A 11 10b 04,3577

; 78-1477

Exploratory Study of Temperatures

Produced by Self-Heating of

Residential Branch Circuit Wiring

When Surrounded by Thermal

Insulation

Robert W. Beausoliel

William J. Meese

Lawrence S. Galowin

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

July 1978

QC —

100

U56

78-1477

Sponsored by

The Department of Energy

Washington, D.C. 20461

NBSIR 78-1477

« • 4 EXPLORATORY STUDY OF TEMPERATURES

PRODUCED BY SELF-HEATING OF

RESIDENTIAL BRANCH CIRCUIT WIRING

WHEN SURROUNDED BY THERMAL

INSULATION

Coital Bureau of Standards APR 17 1971

fi art P.oi~ (2

QCL \DO

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Robert W. Beausoliel

William J. Meese

Lawrence S. Galowin

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

July 1978

Sponsored by

The Department of Energy

Washington, D C. 20461

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman. Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernast Ambler, Director

SI CONVERSION UNITS

In view of the present accepted practice in this country for building

technology, common U.S. units of measurement have been used throughout

this document. In recognition of the position of the United States as

a signatory to the General Conference on Weights and Measures, which

gave official status to the metric SI system of units in 1960, assistance is given to the reader interested in making use of the coherent

system of SI units by giving conversion factors applicable to U.S.

units used in this document.

Mass 1 pound - mass (lbm

) = 0.4535924 kg

Length 1 inch = 0.0254 meter (m)

Temperature t (Celsius) = 5/9 [t(Fahr) - 32]

Torque

Time

1 lbf

•

in = 0.113 newton meter (Nm)

1 hour = 60 minutes = 3,600 seconds
ACKNOWLEDGEMENTS

Work on this preliminary study on the overheating of residential branch

circuit wiring has been conducted as part of an interdisciplinary frame

work. The Center for Building Technology (CBT) of the National Bureau

of Standards (NBS) is concerned primarily with the heat production and

degradation of electrical system performance due to inadequate heat

dissipation and penetration of thermal insulating materials into electrical wiring devices.

The Center for Fire Research of NBS is concerned primarily with the

potential for combustion and smoldering of building materials due to

ignition sources inadvertently created by overheated electrical wiring

or devices. This report deals with the electrical-system side of the

problem.

The effort reported in this document was jointly funded by the Department of Commerce and the Department of Energy (DoE), under DoE/NBS

interagency agreement.

The authors appreciate the recommendations and guidance concerning ther

mal insulation that were received from Dr. Walter J. Rossiter of the

Structures, Materials, and Life Safety Division, CBT, NBS.

ii
CONTENTS

Page

SI Conversion Units ... i

Acknowledgements . . ii

Abstract v

1. Introduction 1 1.1 Purpose 1 1.2 Scope ....... ..... 2

2. Test Procedure and Results for Attic Installation 2 2.1 Temperatures on Parallel Cables in Simulated Attic ... 5 2.1.1 Cables in Open Air 5 2.1.2 Cables between Two Layers of Thermal

Insulation. .................. 7 2.1.3 Cables between Four Layers of Thermal

Insulation 9

2.1.4 Cables between Two Layers of Thermal Insulation

Within Simulated Ceiling Joist Space 12

2.2 Temperatures on Single Cables in Simulated Attic .... 15

2.2.1 Single Nonmetallic-Sheathed Cable Between Two

Layers of Thermal Insulation .... 15

2.2.2 Single Nonmetallic-Sheathed Cable in Simulated

Ceiling Joist Spaces ..... 15

2.2.3 Single Armored Cable in Simulated Ceiling Joist

Spaces . 20

2.2.4 Axial Heat Conduction Along Partially Thermally

Insulated Branch Circuit Wiring 20

2.3 Discussion of Cable Tests in Simulated Attic 26

3. Test Procedure and Results for Cables and Outlet Boxes in

Walls 28

3.1 Temperatures on Cables and Outlet Boxes 29

3.2 Penetration of Thermal Insulation Into Outlet Boxes. . . 32

3.3 Discussion of Tests of Wall Wiring Surrounded by Thermal

Insulation ............... 37

4. Summary ..... ......... 37

5. Recommendations ..... ...... 38

6. References *

Appendix A: Calculation of Wire Temperature Based on Increase in

Wire Resistance ... ....... 43

iii
CONTENTS (Continued)

Page

Appendix B: Chemistry Tests at NBS for Gases and/or Vapors from

Heated Cables and Thermal Insulation 45

Appendix C: Precautions During Installation of "Foamed-in" and

"Blown-in” Thermal Insulation 47

iv
EXPLORATORY STUDY OF TEMPERATURES PRODUCED BY SELF-HEATING OF

RESIDENTIAL BRANCH CIRCUIT WIRING WHEN SURROUNDED

BY THERMAL INSULATION

R. W. Beausoliel, W. J. Meese, and L. S. Galowin

ABSTRACT

The purpose of the work presented in this paper was to make preliminary

determinations under laboratory conditions of temperatures that might

develop on residential electrical wiring covered by thermal insulation

when carrying rated currents or currents slightly above rated values.

The results show that temperatures on conductors surrounded by thermal

insulation can greatly exceed the maximum service temperature for the

wire insulation. Results also show that some types of insulation cur- rently used to retrofit buildings may fill wall outlet boxes and contact

the current-carrying elements and connections of duplex receptacles.

This study indicates need for a concentrated study of temperatures that

might develop on residential electrical wiring covered by thermal

insulation.

Key Words: Branch circuit wiring; electrical fires; heat generation

in receptacles; insulated buildings; overheating conductors;

residential branch circuit wiring; thermal insulation and

electrical wiring.

v

1. INTRODUCTION

Shortages of fuels for residential heating and severe winter weather have

resulted in both State and Federal programs on energy conservation for

buildings. Improvements in thermal efficiency of residential buildings

through increased use of additional thermal insulation are recommended

for new construction and retrofitting existing buildings.

The impact of increased use of building insulation in residences may be

detrimental to electrical wire, cables, and devices comprising the residential branch circuits. The conduction of electric current generates

heat which is normally dissipated by conduction and convection when

reasonably exposed. When the circuits are covered by thermal building

insulation the electrical insulation and wire temperatures will increase

substantially. The local environment of the thermal insulation is correspondingly raised to increased temperature levels. Present standards

and model code [1,2,3] require that the type of electrical insulation

usually used in residential branch circuits should not operate at temperatures in excess of 140°F. The effect of higher temperatures on electrical insulation is of considerable concern. Overheated wiring circuits

may ignite electrical insulation or ignite proximate building materials

or lead to gradual deterioration of dielectric strength of the insulation

which may lead to ignition from arcing or short-circuits.

