NBS BUILDING SCIENCE SERIES 103

Exploratory Study of

wing Electrical Connections

435

U58

no 103

1977 irtment of commerce • national bureau of standards

c. 2
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and

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THE OFFICE OF EXPERIMENTAL TECHNOLOGY INCENTIVES PROGRAM seeks to affect public policy and process

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2 Located at Boulder, Colorado 80302.
NOV 1 6 1977

^c NBS BUILDING SCIENCE SERIES 103

US?

u* 03 Exploratory Study of

Glowing Electrical Connections

William J. Meese

Robert W.Beausoliel

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Sponsored by:

Office of Policy Development and Research

U.S. Department of Housing and Urban Development

Washington, D.C. 20410

\

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

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued October 1977
Library of Congress Catalog Card Number: 77-608341

National Bureau of Standards Building Science Series 103

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 103, 29 pages (Oct. 1977) CODEN: BSSNBV

Supersedes NBSIR 76-1011

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20234

(Order by SD Catalof No. C13.29/2:103) Stock No. 003-003-01859-7 Price $1.30

(Add 25 percent additional for other than U.S. mailing)
SI CONVERSION UNITS

In view of the present accepted practice in this country for building technology, common U.S. units of measurement have been used throughout this document. In recognition

of the position of the United States as a signatory to the General Conference on Weights

and Measures, which gave official status to the metric SI system of units in 1960, assistance

is given to the reader interested in making use of the coherent system of SI units by giving

conversion factors applicable to U.S. units used in this document.

Length

1 in = 0.0254* meter (m)

Temperature

fcoc = 5/

9 (tof " 32) *

Torque

1 in-lb = 0.113 meter-newtons

*Exactly

iii
EXPLORATORY STUDY OF GLOWING ELECTRICAL CONNECTIONS

William J. Meese & Robert W. Beausoliel

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 con- ceivably could be inadvertantly 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

arching/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

iv
EXPLORATORY STUDY OF GLOWING ELECTRICAL CONNECTIONS

William J. Meese and Robert W. Beausoliel

CONTENTS

Page

Conversion Units ±±±

Abstract iv

1 . INTRODUCTION 1

1.1 Scope 1 1.2 Background 1 1.2.1 Use of Term "Glow" or "Glow Discharge" in Electrical

Theory

1.2.2 Definition of "Glow" as Used in this Report

2 1.2.3 Wire-Binding Screw Materials

2. DESCRIPTION OF THE GLOW CONDITION 3

2.1 General Parameters of Glowing Electrical Connections 4 2.2 Glow Behavior 4 2.3 Arcing/Sparking in Electrical Circuits 5

3. LABORATORY INVESTIGATIONS 7

3.1 Environmental Conditions of Laboratory Experiments 7 3.1.1 Open-Air Experiments 8 3.1.2 Simulated Building Wall Experiment

3.2 Test Procedures and Quantification of Data 8 3.2.1 Supply Voltages 8 3.2.2 Circuit Currents 9 3.2.3 Length of Time of Glows 9 3.2.4 Resistance of Connections 10 3.2.5 Voltage Drop Measurements and Connection Power 10 Dissipation Calculations

3.2.6 Temperatures in Glows 11 3.2.7 Temperatures at Points Other than at Connection Interface 12 3.2.8 Time-Temperature Experiments 14 3.2.9 Loose Brass Wire-Binding Screw Investigations 17 3.2.10 Investigations with other Materials 17 3.3 Discussion of Laboratory Data 2.8

4. EFFECTS OF GLOWS 19

4.1 Circuit Loads 19 4.2 Fuses and Circuit Breakers 19 4.3 Ground Fault Circuit Interrupters 20

4.4 Proximate Building Components 20 4.5 Field Existence of Glowing Electrical Connections 20

5. SUMMARY 21

5.1 Conclusions 21 5.2 Recommendations 21

6. REFERENCES 22 v

1 . INTRODUCTION

In 1969 the U.S. Department of Housing and Urban Development initiated Operation BREAKTHROUGH;

one of the purposes of the program 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 project.

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 con- tained 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 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 over- heating 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 wattage

dissipation. These investigations included determining and identifying the mechanisms and

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
1.2.1 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.

1.2.2 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 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 3.2.6 the

relationship of color of glowing bodies to approximate temperatures is discussed.

1.2.3 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. Wire-binding 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
2. DESCRIPTION OF THE GLOW CONDITION

Section 1.2.2 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

.
2 . 1 GENERAL PARAMETERS OF GLOWING ELECTRICAL CONNECTIONS

Every experimental attempt to obtain glows with loose steel wire-binding 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 wirebinding 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 con- tacting point in the conducting path. Torque/pressure, air-gap dimensions, and contact area interrelationships were not systematically investigated.

