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NAT'L INST. OF STAND & TECH R.I.C.

AlllDS OMETSE

NBSIR 79-1912

Temperature Measurement on

Operating Surface Mounted

Lighting Fixtu res

P. Michael Fulcomer

Product Safety Technology Division

Center for Consumer Product Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

September 1979

QC100

056

Sponsored by:

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

Jianontf BurtM

DEC 1 2 1979

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NBSIR 79-1912

TEMPERATURE MEASUREMENT ON

OPERATING SURFACE MOUNTED

LIGHTING FIXTURES

P. Michael Fulcomer

Product Safety Technology Division

Center for Consumer Product Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

September 1979

Sponsored by:

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

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

Luther H. Hodges, Jr., Under Secretsry

Jordan J, Baruch, Assistant Secretary tor Science and Technoiogy

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Director
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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

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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 (Ibjj^) = 0.4535924 kg

Length 1 inch = 0,0254 meter (m)

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TEMPERATURE MEASUREI^ENT ON OPERATING

SURFACE MOUNTED LIGHTING FIXTURES

P. Michael Fulcomer

ABSTRACT

Potentially hazardous temperatures may result from adding thermal

insulation in the attic above surface mounted incandescent lighting

fixtures and/or operating these fixtures with lamps of higher wattage than

specified. This study was concerned with the range of temperatures

generated (1) within the fixture, (2) within the electric junction box

associated with the fixture and (3) on the adjoining ceiling and attic

surfaces.

Test results indicate that the addition of minimal insulation

(equivalent to R-1 1 ) over a surface mounted lighting fixture which contains

two or more rated lamps, is likely to cause normal household branch circuit

sugply wiring associated with the fixture to operate above its specified

60 u temperature rating. Overlamping (using lamps of higher wattage than

specified for the fixture) and/or additional load current flowing through

the branch circuit wire will cause even higher supply vvire temperatures.

With all three conditions present (i.e., insulation over the fixture,

overlaraping, and an additional 15 ampere load current flowing through the

supply wire), the tests indicate that the temperature of associated branch

circuit wiring will exceed 30^0 for a one lamp fixture and 100°C for

fixtures with two or more lamps.

Key Words: Surface mounted incandescent lighting fixture; thermal

insulation; overlamping; hazardous temperatures; branch

circuit wiring; electrical junction box; load current;

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TEMPERATURE MEASUREMENT ON OPERATING

SURFACE MOUNTED LIGHTING FIXTURES

Introduction

Rising utility rates and the decreasing supply of available energy

have resulted in efforts to make both new and existing homes more energy

efficient. For many older homes, one of the most cost effective ways to

reduce energy consumption is to increase the depth of thermal insulation in

the attic. When energy was cheap and plentiful, the extra cost of

increased insulation was greater than the cost of energy saved over a considerable period of time, but this is no longer true. Accordingly,

insulation is now an attractive means of saving energy economically.

Unfortunately, the addition of thermal insulation over the electrical

wiring and lighting fixtures of older homes may cause problems related to

the safety of the household electrical system.

The Consumer Product Safety Commission (CPSC) is currently

investigating various aspects of this potential household electrical system

safety problem. This report is based upon work funded by CPSC to address

one facet of the problem. Potentially hazardous temperatures can result

from (1) adding thermal insulation in the attic above surface mounted

incandescent lighting fixtures and/or (2) operating these fixtures with

lamps of higher wattage than specified. This study was concerned with the

range of temperatures generated (1) within the fixture, (2) within the

electric junction box associated with the fixture and (3) on the adjoining

ceiling and attic surfaces. A companion report, entitled Temperature

Measurement on Operating Recessed Lighting Fixtures, NBSIR79-1913, concerns

potentially hazardous temperatures which may result from adding thermal

insulation in the attic above recessed incandescent lighting fixtures.

Test results presented herein indicate that the addition of minimal

insulation (equivalent to R-1 1 ) over a surface mounted lighting fixture

which contains two or more lamps, and which is operating with rated bulbs,

is likely to cause normal household branch circuit^supply wiring associated

with the fixture to operate above its specified 60^0 temperature rating.

Overlamping (using lamps of higher wattage than specified for the fixture)

and/or additional load on the branch circuit wire will cause even higher

supply wire temperatures. Either over lamping or additional load current,

when combined with minimal insulation over the fixture, may also cause the

temperature of branch circuit wire associated with a one lamp fixture to

exceed a 60^0 rated value.

With all three conditions present (i.e., insulation over the fixture,

overlamping, and an additional 15 ampere load current flowing through the

supply wire), the tests indicate that the temperature of associated branch

circuit wiring will exceed 80 u for a one lamp fixture and 100 C for

fixtures with two or more lamps.
- 2 -

General Method

To determine representative temperatures generated by surface mounted

lighting fixtures, four such fixtures were individually installed in a controlled environment mock-up of a ceiling, complete with an overlying

attic section. The four fixtures ranged from a one-lamp flush mounted (no

space between the ceiling and the fixture enclosure) model to a four-lamp

semi-flush mounted model. In the semi-flush mode, there is some space

between the top of the fixture enclosure and the ceiling.

Each fixture was tested: (1) with no insulation in the attic; (2)

with glass fiber batts equivalent to R-1 1 ; and (3) with glass fiber batts

equivalent to R-33 installed in the attic. Under each of these conditions,

temperature measurements were made with and without an additional 15 ampere

current flowing through the associated branch circuit supply wiring. The

above tests were made with rated 60 watt lamps and also under two

conditions of overlamping, using 100 watt and 150 watt lamps.

Temperatures were recorded at various points on the fixture, the

fixture mounting hardware, the associated ceiling electric box, the nearby

attic and ceiling surfaces, and on the fixture and supply wires. The

pertinent steady state temperatures obtained for each fixture are included

in chart form with this report along with dimensional diagrams showing the

size of and installation details for each fixture.

