NBSIR 76-1011

Exploratory Study of Glowing

Electrical Connections

William J. Meese

and Robert W. Beausoliel

Building Services Section

Building Environment Division

Center for Building Technology

National Bureau of Standards

Washington, D. C. 20234

October, 1976

Final Report

Prepared for

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410

NBSIR 76-1011

EXPLORATORY STUDY OF GLOWING

ELECTRICAL CONNECTIONS

William J. Meese

and Robert W. Beausoliel

Building Services Section

Building Environment Division

Center for Building Technology

National Bureau of Standards

Washington, D. C. 20234

October, 1976

Final Report

Prepared for

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter. Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

SI CONVERSION UNITS

In view of the present accepted practice in this cou. try 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.

Length

1 in = 0.0254* meter (m)

Temperature

to^ = 5/9 (top - 32)*

Torque

1 in- lb = 0.113* meter-newtons

* Exactly

i
ABSTRACT

This report describes and characterizes with quantifiable electrical

and thermal measures the extent to which loose electrical connections in

residential-type branch circuits have overheated in the laboratory. With

loose electrical connections, which conceivably could be inadvertently

duplicated in field installations, but with otherwise normal installation

and operating conditions, visible glows have been observed under laboratory

test conditions in nominal 120 volt, 15 and 20 ampere branch circuits with

both copper and aluminum wire. Characteristics of the glow condition are

differentiated from arcing/sparking as sometimes observed in making or

breaking electric circuits.

Glowing electrical connections may dissipate as much as 35 watts of

power with a current of 15 amps in the circuit and as much as 5 watts with

a current of 0.8 amp in the circuit. Temperatures over 750°F were measured

on the "break-off tab" of receptacles. Metal outlet boxes housing glowing

connections in an insulated wall test set-up representative of a common

type of residential construction attained temperatures in excess of 450°F.

In laboratory tests under repetitive, intermittent and periodic cycles, a

connection on a steel wire-binding screw of a receptacle open to the air

had sustained glow conditions maintained for over 100 hours. Glowing

connections will not perceptibly affect the electrical performance function

of lights, appliances or other electrical loads, and will not "blow" fuses,

trip circuit breakers or operate ground fault circuit interrupters.

Key Words: Arcing/sparking; branch circuit; contact resistance;

electrical connections; fire hazard; glowing electrical

connections
TABLE OF CONTENTS

1. INTRODUCTION 1

1.1 Scope 2

1.2 Background 2

1.3 Use of Term "Glow" or "Glow Discharge"

in Electrical Theory 2

1.4 Definition of Glow as Used in this Report 2

1.5 Wire-Binding Screw Materials 3

2. Description of Arcing/ Sparking in Electrical Circuits 3

3. Description of the Glow Condition 4

3.1 General Parameters of Glow Electrical Connections 4

3.2 Glow Behavior 5

4. Environmental Conditions of Laboratory Experiments 6

4.1 Open Air Experiments 6

4.2 Simulated Building Wall Experiment 7

5. Test Procedures and Quantification of Data., 7

5.1 Supply Voltages 7

5.2 Circuit Currents 8

5 . 3 Length of Time of Glows 8

5.4 Resistance of Connections 9

5.5 Voltage Drop Measurements and Connection Power

Dissipation Calculations 9

5 . 6 Temperatures in Glows 11

5.7 Temperatures at Points Other than at the Connection

Interface 12

5.8 Time-Temperature Experiments 15

6. Effects of Glows on Circuit Loads and Circuit Protection Devices .... 18

6.1 Circuit Loads 18

6.2 Fuses and Circuit Breakers 18

6.3 Ground Fault Circuit Interrupters 18

7. Observed Results of Glows on Proximate Building Components .......... 18

8. Other Investigations 19

8.1 Loose Brass Wire-Binding Screw Investigations 19

8.2 Investigations with Other Materials 20

9. Discussion of Laboratory Data in This Report 21

10. Field Existence of Glowing Electrical Connections 21

11. Conclusions 22

12. Recommendations 23

13. References 23

1. INTRODUCTION

In 1969 the U.S. Department of Housing and Urban Development

initiated Operation BREAKTHROUGH; one of the purposes of the ^jrogram was

to provide incentives to encourage and demonstrate innovations in housing.

In the Operation BREAKTHROUGH program several innovations involving

electrical connections in branch circuits were proposed. Approvals for

innovations involving electrical systems Installations were sparingly

given with conservative stipulations, taking cognizance of the potential

fire hazard and the concerns about lack of data for durability and other

pertinent technical information. However, the possibilities of almost

immediate significant economic benefits were recognized.

Subsequently, The U.S. Department of Housing and Urban Development

agreed to sponsor, at the National Bureau of Standards, a long-term research

project on electrical connections used in residential branch circuit wiring.

The first two publications of this project were reports on "Analysis of

Current Technology on Electrical Connections in Residential Branch Circuit

Wiring" [1] , and "A Preliminary Approach to Performance Requirements and

Criteria for Electrical Connections in Residential Branch Circuit Wiring"

[2]. This Report on glowing electrical connections is the third of this

proj ect

.

After this project was under way for the U.S. Department of Housing

and Urban Development, the National Bureau of Standards undertook another

project for the Consumer Product Safety Commission concerning the safety

of aluminum electrical wiring in residential use. Many of the technical

aspects of the two projects were similar. Some preliminary information

concerning glowing electrical connections was reported to the Consumer

Product Safety Commission. Work on aluminum wire hazards for the Consumer

Product Safety Commission was terminated before laboratory work for this

report on glowing electrical connections was completed. Information

concerning the work of NBS and others on aluminum wiring is contained

in References [3] and [4].

The goals of the project for the U.S. Department of Housing and

Urban Development are the development of performance criteria and test

methods to evaluate electrical connections. As a result of laboratory

investigations focused upon prevention and elimination of the glow

condition and its deleterious effects, an Influence upon performance

criteria and test methods applied to electrical connections is anticipated.

1
1.1 Scope

This report describes and characterizes the "glow" condition of

electrical connections with laboratory-based data. The glow condition is

differentiated from arcing or sparking which sometimes occurs in the

process of making or breaking electrical circuits. Electrical and thermal

data and the materials involved at the interface of glowing connections

are presented and discussed. Also included are laboratory-obtained

results concerning the overheating effects of glowing connections in a

wall section with insulation, which simulated a common type of residential

construction. However, it is not the intent of this report to develop

interrelationships between temperatures and other conditions typical in

buildings which contribute to electrical failure or fire.

