NBSIR 75-672

A Preliminary Approacli to

Performance Requirements and

Criteria for Electrical Connections in

Residential Branch Circuit Wiring

William J. Meese, Ramon L. Cilimberg

and Adolpho A. Camacho

Building Services Section

Building Environment Division

Center for Building Technology

National Bureau of Standards

Washington, D. C. 20234

March 1975

Final Report

Prepared for Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410

NBSIR 75-672

A PRELIMINARY APPROACH TO

PERFORMANCE REQUIREMENTS AND

CRITERIA FOR ELECTRICAL CONNECTIONS IN RESIDENTIAL BRANCH CIRCUIT WIRING

William J. Meese, Ramon L. Cilimberg

and Adolopho A. Camacho

Building Services Section

Building Environment Division

Center for Building Technology

National Bureau of Standards

Washington, D. C. 20234

March 1975

Final Report

Prepared for Office of Policy Development and Research

Department of Housing and Urt)an Development

Washington, D.C. 20410

faff f ^^lii

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Table of Contents

1 . I ntroduct ion ^

1 . 1 Scope 2

1.2 The Performance Approach 3

1.3 Definitions of Special Terms 3

1.^ Significant Traditional Requirements for Electrical

Connections 5

2. Service Conditions 6

2.1 Design Service Conditions 6

2.2 Extreme or Unusual Service Conditions 9

3. Framework for Performance Evaluation of Electrical

Connections JO

k. Performance Requirements and Performance Criteria 12

^.1 Electrical Function Attribute 12

^.2 Fire Safety Attribute 16

^.3 Electrical Safety Attribute l8

k.k Burn Safety Attribute 19 A. 5 Mechanical Safety Attribute 21

^.6 Toxicity Safety Attribute 21

^.7 Building Environment - Non-interference Attribute... 22

4.8 Accessibility, Repa i rab i 1 i ty , Repl aceab i 1 i ty

Attribute 23

5. Test to Evaluate Electrical Function and Fire, Electrical

and Burn Safety Attributes 25

5.1 Continuous Current Path Element Tests 25

5.2 Dielectric Element Tests 30

5.3 Enclosure Element Tests 31

6. Summary 32

7 . References 7

A PRELIMINARY APPROACH TO PERFORMANCE REQUIREMENTS

AND CRITERIA FOR ELECTRICAL CONNECTIONS IN

RESIDENTIAL BRANCH CIRCUIT WIRING

William J. Meese, Ramon L. Cilimberg and Adolfo A. Camacho

ABSTRACT

During the Operation BREAKTHROUGH Research and Demonstration program

the U.S. Department of Housing and Urban Development became concerned

with the inability to properly evaluate innovative electrical connections.

Innovation in electrical connections has been very slow because of the

long-life requirements, stringent fire safety requirements, long established conventional practices and evaluation procedures and lack of a performance base for describing requirements. This preliminary report

presents the framework for a proposed method to evaluate electrical con- nections on a performance basis and supplements information contained in

a previous report on current technology of electrical connections used in

residential branch circuit wiring. Innovations involving electrical con- nections may lead to significant advancements in housing construction if

it can be demonstrated that functional and safety requirements over the

expected life of electrical connections were adequately satisfied. Research is needed to enable prediction of long-term performance of electrical connections based on the results of accelerated performance tests.

Key Words: Branch circuits; electrical codes; electrical connections;

fire safety; housewiring; contact resistance; performance testing.

1. INTRODUCTION

In 1969 the U.S. Department of Housing and Urban Development initiated Operation BREAKTHROUGH, with one of the purposes of the program

being to encourage and demonstrate innovations in housing. In the Operation BREAKTHROUGH program several innovations involving electrical connections were proposed. All such innovations would eliminate the use of

the traditional "box" and in some cases would make connections inaccessible

after completion of building construction. Taking cognizance of the

potential fire hazard and the lack of durability and other technical information, approvals for innovations involving electrical systems were

1
sparingly given with conservative stipulations. However, the possibilities of almost immediate significant benefits were recognized.

Subsequently the U.S. Department of Housing and Urban Development

agreed to sponsor a long-term research project on electrical connections

in residential branch circuit wiring at the National Bureau of Standards.

The first publication of this project was a report on "Analysis of Current

Technology on Electrical Connections Used in Residential Branch Circuit

Wiring" [1].

This report, the second of the project, covers concepts to be used

in generating performance requirements and criteria for evaluation of

innovative electrical connections and identifies areas where research is

needed

1 . 1 Scope

This report contains preliminary performance requirements and criteria intended for the evaluation of electrical connections used in

residential branch circuit wiring and identifies research needs.

"Branch Circuit" is defined by the National Electrical Code [2], as

fol 1 ows : ;

A branch circuit is that portion of the wiring system between

the final overcurrent device protecting the circuit and the

outlet(s) .

A device not approved for branch circuit protection such as thermal

cutout or motor overload protective device, is not considered

as the overcurrent device protecting the circuit.

Branch circuits in housing are generally limited to nominal 115 or 230

volts with rated ampacity (current carrw'wta capacity in ampere*;) r\f not

2
less than 15 or more than 50. Generally wires involved are not larger

than #6 AWG nor smaller than AWG for copper conductors or smaller

than #12 AWG for aluminum or copper clad aluminum conductors. Tap conductors for lighting fixtures (fixture wiring) and similar equipment connected to branch circuits may be as small as #18 AWG for copper conductors.