Test Assembly Description

Tr.e test assembly consists of a 4 foot by 4 foot section of 1/2 inch

sheetrock ceiling nailed to 2 X 5 inch wood joists spaced 16 inches on center. 7ne lighting fixture under test was mounted equidistant between

joists in the center of the test assembly using standard hardware. To

reduce convective heat loss due to higher than normal air flow in the

laboratory, the test assembly includes sides which extend 12 inches above

and 24 inches below the ceiling.

Electrical connections to the fixture were made in a 3 1/2 inch by 1 1/2 inch ieep ceiling box attached beneath a 2 X 4 which was fastened

between the center two 6 inch joists. The fixture was mounted to the

ceiling by machine screws which fastened into the ceiling box.

Supply wiring to the fixture was non-metallic sheath cable with two

1/^14 copper conductors and a separate ground (type XM, 1^-2 wioh ground).

Wiring was arranged so that the cable carrying the branch circuit current

passed ohu'ough the ceiling box into which the light fixture was connected,

Addioional lead could be put on the branch circuit wiring by connecting a 1500 want electric space heater to the circuit through a variable voltage

transformer. Current drawn by the space heater was adjusted by changing

the tran.s former output.
- 3 -

Lighting Fixtures Description and Installation

Dimensional diagrams of the four surface mounted lighting fixtures

tested are shown in figures 1 through 4; all are rated for 60 watt lamps.

Fixture A contains two lamps, fixture B three lamps, fixture C four lamps,

and fixture D one lamp.

Both fixtures A and D were enclosed lamp types, designed for mounting

flush to the ceiling. Fixture B was labeled as "flush mounted" on its

packaging material, but both it and fixture C were actually designed to be

mounted semi-flush, with the fixture frame separated from the ceiling. No

instructions accompanied fixture B, however, and with minor changes in

installation procedure, it could be mounted flush, thereby causing

extremely high temperatures in the electrical box above the fixture. This

will be discussed in greater detail later.

The canopies of fixtures A and D measured 8 1/2 inches and 6 3/4

inches in diameter, respectively. When installed, the upper edges of the

canopies fit flush against the ceiling. In each case, the fixture attaches

directly to the ceiling box above by two machine screws. For fixture D, a separate crossbar is connected between the outlet box ears, and the canopy

is screwed to the crossbar. A glass cover, vhich completely encloses the

lamps, is attached to each canopy by means of three small hand-tightened

screws spaced equidistantly around the lower edge of the canopy. When

installed, the overall depth from the ceiling was 4 3/4 inches for fixture

A and 4 1/4 inches for fixture D.

Both fixtures A and D are designed so that there is a space

approximately 3/4 inch deep between the ceiling surface and the canopy

base. This space (not visible once the fixture is installed) was probably

intended for a glass fiber insulation pad, equal to the diameter of the

canopy and approximately 1 1/4 inches thick, which was supplied with each

fixture. However, the installation instructions furnished with the

fixtures made no mention of the insulation pad nor how it was to be

installed. Therefore, testing of the fixtures was done both with and

without the insulation pad installed in the canopy base.

Fixtures B and C are similar in the way that they are attached to the

ceiling (see figures 2 and 3). The 4 1/2 inch diameter canopy of each is

screwed to the electrical ceiling box via a crossbar which is connected

between the box ears. The socket structure of each (for fixture B, three

horizontally oriented sockets spaced 120 degrees apart, and for fixture C,

four horizontally oriented sockets spaced 90 degrees apart) is attached to

the canopy by a nut tightened down on the socket structure center post

which protrudes up through a hole in the canopy center. The side frame of

each fixture is supported by a glass bezel which is attached to the socket

structure by means of a single decorative cap nut threaded onto the nipple

protruding from the lower end of the socket structure. Tae bezel for

fixture 3 is a convex opal glass 16 inches in diameter which supports a round, simulated walnut side frame. The bezel for fixture C is a 16 inch
- 4 -

square, flat glass diffuser which supports a square, simulated wood side

frame.

No fixture insulation pad and no installation instructions were

supplied with fixture 3. The fixture also had no indication of being UL

rated although it was purchased in Maryland, where UL rating is required.

The fixture was packed in a box which described it as being a ’’flush

mounted” fixture. >/hen mounted with the painted side of the 4 1/2 inch

diameter canopy facing down, however, the top of the 16 inch diameter frame was actually 3/4 inch below the ceiling surface (see figure 2). Inverting

the canopy allowed the socket structure to be raised sufficiently so that

the fixture frame could contact the ceiling and thereby constitute a true

’’flush mC'Unt.” Testing of the fixture was done in both its semi-flush and

flush mounting positions.

When installed, 60 watt lamps extended 2 1/4 inches beyond the outer

edge of the canopy of fixture B; 150 watt lamps extended 3 1/4 inches

beyond. Distance between the ceiling and the lamp surface for flush

mounting was 1 1/4 and 1 1/8 inches, respectively, for 60 and 150 watt

lamps. With the fixture mounted semi-flush, these distances were 2 1/8 and

2 inches, respectively.

Installation instructions were supplied with fixture C and a 4 1/2

inch diameter by 1 inch thick glass fiber insulation pad was attached

inside the fixture pan. When mounted according to instructions, the top of

the 16 inch square frame was approximately 2 3/4 inches below the ceiling

and the distance between the ceiling and the lamp surface was 2 1/4 inches

for 60 watt lamps, and 2 1/8 inches for 150 watt lamps. Overall fixture

depth from the ceiling was 5 1/2 inches.

Testing Procedures

Each fixture was tested with: (1) rated 60 watt lamps installed in

all sockets; (2) 100 watt lamps in all sockets; and (3) 150 watt lamps in

all sockets. Under each of these conditions, the fixtures were tested with

and without an addioional 15 ampere load current flowing through the branch

circuit supply wiring. Total lamp current, lamp voltage and branch circuit

load curreno (if any) were monitored by means of transducers connected into

the test set-up. Prior to each test, supply voltage was adjusted so that

the particular lamps installed would dissipace the total power for which

they were labeled, luring the test this adjusted voltage was held constant

by an ac voltage regulator.