1.1 PURPOSE

The investigation performed in this project was exploratory in order to

provide a preliminary basis for assessment of the problems related to

additional insulation on the installed building systems. The specific

purpose was to establish a basis for other in-depth research. The test

program included the following:

1. Determination of typical temperatures generated on residential

wiring by rated or slightly higher than rated electric currents*

before and after surrounding wiring in building thermal insulation.

2. Evaluation of configurations of residential wiring and building

thermal insulation that result in the generation of typically

high wire temperatures by rated or slightly higher than rated

electric currents*.

* For the purpose of this report "higher than rated electric currents" means currents above rated currents of the wires. However, such currents and times for which data are included in this report are at or below those at which overcurrent devices are normally required

to operate, (i.e.

it is consistent with the accepted test standards

used for approval listing of such overcurrent protection devices).

1
3. Determination of the effects of foamed-in and blown-in thermal

building insulation which migrates into electrical outlet

boxes and the increased temperature effects of such insulation

on electrical wiring and wiring devices.

1.2 SCOPE

Laboratory tests to obtain the dynamic temperature response were con- ducted with simple configurations of branch circuit wiring installed

in simulated attic and wall spaces. These tests were of an exploratory

nature and therefore did not cover all of the conditions that would

be encountered in practice.

Because of these restraints and for simplification, the use of electrical connections and wiring configurations was held to a minimum in the

work presented in this report. The reduction in temperature caused by

heat transfer through connections and along #12 AWG conductors contained

in nonme tallic-sheathed cables (NMSC) was a part of this preliminary

study.

No data concerning actual incidences of fire in thermal insulation or electrical conductor overheating were available for this study.

It was beyond the scope of the preliminary work to study fire potential

resulting from loose electrical connections or failure of electrical

insulation. Fire potential was concurrently being considered by the

Center for Fire Research at NBS.

2. TEST PROCEDURE AND RESULTS FOR ATTIC INSTALLATION

For simplification, safety, and energy conservation purposes, testing

was done with low supply voltage. The heat generated in the wire at

low voltage was the same as it would have been if testing had been

done on a 120-volt supply. This exploratory study was concerned primarily with temperatures on wiring and not with the possibility of

insulation failure which might be accentuated by use of 120-volt supply.

The low voltage setup as shown in Figure 1 serves only the wiring under

test as the load. As shown in Figure 1, the current was controlled

with a variable autotransformer connected to the 120-volt building supply and feeding a step-down transformer having a maximum voltage output

of 12 volts.

The current readings were obtained using a 0.001 ohm +1%, 50 ampere

AC shunt, which is part of the digital AC/DC millivol tmeter used during

the tests. During some of the tests of this report, the same voltmeter

was switched to DC millivolt range in order to read the thermocouple

output. During other tests, temperatures were recorded automatically

every five minutes on a data acquisition system using type "T" thermocouples, and current and voltage drop were recorded every five minutes

2
3
by hand. Current and voltage drop were used to calculate a final wire

resistance for the specimen. Using the final resistance and the initial cold resistance, determined with a kelvin bridge ohmmeter, along

with the initial temperature, the final temperature of the wire was calculated as a check on temperatures recorded from thermocouples.

See Appendix A for details.

The general test procedure was as follows:

(a) Measure the temperature(s) at five-minute intervals and at

controlled currents of 10A, 15A, 20A, and at slightly higher

currents. The cable was in a structure that simulated a typical wiring condition before insulation was added for

energy conservation. The cables were generally either resting on top of the insulation as they might in an attic space

or were installed in empty wall stud spaces.

(b) Fill the attic joist space or wall stud space with insulation

with recognized "R" values [4] and repeat the temperature

measurements of (a) above. Current was recorded every five

minutes. Voltage drops were also recorded periodically.

Residential general purpose branch circuits with 60°C electrical insulations usually use either #12 AWG copper or #14 AWG copper wire. From

temperatures and corresponding resistance values in the copper wire

tables [5]

,

it was determined that #12 AWG wire had a slightly greater

resistance heating at rated current than #14; #12 wiring was generally

used in this work. See Table 1.

The laboratory tests were made to obtain temperatures on residential

wiring at current levels that can exist under normally installed conditions. The cables were resting upon or surrounded by aluminum foilfaced glass fiber blanket (R-ll)*.

* R is the resistance value of a typical glass fiber insulation batt

of 31/2 inches thickness. One such batt is R-ll, two such batts are

R-22, etc. The manufacturer states that the product conforms to

Federal Specification HH-1-521E Type 111 [6], The manufacturer also

instructs that foil facings may either be removed or slashed freely

with a knife when adding to existing attic floor insulation in order

to prevent trapping moisture between old and new insulation.

4
Table 1 - Resistance heating of #14 AWG and #12 AWG copper

wire at rated currents respectively 15A and 20A

Temperature (°C) Resistance Heating (Watts per foot of wire)

#14 AWG #12 AWG

20 0.567 0.636

25 0.578 0.648

50 0.634 0.712

75 0.691 0.772

100 0.747 0.836

200 0.970 1.084

2 . i TEMPERATURES ON PARALLEL CABLES IN SIMULATED ATTIC

Branch circuit cables are close together in the vicinity where they connect to circuit breaker panels or may be close together when pulled

through holes in joists and studs. Several 120-volt 20-ampere branch

circuit cables of this type might serve portable window air conditioners

or portable electric heat units, and such units could load or nearly

load these circuits to their rated current. Two or more building

insulation-surrounded cables in close proximity could reach higher

operating temperatures than a single insulation-surrounded cable.

2.1.1 Cables in Open Air

The nonme tallic-sheathed cable specimen shown in Figure 2 was used to

simulate three branch circuits located close together. In this simulation, the cable configurations are probably somewhat closer than would

be found in an actual installation; for the purposes of this work,

the specimen was considered a worst case. Because of concern for exposure

of the laboratory staff to toxic gas or vapor that might possibly evolve

from hot cables during such tests, the series of tests with cables

located at varying distances from each other were not performed. See

Section 2.1.2 discussion concerning the possible gas emission from

cables

The specimen was placed on a batt of R-ll insulation as shown in

Figure 1, except that the top batt was folded back to expose the cable

to ambient air and simulated some typical installation conditions prior

to adding additional thermal insulation for energy conservation. The

5
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Simulation

of

Three

Parallel

Cables
initial cold resistance of the specimen was measured with a kelvin

bridge and found to be 0.0577 ohms for 36 feet of #12 AWG copper

wire at 72°F. A current of 20A was applied and controlled with

the variable autotransformer to within several tenths of an ampere.

At five-minute intervals, current, voltage drop across the specimen,

and temperature were recorded and the end of the test was based upon

obtaining steady-state temperature readings. The temperature and

current record is presented in Table 2. A temperature check based

on resistance change is presented in Appendix A.

