ASTM B942-21

Standard Guide for Specification and Quality Assurance for the Electrical Contact Performance of Crimped Wire Terminations

SIGNIFICANCE AND USE
4.1 The purpose of this guide is to provide end-product manufacturers and other users with technical information and methods recommended towards the achievement of successful application of crimped wire terminals.  
4.2 For any given use, there is generally a choice of terminal types available, employing different mechanical design, materials, and installation tooling. Although terminals available to choose from may be similarly rated, typically according to wire sizes and combinations, their electrical contact performance in the end product may vary substantially. For many applications, the end-product reliability and user safety is substantially influenced by the choice of terminal and the quality of the completed termination. This guidance document contains specialized information on selection, assembly, and quality control of crimped wire terminals, covering aspects considered to be necessary to achieve reliable long-term operation in the intended application. This information is not generally found in commercial literature or textbooks. The methods discussed utilize connection resistance as the primary measure of termination quality, and change of connection resistance with time as the measure of termination deterioration. The methods are based on a foundation of modern electrical contact theory and practice.
SCOPE
1.1 This guide contains practices for specifying and evaluating the electrical contact performance of crimped-type terminations with solid or stranded conductors.  
1.2 This guide provides information relevant to the electrical contact performance of a crimped wire termination. It does not cover other aspects of selection and use of crimped terminals.  
1.3 The methods discussed in this guide apply only to the wire termination, which is the electrical contact interface between the conductor(s) and the terminal. Other aspects important to terminal evaluation, such as the properties and performance of electrical insulation, the effectiveness of strain relief features, and the quality of contact between the terminal and other electrical circuit elements, are not included.  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to become familiar with all hazards including those identified in the appropriate Safety Data Sheet (SDS) for this product/material as provided by the manufacturer, to establish appropriate safety, health, and environmental practices, and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2021
• ICS: 29.120.20 - Connecting devices
• Technical Committee: B02 - Nonferrous Metals and Alloys
• Drafting Committee: B02.05 - Precious Metals and Electrical Contact Materials and Test Methods

Relations

• Refers: ASTM B845-97(2024) - Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
• Effective Date: 01-Apr-2024
• Refers: ASTM B542-13(2019) - Standard Terminology Relating to Electrical Contacts and Their Use
• Effective Date: 01-Nov-2019
• Refers: ASTM B539-18 - Standard Test Methods for Measuring Resistance of Electrical Connections (Static Contacts)
• Effective Date: 01-Nov-2018
• Refers: ASTM B827-05(2014) - Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests
• Effective Date: 01-Oct-2014
• Refers: ASTM B539-02(2013) - Standard Test Methods for Measuring Resistance of Electrical Connections (Static Contacts)
• Effective Date: 01-Aug-2013
• Refers: ASTM B845-97(2013)e1 - Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
• Effective Date: 01-Aug-2013
• Refers: ASTM B845-97(2013)e2 - Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
• Effective Date: 01-Aug-2013
• Refers: ASTM B845-97(2013) - Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
• Effective Date: 01-Aug-2013
• Refers: ASTM B542-13 - Standard Terminology Relating to Electrical Contacts and Their Use
• Effective Date: 01-Feb-2013
• Refers: ASTM E122-09e1 - Standard Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process
• Effective Date: 01-Aug-2011
• Refers: ASTM B913-05(2010) - Standard Test Method for Evaluation of Crimped Electrical Connections to 16-Gauge and Smaller Diameter Stranded and Solid Conductors
• Effective Date: 01-Oct-2010
• Refers: ASTM B827-05(2009)e1 - Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests
• Effective Date: 01-Oct-2009
• Refers: ASTM B827-05(2009)e2 - Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests
• Effective Date: 01-Oct-2009
• Refers: ASTM E122-09 - Standard Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process
• Effective Date: 01-Aug-2009
• Refers: ASTM B845-97(2008)e2 - Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
• Effective Date: 01-Apr-2008

Overview

ASTM B942-21: Standard Guide for Specification and Quality Assurance for the Electrical Contact Performance of Crimped Wire Terminations provides manufacturers, engineers, and quality assurance professionals with essential guidance for evaluating and specifying the electrical contact performance of crimped wire terminations. Crimped wire terminations are widely used in electrical and electronic systems where secure and reliable wire-to-terminal connections are necessary. This standard focuses on best practices, evaluation methods, and quality control measures to ensure reliable, high-performance electrical contact interfaces in end-products, especially where safety and long-term reliability are critical.