All fixtures were tested under the above conditions with no insulation

in the attic and with antic insulation equivalent to R-33- In addition,

fixtures 3, C and 1 were tested with attic insulation equivalent to P-11.

The latter was achieved winh foil-backed glass fiber batts, approximately 3

V2 inches thicx, installed so that the foil side rested against the

ceiling. Tne P-33 insulation was achieved by adding two more layers of the

r^-’l oatts without a vapor barrier. The 1/2 inch unpainted sheetrock
- 5

-

ceiling, the 3 1/2 inch ceiling box, and the 2X4 crosspiece to which the

box was attached were all replaced when the next lighting fixture was

installed for testing.

Temperatures were recorded at various points (1) in the ceiling box,

(2) on the fixture, (3) on the fixture and supply wires (4) on the

surrounding upper (attic) and lower (ceiling) sheetrock surfaces by means

of #30 chrorael-alumel thermocouples connected to a programmable data

' logging device. The thermocouples were held in place by teflon tape, .003

inches thick, installed so that the thermocouple was in contact with the

subject surface and no more than partially covered by the tape.

The fixtures were tested in the order of their alphabetic designation.

Two series of tests were performed on fixture B: the first set with the

fixture mounted flush to the ceiling and the second set with the fixture

mounted semi-flush. Prior to the second test series, the position of some

thermocouples mounted on the upper and lower surfaces of the sheetrock

ceiling were changed to better relate to the location of the lamps below

the ceiling. Both attic and ceiling surface thermocouples were

repositioned at various distances out from the center of the fixture, but

either on a line which was directly over the axis of a lamp and lamp socket

combination or on a line which bisected the angle between the axes of two

adjacent lamp and lamp socket combinations.

The data logging device contained 40 input channels, of which only 25

were eventually used. Of the 25 channels, two were assigned to monitor

lamp voltage and current, one to record branch circuit load current in

excess of the lamp current, and the remaining 22 to monitor thermocouple

outputs. Three ac-to-dc transducers were used to change ac voltage and

current readings into the low voltage dc accepted by the data logger.

Fewer than 22 thermocouples were used in the tests of fixtures A and B

in their flush mounted positions. Following these two tests, themocouples

were added to measure temperature at additional locations in the ceiling

box and on the ceiling and attic surfaces. At that same time, more

specific locations for measuring ceiling and attic surface temperature were

introduced. Of the 22 points eventually monitored for temperature, five

were in the electrical ceiling box or on associated fixture mounting

hardware, three on the fixture and supply wires, five on the upper

sheetrock surface (attic), three on the lower sheetrock surface (ceiling),

one on the fixture canopy and one on the 2X4 wood support crosspiece.

Three thermocouples were used to monitor air temperature at locations

around the light fixture and one to monitor ambient room temperature.

More precise information on thermocouple location is included in the

first column of the data sheet for each figure as shown in tables 1 through

4. Where a letter symbol appears in the second column, this corresponds to

the thermocouple location indicated by an identical symbol on the

dimensional diagram for that fixture (figures 1-4). Not all locations are indicated on the diagrams.
- 6 -

The data logging device was programmed to monitor voltage, currents

and temperature every 15 minutes. Each test was^continued until none of

the recorded temperatures changed by more than rC in 3 hours or until a reliable prediction could be made of the final steady-state temperatures,

Tesrs that were started with all points at room temperature required 2 to 3

hours before temperatures reached equilibrium with no thermal insulation

above the fixture, and 5 to 9 hours with insulation above the fixture.

However, only 45 and 90 minutes (first without and then with thermal

insulation above the fixture) were required for temperatures to reach 80 to

90 percent of their equilibrium value on the supply wire, in the ceiling

electrical box and on the upper sheetrock surface (attic side).

Temperatures on the fixture wire and on the lower sheetrock surface reached

85 to 95 percent of equilibrium after only 30 and 45 minutes, respectively.

A return to room ambient temperature was not always required between

tests. Tests proceeded without a cool-down period if temperatures in the

following test were expected to be equal to or higher than those in the

preceeding test. Examples of this occurred when an external 15 ampere load

was added without changing the amount of insulation in the attic or when

insulation in the attic was increased without reducing the load. A short

cool down period was allowed when a reduction of some temperatures might be

expected under the new conditions. An example of this occurred when a noload test with insulation equivalent to R-33 in the attic followed a test

with R-1 1 insulation in the attic and a 15 ampere external load on the

supply wire. In this case, the decrease in supply wire temperature

resulting from the reduced load usually more than offset the slight

temperature increase resulting from greater attic insulation depth.

Results

The steady state temperatures recorded for each light fixture under

the various testing conditions are listed in tables 1 through 4. Table 5

is an extraction and compilation of this data to show temperatures at five

critical locations (one location is shown under two different conditions)

ftr each light fixture tested. Table 5 includes results obtained both with

ratec lamps and with higher than rated lamps installed, but except for

fixture 3, it does not include the results obtained in testing a fixture

without the fixture insulation pad in place. Reference must be made to the

individual tables for this latter data. (Table 5 includes the results of

testing fixture 3 without the fixture insulation pad in place because these

are tne only results available for this fixture. No insulation pad was supplied with fixture 3.) All listed temperatures have been corrected for

an ambient of 20 u^. Temperatures exceeding the limits specified for each

location are circled in table 5.

7ne critical temperature locations noted in table 5 and the limiting

temperatures at each location are:

1. Fixture wire insulation - 150°C maximum. None of the fixtures

tested indicate the rating of the fixture wire used. However,

*?oom ambient i^emperature sometimes varied plus or minus a few degrees rrom tne besired 2'1'^C. In suqh cases this difference was either added (if the

arrpient was less than 20'*'C), or subtracted (if the ambient was greater than

from the actual reading to arrive at the temperature listed in the table.
- 7 -

three of the four fixtures are UL rated and as such must have

fixture wire rated for at least 150°C. The wire of the non-UL

rated fixture B was similar in composition to the other three.