TABLE 2

Temperatures on Three Parallel Cables

Exposed to Ambient Air with One Layer

of R-ll Insulation Under Cables

TIME (MINUTES) CURRENT - A TEMPERATURE - °F

0 0 72

5 20.0 83

10 20.1 91

15 20.1 96

20 20.3 99

25 20.2 101

30 20,2 103

35 20.2 103

40 20.3 103

2.1,2 Cables between Two Layers of Thermal Insulation

The purpose of this test was to obtain the difference in temperatures

on wiring surrounded by building insulation from wiring open to the

air on top of building insulation. The specimen was surrounded by

insulation as shown in Figure 1 and the procedure repeated to obtain

data presented in Table 3.

7
TABLE 3

Temperatures on Three Parallel Cables Placed

between Two Layers of R-ll Insulation

TIME (MINUTES) CURRENT - A TEMPERATURE - °F

0 0 74

5 19.6 91

10 19.7 107

15 20.0 120

20 20.2 133

23 20.1 141

25 19.7 145

30 19.8 155

35 20.2 164

40 20.0 173

45 19.9 180

50 20.4 187

55 20.3 194

60 20.2 200

65 20.1 206

70 20.2 210

75 20.3 214

80 20.2 217

85 20.2 220

90 20.1 223

95 20.3 225

100 20.3 228

105 20.3 230

110 20.2 231

115 20.3 233

120 20.2 234

125 20.2 235

130 20.2 237

135 20.2 238

140 20.3 238

145 20.2 239

150 20.3 239

8
It must be recognized that circuit breakers and fuses do not quickly

open circuits that are subjected to currents which are slightly overrated. The Underwriters’ Laboratories Standard 489 for Molded-Case

Circuit Breakers requires circuit breakers to open the circuit within

one hour at 135% of their rated current [7] and the Underwriters’

Standard 198.5 for Plug Fuses requires that fuses operate in one hour

at 135% of rated current [8], Figure 3 shows typical manufacturer's

curves (current versus trip time) for a 20-ampere circuit breaker of

residential type. As shown, overloads of 135% rated current or less can result in relatively long overload periods before the circuit

breaker is expected to open the circuit.

Because of the exploratory nature of the work presented in this report,

it was not practical to test circuit breakers and fuses in order to

gain statistically significant data concerning circuit opening time.

However, because of the likelihood that overloads of 120 - 135% of

rated current can occur, it was decided to determine cable temperatures

within this overcurrent range. It is judged that such currents could occur from homeowner-installed window air conditioners or electric

space heaters or combined currents from various sources on receptacle

circuits. The results of this test are presented in Table 4. As

shown, the test duration was only 60 minutes long, to simulate the

required clear time for breaker or fuse. It should be noted that the

temperature on the cable was still increasing at about 10°F per fiveminute period at the end of the test (one hour).

Examination showed that the cable insulation (sheath) did not appear to

be damaged (burned or scorched) by the test but the sheath did appear

to be somewhat loosened (loss of "elastic" properties) relative to the

unexposed or as-received cable. The glass fiber insulation was not

discolored by heat and the glass fibers did not stick to the cable

sheath. There was an odor of hot plastic when the building insulation

was removed for examination of the cable specimen. A burning sensation

was experienced in mouth, lips and throat of the investigator during

the examination. Also, the sensation was accompanied by nausea. Tests

to determine if noxious fumes were given off by cable and/or glass-fiber

thermal insulation were inconclusive. See Appendix B.

2.1.3 Cables between Four Layers of Thermal Insulation

In order to obtain some insight concerning the effect of additional

thermal insulation on cable temperature, the cable was placed on top

of two layers of R-ll, and two layers of R-ll were placed on top of

the cables; otherwise the test setup was identical to that shown in

Figure 1 and 2. The results are given in Table 5.

The test was terminated at the 115-minute period due to release of possibly toxic gas or vapor.

9
TIME

IN

SECONDS

Figure 3. Manufacturer's Curves Applicable to a 20-Ampere Circuit Breaker

10
TABLE 4

Temperatures on Three Parallel Cables Carrying 135% of

Rated Current While the Cables Were Located between

Two Layers of R-ll Insulation

TIME (MINUTES) CURRENT - A TEMPERATURE - °F

0 0 71

5 26.9 100

10 27.1 128

15 26.9 154

20 27.0 178

25 27.2 200

30 27.0 219

35 26.9 237

40 26.9 252

45 27.1 265

50 27.2 278

55 27.1 289

60 26.8 298

11
TABLE 5

Temperatures on Three Parallel Cables with Two Layers

of R-ll under the Cables and Two Layers of R-ll on Top

of the Cables

TIME (MINUTES) CURRENT - A TEMPERATURE - °F

0 0 70

5 20.3 87

10 20.3 105

13 20.1 117

20 20.1 131

25 20.4 144

30 20.4 156

35 20.3 167

40 20.2 177

45 20.2 186

50 20.1 193

55 20.2 201

60 20.2 207

65 20.2 214

70 - -

75 20.1 224

80 20.0 228

85 20.4 233

90 20.4 236

95 20.3 240

100 20.3 243

105 20.2 246

110 20.2 249

115 - -

2.1.4 Cables between Two Layers of Thermal Insulation within

Simulated Ceiling Joist Space

Because the tests presented in Sections 2.1.1 and 2.1.2 were carried out

with the cable specimen placed between batts of insulation that were placed on the laboratory floor, the effect of the floor on recorded

temperatures and the effect of typical building structures on temperatures were questioned. In order to answer this question, the specimen

and two layers of insulation were placed in the simulated ceiling joist

space shown in Figure 4. The joist space was sixteen inches on center

and contained a sheet rock bottom simulating a ceiling. To maintain a flow of air under the ceiling as would exist in an actual building,

the ceiling joist arrangement was supported above the floor as shown.

Recorded data are presented in Table 6. These data show close agreement

with those presented in Table 3; the maximum temperature of Table 6 is

only 8 degrees less than that of Table 3.

12
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TABLE 6

Temperatures on Three Parallel Cables Placed between

Two Layers of R-ll Insulation in Simulated Ceiling

Joist Space

TIME (MINUTES) CURRENT - A TEMPERATURE - °F

0 0 71

5 20.0 89

10 20.1 106

15 20.0 119

20 20.0 133

25 19.9 144

30 20.0 154

35 20.0 163

40 20.0 172

45 20.1 178

50 20.1 185

55 20.1 191

60 20.0 196

65 20.0 201

70 20.2 205

75 20.2 209

80 20.1 212

85 20.2 215

90 20.2 217

95 20.1 220

100 20.1 221

105 20.1 223

110 20.2 224

115 20.1 226

120 20.1 227

125 20.1 229

130 20.2 230

140 20.2 231

145 20.1 231

150 20.1 231

14
2.2 TEMPERATURES ON SINGLE CABLES IN SIMULATED ATTIC

A single length of nonmetallic-sheathed cable was tested to compare its

temperature for the same current and under the same test conditions

used for the paralleled cables previously discussed in Section 2.1.