No field studies have been carried out up to the present time to

determine whether or not glowing electrical connections develop in actual

residential branch circuits. However, the conditions required for glowing

electrical connections are thought to be well within the realm of

possibility in actual installations.

1.2 Background

As a prerequisite to the development of performance criteria and test

methods to evaluate electrical connections, laboratory investigations were

undertaken to determine quantifiable measures for "bad" electrical

connections by means of temperature measurements or wattace dissination.

These investigations included determining and identifying the mechanisms

and environments that cause electrical connections to fail (so that failure

may be prevented) in nominal 120 volt, 15 and 20 amp branch circuits.

These investigations led to laboratory observations of glowing electrical

connections. In the study and literature review resulting in the first

report of this project [1] it was found that no published material on the

glow condition was reported.

1.3 Use of the Term "Glow" or "Glow Discharge" in Electrical Theory

The terms "glow" and "glow discharge" are used by investigators of

electrical phenomena, such as Windred [5], and Holm [6], in discussing

phenomena associated with electric contacts. The use of term "glow" by

such authorities refers to a transient condition which occurs in the

process of and prior to the development of an arc or arc discharge.

1.4 Definition of "Glow" as Used in this Report

The glow referred to in this report is a sustained source of light

and heat emanating from the vicinity of an electrical connection or from

the vicinity of some other place in an electric circuit, such as where

broken parts of a wire are in contact. Sometimes the glow is only a small

spot in the interface of a connection. Sometimes a wire-binding screw,

other conducting parts of a wiring device, and/or portions of the wire

2
will glow. Sometimes a smaller and brighter spot can be observed in the

interface between a wire and wire binding screw where other parts of the

conducting path are glowing. The colors of or in the glow may be white,

yellow, orange or red, depending on the temperatures. In Section 5.6

the relationship of color of glowing bodies to approximate temperatures

is discussed.

1.5 Wire-Binding Screw Materials

While the glow condition is not limited to electrical connections

with wire-binding screws, most of the quantified data on glowing electrical

connections in this report were obtained with either copper or aluminum

wire connected to receptacles with loose steel wire-binding screws. Wirebinding screws of currently available receptacles and other wiring devices

are usually either steel or brass.

However, from a survey of local retail outlets, there appear to be

more such devices available with steel screws than with brass screws.

Wiring devices listed by Underwriters' Laboratories with the designation

"CO/ALR" must have brass screws. It is the intent that aluminum wire be

used only with "CO/ALR" wiring devices; copper wire may be (but is not

required to be) used with such devices.

It is not obvious by looking at the screws on wiring devices whether

they are steel or brass. All such screws are covered with a brass-colored

plating for connection to "hot" (ungrounded) conductors, a silver-colored

plating for connection to neutral (grounded) conductors or a green-colored

plating for connection to grounding conductors . A magnet will readily

determine if the screws are steel.

2. DESCRIPTION OF ARCING/SPARKING

IN ELECTRICAL CIRCUITS

The purpose of this section is to distinguish the "glow" condition

from "arcing/sparking" in electrical circuits. Although this section

contains some very preliminary laboratory observations on arcing/ sparking,

the primary intent of including this information is to give the reader a

more comprehensive understanding of the glow condition.

In the process of making or breaking an electric circuit, arcing or

sparking may sometimes be observed. For example, arcs or sparks may

occur when operating a switch or when inserting or withdrawing an attachment

plug from a receptacle. In this report arcing/sparking connote transitory

phenomena. Whether a form of repetitive arcing/ sparking occurs in the

"glow" was not determined.

In nominal 120-volt circuits it does not appear to be possible to

maintain arcs or sparks or to have repetitive arcing/sparking other than

momentarily, unless under load there is continual making and breaking of

the circuit at some point in its current path. For example, with

3
continuous vibration or other disturbance, repetitive arcing or sparking

may occur between a loose wire and a terminal on a wiring device or at a

broken point in the wire.

With repetitive arcing or sparking, high temperatures may occur in

the vicinity, and if arcing or sparking continues for a considerable time,

the hazard of overheating resulting in fire could probably occur. Whether

vibration or other disturbances in a building could lead to repetitive

arcing or sparking for other than a momentary period, or if there is much

probability of this, is not known and was not evaluated. However,

laboratory findings indicated that a "glow" may develop immediately, or

at some later time after arcing or sparking has occured and the glow

may remain sustained as long as the circuit in "on".

3. DESCRIPTION OF THE GLOW CONDITION

Section 1.4 defines the term glow as used in this report. The

development of a glow at any particular time or under any particular

circumstances, as well as the intensity of a glow, is not predictable.

Because of this and because no published information describing the glow

condition is known to the authors of this report, this section involving

general laboratory observations is presented with the intent to give the

reader a more comprehensive understanding of the general parameters

involving the effects and behavior of the glow condition.

3.1 General Parameters of Glowing Electrical Connections

Every experimental attempt to obtain glows with loose steel wirebinding screws has been successful; over 100 such attempts, using both

copper and aluminum wire, have been made. In the laboratory, glows

have been established with only minimal pressure or force at the area

of contact of a glowing connection. Glows have been established on

steel wire-binding screws which were backed off one-eighth turn from a

torque of 2 in-lbs. Glows were also produced in the laboratory where

broken parts of an electric wire contacted each other.

In the laboratory the investigators were not able to obtain glows

with tight electrical connections. However, if tight connections with

steel wire-binding screws became loose, glows were readily obtained.

Glows were obtained without any unusual environment, foreign substance,

corrosion or surface coating. In these experiments the only physical

parameters necessary to obtain and sustain glows were small contact area

and/or small pressure at a contacting point in the conducting path.

Torque/pressure, air gap dimensions, and contact area interrelationships

were not systematically investigated.