2. Supply wire insulation - 60°C maximum. Household branch circuit

wiring is normally of the type rated for 60 C. Neither the wire

insulation nor any of the surfaces which it may touch should

exceed this temperature. Since the wire temperature increases

if there is an external load on the branch circuit, both no-load

and load conditions were tested and are included in table 5.

3. Attic and ceiling sheetrock surfaces - 90^0 maximum. Section

410-5 of the 1978 National Electric Code states that "Fixtures

shall be so constructed, or installed, or equipped with shades

or guards that combustible mgterial will not be subjected to

temperatures in excess of 90^0". Either the thermal insulation

that touches the attic side of the sheetrock or the surface

finish applied over the ceiling side of the sheetrock might be

combustible.

The data contained in table 5 provides the basis for statements in the

Summary section.

Table 1 for fixture A does not include all the same data that the

other tables do because the decisions to include tests involving thermal

insulation equivalent to R-1 1 , to reposition attic and ceiling

thermocouples, and to eliminate joist temperature measurements were made

during the testing of fixture B. Table 1 does show, however, that the

temperaturg on the branch circuit supply wire inside the ceiling box

reached 70^C when operated with rated lamps installed in the fixture and

with thermal insulation equivalent to R-33 above. Results from testing the

other three fixtures showed that most of the temperature increase due to

the addition of thermal insulation above a fixture is evident with an insulation thickness equivalent to R-1 1 . The difference in temperatures

with a thictoess equivalent to R-1 1 and one equivalent to R-33 is usually

less than 5 C, hence the temperature of branch circuit wire associated with

fixture A would exceed its specified rating even with minimal thermal

insulation equivalent to R11 over the fixture.

The insulation pad reduces lamp heat transferred to the parts above

it, but increases the heat to parts below the pad. Therefore, temperatures

in the ceiling box are somewhat lower with the fixture insulation pad

installed, while temperatures on the fixture wire are actually somewhat

higher

.

The temperature of the fixture wire in fixture A exceeded 150*^0 when

100 watt lamps were installed and fixture insulation was in place. This

was true with or without thermal insulation overhead. With the fixture

insulation pad in place, the addition of attic thermal insulation caused

only minor increases in fixture wire temperature.
- 8 -

For fixture 3, temperatures in the ceiling electrical box exceeded

60 u even under the least stringent conditions, with the fixture mounted in

the less hazardous semi-flush position, operating with rated lamps, and

with ^ thermal insulation overhead. Addition of minimal thermal

insulation caused temperatures in the box to exceed 90 u. Use of 100 watt

lamps (a real temptation with this fixture because of the poor light

transmission through the opal glass bezel) resulted in temperatures over

120 u in the ceiling box and up to 140°C on the ceiling surface above the

lamps.

Flush mounting of fixture 3 caused temperatures 15 to 30^0 higher than

those under comparable conditions with semi-flush mounting. Data for the

fixture when flush mounted and overlamped with 150 watt lamps is not

complete due to the occurrence of a short circuit failure ig the ceiling

electrical box. The high temperatures in the box (over 200^0) caused

supply wire insulation to become brittle and subsequently crack, then fall

away from the conductor at various locations. A resulting short circuit to

ground caused the ground fault interrupter, which was installed in series

with the electrical supply, to open and thus terminate the test. Less than

65 hours of fixture testing time had elapsed before the wire failure.

Fixture C, with rated lamps installed and R-1 1 thermal insulation

overhead, caused temperatures to exceed 70°C on the supply wire and in the

ceiling electrical box. Over lamping with 100 watt Igmps combined with R-11

insulation overhead caused temperatures to exceed 90 C at these same locations. Although these temperatures are 30 to 35^0 lower than those

'Which resulted in fixture 3 under similar conditions, the temperatures are still considerably above the specified safe values.

While the lamps of fixtures 3 and C are located the same distance

from the ceiling (see figures 3 and 4), the frame of fixture C is farther

from the ceiling. The lower frame position presumably allows greater

inflow of the cooler surrounding air to fixture C. Also, the lack of

fixture insulation for fixture 3 causes temperatures on the supply wire and

in the ceiling box for that fixture to be 3 to (C higher than they

otherwise would have been.

A fixture wire rating of 150^C was not exceeded under any conditions

for fixture C. Attic and ceiling surface temperatures were exceeded under

overlamped conditions with thermal insulation above.

Fixture D, a one lamp fixture, caused no serious over-ratings when

operated 'with its rated 60 watt lamps. The unloaded supply wire

temperat’ures did not exceed 60^0, even with R-33 thermal insulation

overhead. 'When loaded with an additional 15 amperes, however, the supply

wire reached 69 u with R-33 thermal insulation. Overlamping in combination

with thermal insulation and additional load, caused temperatures on the

supply wire and on the ceiling box to exceed 80 C. Specified "safe"

fixture wire and ceiling or attic temperatures were not exceeded under any

conditions
- 9 -

Summary

These test results on surface mounted lighting fixtures indicate the

following:

1. Addition of minimal insulation (equivalent to R-1 1 ) over a surface mounted lighting fixture containing two or more lamps

and operating with rated bulbs, is likely to cause normal

household branch circuit wiring associated with the fixture to

operate above its specified 60°C temperature rating.

2. Addition of minimal insulation (equivalent to R-11) over a surface mounted lighting fixture operating with two or more 100

watt lamps instead of the rated 60 watt lamps is likely to cause

temperatures in excess of 90^0 on the associated branch circuit

wiring. Temperatures will likely exceed 60 C for a one lamp

fixture under the same conditions.

3. Most of the temperature increase due to addition of thermal

insulation above a surface mounted lighting fixture is evident

with an insulation thickness equivalent to R-11. Increase in

insulation thickness from an equivalence of R-11 go one of R-33,

causes only a minor increase (usually less than 5 C) in

temperatures measured in and around the lighting fixture.