This cable had a length of six feet which is identical to the length

of the paralleled group in Figure 1.

2.2.1 Single Nonmetallic-sheathed Cable between Two Layers of Thermal

Insulation

A current of 20-amperes was applied to the cable for a period of 95

minutes as shown in Table 7.

As in the parallel group of cables, the thermocouple was located in the

center of the cable.

A current of 27 amperes was applied to the cable for a period of 60

minutes as shown in Table 8.

2.2.2 Single Nonmetallic-sheathed Cable in Simulated Ceiling Joist

Spaces

The tests presented in this section are similar to those in previous

sections of this report, but additional temperature measurements were taken and other wiring and structural arrangements considered.

The test setup used for this experiment was a modification of preliminary setup shown in Figure 4, page 13 of this report. An adjacent

joist space was simulated on either side of the ceiling joist setup

of Figure 4. This was accomplished by extending the 2x4 supports

shown for a distance of 16 inches on either side of the joist space.

Six-foot long by 15-inch wide by 1/4-inch thick plywood sheets were placed on these supports and 15-inch wide by 3 1/2-inch thick batts

of glass fiber, R-ll, insulation with the foil facing removed, were

placed on the sheets. Insulation was also placed at the ends of the

joist space. A data acquisition system was used to record temperatures

at various time intervals in place of the temperature measuring equipment in Figure 1, page 3. However, current and voltage had to be

recorded at time intervals by hand.

Temperature data were taken every five minutes using the nonmetallicsheathed cable specimen shown in Figure 5. Although test runs would

last about 90 minutes to obtain steady-state temperature conditions,

only the steady-state temperature condition is presented in Table 9.

Figure 6 demonstrates highest temperatures as a function of steadystate currents and amount of thermal insulation.

15
TABLE 7

Temperatures on a Single Cable Placed

between Two Layers of R-ll Insulation

TIME (MINUTES) CURRENT - A TEMPERATURE - °F

0 0 74

5 19.7 89

10 20.2 102

15 20.2 111

20 20.2 119

25 20.1 125

30 20.0 130

35 20.1 134

40 20.2 138

45 20.1 140

50 20.1 143

55 20.1 145

60 20.1 147

65 20.2 148

70 20.0 149

75 20.1 150

80 20.2 150

85 20.3 151

90 20.1 151

95 20.1 152

TABLE 8

Temperatures on a Single Cable Carrying 135% of

Rated Current While the Cable was Located between

Two Layers of R-ll Insulation

TIME (MINUTES) CURRENT - A TEMPERATURE - °F

0 0 68

5 26.8 100

10 27.0 122

15 26.9 139

20 27.0 155

25 27.1 168

30 27.0 176

35 27.0 184

40 27.0 191

45 27.2 196

50 27.1 201

55 27.2 205

60 27.1 208

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200

190

180

170

160

160

140

130

120

110

100

90

80

75

: 6 ,

O THERMOCOUPLE POSITION #1 R 66 ON TOP OF CABLE & R 11 UNDER CABLE

• THERMOCOUPLE POSITION #1 R 11 ON TOP OF CABLE R 11 UNDER CABLE

THERMOCOUPLE POSITION #5 CABLE EXPOSED

5 10 15 20 25 30 35

STEADY CURRENT AMPERES

Highest Wire Temperatures as a Function of Current Applied to

Nonmetallic-Sheathed Cable Specimen of Figure 5

19
2.2.3 Single Armored Cable in Simulated Ceiling Joist Spaces

An armored cable specimen (type AC cable) was tested in open air, resting

on one layer of R-ll glass fiber insulation to obtain cable temperatures.

See Figure 7 for specimen description. For comparison, temperatures were

obtained with the cable surrounded by insulation, with R-66 on top of the

cable and R-ll underneath the cable. The results are shown in Table 10.

In this test, it was decided to surround the outlet boxes with insulation

even though this would not ordinarily be done. An outlet box could

become inadvertently covered in an attic space when retrofitting with

additional insulation for energy conservation.

2.2.4 Axial Heat Conduction Along Partially Thermally Insulated Branch

Circuit Wiring

A branch circuit cable can pass through relatively cool inside wall stud

spaces and enter attic spaces where the cable can be covered by thermal

insulation. Will that portion of the cable in the uninsulated inside

wall conduct enough heat away from the portion of the cable in the attic

to significantly reduce attic cable temperatures? Tests in this section

attempt to answer this question.

Previous tests have been performed without electrical devices connected

to lengths of cable in open air extending from lengths surrounded by

building insulation. It was judged, based on calculation, that the heat

transfer along the length of conductors of nonmetallic-sheathed cable

(NMSC) #12 AWG would be small and have little effect on temperatures of

wiring surrounded by thermal insulation. However, to confirm this by

experiment, the setup of Figure 8 was constructed. Plan view "A" of this

figure shows the specimen of Figure 5 surrounded by insulation within

the simulated joist space. Plan view "B" of Figure 8 shows a nine-foot

addition of nonmetallic-sheathed cable to the single length shown in plan

view "A". The nine-foot length of cable was folded under the insulation

as shown in plan view "C". A current of 27 amperes was applied to the

specimen in each plan view. The results are shown in Table 11. As seen,

the temperatures at all thermocouple positions 3 through 8 on the single

length of cable were substantially unchanged by the addition of nine feet

of cable. However, thermocouple positions 1 and 2 on the single cable

show a significant drop in temperature with the addition of cable.

Because positions 1 and 2 are close to the end of the setup and subjected

to cooling by ambient air, it was judged that the drop in temperature

at position 1 and 2 was caused by heat loss from the surface of the additional nine feet of cable.

Figure 9 demonstrates that the temperature of the single cable shown in

plan view "A" of Figure 8 exceeds the service temperature (140°F) of the

cable for 20 minutes after the current to the cable had been shut off.

Figure 9 is the cooling curve for both plan view "A" and plan view "B".

This curve suggests that the effect of the additional cable of plan view

"B" on cooling the cable of plan view "A" is small.

20
2

FT.