Key Topics

• Electrical Contact Performance: The guide addresses how to specify and evaluate electrical contact performance in crimped-type terminations using solid or stranded conductors. Emphasis is placed on the primary role of connection resistance as the measure of quality and as an indicator of potential deterioration over time.

• Selection of Terminals: There is a wide variety of terminal types available, each with different mechanical designs, materials, and installation tools. While these may be similarly rated for wire size, their electrical performance in real-world applications can differ significantly.

• Crimp Quality Factors: The quality of crimped terminations depends on multiple variables, including terminal and conductor material, tool selection and setup, and environmental conditions. Proper crimping reduces connection resistance and enhances long-term reliability.

• Quality Control and Inspection: Visual inspection, pull testing, and connection resistance measurement are recommended for ensuring the quality and performance of crimped terminations. Periodic metallurgical cross-section analysis is advised, particularly in critical applications, to assess mechanical integrity.

• Statistical Evaluation: Determination of appropriate sample sizes and statistical analysis of connection resistance measurements are encouraged to ensure confidence in quality control processes for crimped wire terminations.

Applications

ASTM B942-21 applies across various industries where electrical wiring and terminations are integral, including:

• Automotive Wiring Harnesses: Ensures critical signal and power connections perform reliably under mechanical vibration, temperature variations, and exposure to contaminants.
• Consumer Electronics and Appliances: Promotes user safety and product reliability, especially in applications with high current loads or sensitive safety circuits.
• Industrial Equipment: Supports robust electrical interconnections in control panels, motors, and industrial machinery.
• Aerospace and Defense: Ensures long-term termination reliability in harsh environments, such as temperature extremes and vibration.

This standard is particularly valuable for applications with stringent safety and reliability requirements, where poor termination performance could lead to product failure, unsafe conditions, or regulatory non-compliance.

Related Standards

ASTM B942-21 references several complementary standards and resources for electrical termination specification and testing:

• ASTM B539: Test Methods for Measuring Resistance of Electrical Connections (Static Contacts)
• ASTM B542: Terminology Relating to Electrical Contacts and Their Use
• ASTM B827: Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests
• ASTM B845: Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
• ASTM B913: Test Method for Evaluation of Crimped Electrical Connections to 16-Gauge and Smaller Conductors
• UL 486-A: Wire Connectors and Soldering Lugs for Use with Copper Conductors
• UL 310: Electrical Quick-Connect Terminals
• ASTM E122: Practice for Calculating Sample Size to Estimate Characteristics of a Lot or Process