4. Addition of a 15 ampere load current on the branch circu

supply wiring increases the wire temperature by 15 to 20

the larger increase occurring for wire covered by thermal

insulation.

it

C, with

5. The associated branch circuit wiring is likely to be the first

component of a surface mounted lighting fixture to exceed its

rating. (For the three multi-lamp fixtures tested, the 60°C

rating for this wire was exceeded even when these fixtures were

operating with rated lamps and no thermal insulation above

them.

)

6. For surface mounted fixtures containing more than one lamp,

overlamping (using lamps of higher wattage than specified for

the fixture) combined with minimal insulation over the fixture

is likely to cause fixture wire temperature and attic and

ceiling surface temperatures to exceed their rated "safe”

values.

Comment

The test results summarized above are based on the testing of four

different surface mounted lighting fixtures. These four appeared to be

representative of fixtures available at the time this investigation was

initiated in 1978, Sufficient information was obtained from the tests to

1
- 10 -

indicate that household branch circuit wiring is likely to operate above

its present 60^C temperature rating when associated with surface mounted

fixtures over which minimal thermal insulation has been placed or in which

higher wattage lamps than specified are used. Further testing is

necessary, however, to (1) establish the upper limit that the wire

temperature may reach when used with various fixtures and conditions of

operation, and (2) to determine whether wire currently rated for 60°C might

actually be operated safely at somewhat higher temperatures. This

information wo^ld provide a basis for future decisions involving either (1)

raising the 60^0 rating for currently used wire, (2) requiring the use of

wire presently rated for 75, 90 or 120°C, or (3) some combination of the

first two.

Testing should also be done on surface mounted fixtures which meet a recently imposed "insulated ceiling" (or IC) specification by Underwriters’

Laboratories. This type of fixture was not available during the period

when tests were in progress for this report.
FLUSH MOUNT

TWO LAMPS RATEn. FOR SO WATTS MAX.

FROM SUPPLY

igurs 1. Dimensional Diagram of Fixture A Installation.

A small circle accamoanied by a letter inci cates a thermocouole location, 'lot all locations are shown,

the latter identi*-'es tempe»-afjre data from -acie 1 which cor'^esponos co t.he location shown.
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THflEE LAMPS RATH) FOfl SO WATTS MAX.

ROM SUPPLY

TO REMAINOEROF 3RANCH

CIRCUIT

TO LIGHT SWITCH

~:gur9 2. SiTiensional jiagram of Fixture 3 '.nsta ’ lation

.

A small tlrcls accomoam'afl ay a lettar inai cates a themocoLiDi e locat'on. .'lot all 'acatlons are snown.

The letter 'centifles tamoerature cata '•on 'aala 2

•<n1 cr. torresocnCs to t.he location shewn.

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SEMI-RUSH' MOUNT

FOUff LAMPS RATED FOR 60 WATTS MAX.

Figure 3. Dimensional Diagram of Fixture C Installation.

A small circle accomoanied by a latter indicates a thermocouple location, 'lot all locations are shown,

“he letter identifies temoerature data "rom “able 3 which corresponds to the location shown.
iKI* .

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\

FLUSH MOUNT

ONE LAMP- RATHn FOR SO WATTS' MAX.

FRON^ SUPPLY

TO REMAINDER

OF BRANCH

CIRCUIT

TO LIGHT SWITCH

Figure 4-. Dimensional Diagram of Fixture D InsraMation.

A small circle accompanied by a letter indicates a thermocQuole location, 'lot all locations are snown.

The latter identifies temoerature data f'^'orn Table ^ which corresponcs to the location shown.
^£4

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' 3

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TABLE 1. TEMPERATURE DATA FOR FIXTURE A Fixture rated for two 60 watt lanps

Temperatures in are listed in the table. Readings have been corrected for an ambient room temperature of 20°C, Top reading made with 15 amp additional load on supply wiring. Bottom

reading made with no additional load.

Lamp

Fixture Insulation

Attic Insulation

Thermocouple Location*

60W

In Place

«/) t/> 4-> +->

*-> fO ro -O ^ 01C r— cn o t— m Z CC QC

60W

None

in

4-> 4-»

-Q -Q

OJC r— ro O »— ro z cc cxl

lOOW

In Place

in in

4-> -*-»

rO

Q)c r— ro o r— ro z q: a:

1 5CW

In Place

i/i in

4->

4-> 4^

ro ro -Q -Q

0)C r— CO Oz q: q:

150W

None

in in

4-> 4-S 4-> 4J

«0 ro -Q -Q

0>C »— fO O r— ro z q: QC

Fixture Wire.

1/4 inch from socket

W 124 129 1 117 123

122 126 I 115 120

162 171 161 168

202 201 194 199

183 191 181 187

Fixture Canopy.

At wire pass-through hole

Fixture Canopy.

Surface facing ceiling box

Supply Wire.

Inside ceiling box

66 89 50 70

74 97

62 81 75 11962 99 86 13569 114

no 147

96 129

Supply Wire Casing.

1/2 inch from box

S 49 74 38 60

54 79 43 66

54 101 44 85 62 114

45 97

76 118

60 102

j Ceiling Box: inside,

j top of crossbar

inside,

top of ear

inside,

top center

T 57 81 50 70 68 92

64 84

66 110

61 99

75 126

67 114

102 140 97 131

1 inside,

on cable clamp

59 82

52 72

69 92

64 85

69 113

63 102

78 128

69 116

103 141 96 132

Attic Surface: overlamp,

4 inches from center

A 44 66

41 59

43 67

41 62

50 89

49 32

57 103

.56 97

58 96 56 87

Ceiling Surface:

8 inches from center

C 31 44

29 38

26 41 25 3835 53

35 49

43 65

42 60

40 65 i 39 59

Wood Joist:

1/2 inch up from ceiling

J1 31 52

29 42

28 51 26 44

32 67

31 59 36 78 34 ' 70 38 81 36 70

V.'ood Joist:

1/2 inch up from ceiling

J2 30 52

28 44 28 51 26 46 33 67 32 62

37 79

35 73

38 79 35 74

Ambient: in test assembly

Ambient: in test assembly

Ambient .Room.