2.2 GLOW BEHAVIOR

In these experiments the development of, extinguishment of, and intensity of glowing electrical connections were somewhat erratic. With time, glows were more likely to remain at approximately the same intensity if left undisturbed. Glows were developed along the sides of wires

where they interfaced with another part of the conducting path; such was the case with loose

steel wire-binding 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 wire-binding 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 amps 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.

4
The mechanism for the glow phenomena is not understood. However, from the test observations

it is possible to consider an explanation. One can hypothesize the physical parameters of the

glow phenomena 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 reached 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 7, the author claims that a chemical breeding process of C^O occurs which is

essential to the development of the heating mechanism in loose connections.

2.3 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 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 occurred, and the glow may remain sustained as long as the circuit is "on".

3. LABORATORY INVESTIGATIONS

3.1 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 3.2.

7
3.1.1 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.

3.1.2 Simulated Building-Wall Experiments

In order to obtain data under conditions simulating the actual installed use of connections

in the field, some experiments were 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 4's; 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.

3.2 TEST PROCEDURES AND QUANTIFICATION OF DATA

Data in this section of the report 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 3.1. 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.

3.2.1 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 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

8
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.

3.2.2 Circuit Currents

(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)

3.2.3 Length of Time of Glows

(a) Test Procedures

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

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.

9
3.2.4 Resistance of Connections

In this report, the power dissipated at glowing 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.

3.2.5 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. 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 = I^R) . 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

(Amps)

Voltage

Drops

(Millivolts)

Power

Dissipated

(Milliwatts)

20

1510

50.8

4-10

3-8

2-5

1-3

0.15-0.4

80-200

45-120

20-50

5-15

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.

10
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 = I^R) . Some typical voltage drop measurements and calculations of power dissipated

in glowing connections are listed below:

TABLE 2. TYPICAL GLOWING CONNECTIONS

Current Voltage Power

(Amps) Drops Dissipated

(Mill ivolts) (Milliwatts)

20 1000 - 2000 20,000 - 40,000

15 1200 - 2400 18,000 - 36,000

10 1500 - 3000 15,000 - 30,000

5 2000 - 4000 10,000 - 20,000

0.8 4000 - 7000 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).

3.2.6 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 [8] indicates that in measuring the temperature of non-black bodies their emissivity must be

taken into account. However, Bramson 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 8 (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

[2] William Piatt Wood and J. M. Cork, Pyrometry, 2nd Edition, (New York, McGrawHill, 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

Bauingernieure, 2 AUFL (Berlin, Springer, 1923) PP. 700,

11
THE COLOR SCALE [8]

Color of incandescence according to various authors

t, [2] [3] [4]

470

600

650

700

750

800

850

900

950

1000

1050

1100

1150

1200

1300

Barely perceptible red

Dark red Dull Brown

Brownish red

Dark cherry

Cherry

Bright cherry

Red

Bright red

Reddish yellow

Yellow

Bright yellow

Yellowish white

Cherry red Dark red

Dark cherry

Bright red

Bright cherry

Yellow Bright red

Orange

White

White Lemon yellow

Bright yellow

(b) Results and Discussion

At various times and in various locations within glowing electrical connections, colors o glows were observed to be red, yellow, orange and white.

3.2.7 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
GLOWING CONNECTION

A - BREAKOFF TAB E B - IDLE SCREW F C - BLACK WIRE IN PLUG G

D - TOP OF BOX

SIDE OF BOX NEAR GLOWING SCREW

OUTSIDE PLASTIC COVER PLATE

IN BUILDING INSULATION - 2 INCHES FROM

GLOWING SCREW

Figure 1. Location of thermocouples — laboratory experiments.

13
(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 1 2/3 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 connections 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 4.4, 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" screws, (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 current path. Because heat can dissipate rapidly, there appears to be little significance of such measurements.

3.2.8 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 3.1.2 describes the type of construction

used in these experiments. This data when combined with the information in Section 4.4

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.

14
Figure 2. Effects of glowing electrical connection-aluminum wire

15
0

LsJ 400

tr

or 360

Q.