Conclusion

Adhering to ASTM B942-21 supports consistent and reliable electrical contact performance in crimped wire terminations. By following this standard, organizations can enhance product safety, maintain high quality, and meet industry acceptance criteria. The guide provides actionable procedures for selection, assembly, and quality control, contributing to long-term operation and reliability in diverse electrical applications.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B942 − 21
Standard Guide for
Specification and Quality Assurance for the Electrical
Contact Performance of Crimped Wire Terminations
This standard is issued under the fixed designation B942; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This guide contains practices for specifying and evalu-
B539 Test Methods for Measuring Resistance of Electrical
ating the electrical contact performance of crimped-type ter-
Connections (Static Contacts)
minations with solid or stranded conductors.
B542 Terminology Relating to Electrical Contacts and Their
1.2 This guide provides information relevant to the electri-
Use
cal contact performance of a crimped wire termination. It does
B827 Practice for Conducting Mixed Flowing Gas (MFG)
not cover other aspects of selection and use of crimped
Environmental Tests
terminals.
B845 Guide for Mixed Flowing Gas (MFG) Tests for Elec-
trical Contacts
1.3 The methods discussed in this guide apply only to the
B913 Test Method for Evaluation of Crimped Electrical
wire termination, which is the electrical contact interface
Connections to 16-Gauge and Smaller Diameter Stranded
between the conductor(s) and the terminal. Other aspects
and Solid Conductors
important to terminal evaluation, such as the properties and
E122 Practice for Calculating Sample Size to Estimate, With
performance of electrical insulation, the effectiveness of strain
Specified Precision, the Average for a Characteristic of a
relief features, and the quality of contact between the terminal
Lot or Process
and other electrical circuit elements, are not included.
2.2 Other References:
1.4 The values stated in SI units are to be regarded as
UL 486-A Wire connectors and Soldering Lugs for Use With
standard. No other units of measurement are included in this
Copper Conductors
standard.
UL-310 Electrical Quick-Connect Terminals
1.5 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to become familiar 3.1 Many terms related to electrical contacts used in this
with all hazards including those identified in the appropriate guide are defined in Terminology B542.
Safety Data Sheet (SDS) for this product/material as provided
3.2 Definitions of Terms Specific to This Standard:
by the manufacturer, to establish appropriate safety, health,
3.2.1 connection resistance, n—the electrical resistance at-
and environmental practices, and determine the applicability
tributable to a wire termination over and above that of an
of regulatory limitations prior to use.
identical solid metallic structure without pressure contact
1.6 This international standard was developed in accor-
interfaces. For crimped terminations that are the subject of this
dance with internationally recognized principles on standard-
guide, the connection resistance results from the resistance of
ization established in the Decision on Principles for the
a multitude of contact regions having both film and constriction
Development of International Standards, Guides and Recom- resistance, plus, where stranded wire is involved, an additional
mendations issued by the World Trade Organization Technical amount due to unequal current distribution among the wire
Barriers to Trade (TBT) Committee. strands at the termination.
1 2
This guide is under the jurisdiction of ASTM Committee B02 on Nonferrous For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Metals and Alloys and is the direct responsibility of Subcommittee B02.05 on contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Precious Metals and Electrical Contact Materials and Test Methods. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2021. Published April 2021. Originally the ASTM website.
approved in 2005. Last previous edition approved in 2015 as B942 – 10 (2015). Available from Underwriters Laboratories (UL), UL Headquarters, 333 Pfing-
DOI: 10.1520/B0942-21. sten Road, Northbrook, IL, 60062, http://www.ul.com.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B942 − 21
3.2.2 crimp, v—to establish an electrical and mechanical maintain that contact over many decades of service without
attachment between the two members by mechanically deform- maintenance or inspections.
ing one contact member around another. In most cases, one
5.2 A crimped wire termination is intended to be a perma-
member is a stranded or solid wire, or a group of wires, the
nent electrical contact. Current passes through a multitude of
other is a hollow cylinder or partial cylinder that is deformed
contact interfaces among the wire strands and from some of the
around the wire(s).
strands to the connector body.
3.2.3 crimp barrel, crimp tab, n—the portion of the crimp
5.3 In many applications, substantial connection deteriora-
terminal that is deformed in the crimping operation.
tion can be tolerated because there are no harmful conse-
quences of increasing connection resistance. Crimp termina-
3.2.4 crimped termination, n—a mechanical and electrical
tion failures in other applications have potentially severe
connection between a conductor, generally a wire, and a
consequences, however, which may be avoided by use of
component, typically a terminal specifically made for the