*Symbols in second column (if any) indicate thermocouple locations on the corresponding diagram

of figure 1

.
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TABLE 2. TEMPERAXUSE DATA FOR FIXTURE B Fixture rated for three 60 watt lamps

Temperatures in °C are listed iu the table. Readings have been corrected for an ambient room temperature of 20“C. Top reading made with 15 Amperes additional load on supply wiring.

Bottom, reading made with ao additional load. Lamp

MountingAttic Insulation

Thermocouple Location*’

Semi

60W

-flush

3) -ii imt iJ. 13' C3

60W

Flush

aU

- --4 0z

'»

03 u

ui

:a

lOOW

Semi- flush

a a

73 a - ^

3 —* —

0 ^ ^ Z 2S.

150W : Semi-flush j

1 03 'rt 1 y ^ 1 ^ i 73 73 1 ^ ^ 1 - -t •n z =! =:

j

150W

Flush

a

ij

73 V

0Z X

1

i 05 i i i 73 1

1

:

•

Fixture Wire. 109 117 U8 123 140 143 142 153 154 179 196 197 1 202

1/ 4 inch from socket 109 118 123 140 141 151 154 177 195

i 202 224

Fixture Canopy. a 99 111 112 131 146 143 168 195 196 i -At wire pass-through hole 97 111 129 143 147 165 192

t r ixtxirs i-anopy

.

95 110 112 125 146 149 159 195 196 Surface facing ceiling box 93 110 123 142 147 156 191

1

1

i Supply — 71 106 111 36 131 139 91 140 146 113 133 192 i 137 Inside ceiling box 59 96 74 122 77 L22 130 97 170 122 200 ‘

Supply >/ire Casing. s 56 96 104 54 116 125 66 130 137 69 173 179 94 1/2 inch from box 47

.. 92 56 111 59 113 124 60 158 35 133 Ceiling Box: inside. 3 73 102 106 94 136 142 119 134 188

too of crossbar 63 100 38 127 135 114 176

inside. 68 99 104 39 133 139 114 131 135

top of ear 99 35 125 134 109 175

1

i inside. T 62 96 103 —30 125 132 31 130 137 103 177 132 129

i top center 59 97 77 124 77 121 130 97 170 125 202

i inside. 61 96 102 33 128 135 79 123 136 100 177 131 140

! on cable clamp 58 97 79 127 75 122 131 ^5 171 135 205

; .Attic Surface: over lamp. -A3 52 38 99 53 121 130 62 163 173

I 3 inches from center 51 94 54 114 125 51 161

1 over lamp

,

A4 53 90 100 59 111 120 56 : '70 130 30 164 174 93

1 4 inches from center 55 96 53 116 55 113 126 79 163 93 139

1 over lamp

,

.A6 49 79 39 54 109 113 69 150 150

; 0 inches from cancer

{ 49 34 54 103 11^ 59 143

between lamps

,

50 34 94 55 120 126 ! 66 157 155

4 inches from center 43 90 ' 53 114 123 1 64 154

Ceiling Surface; over lamp^C4 91 112 114

i 117 14'> 1^5 ! 166 204 205

4 inches from center 90 113 1 116 139 143 i 154 201

over lamp, Co 6 7 90 95 1

1 94- T 129 : 134 130 135

6 inches crom cancer 57 95 ; 94 119 123 132 131

Ambient: in test assembly,; : 24 26 26 16 30 OQ : 29 31 32 ! 3 inches below ceiling : 27 26 28 30 ' 23 32 1

.-imbient: in test assembly, 21 22 22 *» 0 24 23 ; 14 24 24 i 13 inches below ceiling *> 0 n 23 23 24 ; 23 25

Ambient "Room : 20 20 10 20 19 20 20 20 7 7

= 20 19 19

20

i 19 - 3j 20 20 19 20 29 ; 20 17 1 20 20 "SyaboiS in second coluicn (if any) in dice te t hemocoupLe locations on the corr esponding diagram
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I

... ,.»*/ ^ 4.

N»^»^Wliliiwl|p H irfl I <ir^ 11 ''WII II I mm > ,

.'jfc

,' jicii

yfi '4. W-*#

^ '‘--7 *<f I

f. 4)i. >V 'iv r,-

' *i i.

m. f>f tw''v .'»;

|t«

^ a

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ijp^ %

;'| '#* -lid''’ ipr: ; \i

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TABLE 3. TEMPERATURE DATA- FOR FIXTURE C Fixture rated for four 60 watt lamps

Temperatures in °C are listed in the table. Readings have been corrected for an ambient room temperature of 30*^0. Top readings made with 15 amp additional load on supply wiring. Bottom

reading made with no additional load.

Lamp

Fixture Insulation

Attic Insulation

Thermocouple Location*"

60W

In Place

«/» W 4^

rO ro .a

iUC'o —

60W None

51 3-5 ^

cyi

3

lOOW

In Place

ul %

O ^

1

i

' w ! ^ I

1 m »

1

lOOW None

(/) W

to

Sio ^

(/» kJ

13 mcnCC

150W

In Place

13

OJO

2: X,

i

i

1

i ^ 1

! >-3 ;

i

!