Both wire-to-wire and wi re-to- termi na I (such as wi re-to-termi nal

on receptacles, switches, lighting fixtures or permanent appliances),

connections which are made in the field or in a housing or mobile home

factory are covered. Connections which are normally made as a part of

the manufacturing process of electrical equipment are not covered.

1.2 The Performance Approach

A goal of this project is to develop requirements and criteria based

on performance. Performance requirements should state functions and

operational characteristics needed. Performance criteria should state

at what level the item must perform when tested in a prescribed manner.

The criteria should not state how a connector should be designed, what

materials it should be made of, its size or other quantities not directly

related to performance.

1.3 Definitions of Special Terms

To assist in common understanding, special terms used throughout

this report are defined below.

1.3-1 Electrical Connection Component :

All parts of the hardware directly concerned with the proper functtioning and safety of the electrical connection. As described below,

this would include the continuous current path elements, the dielectric

element and the enclosure element.

3
].3'2 Continuous Current Path Element :

The electric connection point or area and electric wire and other

metal parts in the vicinity of the connection point through which current

is intended to flow and which are directly involved in the proper functioning and safety of the connection. in conventional construction this

would include metal portions of "wire-nuts" in wire-to-wire connections

and wire-binding screw terminals on wire-to-terminal connections.

Also included is the grounding connection point or area and wire

and metal parts in the vicinity directly involved in the proper functioning and safety of the grounding connection. In this report "continuous current path elements" are generally referred to in the plural

because an electric connection usually involves more than one joint or

connection.

1.3-3 Dielectric Element :

Insulating material in the vicinity of the electric connection point

or area. Insulating material must completely surround the continuous

current path elements. The dielectric element may be "air". This is the

case where receptacles or switches are rigidly held in place within an

outlet box and electrical connections are made by means of wire-binding

screws .

'

,

].3-^ Enclosure Element:

Rigid metallic or non-metallic material which surrounds an electrical

connection and prevents persons, other building components or other objects

from coming in contact with the continuous current path elements. In

conventional construction a switch, outlet or junction box is the enclosure.

k
The same piece of hardware may perform both the function of the

dielectric element, which is an electrical function, and the function of

the enclosure, which is a mechanical function.

1.3.5 Other Building Components:

Parts of the building other than electrical connection coipponents.

This would Include studs and other structural parts, nails, gypsum board,

pipes, ducts, and wiring other than that included in definition 1.3.1.

1.^ Significant Traditional Requirements For Electrical Connections

Traditional requirements for electrical connections are discussed

in detail in the report "Analysis of Current Technology of Electrical

Connections Used In Residential Branch WJrtng" [1]. Code requirements which have been the most constrictive to Innovation are summarized

below.

1.^.1 "Box" Requirements

It is the code requirements for a "box" and not the requirements

directly related to electrical connections which have been the primary

elements of non-compliance for nearly all recent Innovative electrical

connections. The performance requirements and criteria in this report

do not directly, or indirectly, require that electrical connections be

made in traditional "boxes."

1.^.2 Accessibility Requirements

A long established code requirement for all electrical connections

is accessibility (without disturbing the structure or finish of a building after building construction has been completed) in addition to being

located in boxes. There appears to be very little demand for inaccessible

connections at the present time. However, some innovators and housing

. . 5
producers believe it to be unduly restrictive and an impediment to advances

in the manufactured housing construction process. With advanced developments in housing construction the demand for inaccessible connections will

probably increase. Subsection ^.8 of this report outlines a procedure to

evaluate inaccessible electrical connections. Because of the lack of

technical information and considering the long-life requirements which

would be necessary for connections not accessible for repair or replacement purposes, a conservative evaluation of inaccessible connections is

necessary. •

2. SERVICE CONDITIONS

In the evaluation of electrical connections it is important that

service conditions be known and well defined. Service conditions are

conditions involving durability (time), environment (ambient temperature,

humidity, chemical content of the surrounding atmosphere, etc.), mechanical stresses (vibration, wire bending, etc.) and electrical loading

(current loads and cycling patterns). Tests to determine compliance

with performance criteria should address applicable service condition.

Service conditions to be considered in the evaluation of innovative

electrical connectors are (1) "design service conditions" and (2) "unusual

or extreme service conditions." The term "applicable service conditions",

as used in the presentation of criteria in Section k, includes both conditions in accordance with the discussions below.

"\ 2.1 Design Service Conditions

Service conditions under which an electrical connection component is

expected to perform satisfactorily (design service conditions) need to

be determined. Design service conditions should be the most severe
conditions which can be anticipated under normal usage in housing installations. These are, generally, the conditions to which an electrical

connector should be designed.

2.1.1 Time

An electrical connection component should be designed to perform

safely for the life of a house, the exception being that the occurrence

of a failure must not cause a hazard and the electrical connection component must be readily repairable or replaceable.

2.1.2 Environment Subsequent to Installation

The temperature in the vicinity of the electrical connection may be

more of a factor in the failure of electrical connections than current

passing through it and the two are not necessarily directly related

because of heat dissipation aspects. Temperatures of a connection and

of components in the vicinity of a connection should be correlated with

typical insulation types and configurations surrounding them.

Anticipated humidity and moisture conditions in the vicinity of the

connection need to be determined. Also, the effect of different environments which come into contact with electrical connection components,

such as marine or industrial environments, need to be determined. The

influence of varying local conditions upon connector elements must be

assessed in terms of the performance, degradation and increased hazards.