LENGTH

OF

NMSC

#12AWG

2-CONDUCTORS

WITH

GROUND

Qu UJ 0 . 1 *

t— CD

Figure 7. Armored Cable Specimen

21

TO

POWER

SUPPLY

SEE

FIGURE

1
TABLE 10

Steady-State Temperatures on Armored Cable in Open Air

and Covered with Thermal Insulation at 20 A and 27 A

Temperatures - °F TtiERMOCOUPLE # Thermocouple Position In Ope n Air R-66 over & R-ll Over

20 A 27 A 20 A 27 A

1 On bare "black" wire in outlet box 107.4 134.2 129.5 161.2

2 On outlet box end 87.2 98.2 110.3 127.9

3 On armored cable sheath 95.9 114.8 127.0 164.1

4 On armored cable sheath 98.3 119.1 130.3 171.6

5 On armored cable sheath 105.7 132.6 129.2 167.5

6 On outlet box end 97.7 117.8 123.7 152.2

7 On bare "black" wire in outlet box 116.7 115.4 140.8 182.5

8 On nonme tallic-sheathed cable sheath 84.4 94.0 120.6 146.7

9 Between the insulation and sheet rock 73.3 74.1 80.1 81.4

10 Top surface of the building insulation 72.7 72.4 74.0 73.3

11 Center inside joist space end 71.9 72.1 74.7 73.6

12 Center inside joist space end

(power input end) 72.0 72.0 76.9 76.9

13 Center of right side joist

(facing power end) 72.2 72.4 75.0 74.4

14 Center of left side joist

(facing power end) 72.5 74.3 91.5 95.5

15 Ambient air temperature 3" above the

center of the joist space 72.1 71.8 72.0 71.2

16 On simulated sheet rock ceiling

directly under thermocouple #9 72.4 72.5 76.0 74.7

22
THERMAL INSULATION

DETERMINE EFFECT ON THERMOCOUPLE REAOINGS 1 18

Figure 8. Extended Cable Test Setup

23
1

2

3

4

5

6

7

8

9

10

11

12

13

14

13

16

17

18

19

TABLE 11

Effect of Additional Cable Extending into Room Temperature Air on Cable

Temperatures Under Thermal Insulation when the Current was 27 A

Thermocouple Position

On the bare wire

On the sheath above thermocouple #1

On the bare wire

On the sheath above thermocouple #3

On the bare wire

On the sheath above thermocouple #5

On the bare wire

On the sheath above thermocouple #7

Between the insulation and sheet rock

Top surface of the building insulation

Center inside joist space end

Center inside joist space end

(power input end)

Center of right side joist

(facing power end)

Center or left side joist

(facing power end)

Ambient air temp. 3” above the

center of the joist space

On simulated sheet rock ceiling

directly under thermocouple #9

2* from connection on extended cable

4' from connection on extended cable

Single Cable

Additional

Cable in Air

Additional

Cable in

Insulation

228. 2°F 169. 7°F 172. 6°F

223.6 168.8 171.7

222.4 223.2 223.6

221.5 221.8 222.2

211.0 211.4 212.1

206.4 207.1 207.7

158.6 154.3 154.7

152.0 149.6 150.3

86.7 87.0 86.7

72.7 72.4 72.7

73.5 74.4 73.5

77.7 79.6 78.0

75.3 82.4 81.5

110.9 96.5 96.7

70.5 70.7 71.1

73.4 73.5 73.6

- 135.0 169.6

- 95.3 163.6

_ On side wire binding screw 113.9 132.9

24
270

250

230

210

190

170

150

130

110

90

70

9.

T

5 10 15 20 25 30 35

TIME - MINUTES

Cooling of Thermocouple #4 as Shown in Table 9 with Additional

Cable in Air as Shown in Figure 8 - Planview "B"

25
2.3 DISCUSSION OF CABLE TESTS IN SIMULATED ATTIC

Figure 10 shows a comparison of the temperatures on paralleled cables

carrying rated and 135% rated current while surrounded by thermal insulation. The figure demonstrates the following:

1.

The temperatures on paralleled cables carrying rated current

of 20 A surrounded by one layer of thermal insulation reached

239°F in 150 minutes. This temperature exceeded the maximum

allowable operating temperature for nonmetallic-sheathed cable

by 99°F.

2. The temperature on paralleled cables carrying rated current

of 20 A and exposed to ambient air temperature of 72°F reached

103°F steady temperature in 40 minutes.

3. A single length of nonmetallic-sheathed cable carrying rated

current and surrounded by one layer of thermal insulation

reached 152°F in 95 minutes and exceeded the maximum allowable

operating temperature of the cable by 12°F.

4. The temperature on paralleled nonmetallic-sheathed cables carrying 135% of rated current and surrounded by one layer of thermal insulation reached 298°F in 60 minutes and exceeded the

maximum allowable operating temperature by 158°F.

5. The temperature on a single length of nonmetallic-sheathed cable

carrying 135% of rated current and surrounded by one layer of

thermal insulation reached 208°F in 60 minutes and exceeded the

maximum allowable operating temperature by 68°F.

The maximum temperatures recorded on a single length of nonmetallicsheathed cable in a simulated attic space were as follows. The data are from Section 2.2.2, Table 9 of this report. The temperature, 160°F,

developed on the cable covered with R-66 is only 11°F higher than the

temperature, 149°F, ueveloped on the cable covered by R-ll.

In Open Air & R-ll Under R-ll Over & R-ll Under R-66 Over & R--11 Under

10 A 15A 20A 10 A 15 A 20 A 10 A 15 A 20 A 27 A

81°F 92°F 105°F 90°F 118°F 149°F 94° F 122°F 160°F 228°F

26
Figure 10. Comparison of Parallel Cables and Single Cable Carrying

Rated or 135% Rated Currents and Surrounded by One Layer

of R-ll Glass Fiber Insulation Above the Cables and

One Layer of R-ll Glass Fiber Insulation Below the Cables,

Including Comparison with Cables in Open Air with One

Layer of R-ll Under the Cables

27
A branch circuit cable can pass through relatively cool inside wall stud

spaces and enter attic spaces, where the cable can be covered by thermal

insulation. Will that portion of the cable in the uninsulated inside

wall conduct enough heat away from the portion of the cable in the attic

to significantly reduce attic cable temperatures? Data presented in

Section 2.2.4, Table 11 of this report and the following summary table

indicate that significant reduction in temperature will not take place

for cable carrying 135% rated current, 27 A.

Single Cable

Additional Cable & Connections in Air

Additional Cable & Connection in

Thermal Insulation

228°F 223°F 224°F

During the armored cable test in simulated ceiling joist space, as presented in Section 2.2.3 and Table 10 of this report, maximum temperatures

occurred in the outlet box having four 8-inch long conductors and on

the cable-sheath, as shown below:

In Air

R-66

R-llover andunder

20 A 27 A 20 A 27 A

117°F 115 °F 141°F 183°F Outlet Box Wiring

98°F 119 °F 130°F 172°F Cable Sheath

Tables 9 and 10 show generally that maximum armored cable temperatures

were about 50°F cooler than maximum nonmetallic-sheathed cable temperatures. This results from heat conduction along the metal sheath.

3. TEST PROCEDURE AND RESULTS FOR CABLES AND OUTLET BOXES IN WALLS

To determine temperatures on current-carrying wiring on thermal insulated

walls and to determine whether or not "foamed-in" and "blow-in" thermal

insulation would penetrate and fill wall outlet boxes, tests were carried

28
out in three wall sections. These wall sections each contained three

stud spaces and were one-half full-size wall height or four feet high.