4
3.2 Glow Behavior

In these experiments the development of, extinguishment of, and

Intensity of glowing electrical connections were somewhat er atlc. With

time, glows were more likely to remain at approximately the same Intensity

If left undisturbed. Glows were developed along the side of wires where

they Interfaced with another part of the conducting path; such was the

case with loose steel wlre-blndlng screws. Glows were developed at the

end of the wire; such was the case when the end of the wire contacted

the head of a steel screw. Glows were also developed at the Interface

of broken parts of the wire. Sometimes glows were developed without

vibration, wire disturbance or arcing. At other times they were developed

by the disturbance created when an attachment plug was Inserted In a

receptacle. In other cases glows were only developed after severe

vibration or other severe disturbance. In some cases glows appeared,

disappeared, and reappeared many times.

Glows reappeared at the same point at times and In other Instances

at another point In the connection Interface. In some cases glows shifted

from one point In the Interface to another without disappearing. Sometimes

the entire wlre-blndlng screw, other conducting parts of receptacles and

portions of the wire near the connection glowed. At times when a glow

was extinguished, after a short time the temperature was little more than

that of a good connection.

Occasionally when a glow expired there was an open circuit. Sometimes

with slight disturbance electrical continuity was restored and the glow

randomly did and did not reappear.

Glows varied In Intensity as the current In the circuit varied. For

example, decreasing brightness was sometimes discernible to the eye when

current was lowered from 15 amps to 12 and then to 10, 7, and 5 amps.

In some Instances the glow became brighter again as current was Increased.

In this series of laboratory tests some glows with 0.8 amp appeared to be

brighter than some glows with 15 amps.

Glows, of course, expired when current was not flowing In the

circuit. Sometimes after being off they Immediately reappeared when

current was turned on.

When power to the circuit Is shut off, the two parts of the circuit

In the vicinity of the glowing connection may or may not be connected by

a small weld. The authors found In this study that when the circuit was

off, a resistance meter sometimes Indicated an open circuit at the binding

screw and at other times Indicated a conducting path whose resistance

varied In different tests. This latter condition could Indicate either

a weld of small cross section or a non-welded contact of two surfaces.

In either case, the glow could usually be reestablished without difficulty

when power was reapplied to the circuit.

The mechanism for the glow phenomena Is not understood. However,

from the test observations It Is possible to consider an explanation.

5
One can hypothesize the physical parameters of the glow phenomenon as

follows: When a wire-binding screw on an electrical connector is backed

off 1/8-turn from a tight position, an air gap ranging from zero to .0002

inch could be created somewhere between the circuit elements depending on

the orientation of the wire. Since the dielectric strength of air is

about 56kV (rms) per inch, an air gap smaller than about 0.002 inch could

be breached at 120 volts. When voltage is applied to the circuit an arc

is created at this gap or at some contact point of light pressure which

is accompanied by high temperature, a glow, and perhaps some vaporized

metal. The exact location of the arc will be somewhat variable, because

the location of the smallest air gap will depend on the unpredictable

positions of the wire and binding screw. The presence of the glow is

relatively stable, but not completely so, because the width of gap tends

to be maintained physically by the binding screw.

As previously stated, glows were also produced in the laboratory

where broken parts of an electric wire contacted each other. The test

results suggest that actual air gap is not essential to the development

of a glow, but that a small air gap or a contact of small area and

relatively high electrical resistance is required to initiate a glow

condition. Another investigator at NBS found that he could produce the

glow condition when he closed a circuit by touching a wire to a steel

nail. When the current was shut off, the wire and the nail were welded

together and the nail could be lifted by raising the wire. This experiment

was performed several times using both copper and aluminum wire with

identical results.

In reference 8, the author claims that a chemical breeding process

of CU2O occurs which is essential to the development of the heating

mechanism in loose connections.

4. ENVIRONMENTAL CONDITIONS OF

LABORATORY EXPERIMENTS

Data presented in this report were obtained with electrical

connections exposed to open air or in a simulated, insulated wall of

typical residential-type construction. Descriptions of the open air

and simulated building wall experiments are described below. Test

procedures used to obtain electrical and thermal data are described in

Section 5.

4.1 Open Air Experiments

Many laboratory tests involving glowing connections were performed

with connections open to the air in the laboratory where the heat produced

by the connections was readily dissipated. Wiring devices (usually

receptacles with steel wire-binding screws) were fastened in metal outlet

boxes. The outlet boxes were fastened to a piece of wood which was

rigidly held in place with a vise. Copper wires (#14 and #12) and

aluminum wires (#12 and #10) were used in different experiments. Glowing

connections could be readily observed by the investigators. Outlet boxes

with removable sides were used.

6
4.2 Simulated Building Wall Experiments

In order to obtain data under conditions simulating the actual

installed use of connections in the field, some experiments ^ere performed

in a simulated, insulated exterior wall of typical residential-type

construction. In these experiments wall sections approximately 17 1/2

inches wide by 18 inches high and 4 5/8 inches thick were constructed.

The frame was constructed of nominal 2 x 4s ; plywood (3/8 inch) was

fastened to the front and gypsum board (3/4 inch) was fastened to the

rear of the building wall section. The building wall section was filled

with balsam wool (batts) insulation. Typical receptacle outlets were

installed in the wall section. Both metal and plastic outlet boxes of

typical dimensions (usually 2x2x3 inches) meeting National Electrical Code

requirements were used. Receptacles with steel wire-binding screws and

aluminum (#12 and #10) and copper (#14 and #12) wires were connected

in various tests. Except for one or more purposely loose connections

these experimental setups were made, as closely as possible, to simulate

residential field installations.

5. TEST PROCEDURES AND QUANTIFICATION OF DATA

Data in this section of the repo^-t concerning the glow condition

were principally obtained with either copper or aluminum wire and steel

wire-binding screws on receptacles at the interface of loose connections

in either open air or simulated building wall experiments as described

in Section 4. Receptacles and other wiring devices are designed so that

not only the screw but also a brass plate interfaces with the wire when a

connection is made. Glowing connections were established with steel

screws when the wire appeared to also be in physical contact with the

brass plate on a wiring device.

5.1 Supply Voltages

(a) Test Procedures

Most laboratory investigations of the glow condition were made with

supply voltages of 110 to 120 a-c, 60 hertz. These are the characteristic

parameters of residential branch circuits. However, to determine if

supply voltages significantly affect the glow condition, attempts were

made to establish glows with low voltage a-c and low voltage d-c power

supplies.