2.1.3 Environment Prior to Installation

The environment to which an electrical connector and electrical

wire have been exposed prior to installation may produce or induce surface

chemical reactions when connections are made and thereby affect subsequent performance. This may result from exposure to various environ7
ments of the connector and wire during manufacturing and storage operations. It appears that surface chemistry aspects need investigation.

2.1. A Mechanical Stresses

Mechanical stresses, particularly those to which the connector and

wire are subjected during installation and maintenance operations, need

to be determined and defined. Wire breakage (at or in the vicinity of

a connection) as a result of installing or making connections could be a

major factor in connection failure. Mechanical properties such as bend

ductility and tensile elongation of conductors may be important in the

consideration of service conditions and potential for inducing failures.

Loosening of connections appears to be a major factor in their

failure. Vibration may be a contributing cause of loose connections.

Some types of housing, such as mobile homes, may require connections to

be more vibration resistant. Vibrations to which electrical connections

are subjected need to be determined.

2.1.5 Electrical Loading

In electrical connection testing, the amount of current and the

number and length of "on" and "off" cycles under which the tests are

conducted are specified and closely controlled. However, there appears

to be no back-up information in the literature relating such tests to

field performance [I]. In testing, it is the general practice to subject

electrical components to considerable current overloads to accelerate

failure. Establishment of a better relationship between short-term

accelerated testing and long-term field performance is needed.

8
2.2 Extreme or Unusual Service Conditions

In the evaluation of electrical connections, severe service conditions

under which connections may generally not be expected to operate satisfactorily, but to which a particular type of connection may be exposed or

utilized, should be considered. The effect and probability of extreme or

unusual service conditions as they relate to a particular connector should

be determined. It is not the intent that specific tests under extreme or

unusual circumstances be conducted except when those evaluating the connection determine that such tests are important to the evaluation.

2.2.1 Improper Installation

Improperly installed connectors should not be expected to perform

satisfactorily. However, ways in which the connector may be improperly

installed, the chances of such improper installation and the effect of

improper installation should be considered.

2.2.2 Other Extreme or Unusual Service Conditions

The effect of temperatures beyond those normally expected and the

effect of prolonged high humidity or rrxDisture should be evaluated. Included in these evaluations are extreme environmental conditions to which

connectors may be exposed in manufacturing and storage operations.

The effect of extreme vibrations and unusual stresses on electrical

connections should be evaluated. For example, what would happen if the

wire were bent over a smaller radius than required or expected? Other

extreme or unusual service conditions, such as prolonged "on" current or

different cycling patterns should be evaluated.

2.2.3 Evaluation for Extreme or Unusual Service Conditions

Performance under unusual or extreme service conditions must be

9
evaluated and may result in the non-approval of connectors which perform

satisfactorily under design service conditions. For example, if it could

be determined that the probability of an incorrect installation is high,

and such an installation would pose an extreme fire hazard, the connector

should not be approved.

The results of the evaluation for unusual or extreme service conditions may result in restrictions on the use of the connector. Possibly,

a connector which would perform poorly when subjected to extreme vibrations

may be prohibited from use in mobile homes but not in conventional housing.

Connectors made of certain material may be prohibited under certain conditions, such as a marine environment.

Evaluation of electrical connections under design conditions is

principally a matter of determining conformance under specific conditions.

For a complete and competent evaluation under extreme or unusual conditions, judgment supplemented by test data and other measurable criteria

is necessary.

3. FRAMEWORK FOR PERFORMANCE EVALUATION OF ELECTRICAL CONNECTIONS

,, Figure I outlines a proposed framework for the evaluation of electrical connections on a performance basis. The key to this evaluation is

"Performance of Essential Physical Elements" when subjected to "Applicable

Service Cond ? t lons"sha I I be in accordance with necessary "Attributes."

An electrical connection has three essential physical elements which

are: (A) a continuous current path element, (B) a dielectric element,

and (C) an enclosure element. These terms are defined in Subsection 1.3.

10
ID

CD

GO

OO

All llavnJv Iddd

/AiniavNiviNivi/\i

/AiniaissBoov • 30NBU3dH3iNI'NON

lN3l/\IN0dlANB

9NIG1ina

CO KBm

>UJ3IX01

A13JVS

1V3INVH33IAI

Ai3dVS

CO AlBdVS

1V3mi3313

Csla Ai3dVS

dUld • NOI13Nnd

lV3mi3313 \

ahributes

essentiaK physical \

elements

A CONTINUOUS

CURRENT

PATH o

—J

LUO

LU

CC

GO

cj

go

LU

CO

CO

03

CO^

GO

CO

hOo S

1^ ^<

GC

LU

CO

CD

CO

CO

cuo

zz CQ -9

CO <

>-

O ^

Q- < <

cuo

h—

O CU

2: -H- -a

LU TO

O

CO » o

LU 5

CD ^ S " cz g ^

CO ^ > CO ^ • •

o.
k. PERFORMANCE REQUIREMENTS AND PERFORMANCE CRITERIA

In Section 3 a framework for the performance evaluation of electrical

connections was presented. This section, on performance requirements and

performance criteria, details the concepts to be used In these evaluations

For each attribute, the performance requ i rement (s) of each essential

physical element is listed first. This is followed by the listing of

performance criteria, which describe the performance requirements in

more specific terms. This is followed by a description of applicable

tests and commentaries which explain and discuss each requirement and

cr i ter ion

Section 5 further discusses and describes tests to evaluate electrical function and safety (fire, electrical and burn) attributes. In

many cases the same tests may be used to evaluate two or more of these

attributes.