Generally , the construction of these walls was typical of walls in residences.

The wall sections were constructed as shown in Figures 11 and 12.

Wall "A" and wall "B” were covered with sheet rock. Wall "C" was covered

with a clear transparent plastic sheet to observe the filling process

around the cables and boxes.

The type boxes and openings for thermal insulation penetration are as follows:

(a) A gangable 2-1/2 inch deep by 3 inch long by 2 inch wide steel

box having side bracket and armored cable clamps had twenty

holes as follows:

Six 0.15-inch-diameter holes

Two #10-32 threaded holes —- Eight rectangular shaped holes, 0.1 by 0.14 inch —* Four odd-shaped holes having an estimated area of 0.04 in^

each.

O (b) A plastic box was labeled as having a volume of 20.5 in . Although this box did not have holes, it did have knockouts.

With one cable entering and another leaving through knockouts,

it is estimated that this box had about 0.15 in^ through which

insulation could enter.

(c) A gangable 3-1/2 inch deep by 3 inch long by 2 inch wide steel

box having side bracket and nonmetallic-sheathed cable clamps

had eighteen holes as follows:

-—- Eight 0.1-inch-diameter holes

Four 0.2-inch-diameter holes

Two 0.24-inch-diameter holes

Four rectangular holes, 0.75 inch by 0.1 inch

3.1 TEMPERATURES ON CABLES AND OUTLET BOXES

For a range of currents, temperatures were measured on wire binding screws (torqued to twelve inch-pounds) of duplex receptacles, on outlet boxes,

and on cables. Temperatures were obtained before filling the wall sec- tions with insulation. The walls were then filled by an insulation con- tractor (See Appendix C concerning filling precautions). Walls "A" and

"C" were filled with urea-formaldehyde (UF) and wall “B" was filled with

29
Figure 11. Backview of Wired Wall Sections

30

IK

INCH

DEEP

STEEL

BOX

WITH

AROMORED

CABLE

CLAMPS

BOX

IS

2"

WIDE X

3"

LONG
TOP

VIEW

Figure 12. Single Wall Section

31

FRONT

VIEW

SIDE

VIEW
cellulose*. The contractor indiated that the application density for

UF insulation was 2.5 lb/ft^. Final dry density would be about 0.7

lb/ft . After filling the walls, the UF had about 65 hours to dry,

at which time temperatures were obtained for comparison with currents

applied prior to filling. Results are shown in Table 12. Figure 13

contrasts temperatures on the head of a wire binding screw located

in the cellulose-filled wall for the same currents applied before and

after filling.

3.2 PENETRATION OF THERMAL INSULATION INTO OUTLET BOXES

After filling walls with insulation, the wall outlet box cover plates were removed to determine if insulation had entered the outlet boxes.

The UF foam stuck to and covered the back side of cover plates and

filled one side of each outlet box. See photograph, Figure 14. The

side of the box away from the wall stud (bracket side) contained foam

so that the foam was flush with the front edge of the box. Foam was

in tight contact with wire binding screws of each duplex receptacle

on the "black wire side." The cellulose insulation entered all boxes.

See photograph, Figure 15. The insulation was located in contact with

current-carrying elements on each side of the duplex receptacles and

extended to about three quarters of the height of the box.

The penetration of thermal insulation into electrical outlet boxes may

be in violation of Rule 370-6 of the National Electrical Code [3], This

rule requires that boxes be of sufficient size to provide for free space

for conductors enclosed in the box. The specific volume of free space

which is required depends on the size and number of conductors and other

devices in a box. The National Electrical Code Handbook [10] states

"The purpose of these provisions is to prevent the excessive crowding

of wires and splices in outlet and junction boxes."

Whether the penetration of thermal insulation into electrical outlet

boxes may cause hazards or detrimental effects on the electrical system

should be analyzed. Whether it is necessary to remove thermal insulation from electrical boxes for safety or functional purposes should be

determined. Data are needed on dielectric characteristics, increased

temperature effects, the fire hazard potential, and corrosion effects

on electrical components of such installations.

* The contractor stated that the cellulose insulation was in conformance

with Federal Specification HH-1-515C [9]. However, no standard was found

for Urea-formaldehyde-based foam insulations.

32
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Temperatures

on

Wall

Section

Before

and

After

Filling

with

Insulation

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above

center

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"B"

77.7

77.9

72.4

75.7

75.2

74.4

74.8

75.3
170

160

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140

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90

60

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24A

- Before filling

O - After filling

J I I L J I J L

10 20 30 40 SO 60 70 80 90 100 HO 120 130 140

TIME MINUTES

13. Cellulose Wall, Thermocouple Position #10, Wire Binding

Screw Temperature as a Function of Time for Constant

Currents

34
Figure 14. Penetration of Ureaf ormaldehyde Thermal Insulation

Into Wall Outlet Box

35
Figure 15. Penetration of Cellulose Thermal Insulation Into

Wall Outlet Box

36
3.3 DISCUSSION OF TESTS OF WALL WIRING SURROUNDED BY THERMAL INSULATION

The data presented here are from Section 3 and Table 12 of this report.

The maximum temperature of 163. 5°F occurred on the head of a wire binding screw in the cellulose-insulated wall at 24 amperes. At 20 amperes

this same screw reached only 133. 2°F.

The highest temperature in the UF insulation occurred in wall section "A"

with the sheet-rock cover. This temperature, 146. 6°F, occurred on the

head of a wire binding screw with 24 amperes. At 20 amperes, this same screw head was 119. 2 °F.

The low temperatures recorded for UF insulation suggest that the UF had

not dried sufficiently to reach full insulating properties. The data

presented in this report for UF were obtained 65 hours after filling

the walls

Both UF-foam and cellulose thermal building insulation penetrated outlet

boxes and filled space between the walls of the box and receptacle.

4 . SUMMARY

(a) A temperature of 298°F was measured on closely paralleled

nonmetallic-sheathed cables carrying 135% of rated current, 27A,

for one hour, and located between two layers of R-ll glass

fiber insulation simulating a ceiling joist space. See Table 4.

Also, a temperature of 239 °F was measured on thermal insulationcovered parallel cables carrying rated current, 20A, for 2 1/2

hours. See Table 3. These cable temperatures and some others

exceeded the 140°F maximum allowable operating temperature of

the Underwriters' Laboratories Standard for nonmetallic-sheathed

cable [1] and are therefore in violation of the National Electrical Code (NEC) [3].

(b) A temperature of 208°F was measured on a single length of

nonmetallic-sheathed cable carrying 135% of rated current, 27A,

for one hour and located between two layers of R-ll glass fiber

insulation simulating a ceiling joist space. See Table 8.