(b) Results and Discussion

Glows were established with a-c supply voltages under 10 volts with

approximately the same electrical (voltage drop) measurements recorded

across the connection as when the same currents were used with a 110-120

volt supply. The resistance of electrical connections, even glowing

connections, is small in comparison to the resistance of lights, appliances

or other usual electrical loads on nominal 120-volt circuits. In the case

7
of a low voltage supply, the resistance of a connection will represent a

much larger part of the total resistance of the circuit. Therefore,

glowing connections will have more effect on current and consequently

voltage drop values with low voltage power supplies than with nominal

120-volt power supplies, unless other means to control current levels

are employed.

If, prior to energizing a circuit, there is a high resistance at a

bad connection, most of the available supply voltage will be across the

connection instead of across the intended electrical load. In this case

supply voltage may have an effect on investigations involving the glow

condition.

Glows have also been established with low voltage d-c (under 10 volts)

with approximately the same electrical (voltage drop) measurements recorded

when the same currents (15 amperes) were used with 110-120 volt, a-c

supply. This appeared to indicate that the impedance in glowing connections

was substantially all resistance.

5.2 Circuit Current

(a) Test Procedures

Current (amps, r.m. s.) was measured by an ammeter, and in some cases

by an auto-ranging digital multimeter. Current was adjusted to various

values by varying the electrical load and in some cases by varying supply

voltage. In most cases, one to four adjustable 660-watt hot plates were

used for the electrical load. In some cases light bulbs were used for

the load or as part of the load.

(b) Results and Discussion

Visible glows, sustained for at least five minutes, have been observed

with as little current as 0.3 amp, with many incremental values up to and

over 20 amps in the circuit. A current of approximately 0.3 amp represents

the electrical load of one 40-watt light bulb. The ampacity (current

carrying capacity in amperes) of most residential branch circuits does

not exceed 20 amps. Visible glows were sustained for currents up to 50

amperes using low a-c supply voltage (under 20 volts)

.

5.3 Length of Time of Glows

(a) Test Procedures

In the laboratory, glows have been established both in open air and

in simulated building wall experiments for many hours. To determine just

how long a glow would last, current (15 amps) was applied to a glowing

connection for an extended period. The glow was established with aluminum

wire on a receptacle with steel wire-binding screws. The connection was

in open air and with the test specimens under a laboratory hood. Voltage

drop measurements were periodically recorded.

8
The circuit with the glowing connection was turned on and off many

times. It was never left on overnight and, therefore, never stayed on

for more than about nine hours at any one time. At one time power was

not applied to this circuit for three weeks. Then, when power was applied,

the glow reappeared.

(b) Results and Discussion

From the measurements it was determined that the connection had

glowed for 129 hours and that power dissipated In the glowing connection

averaged approximately 20 watts for the 129 hours. At times in excess

of 35 watts were dissipated.

When the experiment ended the connection had not failed in its ability

to transmit current to the electrical load. About five inches of PVC

insulation on the wire attached to the glowing connection, and considerable

amounts of the non-metallic parts of the receptacle were gone. However,

the wire and metal parts of the receptacle were intact. There appeared

to be no pitting or burning away of metal parts, although there was

discoloration of the surface of metal parts.

5.4 Resistance of Connections

In the report, the power dissipated at glox^ring connections (rather

than resistance) is quantified. The term, "resistance" as used in this

report requires some explanation. Resistance of a connection at a

particular time may be determined by dividing the voltage drop across a

connection by the current in the circuit. Such calculations show that

the resistance of a glowing connection may be quite variable.

5.5 Voltage Drop Measurements and Connection Power Dissipation

Calculations

(a) Test Procedures

Voltage drop measurements were made with a digital voltmeter. Power

dissipated by an electrical connection was calculated by multiplying the

circuit current by the voltage drop measured across the connection. When

voltage drop measurements included substantial lengths of wire or other

parts of the conducting path, the voltage drop of such components was

measured and subtracted to obtain the voltage drop of the connection.

(b) Results and Discussion

Preliminary laboratory measurements indicated that voltage drop

measurements, and hence determinations of power dissipated at a connection

are substantially free of environmental effects. That is, determinations

of power dissipated at connections are substantially the same in open air

as they are in a simulated building wall, provided other factors,

particularly current, are the same.

Voltage drop measurements (and subsequent power dissipation

calculations) appear to be a more meaningful way than temperature

measurements to compare the characteristics of electrical connections.

9
Temperatures depend not only on heat generation but also on heat

dissipation factors. However, temperature is the primary performance

criterion concerning fire safety aspects. Therefore, there must be

correlation between power dissipated by a connection and temperatures

expected under actual installation conditions.

In tight, well-made electrical connections as well as in wire and

other conducting components of electrical circuits, voltage drop will

vary (substantially) directly with current. This is because resistance

is substantially constant (E = IR)

.

Power dissipated in a tight, well-made connection, as well as in

wire and other conducting components of electrical circuits, will vary

substantially with the square of current. (Power in watts = EI = i2r) . With 10 amps in a circuit a tight, well-made connection will dissipate

approximately 100 times the power that it will with one amp in the

circuit.

Typical voltage drop measurements and calculations of power

dissipated in tight well-made connections are listed in Table 1. These

values are for comparison with values listed for glowing electrical

connections in Table 2.

TABLE 1 - TYPICAL GOOD CONNECTIONS

CURRENT VOLTAGE POWER

(Amps) DROPS DISSIPATED

(Millivolts) (Milliwatts)

20 4-10 80-200

15 3-8 45-120

10 2-5 20-50

5 1-3 5-15

0.8 0.15-0.4 0.1-0.3

With 15 amps in a circuit, one foot of #14 copper or #12 aluminum

wire will have a voltage drop of approximately 40 millivolts, and

dissipate about 600 milliwatts. With 15 amps in a circuit, one foot of

#12 copper or #10 aluminum wire will have a voltage drop of approximately

25 millivolts and dissipate about 375 milliwatts.

Voltage drop measurements and power dissipation calculations were

repeatedly carried out in many experiments involving glowing connections

in both open air and in simulated building wall construction. While

glow behavior is quite unpredictable and difficult to quantify, it was

observed from these experiments that higher voltage drops are apparently

possible as the current in the circuit becomes smaller. This is opposite

to experimental findings with good connections. However, in these

experiments more power was generally dissipated as current increased.