A.I Electrical Function Attribute

A.l-A Continuous Current Path Elements

Requ i rement A .

1 -A

The continuous current path elements shall provide for adequate flow

of current through the connection point or area.

Cr i ter ion A . 1 -A

Under applicable service conditions the continuous current path elements shall permit rated current of connected wires or other specified

current values to flow through the connection point or area without excessive voltage drop. Specific values for allowable voltage drops are

to be determined.

12
Test A.) -A

Evaluative test methods for determining performance need to be

developed. See Subsection 5.1| Continuous Current Path Element Tests.

Commentary 4 . 1 -A

Rule 210-6(d), Voltage Drop, of the National Electrical Code [2]

states that the size of conductors for branch circuits should be such

that the voltage drop will not exceed 3 percent to the farthest outlet

for power, heating or lighting purposes or combination thereof. This rule

also states that the maximum total voltage drop for feeders should not

exceed 5 percent overall.

Voltage drop at the connection point will be in proportion to the

effective contact resistance. However, experience indicates that high

contact resistance will result in excessive heating and a fire hazard

before there is any impairment of electrical function. Specific limits

for voltage drop will probably be established in response to fire safety

(temperature) requirements (see Requirement ^.2-A) rather than In response

to electrical function requirements.

A.l-B Dielectric Element

Requ i rement ^. 1 -B

The dielectric element shall provide adequate electrical insulation

between individual continuous current path elements and between the

continuous current path elements and other building components.

Criterion 4.1-B

Under applicable service conditions, the dielectric element shall

provide electrical insulation which will withstand, without breakdown,

a suitable voltage between the continuous current path elements and the

13
surface of the electrical connection enclosure element when the

electrical connection component is properly installed.

Test k. 1-B

Evaluative test methods for determining Insulation performance need

to be developed. See Subsection 5.2, Dielectric Element Tests.

Commentary ^ . 1 -B

Adequate electrical insulation is necessary for electrical function

and safety requirements. Specific criteria need to be developed. Criteria

do not exist for dielectric withstand tests for this application; however,

as related items of interest, examples of starting points are cited below.

For attachment plugs and receptacles, Underwriters' Laboratories

requires a dielectric withstand test as follows: [3]

i "The assembly of a cord and wiring device shall be capable of

withstanding without breakdown, for a period of one minute

, . , the application of a 60-cyc 1 e-pe r-second (60 hertz) essentially

sinusoidal potential of 1250 volts between the two conductors

of the flexible cord."

For non-metallic sheathed cable Underwriters' Laboratories requires

a dielectric withstand test as follows: [4]

"After immersion in water at room temperature for 2k hours

and while still immersed, speciments from finished cable wound

around a mandrel shall withstand for one minute a 60-cycleper-second (60 hertz) essentially sinusoidal potential of

5000 volts. The potential shall be applied from each conductor

separately, to the other conductor or conductors, the grounding

conductor if any, and the water/mandrel ground."
^.]-C Enclosure Elements

Requ i rement ^. I -C

The enclosure element shall prov ide adequate electrical protection

from contact with the continous current path elements for persons and

other building components.

Criterion ^. l-C

Under applicable service conditions, the enclosure element shall be

so constructed and installed, and possess sufficient rigidty and strength

so that any objects in contact with any part of the surface of an electrical connection component will have electrical insulation at least

equal to that specified in Criterion ^.l-B between the object and the

continuous current path elements.

Test ^.1-C

Evaluative test methods for determining protection performance need

to be developed. See Subsection 5-3, Enclosure Element Test and Test

4.3-C.

Commentary ^ . 1 -C

The enclosure element is needed to afford structural protection to

the continuous current path elements as well as for safety purposes. U.

L. performance tests for conventional outlet boxes [5], include tests for

tensile strength, flexural strength, resistance to crushing, and resistance

to impact. Innovative devices may require additional criteria.

15
k.2 Fire Safety Attribute

Continuous Current Path Elements

Requ i rement k. 2-A

Under applicable service conditions, the continuous current path

elements shall be capable of operating without causing overheat'ng of

proximate building materials.

Criterion k.2-/\

Under applicable service conditions the continuous current path

elements shall exhibit connectab i 1 i ty which will not permit overheating.

Test ^.2-A

Evaluative test methods for determining current path performance

need to be established. See Subsection 5.1, Continuous Current Path

Tests.

Commentary ^.2-A

Research is needed to establish specific values pertaining to heat

generation, temperatures, contact resistance, meta I -to-meta I contact or

other properties pertaining to overheating, or to characteristics which

may result in overheating of the continuous current path elements. Therefore, the above criterion fs stated in general terms. Heat generation,

heat dissipation, and the ability of different materials to withstand

the effect of heat need to be examined further. Subsection 5.1,

Continuous Current Path Element Tests, further discusses the problems of

connectab i I i ty and wire breakage.

k.2-B Dielectric Element

Requi rement 2-B

The dielectric element shall be fire resistive and prevent arcing

16
between phases of the circuit or to ground.

Criterion

(a) Under applicable service conditions, the dielectric element shall be

of non-combustible construction as defined by NFPA Life Safety Code [6].