stringent acceptance criteria and quality control methods that
purpose. The crimped termination is made by compressing
assure high quality connections.
(crimping) the crimp barrel or tab(s) of the component around
the conductor using a tool specifically designed for the 5.4 A crimp termination is conceptually visualized as com-
pressed into a virtually solid mass of metal, with wire and
purpose.
terminal in intimate contact at the interfaces. Because of an
3.2.5 crimp terminal, n—a metal component designed to be
effect generally called “spring-back,” this is often incorrect.
electrically and mechanically attached to a wire by deforming
Spring-back is the elastic recovery of the distorted metal back
a portion of the component in a crimping operation to form an
towards its original shape. While the crimping dies are closed
attachment to the wire. The other end of the terminal usually
on the terminal, the surfaces are in contact. Spring-back then
has a ring, fork, spade, tab, or related configuration designed to
occurs when the crimping die is removed.
attach to another circuit element. Some crimp terminals termi-
5.5 If the outer terminal springs back more than the wire
nate multiple wires within the same crimp barrel.
strands, then the normal force and the real area of contact at the
contact interfaces within the termination are substantially
4. Significance and Use
reduced. When this occurs, there may be little or no residual
4.1 The purpose of this guide is to provide end-product
compressive force at the contact interfaces within the termina-
manufacturers and other users with technical information and
tion. This degrades the mechanical integrity of the termination
methods recommended towards the achievement of successful
and also makes it more susceptible to corrosive deterioration.
application of crimped wire terminals.
Spring-back causes open spaces to develop where intimate
surface-to-surface contact is expected, allowing ingress of
4.2 For any given use, there is generally a choice of terminal
moisture and atmospheric contaminants, thereby accelerating
types available, employing different mechanical design,
oxidation and corrosion related deterioration.
materials, and installation tooling. Although terminals avail-
able to choose from may be similarly rated, typically according
5.6 The selection and setup of the correct die set for the
to wire sizes and combinations, their electrical contact perfor- particular terminal are critical factors. For a given terminal and
mance in the end product may vary substantially. For many
wire fill, there is a narrow range of compression within which
applications, the end-product reliability and user safety is satisfactory results will be obtained. Inadequate crimping
substantially influenced by the choice of terminal and the
generally results in shortened service life. Over-crimping may
quality of the completed termination. This guidance document also be harmful, due to crack formation in the crimp barrel,
contains specialized information on selection, assembly, and
severing of wire strands, or excessive deformation of the wire.
quality control of crimped wire terminals, covering aspects
5.7 The typical connection resistance of crimped wire ter-
considered to be necessary to achieve reliable long-term
minations when initially made will be low, about the same
operation in the intended application. This information is not
order of magnitude as the bulk resistance of the terminal. A
generally found in commercial literature or textbooks. The
newly-made termination of #16 AWG stranded copper wire, for
methods discussed utilize connection resistance as the primary
example, is expected to have a connection resistance of less
-4
measure of termination quality, and change of connection
than 10 Ω (0.1 mΩ). Deterioration at the metallic contact
resistance with time as the measure of termination deteriora-
interfaces within the crimped termination may occur after
tion. The methods are based on a foundation of modern
initial installation, causing increasing connection resistance
electrical contact theory and practice.
with time in service. Termination deterioration may be due to
oxidation, corrosion, mechanical and/or thermal effects, any of
5. Connection Resistance Considerations
which may occur within the normal and expected conditions of
use in a particular application.
5.1 The required performance of a crimped wire termination
depends on the application, and it must be determined by the 5.8 Increasing connection resistance of terminations in a
user or end-product manufacturer based on the effect that particular end-product may influence reliability or safety, or
connection resistance may have on the reliability or safety, or both, depending on the particular function and current for each
both, of the end product. To satisfy the more demanding crimped termination in the circuit. Within a given product,
application requirements, it is necessary to establish adequate there may be crimp terminations having substantially different
initial metallic contact at the wire-to-connector interface and reliability and safety requirements.
B942 − 21
5.8.1 An example is a portable heater intended for retail sale ture can result in metallurgical changes (dezincification of
and residential use. There are eight crimped wire terminations brass, annealing) and loss of contact force (creep, stress
in the unit’s internal wiring that are in series with the heating relaxation). The specific operating conditions in many common
element, which draws 12 A. There are also seven crimped wire applications impose harsh thermal conditions, such as in the