Also, a temperature of 152°F was measured on thermal insulationcovered cable carrying rated current, 20A, for 11/2 hours.

See Table 7. These cable temperatures exceed the 140°F maximum

allowable operating temperature of Underwriters' Laboratories

Standard for nonmetallic-sheathed cable [1] and are in violation

of the NEC.

(c) Temperatures generated on cables during the tests presented in

this report did not become high enough to ignite thermal building materials.

37
(d) The insulated wiring often resulted in high temperature in

violation of NEC—-Article 310-9 which states: "No conductor

shall be used under such conditions that its operating temperature will exceed that specified for the type of insulation involved*

(e) Both UF insulation and cellulose insulation can penetrate

and fill outlet boxes and contact screws of duplex receptacles contained in the boxes. This also may be in violation

of the NEC.

5 . RECOMMENDATIONS

The work presented in this paper indicates a need for a comprehensive

study of temperatures that may develop on residential electrical wiring

covered by thermal insulation. The recommended study should provide

information concerning the potential for electrical ignition of building insulation or proximate combustibles. Evaluation and analyses of

test data should provide means for consideration of performance solutions and guide criteria to prevent identified problems.

The study should also include determination of the potential for toxic

gases/vapor emissions from electrical wiring at operating temperature

and/or from surrounding thermal insulation.

The following briefly summarize some research tasks which should be

undertaken

(a) Field investigations of fire incidents known or suspected to

have been started by electrical systems surrounded by thermal

insulation should be carried out in order to better understand

the problem(s).

(b) Temperature measurements on wiring in buildings (dwellings)

should be carried out with various amounts/types of thermal

insulation, using a range of electrical currents and ambient

temperature conditions.

(c) Attempts to correlate the field data via analysis of thermal

conduction and convection should be undertaken.

Laboratory investigations should include:

(1) Long-term cyclic tests of cables including cycling at slightly

higher than rated currents while surrounded by thermal building

insulations of various types are needed to determine if electrical insulation will fail or cause hazards. Also, during these

tests, connection corrosion and/or chemical reaction between

electrical insulation and thermal insulation should be studied.

38
The performance of overcurrent devices and ground fault circuit

interrupters should be included in cognizance of the operating

requirements of overcurrent devices.

(2) Wire temperatures in thermally-insulated, full-scale structures

or simulated structures with various wiring configurations,

devices, and wiring methods should be studied under controlled

environmental chamber conditions with various simulated electrical loads. Such data are needed for establishment of

temperature/ loading relationships for use in mathematical modeling and in the establishment of performance criteria.

(3) Because the service temperatures of residential branch circuit

wiring (usually 60°C, 140°F) appear to exceed the service temperatures of some building thermal insulations, a study should

be carried out to determine wiring temperature effects on building insulation.

There appears to be uncertainty among various literature sources concerning the maximum service temperature to which ureaformaldehyde-based foams can be subjected [11]. The maximum

service temperature has been given as low as 120°F and as high as 210°F.

Glass-fiber insulation of residential type is for use at ambient

temperatures [6], The definition of ambient temperature was

not found in the standard [6] and it is not known if the

maximum operating temperature of wiring in residences, 140°F,

would be considered "’ambient" temperature.

Cellulose insulation has a maximum service temperature of 180°F.

The temperature for cellulose was given on the insulation package of a manufacturer, but the temperature was not found in

the standard [9],

(4) Investigations should be made to determine whether it is necessary to remove thermal insulation from electrical outlet boxes

(See Section 3.2). Included should be the dielectric resistance

and high voltage withstand tests for receptacles and switches

when such devices and wiring are located in outlet boxes con- taining building thermal insulation. Such tests should be

made under various environmental conditions of temperature

and humidity.

(5) The possibility of arcing and subsequent tracking in thermal

insulation should be investigated.

(6) The heating effects resulting from loose connections should be

investigated to determine short-term and long-term effects [12].

39
(7) Failure modes in electrical circuits should be investigated for

impact on thermal insulation [13-15],

40
6 . REFERENCES

1. NONMETALLI C- SHEATHED CABLE, UL 719, Underwriter's Laboratories, Inc.

June 3, 1974.

2. ARMORED CABLE, UL 4, Underwriter's Laboratories, Inc., October 2,

1974.

3. NATIONAL ELECTRICAL CODE, National Fire Protection Association,

1975.

4. MAKING THE MOST OF YOUR ENERGY DOLLARS IN HOME HEATING & COOLING,

U.S. Department of Commerce, National Bureau of Standards.

5. COPPER-WIRE TABLES, HANDBOOK 100, United States Department of

Commerce, National Bureau of Standards, February 21, 1966.

6. FEDERAL SPECIFICATION HH-1-521E, Insulation Blankets, Thermal

(Mineral Fiber, for Ambient Temperatures) (7-24-72).

7. MOLDED-CASE CIRCUIT BREAKERS AND CIRCUIT- BREAKER ENCLOSURES, UL 489,

Underwriter's Laboratories, Inc., November 1, 1972.

8. PLUG FUSES, UL 198.5, Underwriter's Laboratories, Inc., May 30, 1973

9. FEDERAL SPECIFICATION HH-1-515C, Insulation Thermal (Loose-Fill for

Pneumatic or Poured Application): Cellulose or Wood Fiber (4-12-76)

10. National Electrical Code Handbook, Eleventh Edition (1962) by

Arthur L. Abbott and Frank Steka (McGraw-Hill).

11. UREA-FORMALDEHYDE-BASED FOAM INSULATIONS: An Assessment of Their

Properties and Performance, Rossiter, Jr., W.J., Mathey, R.G.,

Burch, D.M., and Pierce, E.T. NBS Technical Note 946, July 1977.

12. EXPLORATORY STUDY OF GLOWING ELECTRICAL CONNECTIONS, Meese, W.J.,

and Beausoliel , R.W. , NBSIR 76-1011, also BSS 103, July 1977.

13. SURGE VOLTAGES IN RESIDENTIAL AND INDUSTRIAL POWER CIRCUITS, by

Francois D, Martzloff, IEEE Transactions of Power Apparatus and

Systems, Vol. PAS-89, No. 6, July/ August 1970.

14. EXPERIMENTAL DETERMINATIONS OF TEMPERATURES AND POWER LOSSES AT THE

ELECTRICAL CONNECTIONS OF SOME DUPLEX RECEPTACLES, Burns, G.W.,

Scroger, M.G., Beausoliel, R.W., Meese, W.J., NBSIR 77—1380, April

1978.

15. ANALYSIS OF CODE RESTRICTIONS ON THE USE OF NONMETALLIC-SHEATHED

CABLE, Meese, W.J., and Beausoliel, R.W. (NBSIR and BSS in review

October 1977).