Power dissipated is proportional to the square of the current (power in

watts = i2r) . Some typical voltage drop measurements and calculations

of power dissipated in glowing connections are listed below:

10
TABLE 2 - TYPICAL GLOWING CONNECTIONS

CURRENT

(Amps)

VOLTAGE

DROPS

(Millivolts)

POWER

DISSIPATED

(Milliwatts)

20

15

10

5

0.8

1000-2000

1200-2400

1500-3000

2000-4000

4000-7000

20,000-40,000

18,000-36,000

15,000-30,000

10,000-20,000

3,000- 5,000

The range of values in Table 2 may be compared with values previously

listed in Table 1 for good connections. It should be noted that with 20

amps in the circuit, power dissipated in glowing connections was sometimes 100 to 200 times that produced in a good connection; with 0.8 amps

the corresponding difference was sometimes 10,000 to 20,000 times. (An

electrical load of one 100-watt light bulb will give a circuit current

of about 0.8 amps).

5.6 Temperatures in Glows

(a) Test Procedures

Temperatures in the glow of a glowing electrical connection are

difficult to measure directly. Placing of thermocouples or other

materials in the connection interface where the glow appears affects the

characteristics of the glow. Non-contact methods of measurement (e.g.

infrared thermography) would be necessary to obtain temperatures of the

glow. Bramson [7] indicates that in measuring the temperature of nonblack bodies their emissivity must be taken into account. However,

Branson states that "The optical properties of radiation in the visible

spectral region have long been used to furnish approximate estimates

for the temperature of glowing bodies from the color of their incandescence."

From Reference 7 (Bramson) , it is indicated that when a body is

heated to temperatures less than about 500''C (932 °F) its radiation is

not yet perceptible to the human eye. He states that when temperature

of the body rises to 550-600°C (1022-1112°F) a faint glow appears and

the outline of the heated body can be traced in darkness. At a somewhat

higher temperature the heated body will exhibit a dark red tint and with

further rise in temperature the radiation will change from dark red to

red, orange, yellow and, white. However, the color scale depends on the

selectivity of the radiation, and on the properties of the individual

human eye.

Bramson summarizes the color of the incandescence by giving

descriptions of the color at various stages as seen by various authors.

These descriptions of color are given in Bramson' s color scale, which

is shown below. The authors referred to by Bramson are as follows:

11
[2] William Piatt Wood and J. M, Cork, Pyrometry, 2nd Edition,

(New York, McGraw-Hill, 1941) pp. 263.

[3] Franz Rapatz, Die Ed El Sta Hie, 2. AUFL (Berlin, Springer,

1934) pp. 386.

[4] Otto Wawrziniok, Hand Buch Des Material Prufungswesens

Fur Maschinen-Und Bauingemieure, 2 AUFL (Berling,

Springer, 1923) pp. 700.

THE COLOR SCALE [7]

Color of incandescence according to various authors

t, °C [2] [3] [4]

470

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

1300

Barely perceptible red

Dark red

Cherry red

Bright red

Yellow

White

Dull brown

Brownish red

Dark cherry

Cherry

Bright cherry

Red

Bright red

Reddish yellow

Yellow

Bright yellow

Yellowish

white

White

Dark red

Dark cherry

Bright cherry

Bright Red

Orange

Lemon yellow

Bright yellow

(b) Results and Discussion

By observing colors (according to Bramson's Color Scale) an

approximation may be made of temperatures at various placed in, or in

the vicinity of the glowing connection shown in the photograph at the

back of this report. Note, however, there are considerable differences

in the relationship of temperature to color by the various authors.

5.7 Temperatures at Points Other Than at the Connection Interface

(a) Test Procedures

In the laboratory thermocouples were used to record many temperatures,

at various points on the conducting current path and at other locations

being heated by glowing connections. Figure 1 identifies thermocouple

locations referred to below.

12
o

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X

o

ffi

CO

O

UJK UJ

CM

UJ

>

o

o

o

h-

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(/)C!)

ZO

Ul ".O Q -J

OQO

<o o

I I I UJ U. C£)

3

CD Z

I- ^ UJ X

u. S ^ o

U- CK ^ flD O O u- < ... o

^ < Q.

£ 9 oQ hI I I < m o
(b) Results and Discussion

In an electric circuit the entire current path has some resistance

and therefore increases in temperature when under electrical load. A

resistance of about 12/3 ohms per 1000 ft. occurs with #12 copper and

#10 aluminum wire. A resistance of about 2 2/3 ohms per 1000 ft. occurs

with #14 copper and #12 aluminum wire. The heat produced by a tight

well-made connection will only increase temperatures very slightly near

the connection when compared to temperatures at other points on the

current path. The opposite is true with glowing connections where the

heat produced by the current path is insignificant when compared with

heat produced at the connection interface.

In open air experiments, on receptacles with tight connections,

temperatures recorded on break-off tabs (See Figure 1) or other points

on the current path near connections will usually range from 20°F to

35°F above ambient after equilibrium conditions have been reached with

rated current in the circuit. Rated current is usually 15 amps in

circuits with #14 copper or #12 aluminum wire and 20 amps with #12 copper

or #10 aluminum wire. Thermal equilibrium conditions in open air

experiments are usually reached or nearly reached within 30 minutes to

one hour.

In a simulated, insulated building wall, temperatures near tight

connection will not usually exceed 30°F to 50°F above ambient with rated

current in the circuit. In a simulated building wall thermal equilibrium

is not reached as quickly as it is in open air; equilibrium temperatures

are usually reached in one or more hours in building walls.

With tight well-made electrical connections in a simulated building

wall, temperatures of proximate building materials after thermal equilibrium, depend on various conditions. In some cases temperatures on steel

outlet boxes may be 10°F to 15 °F above ambient. However, one to two feet

or more of wire (not including grounding wires) are usually in an outlet

box and it is this wire, and not "good'' electrical connections which

generates most of the heat.

In open air experiments with glowing connections, temperatures

recorded using thermocouples at points on the current path near the

connections have exceeded 600°F within three minutes and 700°F within

ten minutes after current was applied. (See Section 7, Item 2 concerning

effect on wire insulation.) Such points would include the break-off tab

on receptacles with wire-binding screws or points on the wire very near

(1/4 to 1/2 inch from) the glowing connections. Temperatures on the

"idle" screw, (See Figure 1) have exceeded 600°F within five to ten

minutes after current was applied. In open air experiments temperature

measurements were not taken on components which were not a part of the

14
current path. Because heat can dissipate rapidly, there appears to be

little significance of such measurements.