Fixture Wire. 83 95 94 36 91 91 115 121 122 111 120 119 122 132 135 ! 1/A inch from socket 37 93 94 35 90 90 113 120 123 109 113 117 120 130 131 ;

Fixture Canopy. H 31 38 88 30 37 37 108 116 117 103 112 114 121 133 134

At wire pass-through hole 30 37 37 30 36 86 106 115 117 102 111 112 120 131 131 i

Fixture Canopy. F 73 33 32 96 107 109 i Surface facing ceiling box 72 80 81 93 105 106

Supply Wire. 51 39 91 54 86 86 74 114 113 78 107 112 31 132 137 I —

Inside ceiling box 46 71 73 53 70 72 57 93 97 55 90 94 66 113 117 1

Supply Wire Casing. S 51 84 86 46 32 82 50 107 112

^ r* 33 102 109 58 126 132 ' 1/2 inch from box 39 70 72 41 59 71 46 90 95 49 38 93 50 111 115 ,

Ceiling Box; inside B 1 top of crossbar i

inside. E 52 79 80 56 75 74 56 101 105 71 95 93 73 120 124 j top of ear 49 73 75 54 71 73 61 95 99 53 91 94 70 114 117 1

inside. T 50 30 82 55 77 77 61 102 107 53 96 101 57 122 127 1 top center 45 71 73 52 70 72 ! 93 97 53 90 94 63 113 117 ,

inside. i 49 78 80 54 75 74 : 61 100 105 57 94 97 . 57 120 124

on cable clamp : ^5 72 73 51 70 72 : 96 93 98 54 39 93 1 54

1 113 116 i

Attic Surface: over lamp. A3 : 47 75 75 44 74 74 i 95 102 52 94 99

i 119 124 1 3 inches from center ; 47 72 73 44 72 75

1

1 93 100 51 92 98 I 58 116 121

over lamp. A4 ! 47 75 75 45 73 76 : 48 94 101 52 93 98 57 117 123

4 inches from canter : A7 74 74 43 72 76 A7 93 99 50 92 98

1 115 119

over lamp, A6 42 70 69 38 53 67 ' 48 33 92

1 -^3 33 38

'' 50 109 115

5 inches from center 42 58 59 38 53 57 ! 33 90

1 32 38 ! 50 107 112

oe tween lamps. i A 42 73 73 39 76 76 1 49 93 99 i -15 96 102 : 52 120 126

4 inches from canter 1

! A1 70 71

1 72 73 1 47 39 95

i 92 98 ; 51 116 121

Ceiling Surface: over lampiCA 53 35 37 I 73 39 39 1 37 112 114

\

I 39 110 113 ; 111 143 1 46

4 inches from center i 53 32 35 73 37 38 ; 35 110 112 36 107 no 1 no 140 142

overl amo

,

• Co 52 71 72 j 56 75 75 59 95 100 7? qc 98 : 101 120 135

5 incnes from canter 1 52 59 70

1 - 73 72 57 92 99 ! 71 93 96 100 1 23 131

Ambient; in test assemoly . 27 29 29

1 26 23 27 30 33 32 ! 29 31 31 i 33 35 35

3 inches below ceiling ! 27 29 29 ! 26 23 23 ; 30 33 32 i -3 30 31 ! 52 34 34

Amoient: in test assembly 1 22 22 22 i 22 23 23 22 24 23 ^ 23 24 24 ! 24 25 25

13 inches below ceiling ' 22 22 22 i 22 22 23 22 24 23 33 23 24 i 25 25 25

Ambient Room 20 13 20 ' 21 20 21 20 21 20 i 21 21 21

' 21 21 21

1

! 19 13 13 1 20 19 19 : '5 19 1 9 21 20 20 ; 50 20 21

'Symcols in sacono column ( T ^ any; ino" cate t.nermocoupl e 1 oca cions on the corraspcnding diagram

of figure 3.

TABLE 4. TEMPERATURE DATA FOR FIXTURE 0 Fixture rated for one 60 watt lamp

Temperatures in are listed in the table. Readings have been corrected for an ambient room temperature of 20°C. Top readings made with 15 amp additional load on supply wiring. Bottom

readings made with no additional load.

Lamp

Fixture Insulation

Attic Insulation

Thermocouple Location*

50W

In Place

(/) </»

4^-

d3 .-0 -a-

<uC ^ cn o

2: 2^ ^ i

60W None

</)

-a- o i

3 31

(/I

cn

cn

lOOW

In Place

(/)

>-0 -a. O ' 3 31

j

(/!

'

;

! 'O - -a ; m • cn

31

’

lOOW None

(/)

-a o

j-a

-a

cn

cn

150W

In Place

c/1 w

T5

a —

2T

1

(/>

13 m3 ! Fixture Wire. 79 82 32 76 73 77 103 104 105 100 101 101 122 124 125 I 1/4 inch from socket 79 78 31 1 75 78 77 102 105 105 98 101 100 122 124 1 25 I Fixture Canooy. H 79 82 33 73 76 76 103 105 106 96 100 101 121 125 1 26 I At wire pass-through hole 79 78 81 72 76 75 102 105 105 95 100 100 121 124 1 25

j Fixture Canopy. c 1

1 37 92 92 119 123 125 i Surface facing ceiling box 1

! 35 91 91 1 1

5

123 123

Supoly Wire. 54 68 69 1 66 79 30 67 80 34 34 101 104 75 99 lOO : Inside ceiling box 39 47 53 64 o5

‘ 43 62 65 71 37 39 58 82 82 ;

! Supply Wi re Cas ing. S 43 53 59 i 52 56 67 51 65 69 62 33 36 55 32 32

1 1/2 inch from box 33 42 46 1 38 55 56 38 54 56 53 71 74 46 59 69 i

i Ceil ing Box: inside, 3 57 70 71 i 71 31 81 74 36 91 94 107 109 37 109 111 I

I top of crossbar 52 57 61 54 75 75 66 79 32 39 101 103 32 102 103 I

I

j inside. E 49 62 63 63 74 75 60 74 79 32 98 100 71 94 96

j

• top of ear 45 52 56 59 70 70 55 69 72 79 93 96 : 66 38 39 j

1 inside. T 45 58 61 52 74 74 56 71 76 30 97 99 56 91 93 I top center

i 40 48 53 57 58 69 50 64 67 76 92 94 ' 50 32 84 i

! inside, 44 53 59 53 71 71 54 68 73 74 92 95 52 86 38 I

; on cable clamp 40 43 52 53 66 57 47 53 66 71 37 39 56 30 3l i

I Attic Surface: over lamp. A3 36 52 53 40 55 55 42 58 63 47 71 74 i 59 35 86

3 inches from canter 36 48 47 38 19 52 41 54 53 46 55 69 55 32 82

over lamp. A4 30 44 A5 34 48 53 , 46 72

4 inches from canter '30 41 40 33 46 47 44 70

over lamp. A6 i 25 37 38 1 28 40 44 : 33 57 j 5 inches from canter 1 34 34 1 27 38 40 : 32 54 J

I opposi ta side A 29 41 42 i 34 46 50

.