(b) See Cri terion k. 1-B.

Test 4.2-B

Test methods for determining performance of the dielectric element

need to be developed. See Subsection 5.1, Continuous Current Path Tests.

Commentary ^.2-B

The dielectric element provides a fire safety function; by

separating the conductors, and should not be constructed of combustible

mater i a 1 s

^.2-C Enclosure Element

Requ i rement 4. 2-C

The enclosure element shall be fire resistive and shall be so

constructed in combination with the dielectric and continuous current

path elements and/or located, to prevent ignition of other building

components as a result of the flow of current through the continuous

current path elements.

Criterion ^.2-C

(a) Under applicable service conditions the enclosure element shall be

of non-combustible construction as defined by the NFPA Life Safety

Code [6].

(b) Temperature on the surface of the enclosure element shall be

governed by Criterion k.h-C.

17
Test ^.2-C

Evaluative test method to determine performance of enclosure

elements need to be developed. See Subsection 5-3, Enclosure Element

Tests

Commentary k.2-C

The enclosure element should protect people and other building

components from heat generated in the continuous current path elements,

and should be constructed of non-combustible materials.

4.3 Electrical Safety Attribute

^.3~A Continuous Current Path Elements

Commentary ^.3"

.,

Protection against electrical hazards is the function of the dielectric

and enclosure elements.

A.3~B Dielectric Element

Requirement ^.3~B

The dielectric element shall provide adequate electrical insulation

from the continuous current path elements to a person or building component

which may come in contact with the surface of the enclosure element.

Cr i terion 4. 3-B

Same as Criterion A.l-B.

Test 4.3-B

See Subsection 5.2, Dielectric Element Test.

Commentary ^.3~B

Adequate insulation is needed for both electrical safety and

electrical function purposes. It Is anticipated the criteria and tests

indicated by criteria ^.l.-B and A.3"B, will cover both the electrical

18
safety and electrical function attributes.

A.3~C Enclosure Element

Requ i rement 4 . 3"

The enclosure element shall provide adequate physical protection

to persons and other building components from the continuous current

path elements.

Criterion 4.3~C

(a) See Criterion A.l-C.

(b) Any exposed metal parts on the surface of the enclosure element shall

have provisions for and, when installed, shall be grounded in accordance

with the National Electrical Code [2].

Test ^.3-C

Inspection of enclosure element and of any nonmetallic material

used in its construction, and of grounding provisions of any exposed

metal parts for determination of electrical safety. Also, see

Subsection 5-3. Enclosure Element Tests.

Commentary 4.3~C

In conventional construction, the enclosure element, which is the

"box", performs the function described in Requirement ^.3"C when

properly installed with covers in place. It is the intent that the

electrical connection component have no exposed live parts, and when

properly installed, any exposed metal parts be effectively grounded.

k.k Burn Safety Attribute

A.^-A Continuous Current Path Elements

Commentary k.k-k

Performance requirements concerning burn safety apply to the

19
enclosure element only.

^.^-B Dielectric Element

Commentary k.k-B

Performance requirements concerning burn safety apply to the

enclosure element only.

k.k-C Enclosure Element

Requ i rement k. ^-C

The enclosure element shall not attain temperatures sufficient

to burn persons or animals who may inadvertently touch the enclosure

el ement

Criterion A.A-C

Under applicable service conditions, no part of the surface of

the enclosure element shall exceed a temperature of kO°F above ambient

temperature.

Test k.k-C

See Subsection S-3, Enclosure Element Tests.

Commentary k.k-C

It is anticipated that many Innovative connections will not have

"free space" which Is now required in conventional outlet boxes by the

National Electrical Code [2]. It is the Intent of this requirement that

any heat generated by the connection be dissipated in such a way as

to not burn persons or animals who may Inadvertently touch the

enclosure element. The above criterion, which is subject to further

qualifications. Is based on judgment following tests which were performed

at the National Bureau of Standards.

20
4.5 Mechanical Safety Attribute

Requ i rement k .

All parts of the electrical connection component; including the

continuous current path elements, the dielectric element and the

enclosure element; shall present no unreasonable mechanical hazards.

Criterion 4.5

Under applicable service conditions and during installation and

maintenance operations, all parts of the electrical connection component

shall be so constructed and installed that no unreasonable mechanical

hazards exist, such as cutting, pinching, abrasion, tripping or snagging.

Test 4.5

Physical inspection of electrical connection components and evaluation

of methods of installing and maintaining electrical connection components

should be conducted to determine mechanical safety.

Commentary k. 5

It is the intent that electrical connection components be examined

for mechanical hazards to people which may exist in installation,

maintenance or replacement operations or after installation.

4.6 Toxicity Safety Attribute

Requirement 4.6

Electrical connection components shall present no unreasonable

potential toxic hazards.

Cr i ter i on 4.6

Under applicable service conditions including overheating conditions,

all parts of the electrical connection component, including the continuous

21
current path elements, the dielectric element and the enclosure element,

shall be so constructed and installed that no unreasonable potential

toxic hazards exist.

Test A.

Inspection and evaluation is required of electrical connection

components and materials, including paints and finishes, used in

their construction. In the event of any suspicion of toxic hazards,

the opinion of experts in this field should be sought.

Commentary ^.6

While conventional materials used in electrical construction are not

believed to be toxic, the possibility of toxic hazards should not be

overlooked, particularly if new materials are introduced. Also,

because electrical connection components, even under normal conditions,

operate at higher temperatures than most building components, toxicity

hazards should be considered.