5.8 Time-Temperature Experiments

(a) Test Procedures

Experiments were made with glowing electrical connections to obtain

time-temperature data at various points on electrical and proximate

building components of electrical installations in a simulated exterior

residential wall. Section 4.2 describes the type of construction used

in these experiments. This data when combined with the information in

Section 7 concerning the observed effects of glowing connections on

proximate building components gives an indication as to the hazards which

may be involved.

(b) Results and Discussion

Figures 2 and 3 present results of two experiments involving loose

steel wire-binding screws, one in which copper wire was used and one in

which aluminum wire was used. Figure 1 illustrates thermocouple locations

of temperature measurements which are plotted in Figures 2 and 3, It

should be noted that laboratory experiments did not indicate any substantial difference in the thermal performance between copper and aluminum

wire with glowing electrical connections. However, it must be realized

that these data are not statistically large enough to compare copper

with aluminum wire when electrical connections are glowing.

It should be noted that the graphs illustrate typical data which can

be obtained with glowing connections. Because of the erratic behavior

which may be typical of glowing connections (see Section 3.2), other

experiments in which all parameters are repeated as closely as possible

may result in somewhat different time-temperature data. From other

limited laboratory experiments, temperatures shovm on the graphs (Figures

2 and 3) however, are not extreme but are typical. Also, quickly rising

temperatures on the current path at points near the connection and more

slowly rising temperatures at points on other components are typical.

It should be noted that in the experiment involving copper wire

(Figure 3) a ground fault circuit interrupter (GFCI) which was used for

laboratory safety operated twice opening the circuit. (In the process

of insulation deterioration either a "hot" or neutral conductor came in

contact with the grounding wire or with some object which was in contact

with the grounding wire) . The GFCI did not operate during the experiment with

aluminum wire. (Figure 2). Operation of GFCIs is a chance occurrence,

which can occur in laboratory or field Installations with either copper

or aluminum wire. The GFCI was removed from the circuit, permitting

the experiment to proceed. Having a GFCI on most branch circuits is,

at the present time, not common practice.

15
760

40

TIME -TEMPERATURE PROFILES

"GLOWING" ELECTRICAL CONNECTION

bJOOSE WIRE BINDING STEEL SCREW)

#12 ALUMINUM WIRE - RECEPTACLE IN 2x2-x3

STEEL OUTLET BOX IN SIMULATED, INSULATED

EXTERIOR WALL

15 AMPS -1 12 VOLTS

0 1 1 1 1

0=20 040 hOO IZO 1=40 2O0 2=20 2=40

TIME - H0URS=MINUTES

3=00 3=20 3=^ 4=00

Figure 2- EFFECTS OF GLOWING ELECTRICAL CONNECTION -ALUMINUM WIRE
760

NO DATA TAKEN tETWEEN BROKEN LINES

GFa OPENED CmCUITAT 1:07

CIRCUIT ON AT 1:10 6FCI OPENED CIRCWT AT_fc|4

CIRCUIT 0N(6Fa REMOVED)AT 1:1

520 -

40

1

IN BUILDING INSULATION

2 IN. FROM GLOWING SCREW

(PEAK 204 'F)

TIME TEMPERATURE PROFILES

'GLOWING" ELECTRICAL CONNECTION

(LOOSE WIRE BINDING STEEL SCREW)

No. 14 COPPER WIRE - RECEPTACLE IN 2x2x3

STEEL OUTLET BOX IN SIMULATED, INSULATED

EXTERIOR WALL

IS AMPS - III VOLTS

1 1

0:20 0:40 1:20 1.40 2:00 2:20 2:40 3:00 3:20 3:40 4:00

TIME-HOURS: MINUTES

Fiflor* 3 -EFFECTS OF GLOWING ELECTRICAL CONNECTION-COPPER WIRE
6. EFFECT OF GLOWS ON CIRCUIT

LOADS AND CIRCUIT

PROTECTION DEVICES

During the course of the laboratory investigations described in

Section 5, the effect of glowing connections on (1) circuit loads, (2)

fuses and circuit breakers, and (3) ground fault circuit interrupters

was observed. These observed results are discussed below.

6.1 Circuit Loads

Glowing electrical connections will not perceptibly affect the

performance of lights, appliances or other electrical loads. Glows will

reduce the voltage to the circuit load from less than one to up to

approximately 7 or 8 volts. Except under very unusual circumstances,

such reduced voltages would go unnoticed in (nominal 120-volt) electrical

circuits in residences and most other buildings.

6.2 Fuses and Circuit Breakers

Glowing electrical connections will not "blow" fuses or trip circuit

breakers. Fuses and circuit breakers operate when current in a circuit

exceeds some value, such as 15 amps. A glowing connection, in effect,

adds load in series with lights, appliances or other circuit loads; it

will decrease current slightly. Only if the glow produces some secondary

effect, such as when deteriorating insulation allows the "hot" electrical

conductor to contact the neutral conductor, (causing what is sometimes

referred to as a "dead short"), will fuses or circuit breakers operate.

6.3 Ground Fault Circuit Interrupters

Glowing electrical connections will not operate ground fault circuit

interrupters (GFCIs), except as noted below. GFCIs will only operate if

current at some point in the circuit goes to ground. A glowing connection

in effect becomes a secondary electric load with no current going to

ground. Only if the glow produces some secondary effect, such as

deteriorating insulation, which then allows either the"hot"conductor or

the neutral conductor to contact a grounded object, will GFCI's operate.

7. OBSERVED RESULTS OF GLOWS ON

PROXIMATE BUILDING

COMPONENTS

Some effects of glowing connections, were observed during both open

air (see Section 4.1) and simulated building wall (see Section 4.2)

experiments. Highlights of these observed results are listed below.

Systematic attempts to evaluate and relate glow characteristics, such as

temperature or connection power dissipation to fire starting on proximate

building components were not undertaken. Additional laboratory work should

be performed on this aspect to characterize the potential fire hazard.
1. Combustible material, including wood, paper and balsam wool

insulation, in contact with glowing connections readily ignited.