41
16. DIRECT AND ALTERNATING CURRENTS, by E.A. Loew (McGraw-Hill Book

Company, Inc., 4th ed., 1954.

42
APPENDIX A

CALCULATION OF WIRE TEMPERATURE BASED ON INCREASE

IN WIRE RESISTANCE WITH TEMPERATURE

Experiments have shown that over a certain practical temperature range,

the resistance of pure copper varies directly with the temperature as shown in the following figure [16],

TEMPERATURE “C

As shown, over a range copper resistance appears to be linear with a zero resistance intercept of -234. 5°C. The temperature range used in

this work was from 20°C to about 150°C. Over this range a straight line

law is usually assumed for resistance variation with temperature. The

figure above shows that the rule of similar triangles may be applied

to compute R ? of a conductor at any temperature t

2 providing that R^

at t

1 is known, and also that the temperature intercept of the copper

conductor is known. From similar triangles,

R

2 (234.5 + t 2

) R^ ~ (234TTTTJT

Quantities such as (234.5 + t

x

) and (234.5 + t

2

) can be considered

"apparent absolute temperature [16]".

R

2 (234.5 + t ±

) - 234.5

R

1 43
For the work presented in this report, Rj for the wire specimens was determined with a kelvin bridge ohmmeter and t, was determined from

initial wire temperature measurement. R

2 was determined from the final

recorded current and voltage drop across the specimen. The following

presentation in Table 13 shows fair agreement between measured temperatures and calculated temperatures. As a general rule, calculated temperature was lower than measured temperature. This is judged to be the

result of variation in the tightness of the thermal insulation against

the specimen; and also, due to some minimal effect of heat transfer

along the conductors and venting of ambient air, perhaps through voids

between insulation batts and wiring. Temperatures in the following

Table 13 were taken on electrical insulation of cable jacket. Therefore, some disagreement can be attributed to this. However subsequent

tests have indicated that temperature drop through the electrical

insulation was only several degrees F.

Table 13. Comparison of Calculated and Measured Temperatures

Table No.

In This

Report

Maximum

Temperature

Maximum

Temperature

Calculated

Final

Current

Final

Voltage

Drop

Initial

Temperature

Initial

Resistance

( °F) ( °F) (Amperes) (Volts) ( °F) ( Ohms

)

2 103 109 20.3 1.266 72 0.0577

3 239 206.2 20.3 1.510 74 0.0579

4 298 274.6 26.8 2.23 71 0.0577

44
APPENDIX B

CHEMISTRY TESTS AT NBS FOR GASES AND/OR VAPORS

FROM HEATED CABLES AND THERMAL INSULATION

The Bioorganic Section of NBS's Analytical Chemistry Division attempted

to determine if noxious fumes were given off when nonmetallic-sheathed

cable (NMSC) and thermal insulation were heated to greater than 200°F.

The preliminary tests of small samples were inconclusive. The test

procedure, results and conclusions are summarized below.

The analytical scheme involved heating the cable and insulation in a closed system, trapping any volatile organics on a liquid N

2 cold finger

for subsequent mass spectrometric identification. The apparatus built

for trapping the compounds is shown in the sketch.

A 6 cm piece of NMSC was placed into the vessel between small pieces of

insulation. The stopcock was opened and the temperature in the vessel

raised to ^200°C with heating tape. The first analysis involved bringing the U-tube up to room temperature and sampling the headspace vapor

in the U-tube. A gas withdrawn was injected into the Heated Expansion

Volume on a Hewlett Packard 5930A Mass Spectrometer. The sample was

then passed through a leak into the ion source where electron impact

spectra (70ev) were scanned repetitively every three seconds (m/e34-

400). The spectra were stored on magnetic disk (HP5933A Data System)

where they were available for subsequent interpretation.

In a second experiment, the U-tube was connected directly to the Heated

Expansion Volume with the use of a 26-gauge needle and an adapter. The

sample was leaked through a valve into the ion source of the mass spectrometer where electron impact spectra were again recorded under com- puter control. In order to aid the transfer of volatile components

through the small conductance of the 26-gauge needle, heat was applied

to the U-tube with a hot air gun as the spectra were being recorded.

Mass spectra recorded during each run showed no significant peaks other

than m/e40 argon and 44 carbon dioxide which arose from the air background in the Heated Expansion Volume and/or the ion source. These

preliminary experiments indicate that additional steps are necessary

45
to concentrate the evolved gases prior to mass spectrometric identification. Also, some sort of fractionation or separation step will be

required in order to resolve the expected mixture of gases into pure

components prior to introducing them to the mass spectrometer.

46
APPENDIX C

PRECAUTIONS DURING INSTALLATION OF

"FOAMED-IN" AND "BLOWN-IN" THERMAL

INSULATION

There is a considerable quantity of water in ureaf ormaldehyde (UF)

based foam thermal insulation; consequently, wet foam may subject the

applicator to possible electric shock. The risk of electric shock to

the applicator should be analyzed and, if necessary, adequate safety

precautions developed. The potential hazard of electric shock to

installer by possible penetration of wiring while drilling holes into

building walls for insulation application should be analyzed. Whether

precautions are necessary such as turning off electric power during

installation should be determined. Also, the possibility of damage to

wiring by drilling holes should be determined.

47

NBS-U4A (REV. 7-73)

U.S. PEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 78-1477

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

EXPLORATORY STUDY OF TEMPERATURES PRODUCED BY SELF-HEATING

OF RESIDENTIAL BRANCH CIRCUIT WIRING WHEN SURROUNDED BY

THERMAL INSULATION

5. Publication Date July 1978

6. Performing Organization Code

7. AUTHOR(S)

R. Beausoliel , W. Meese and L. Galowin

8 . Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 462 1204

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Joint NBS/Department of Energy

Washington, D.C. 20461

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less tactual summary ot most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The purpose of the work presented in this paper was to make preliminary determination

under laboratory conditions of temperatures that might develop on residential

electrical wiring covered by thermal insulation when carrying rated currents or currents slightly above rated values.

The results show that temperatures on conductors surrounded by thermal insulation can greatly exceed the maximum service temperatures for the wire insulation. Results also

show that some types of insulation currently used to retrofit buildings may fill wall

outlet boxes and contact the current carrying elements and connections of duplex

receptacles.

This study indicates need for a concentrated study of temperatures that might develop

on residential electrical wiring covered by thermal insulation.

17. KEY WORDS ("six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Branch circuit wiring; electrical fires; heat generation in

receptacles; insulated buildings J overheating conductors; residential branch circuit

wiring; thermal insulation and electrical wiring.

18. AVAILABILITY ^.Unlimited

[_" i For Official Distribution. Do Not Release to NTIS

rn Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SO Cat. No. CI3

fx~| Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

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(THIS REPORT)

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21. NO. OF PAGES

52

22. Price

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USCOMM-DC 2904 2- P74


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