terminations associated with neon indicator lights (less than
engine wiring harness of an automobile, or at the terminal of a
0.01 A), and another four in the heater’s blower motor circuit heating element.
(1.2 A). (Note: There may be more than one subcircuit
5.10.3 Deterioration may also occur due to mechanical
terminated within a single crimp fitting.) The influence of
vibrations (causing fretting) and due to mechanical motions
connection resistance on reliability and safety for each of the
and stresses that cause conductor strand breakage.
crimped termination types in this example heater is outlined in
Table 1. Adverse consequences of connection resistance in-
6. Specification of Required Crimp Termination
crease are generally more severe with higher circuit current.
Performance
5.8.2 A second example is a temperature sensitive control or
6.1 The sensitivity of each particular circuit to connection
safety device, on which the effective operating set point may be
resistance of its crimp terminations must be assessed, and a
substantially offset due to self heating (I R) at its wire
maximum allowable connection resistance must be specified.
terminals. For instance, a manually-reset thermal safety device
Connection resistance is a series resistance, and, in a newly-
may erroneously trip due to connection heating, causing
made wire termination, is generally negligible, of the order of
malfunction of the product or system in which it is installed.
less than 0.001 Ω. With time in service, however, or if poorly
5.9 Factors Influencing Connection Resistance:
made, connection resistance may exceed 1 Ω.
5.9.1 Acceptably low initial resistance of crimp termina-
6.1.1 Relatively high series resistance of one or more crimp
tions is very easily achieved. To assure that it will remain
terminations in a circuit may have an adverse effect on the
acceptably low in the intended application is the greater
circuit’s functionality. For example, some battery chargers will
challenge, since the rate of deterioration (resistance increase)
malfunction (improperly regulate the charging cycle) if a series
in service is sensitive to many variables of the terminal/wire/
resistance of the order of 0.1 Ω or more is introduced in the
tooling system.
output circuit.
5.9.1.1 Terminal variables include the physical
6.1.2 Resistive heating (I R) at a high resistance termination
configuration, the materials of construction (including plating)
and their properties, and the surface finish. may have an adverse effect on both the functionality and also
on the safety of the product.
5.9.1.2 Conductor variables include the material, hardness,
plating material and thickness, stranding, and surface cleanli-
6.1.2.1 An example of thermally-induced malfunction due
ness. If wire strands are to be pre-tinned, it is especially
to excessive crimp termination resistance is at a manually reset
important to specify and control the thickness, since most
over-temperature cutout device in a portable electric heater.
tinning materials are self-annealing at room temperature. If the
Normally, with connection resistance of the order of 0.0001 Ω,
tinning is too thick, loss of contact force due to self-annealing
at 12 A, the I R heating from the two crimp terminations on the
(or creep/stress relaxation) may result in premature failure.
device (0.03 W) results in a negligible temperature increase at
5.9.1.3 Tooling variables include selection of the tooling
its temperature sensing element. If the connection resistance
(dies and associated crimping tool or machine), its setup, its
increases to 0.01 Ω at one of the terminations, the resulting
operation, and its wear and maintenance.
heat generation (1.4 W) causes sufficient temperature rise at the
over-temperature device to activate it, incorrectly shutting off
5.10 The rate of deterioration is also influenced by the
the heater.
environmental and mechanical conditions of the application.
5.10.1 Deterioration due to corrosion and oxidation can 6.1.2.2 A safety problem arises if self-heating at a termina-
occur in ordinary environment, and is generally accelerated by tion causes damage to the electrical insulation or is extreme
high temperature and high humidity. Corrosive agents are enough to pose a direct fire hazard. For example, if the
present in the normal atmosphere as well as in special connection resistance of a crimp termination carrying 12 A
industrial and household situations. increases to 0.1 Ω, (14 W heat generation), the temperature on
5.10.2 Temperature variations in service may cause deterio- the wire would become high enough to destroy the insulation
ration due to differential thermal expansion effects (causing on the adjacent section of wire and present a fire ignition
fretting and thermal ratcheting), while extreme high tempera- hazard if any combustible materials are in contact with it.
TABLE 1 Example—Crimp Terminations within a Portable Electric Heater
Maximum Allowable
Circuit Application within Maximum Current, No. of Terminals/ Consequence(s) of Exceeding
Connection Resistance,
Heater Assembly Amps No. of Different Types Maximum Allowable Resistance
Ohms
Main power 13.2 2/1 0.005 damage to wire insulation
Heater element power, general 12 4/2 0.005 damage to wire insulation
Temperature limit switch (heater element power) 12 2/1 0.001 offset of trip point, product malfunction
Blower Motor 1.2 2/1 2.0 motor may fail to start
Indicator Lights nil 7/3 >10 000 indicator light malfunction
B942 − 21
6.2 The minimum life requirement must be determined and system can be changed without risk of adversely changing the