2. In open air and in simulated building walls, the PVC insulation

on the wire attached to loose wire-binding screws was completely

consumed for a distance of four or five inches. Until there was

a considerable portion of the wire exposed, smoke or gas from

the insulation was observed,

3. In a simulated building wall, approximately one-third of the

non-metal parts of receptacles with a glowing connection were

completely consumed with the metal current path still performing

its function. Considerable portions of non-metal parts of

receptacles in open air experiments also were consumed.

4. Considerable insulation material on attachment plugs, which

were in receptacles with glowing connections, was consumed;

such plugs were badly deformed and on some occasions have

ignited.

5. In simulated building wall experiments considerable charring

of wood paneling and balsam wool insulation has occurred.

These building components were outside of steel outlet boxes

housing glowing connections.

6. In simulated building walls non-metallic outlet boxes housing

glowing connections were charred through and were greatly

deformed.

7. Plastic cover plates on the wall of simulated building wall

experiments have charred through and were observed to be

visibly red hot.

8. Pillow cases placed against receptacles with cover plates

attached in simulated building wall experiments "scorched

through." In such cases "scorching" first occurred opposite

the holes in the receptacle where the prongs of attachment

plugs are intended to enter.

8. OTHER INVESTIGATIONS

Preliminary laboratory investigations were made with materials

where no steel was present at the interface of electrical connections.

Results of these preliminary investigations are discussed below.

8.1 Loose Brass Wire-Binding Screw Investigations

Repeated attempts with over 20 connections were made in the laboratory

to develop glows on wiring devices with loose brass wire-binding screws

,

using both copper and aluminum wire. None of these attempts were successful

even with considerable vibration or wire disturbance. Continual vibration

19
or wire disturbance with either copper or aluminum wire on devices with

loose brass screws resulted in repeated arcing or sparking and high

temperatures. In fact, it appears that with vigorous wire disturbance,

higher temperatures can be developed on brass screws than on steel screws

because it was possible to melt aluminum wire on brass screws. In these

tests it was not possible to melt aluminum wire with steel screws.

Explanations of the repeated arcing or sparking conditions, whereby

the effects appear to be more severe with brass than with steel, were

not explored further. The significance of this experimentation is that

glows did not develop with loose brass wire-binding screws after the

vibration or wire disturbance ceased. Also, voltage drop and temperature

measurements indicated values which were not substantially above those

of tight connections, as shown in Table 1. However, investigations in

other laboratories indicate that connections with brass wire-binding

screws have overheated without wire disturbance.

8.2 Investigations with Other Materials

Subsequent experimentation was performed with common materials which

may be in contact in electric circuits. Some of these experiments

simulated broken wire with the broken ends in contact. In every case

an electric current of 15 amps was used.

Glows were established and sustained for at least five minutes at

the interface between the following materials.

1. Copper wire and steel block

2. Aluminum wire and steel block

3. Copper wire and aluminum wire

4. Copper wire and copper wire

5. Aluminum wire and aluminum wire

With repeated attempts glows were not established between either

copper wire and brass blocks or between aluminum wire and brass blocks.

The brass and steel blocks used were approximately 1/4" x 2" x 2" and

were inserted in the conducting paths of the circuits. Contacts were

made between the ends of wire and the 2" x 2" surface of blocks. Wire

to wire contacts were made at the ends of the wires.

Repetitive arcing will readily continue between either copper and

brass or aluminum and brass as long as there is disturbance at the interface. However, after the disturbance ceased, electrical and temperature

measurements indicated that either an open circuit or a relatively good

contact existed. Considerable experimentation and analysis would be

necessary to establish scientific explanations. It should be noted that

steel is not necessary to establish glowing interfaces: however, the

failure to obtain glows with brass is quite peculiar and should be

investigated further.

20
9. DISCUSSION OF LABORATORY DATA IN THIS REPORT

These laboratory investigations were of an exploratory i.ature in an

area where no published reference information was found. However, these

data are believed to warrant significant conclusions on some aspects of

the effects of the glow phenomenon.

The data presented in this report cover a wide range of conditions

since fine details were not intially of interest. The range of voltage

drops and temperatures relating the difference between glowing connections and good connections are so great that precise laboratory

procedures will not greatly affect the significance of the data presented.

For example, with 15 amps in the circuit, the break-off tab (see Figure

1) on a receptacle with good connections may attain temperatures on the

order of 30 to 50°F above ambient. However, the break-off tab on a

receptacle with one glowing connection may, within two or three minutes,

reach 300 to 600°F above ambient. (See Figures 2 and 3)

Quantified data presented in Section 5 of this report reflects

information which has been obtained in the laboratory. Data reflecting

approximate extreme measurements which could be readily obtained are

given. For example, with 15 amps in the circuit, sustained glows have

been established with voltage drops on the order of 2 1/2 volts across

the connection. Whether glows can be established at the same current

level with voltage drops on the order of 5 or more volts, for which

the wattage dissipation and hence the potential fire hazard would be

much greater, is not known. The authors have been unable to establish

glows with voltage drops of such magnitude with 15 amps in the circuit.

Sustained glows with voltage drops of 5 to 7 volts have been established

with one amp or less in the circuit.

10. FIELD EXISTENCE OF GLOWING ELECTRICAL CONNECTIONS

Glowing electrical connections may possibly be the cause of some

electrical failures in the field; fires have been started in the NBS

laboratory from glowing connections. Conditions necessary to establish

glowing electrical connections probably exist in many residential and

other buildings. Review of the transcript proceedings of hearings by

the Consumer Product Safety Commission on aluminum wire problems disclosed instances such as "a hot outlet into which nothing was plugged"

and also numerous citings on loose connections. Reference 3 contains

an abstract of these hearings.

Field studies have not been undertaken to establish the frequency

of loose connections in field branch circuits, or whether or not the glow

phenomenon develops in the field. NBSIR 75-723 [3] in discussing tests

made on receptacles removed from a house in which a fire attributable to

aluminum wiring occurred states: "Of the 6 receptacles tested (24 screw

terminals) 12 connections were loose to the point where it was difficult

if not impossible to measure a stable value of resistance. This seemed

to be more true of receptacles wired with the heavier gauge #10 wires

21
than those wired with #12 wire. It could be inferred that at least part

of the problem is the increased stiffness of the heavier wire which is

more likely to be loosened when stuffed into a receptacle box." However,

a substantial field study would be required to obtain statistically valid

information on loose or overheating electrical connections.

