investigation of the effects of

thermal aging on the fire damageability of electric cables. Two popular types of

nuclear qualified cables were evaluated. For each cable type, both unaged (i.e., new

off the reel) and thermally aged samples were exposed to steady-state elevated

temperature environments.until condueltor-to-conductor electrical shorting was observed.

Plots of the time to electrical failure versus the exposure temperature were developed

and thermal damage thresholds were determined. For one cable type, the thermally aged

cables were less vulnerable to thermal damage than were the unaged samples as

demonstrated by an increase in the thermal damage threshold for the aged samples, and

an extended survival time at exposure temperatures above the damage threshold for agedsamples compared to unaged samples. For the second cable, the threshold of thermal

damage was lowered somewhat by the aging process, an indication of an increased

vulnerability to thermal damage due to aging. However, for the higher temperature

exposures, no statistical difference between the damage times for aged and unaged cable

samples was noted. For both cable types, the changes in the thermal damage threshold

observed were not considered significant in terms of fire risk.

12. KEYWORDS/DESCRIPTORS(tiw. ms onpham oat awwoz"g mm & A8h*9t1h'Memt.P 13. AVAILABIUTY STATEMENT

Fire Safety, Cable Damageability, Nuclear Power Plant Aging Unlimited

14. SECURtTY CLASSIFICATION

trA), Pax)o

Unclassified

ITA)s fiepaof

Unclassified

15 NUMBER OF PAGES

16 PRICE

KRC FORM 335 12491