4.7 Building Environment Non-interference Attribute

Requ i rement h. 7

The electrical connection component shall not produce an

environment that will interfere with building functions.

Cr i ter ion k. 7

Under applicable service conditions, all parts of electrical

connection components, including the continuous current path elements,

the dielectric element and the enclosure element, shall be so

constructed and installed to prevent excessive air and moisture

transmission and so that there is no unreasonable interference or

unusual interactions with communication, acoustical or other building

f unct ions . 22
Test k.l

Physical inspection of electrical connection components should

be conducted to evaluate the potential for interference with building

functions. Applicable tests, such as radio interference tests,

should be conducted if interference with any building function is

suspected.

Commentary ^.7

For tight well-made connections with low contact resistance, there

appears to be little likelihood of interference with building

functions. Therefore, specific tests, such as a radio interference

test, to ascertain this criterion are not proposed. However, the

evaluation of innovative electrical connections should consider the

possibilities of such interference.

^.8 Accessibility, Repa I rab i 1 i ty , Repl aceab i 1 i ty Attribute

Requirement 4.8

Inaccesible electrical connections should retain all necessary

attributes for the expected life of the building in which they are

installed. Otherwise electrical connection components, or parts of

electrical connection components which contain the connection point or

area of the continuous current path element shall be reasonably

accessible and either reasonably repairable and/or replaceable.

Cri terion 4.8

Inaccessible electrical connections should retain Attributes 1

through 7 for a minimum of 50 years. Other electrTcal connection

components or parts of electrical connection components which contain

the connection point or area of the continuous current path elements

23
shal 1 be

(1) accessible without disturbing any building component

other than the electrical connection component and

(2) either

(a) repairable with the entire electrical connection

component restorable to its original condition, or

(b) replaceable with readily available hardware or with

other readily available electrical connection components

without major d i sturbance of other building components

and with the electrical connection in conformance with

the criterion listed above.

Test ^.8

Inspection to determine accessibility, repa i rab i 1 i ty , repl aceabi 1 i ty

aspects of electrical connection components should be conducted. For

inaccessible electrical connections see commentary below.

Commentary 4.8

See Subsection 1.4.2, concerning the subject of "Accessibility"

requirements in codes. Considerable research and test development

is needed for the evaluation of inaccessible connections. Inaccessible

connection development should be encouraged and any innovative connector,

which on preliminary examination, appears to be suitable for use in

inaccessible locations, should receive extensive evaluation for such use.

2k
5. TESTS TO EVALUATE ELECTRICAL FUNCTION AND FIRE,

ELECTRICAL AND BURN SAFETY ATTRIBUTES

It is anticipated that testing to evaluate the performance of electrical

connections will, in general, address the first four Attributes shown in

Figure 1, which are (A.l) Electrical Function, (^.2) Fire Safety, ('.3)

Electrical Safety and {h.k) Burn Safety. It is anticipated that the other

four attributes, which are (A. 5) Mechanical Safety, (4.6) Toxicity Safety,

(A. 7) Building Environment Non-interference, and (4.8) Accessibility,

Maintainability, Rep 1 aceab i 1 i ty will, in general, be evaluated by inspection.

If there i s uncer ta i nty about compliance with the criterion pertaining to

any of these attributes, testing methodologies must be developed. See

Subsection 4.8 for the evaluation procedures of inaccessible connections.

5.1 Continuous Current Path Element Tests

To evaluate Attributes (4.1) Electrical Function, (4.2) Fire Safety,

and (4.4) Burn Safety, tests and research to determine both the performance

of the continuous current path element and the performance of materials

used in the continuous current path element are needed. As discussed

in "Analysis of Current Technology on Electrical Connections Used in

Residential BRANCH Circuit Wiring" [1] failures in electrical connections,

after exposure to time, power cycling, mechanical stresses and

environmental conditions usually occur for two basic reasons, which are:

(1) properties of the wire and connection, which promote loose

connections and/or increased contact resistance, usually resulting

in overheating. This is termed unsatisfactory "connectabi 1 ity", and

25
(2) wire breakage in the vincinity of the connection point or area,

which may result from added stresses during installation or maintenance operations. This may also result in overheating.

Overheating of an electrical connection is caused by the resistance

to the flow of current at the wi re-connector interface. With an increase

in resistance there will be an associated increase in temperature. The

resistance will not increase unless certain changes occur in the wireconnector interface with time and exposure to various environments. The

contact resistance will tend to increase with reduced contact pressure

and with the formation of a nonconduct i ve layer in the contact interface.

Contact pressure may be reduced by manual movement of the wire, vibration,

stress relaxation or creep of the wire and differential thermal expansion

between the wire and the connector.

A performance test needs to be developed to simulate vibration and

manual movement (wire disturbance). An accelerated short term test may

not simulate stress relaxation or creep, which are long term mechanisms.

The contact resistance (and thus temperature) may tend to increase

with time, and exposure of the wire-connector interface to oxygen, water,

chloride, and sulfur compounds. Oxygen and water exist in nearly all

environments while chloride is found in marine atmospheres and sulfur

compounds are prevalent in industrial atmospheres. A performance test

should be developed which will simulate the effects of these compounds

on contact resistance for electrical connectors that will be used in

building at sites which are exposed to the respective compounds.