LU 320

(-

240 r -

200 -

1

1 1 1 NO DATA TAKEN BETWEEN BROKEN LINES

6FCI OPENED CIRCUIT AT 1.07 CIRCUIT ON AT 1:10 6FCI OPENED CIRCUIT AT 1:14 CIRCUIT 0NI6FCI REMOVED) AT 1:18

40-

1 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

15 AMPS - III VOLTS

±

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

TIME-HOURS: MINUTES

Figure 3. Effects of glowing electrical connection-copper wire

16
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 2.2), 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 shown 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.

3.2.9 Loose Brass Wire-Binding Screw Investigations

Preliminary laboratory investigations were made with materials where no steel was present

at the interface of electrical connections.

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 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.

3.2.10 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-towire contacts were made at the ends of the wires.

17
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.

3.3 DISCUSSION OF LABORATORY DATA

These laboratory investigations were of an exploratory nature 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 initially of interest. The range of voltage drops and temperatures relating the

difference between glowing connections and good connections is 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 3.2 of this report reflect 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.

18
4. EFFECT OF GLOWS

During the course of the laboratory investigations described in Section 3, the effect of

glowing connections on (1) circuit loads, (2) fuses and circuit breakers, (3) ground fault

circuit interrupters and, (4) proximate building components was observed. These observed

results are discussed below.

4.1 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.

4.2 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.

L9
4.3 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 GFCIs operate.

4.4 PROXIMATE BUILDING COMPONENTS

Some effects of glowing connections were observed during both open air (see Section 3.1.1)

and simulated building wall (see Section 3.1.2) 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 ignited readily.

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 receptacles where the prongs of attachment plugs are intended to enter.

4.5 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.

20
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 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 over- heating electrical connections.

5. SUMMARY

5.1 CONCLUSIONS

1. Glowing electrical connections appear to be most likely at copper-steel or aluminumsteel 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.

2. Glowing electrical connections may exist for protracted periods of time (hours, days,

months) without breaking the electrical circuit.

3. In these experiments a glow was not developed in connections when there was only a copper-brass or aluminum-brass interface.

4. 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.

5. Glowing electrical connections may occur over nearly the entire range of current likely to be present in residential branch circuits.

6. With loose connections or where broken wires contact each other, glows may occur.

7. Glowing electrical connections will not operate fuses, circuit breakers or ground fault

circuit interrupters unless the glow causes a secondary effect (see Section 4)

.

8. Glowing electrical connections will not perceptibly affect the performance of lights,

appliances, or other electrical loads.

9. In loose connections with copper-brass or aluminum-brass interfaces, repetitive arcing

or sparking may lead to overheating.

10. Combustible material in contact with glowing electrical connections can ignite.

11. Glowing electrical connections in simulated building walls may heat proximate building

materials to above their ignition temperatures.

5.2 RECOMMENDATIONS

Consideration should be given to establishing the extent of 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 connection.

21
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 over-heat 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 connections, and determine if

such modifications are feasible from both technical and economic standpoints.

6 . 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.

[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] Windred, G. , Electrical Contacts, McMillan and Co., Ltds., London, 1940.

[6] Holm, Ragnar, Electric Contacts Theory and Application, Spr inger-Verlog , Inc., New

York, N.Y. , 1967.

[7] Kawase, Taro, Chiba University, Dept. of Electrical Engineering, Chiba, Japan.

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

[8] 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.

22
ftBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS BSS 1032. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE-. AND SUBTITLE

Exploratory Study of Glowing Electrical Connections

5. Publication Date October 1977

6. Performing Organization Code

7. AUTHOR(S)

William J. Meese and Robert W. Beausoliel

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

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. 20410

13. Type of Report & Period CoveredFINAL

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary of most significant 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 normal 120-volt, 15 and 20 ampere branch circuits

with both copper and aluminium 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.

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)

Arcing/sparking; branch circuit; contact resistance; electrical connections;

fire hazard; glowing electrical connections.

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Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and

illustrations provide useful background knowledge for shopping in today's technological marketplace.

Order above NBS publications from: Superintendent of Documents, Government Printing Office, Washington, D.C.

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the National Technical Information Services, Springfield, Va. 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register.

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pursuant to the Federal Property and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717

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BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey bibli- ographies are issued periodically by the Bureau: Cryogenic Data Center Current Awareness Service. A litera- ture survey issued biweekly. Annual subscription: Domestic, $25.00; Foreign, $30.00.

Liquified Natural Gas. A literature survey issued quarterly.

Annual subscription: $20.00.

Superconducting Devices and Materials. A literature survey

issued quarterly. Annual subscription: $30.00. Send subscription orders and remittances for the preceding bibliographic

services to National Bureau of Standards, Cryogenic Data

Center (275.02) Boulder, Colorado 80302.
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