' 36 57 I 4 inches from canter 1

1

t 30 40 40 ! 33

1 46 49 : 35 56 ;

, Ceiling Surface: aver lam.p C4 40 46 13 33 46 4-0 49 55 53 dp 53 50 ! 74 36 37

4 inches from canter ! 40 i6 -6 57 45 45 i 48 55 56 : 15 55 57 ; 73 35 35

over lamo C5 ! 29 36 37 34 41 d3 46 59

0 incnes from center i |29 35 34 ’ 33 40 41 46 53

Amoient: in test assembly 1

i 22 22 22 ! 23 22 23

1

! 23 22 23 ; 21 23 23 24 24 25

3 inches below ceiling

i

1 21 20 22

i 21 22 ' 22

} 22 21 ; 22 22 22 22 24 24

Ambient; in test assembly 1

1 21 21 21

1 22 21 22 1 21 22 21 21 21 ' 22 22 23

13 inches celow ceiling ' 21 19 21

1 21 20 21

; 21 22 20 1 20 21 21 20 22 22

Ambient Room

i i 21 20 20 ! 21 20 21i 20 21 20 ; 20 20 20 , 21 21 2l

!

1

1

! 20 13 20 ! 21 19 20 ; 21 20 19 : 20 19 20 - 19 21 20

’Symbols in second column (if any) indicate thermocouple locations on the corresocncing diagram

of figure 4,
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TABLE 5. EXTRACTION AND COMPTLATTON OF CRITICAL

TEMPERATURE. DATA FROM TABLES 1 , 2, 3 AND A

All readings below were taken with the fixture insulation pad installed except

those for fixture 3. No pad was supplied with this fixture. Temperature

readings without the pad installed are 3-7°C higher on the supply wire and in the ceiling, box but 3-7°C lower on the fixture wire. Readings below for fixture

3 were taken in a semi-flush mounting position. Flush mounting produced higher

temperatures (see table 2).

j Temperatures in listed

j

in table.

! Circled readings are above

I the maximum specified for

j that location (see text).

Lamps

Fixture Measurement Locations

Fixture Wire

A Supply Wire - No Load

t’WO Supply Wire - 1 5A Load

lamps Ceiling 3ox (maximum)

oOW Attic Surface (maximum

Ceiling Surface (maximum)

3 three

lamps

50W

I Fixture Wire

Supply Wire - No Load

! Supply Wire - 15A Load

: Ceiling Sox (maximum)

! Attic Surface (maximum)

; Ceiling Surface (maximum)

36 i@0SI

C four

lamps

60W

Fixture Wire

Supply Wire - No Load

Supply Wire - ISA Load

Ceiling 3ox (maximum)

Atmic Surface (maximum)

Ceiling Surface (maximum)

120 130 131 @@@

Fixture Wire

0 Supoly Wire - No Load one Supply Wire - ISA Load

lamp

^ Ceiling Sox (maximum)

SOW ; Attic Surface (maximum)

j Ceiling Surface (maximum)

79 73 31 i 102 105 105 122 124 125 58 'H

00) \ /’sj) 04 :

' 32 102 ,101

41 5i 58 I 55 32 32 | -8 55 56 i 73 35 35 i
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nHBS-114A iREv. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR79-1912

4, TITLE AND SUBTITLE

Temperature Measurement on Operating

Surface Mounted Lighting Fixtures

5. PuDlication Date September 1979

, ilv

7. AUTHOR(S)

P. Michael Ful comer

8. Performing Organ. Report No.

PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS rstreet. City, state, ZIP)

Consumer Product Safety Commission

5401 Westbard AVenue

Bethesda, Maryland 20016

13. Type of Report & Period Covered

^

'' '

15. SUPPLEMENTARY NOTES

Lj Document describes a computer program; SF-185, FIPS' Software Summary, is attached.

16. ABSTRACT (A 200-word or lesa factual auaanary of moat aignificant information. If document includes a significant bibliography or

literature aurvey, mention it here.) Potentially hazardous temperatures may result from adding thermal insulation in

the attic above surface mounted incandescent lighting fixtures and/or operating

these fixtures with lamps of higher wattage than specified. This study was

concerned with the range of temperatures generated (1) within the fixture,

(2) within the electric junction box associated with the fixture and (3) on the

adjoining ceiling and attic surfaces.

Test results indicate that the addition of minimal insulation (equivalent to R1 1

)

over a surface mounted lighting fixture which contains two or more rated lamps,

is likely to cause normal household branch circuit supply wiring associated with

the fixture to operate above its specified 60°C temperature rating. Overlamping

(using lamps of higher wattage than specified for the fixture) and/or additional

load current flowing through the branch circuit wire will cause even higher supply

wire temperatures

.

With all three conditions present (i.e., insulation over the fixture, overlamping,

and an additional 15 ampere load current flowing through the supply wire), the tests

indicate that the temperature of associated branch circuit wiring will exceed 80*^0

for a one lamp fixture and lOO^C for fixtures with two or more lamps.

^1.7, KEY WORDS (six to twelve entries ; slphebeticsl order; cspitslize only the first letter of the first key word unless a proper name;

separated by semicolons)

Surface mounted incandescent lighting fixture; thermal insulation; overlamping;

hazardous temperatures ; branch ci rcui t wiri ng; electrical junction box; load

current; thermocouple

18. AVAILABILITY 23 Unlimited

I

' For Official Distribution. Do Not Release to NTIS

I Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SO Stock No. SN003-003-

l~^ Order From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS 21. NO. OF

(THIS REPORT) PRINTED PAGES

UNCLASSIFIED 22

20. SECURITY CLASS 22. Price (THIS PAGE)

$3.00

UNCLASSIFIED

USCOMM-DC
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