26
The temperature of electrical contacts is also dependent on the tendency

of the air or other materials surrounding the electrical connector to conduct heat away from the contact interface. A performance test should simulate

the highest ambient temperature that may exist in the wall of a building.

A reliable performance test of an electrical connection would be

the measurement of the temperature of the wire-connector interface of a

device exposed to the worst conditions in a building for the life of

the building. The time required for such a test under real life conditions

is prohibitive for performance testing. However, long-term tests should be

performed in an electrical connector research program to establish the

validity of acceleration factors for performance testing.

On a pract ical bas i s acceleration factors must be assumed, to conduct

performance tests. Since these factors have not been established, tests

should be performed for various factors and attempts made to extrapolate

these short term results to estimates of long term performance. However,

validation of the acceleration factors is needed.

An example of an interim performance test of an innovative electrical

connector is the power cycling with wire disturbance test performed by

Underwriters' Laboratory [7]- The acceleration factors are current

(53 amperes for a device rated 20 amperes) cycle rate (3-1/2 hours current

ON, 1/2 hour current OFF), total cycles (500), wire disturbance (bend wire

from horizontal to vertical), and ambient temperature (25*C). Bulk

terminal temperatures are measured during the test and failure Is based

on a single reading In excess of 175*C or a temperature rise greater than

10*C of any one data point above the average temperature rise of eleven

data points of one test connection.

27
To determine reasons for failure of materials and properties

necessary for acceptable connections, tests and research on characteristics

of materials are needed. Testing is needed to determine that installation

and maintenance operations will not deteriorate mechanical properties

to the extent that wire breakage will subsequently occur. Testing is

also needed to determine properties affecting the connectab i 1 i ty of an

electrical connection.

Wire strength criteria may be needed to ensure that mechanical

property modifications to meet connection criteria do not lower the

wire strength sufficiently to cause failure during installation. Wire

ductility criteria may be needed to ensure that the wire can be

manipulated before and after making a connection without breaking or

impairing heat cycle performance. The ductility of the wire can be

lowered by the stress produced in making mechanical connections.

Subsequent bending of the wire for connector replacement or other repairs

can result in wire breakage if the ductility is too low. Possibly,

some innovative connectors may require less manipulation and, therefore,

less ductile wire than conventional connections.

Connectab i 1 i ty is usually a function of the properties of the wire

and the properties of the connector which will promote metal -to-metal

contact at the interface between the wire and the connector. Metal -to-metal

contact can generally be assured by designs which break the oxide layers

on the surfaces of the wire and the connector and provide sufficient

normal force or pressure to effect cold welding of the metal in the wire

to the metal in the connector. Metal -to-metal contact is measured

destructively by metal lograph i c techniques such as scanning electron

28
microscopy. Contact resistance measurements may give non-destructive

indication of metal -to-metal contact. The relationship between the number

of micro-contacts, contact resistance, contact pressure, and subsequent

heat cycle temperature rise may need to be established for electrical

connectors.

There may be correlations between mechanical properties such as wire

yield strength and creep strength and the heat cycle performance of

electrical connectors. Tests may need to be performed to determine if

quantitative values should be established for mechanical properties.

There may be correlations between the chemistry of the wire-connector

interface and the heat cycle performance of electrical connectors. Tests

may need to be performed to determine if quantitative performance values

should be established as a function of surface chemistry.

A test program should be developed to determine the causes of

overheating which is apparently the most critical factor in connector

evaluation. The ultimate goal will be to determine the approximate service

life and conditions of an electrical connection before failure, particularly

failure resulting in overheating, on the basis of relatively short term

tests.

Tentatively, it has been determined that tests or research in the

areas listed below are needed for the evaluation of the continuous

current path elements. Specific test conditions and methods for testing

need to be established.

(1) Power cycling with wire disturbance

(2) Power cycling v/ith vibration

(3) Environmental exposure

29
Humidity Expose wire and connector separately

to each environment and then connect

and perform power cycle test.

Salt Spray Connect wire and connector, then expose

to each env i ronment ^then perform power

cycle test.

(k) Creep strength of wire

. (5) Surface chemistry of wire, connector and wire-connector

interface

(6) Contact pressure of interface

(7) Contact resistance of interface

(8) Coefficient of expansion of wire and connector

(9) Bend duct i 1 i ty

(10) Bend test in a simulated wall

(11) Effect of high ambient temperature

(12) Effect of temperature rise on various structural arrangements.

5.2 Dielectric Element Tests

To evaluate Attribute (^.1) Electrical Function, (4.2) Fire Safety,

and (4.3) Electrical Safety, determination of the dielectric element performance

characteristics is necessary. Reasonable assurances are needed that the

dielectric elements, after exposure to time, heat cycling, mechanical

stresses and environmental exposures, will retain needed electrical and

fire resistance properties. In some tests performed on the continuous

current path elements, such as the power cycling and environmental tests,

the dielectric element will be subjected to simulated performance, after

which satisfactory dielectric withstand and fire resistance properties should

be unaffected.

30
Tentatively, it has been determined that tests or research in the

areas listed below are needed for the evaluation of the dielectric

element. Specific test conditions and methods of testing need to be

estab 1 i shed

(1) Dielectric withstand

(2) Fire resistance

Performance criteria for the dielectric element can probably be

established without extensive research. The required performance of the

dielectric element in the vicinity of connections is not significantly

different from its required performance near other parts of an electric

c i rcu it.