11. CONCLUSIONS

Glowing electrical connections appear to be most likely at coppersteel or aluminum-steel interfaces. Many wiring devices have steel

wire-binding screws. Glows may develop at such interfaces even when

there appears to be physical contact between the wire and a brass plate

on wiring devices.

Glowing electrical connections may exist for protracted periods of

time (hours, days, months) without breaking the electrical circuit.

In these experiments a glow was not developed in connections when

there was only a copper-brass or alumintim-brass interface.

Glows have been established where no steel existed. Specifically

glows have been established between contacting ends of copper wires,

between contacting ends of aluminum wires and between copper and

aluminum wires

.

Glowing electrical connections may occur over nearly the entire

range of current likely to be present in residential branch circuits.

With loose connections or where broken wires contact each other

glows may occur.

Glowing electrical connections will not operate fuses, circuit

breakers or ground fault circuit interrupters unless the glow causes a

secondary effect (See Section 7)

.

Glowing electrical connections will not perceptibly affect the

performance of lights, appliances or other electrical loads.

In loose connections with copper-brass or aluminum-brass interfaces,

repetitive arcing or sparking may lead to overheating.

Combustible material in contact with glowing electrical connections

can ignite.

Glowing electrical connections in simulated building walls may heat

proximate building materials to above their ignition temperatures.

22
12, RECOMMENDATIONS

Considerations should be given to establishing the extent cf potential

hazards from glows developing in existing buildings and additional laboratory

research undertaken to provide resolution of glow phenomena.

1. Research addressing realistic installations and practices involving

glowing electrical connections should be undertaken, toward the

following objectives:

A. Advance quantification of characteristics of glowing connections

presented in this report.

B. Scientifically explain reasons for the glow condition.

C. Determine how electrical connections become loose (creep, thermal

expansion and contraction, stress relaxation, corrosion, installation procedures, etc.) and determine whether any other mechanisms

may lead to the glow condition.

D. Investigate and quantify data concerning loose brass screws;

determine if there are conditions under which copper-brass and

aluminum-brass interfaces will develop glows or otherwise overheat under static conditions.

E. Explore the possibility of using a portable device to quickly

determine the quality of electrical connections in houses or

other buildings.

F. Obtain statistically significant field data on the quality

(voltage drop, power dissipation) of electrical connections.

G. In a systematic manner, characterize the fire starting potential

of glowing electrical connections in typical types of building

walls.

2. Criteria and tests or other evaluative procedures should be developed

and regulations put into effect which will ascertain that electrical

connections installed in the future will not be vulnerable to the

glow or to other overheating conditions.

3. Determine modifications which can be taken to lessen the vulnerability

of existing electrical connections to the glow or other overheating

conditions and determine if such modifications are feasible from both

technical and economic standpoints.

13 . REFERENCES

[1] Analysis of Current Technology on Electrical Connections Used in

Residential Branch Circuit Wiring, BSS 63, National Bureau of

Standards, William J. Meese and Ramon L. Cilimberg, March 1975.

23
[2] A Preliminary Approach to Performance Requirements and Criteria for

Electrical Connections in Residential Branch Circuit Wiring, NBSIR

75-672, National Bureau of Standards, William J. Meese, Ramon L.

Cilimberg and Adolfo A. Camacho, March 1975.

[3] Aluminum Branch Circuit Wiring in Residences; Summary Report for the

Consumer Product Safety Commission, January-September 1974, NBSIR

75-723.

[4] Hazard Assessment of Aluminum Electrical Wiring in Residential Use,

NBSIR 75-677, January 1974, E. Bunten, J. Donaldson, and E. McDowell.

[5] Holm, Ragnar, Electric Contacts Theory and Application, SpringerVerlog, New York, Inc., 1967.

[6] Windred, G. Electrical Contacts, McMillan, and Co., Ltd., London,

1940.

[7] Bramson, Mikael A., Infrared Radiation, A Handbook for Applications,

(Institute of Mineral Fuel, Academy of Sciences of the USSR, Moscow)

Plenum Press, New York, 1968.

[8] Kawase, Taro, Chiba University, Dept. Electrical Engineering, Chiba,

Japan. Attachment Report to Letter of May 6, 1975, to Mr. R. Simpson,

Chairman, CPSC.

USCOMM-NBS-DC

24
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

bidLiogkaphic data

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1011

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

EXPLORATORY STUDY OF GLOWING ELECTRICAL CONNECTIONS

5. Publication Date

November 1976

6. Performing Organization Code

7. AUTHOR(S)

William J. Meese and Robert W. Beausoliel

0. Pertorming Urgan. Keport No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

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

Office of Policy Development and Research

The Department of Housing and Urban Development

Washington, D.C. 20234

13. Type of Report & Period

Covered

FINAL

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary ol most si^ilicant information. If document includes a significant

bibliography or literature survey, mention it here.)

This report describes and characterizes with quantifiable electrical and thermal

measures the extent to which loose electrical connections in residential-type branch

circuits have overheated in the laboratory. With loose electrical connections, which

conceivably could be inadvertently duplicated in field installations, but with otherwise normal installation and operating conditions, visible glows have been observed

under laboratory test conditions in nominal 120-volt, 15 and 20 ampere branch circuits

with both copper and aluminum wire. Characteristics of the glow condition are differentiated from arcing/sparking as sometimes observed in making or breaking electric

circuits

.

Glowing electrical connections may dissipate as much as 35 watts of power with a current

of 15 amps in the circuit and as much as 5 watts with a current of 0.8 amp in the

circuit. Temperatures over 750°F were measured on the "break-off tab" of receptacles.

Metal outlet boxes housing glowing connections in an insulated wall test set-up representative of a common type of residential construction attained temperatures in excess

of 450°F. In laboratory tests under repetitive, intermittent and periodic cycles, a

connection on a steel wire-binding screw of a receptable open to the air had sustained

glow conditions maintained for over 100 hours. Glowing connections will not perceptibly

affect the electrical performance function of lights, appliances or other electrical

loads, and will not "blow" fuses, trip circuit breakers or operate ground fault circuit

interrupters.

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)

Key Words: Arcing/sparking; branch circuit; contact resistance; electrical

connections; fire hazard; glowing electrical connections

18. AVAILABILITY Unlimited

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