5.3 Enclosure Element Tests

To evaluate Attributes (A.l) Electrical Safety, (A. 2) Fire Safety,

(A. 3) Electrical Safety and {k.k) Burn Safety, determination of the enclosure

element performance characteristics is necessary. Reasonable assurances

are needed that the enclosure element, after exposure to time, heat cycling,

and mechanical and environmental absuses, will retain its structural,

fire resistive and surface temperature properties and that insulation

between the continuous current path elements and the enclosure element be

kept intact. In some tests performed on the continuous current path element,

the enclosure element will be subjected to simulated performance, after

which satisfactory properties of the enclosure element should be retained.

Tentatively, it has been determined that tests or research in the

areas listed below are needed for the evaluation of the enclosure

element. Specific test conditions and methods of testing need to be

establ i shed

31
(1) Strength

(2) Deflection

(3) Surface temperature

{k) Insulation from continuous current path elements

Performance criteria for the enclosure element can probably be

established without extensive research. The required performance of the

enclosure element in the vicinity of connections is not significantly

different from its required performance near other parts of an electric

c I rcu it.

6. SUMMARY

This report presents the framework for generating methods of evaluation

for determing performance of electrical connections used in residential

branch circuit wiring. Figure I summarizes this approach. This is a

"black box" approach. Determining satisfactory performance regardless of

materials, design geometry, methods of installation or other specification

type requirements is the aim of this project.

Information on environmental and other service conditions under which

electrical connections operate, as well as the effect of these service

conditions, is required for the development of performance criteria.

Information on some materials properties of electric cable and connectors,

and the effect of these properties on performance may also be needed.

Tests sufficiently representative of real exposure will then be developed.

Such tests will need to be supplemented by judgment because of the many

attributes and unusual service conditions which may be encountered.

32
The thermal performance of the continuous current path elements under

various service conditions appear to be the most significant performance

aspect to be determined in evaluating electrical connections. The methods

of evaluation which must be developed are dependent upon accelerated testing

to accomplish in a reasonable time the determination of long term

characteristics. Additional research should be undertaken to relate real

exposure to acceleration factors.

Suitable performance criteria for the dielectric element (electrical

protection) and for the enclosure element (structural protection) can

probably be developed without extensive research. The dielectric and the

enclosure elements are essential physical elements for electrical connections

but they are also essential physical elements for all other parts of branch

circuits. However, unlike the performance of the continuous current path

elements, the performance of the dielectric and enclosure elements are

not significantly different in the vicinity of the connections.

33
7. REFERENCES

!• Analysis of Current Technology on Electrical Connections used in

Residential Branch Circuit Wiring, BSS63, William J. Meese and

Ramon L. Cilimberg. March 1975

Z, National Electrical Code - 1971, ANSI C-1-1971, NFPA #70-71.

3. U. L. Standard ^98 Attachment Plugs and Receptacles (May 1962,

Revised July 7, 1972)

k. U. L. Standard 719 - Non-metallic Sheathed Cable (July 1, 1969).

5. U. L. Standard 51^ (May 1971) - Outlet Boxes and Fittings.

6. Life Safety Code, NFPA No. 101-1970.

7. Tentative Program for the Investigation of Wiring Devices Intended

for Use with Aluminum Wire - Appendix A, enclosed with U. L. Memos

. ; dated January 25, 1972, November 2^4 , 1972 and September 29, 1972

on Subjects A, it4 ,83,^468,719 and 85^+.

USCOMM NHS U(
NBJ.-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR RICPORT NO. NBSIR 75-672

2. Gov't Accession

No.

3. Recipient's Accession No.

4, TITLE AND SUBTITLL

A PRELlMtNARY APPROACH TO PERFORMANCE REaUIREMENTS

AND CRTTERIA FOR ELECTRICAL CONNECTIONS IN RESIDENTIAL

BRANCH CIRCUIT WRING

5. Publication Date

i ICU. \^Ll -L / ( ^

6. Performing Organization Code

7. AUTHOR(S)

William J. Meese, Ramon L. Cilimberg, and Adolfo A. Camacho

8. Performing Organ. Report No. NBSIR 75-672

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

Department of Housing and Urban Development

Washington, D.C. 20410

13. Type of Report & Period Covered

FINAL

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.) During the Operation BREAKTHROUGH Research and Demonstration program the U.S.

Department of Housing and Urban Development became concerned with, the inability

to properly evaluate innovative electrical connections. Innovation in electrical

connections has been very slow because of the long-1 Tfe requirements, stringent

fire safety requirements, long established conventional practices and evaluation

procedures and lack of a performance base for describing requirements. This

preliminary report presents the framework for a proposed method to evaluate

electrical connections on a performance basis and supplements information

contained in a previous report on current technology of electrical connections

used in residential branch circuit wiring. Innovations involving electrical con- nections may lead to significant advancements in housing construction if

it can be demonstrated that functional and safety requirements over the expected

life of electrical connections were adequately satisfied. Research is needed

to enable prediction of long-term performance of electrical connections based

on the results of accelerated performance tests.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Branch circuits; electrical codes; electrical connections; fire safety;

housewiring; contact resistance; performance testing.

18. AVAILABILITY [T Unlimited

1 For Official Distribution. Do Not Release to NTIS

1

^ Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402. SO Cat. No. C13

1

1 Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

35

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

USCOMM.DC 29042-P74