specified. This is the time that must pass before a termination rate of deterioration in service.
can deteriorate to its allowable maximum connection resis-
tance. 8. Manufacturing Considerations
6.2.1 When there is no safety consequence of failure, the
8.1 For non-critical applications, follow the terminal manu-
specified crimp termination minimum life may be set as low as
facturer’s general recommendations.
the expected (or guaranteed) life of the system of which it is a
8.2 For resistance-sensitive or critical applications, it is
part.
generally required to establish tight control of materials and
6.2.2 When there may be safety consequences of failure, it
manufacturing beyond the terminal manufacturer’s general
is recommended that the required life be considered as indefi-
recommendations.
nite. In terms of connection resistance, that requires that there
8.2.1 Assure that all materials, tooling, and procedures are
be no reasonable possibility that the resistance will increase to
specified and held constant. Seemingly harmless changes, such
its allowable maximum n
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B942 − 10 (Reapproved 2015) B942 − 21
Standard Guide for
Specification and Quality Assurance for the Electrical
Contact Performance of Crimped Wire Terminations
This standard is issued under the fixed designation B942; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide contains practices for specifying and evaluating the electrical contact performance of crimped-type terminations
with solid or stranded conductors.
1.2 This guide provides information relevant to the electrical contact performance of a crimped wire termination. It does not cover
other aspects of selection and use of crimped terminals.
1.3 The methods discussed in this guide apply only to the wire termination, which is the electrical contact interface between the
conductor(s) and the terminal. Other aspects important to terminal evaluation, such as the properties and performance of electrical
insulation, the effectiveness of strain relief features, and the quality of contact between the terminal and other electrical circuit
elements, are not included.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to become familiar with all hazards including those identified in the appropriate Safety Data Sheet
(SDS) for this product/material as provided by the manufacturer, to establish appropriate safety safety, health, and healthenvi-
ronmental practices, and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
B539 Test Methods for Measuring Resistance of Electrical Connections (Static Contacts)
B542 Terminology Relating to Electrical Contacts and Their Use
B827 Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests
B845 Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
B868 Practice for Contact Performance Classification of Electrical Connection Systems (Withdrawn 2017)
This guide is under the jurisdiction of ASTM Committee B02 on Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee B02.11 on Electrical
Contact Test Methods.
Current edition approved Oct. 1, 2015April 1, 2021. Published October 2015April 2021. Originally approved in 2005. Last previous edition approved in 20102015 as
ɛ1
B972B942 – 10 (2015). 10 . DOI: 10.1520/B0942-10R15.10.1520/B0942-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B942 − 21
B913 Test Method for Evaluation of Crimped Electrical Connections to 16-Gauge and Smaller Diameter Stranded and Solid
Conductors
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
2.2 Other References:
UL 486-A Wire connectors and Soldering Lugs for Use With Copper Conductors
UL-310 Electrical Quick-Connect Terminals
3. Terminology
3.1 Many terms related to electrical contacts used in this guide are defined in Terminology B542.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 connection resistance, n—the electrical resistance attributable to a wire termination over and above that of an identical solid
metallic structure without pressure contact interfaces. For crimped terminations that are the subject of this guide, the connection
resistance results from the resistance of a multitude of contact regions having both film and constriction resistance, plus, where
stranded wire is involved, an additional amount due to unequal current distribution among the wire strands at the termination.
3.2.2 crimp, v—to establish an electrical and mechanical attachment between the two members by mechanically deforming one
contact member around another. In most cases, one member is a stranded or solid wire, or a group of wires, the other is a hollow
cylinder or partial cylinder that is deformed around the wire(s).
3.2.3 crimp barrel, crimp tab, n—the portion of the crimp terminal that is deformed in the crimping operation.
3.2.4 crimped termination, n—a mechanical and electrical connection between a conductor, generally a wire, and a component,
typically a terminal specifically made for the purpose. The crimped termination is made by compressing (crimping) the component
(crimp barrel) crimp barrel or tab(s) of the component around the conductor using a tool specifically designed for the purpose.
3.2.5 crimp terminal, n—a metal component designed to be electrically and mechanically attached to a wire by deforming a
portion of the component in a crimping operation to form an attachment to the wire. The other end of the terminal usually has a
ring, fork, spade, tab, or related configuration designed to attach to another circuit element. Some crimp terminals terminate
multiple wires within the same crimp barrel.
4. Significance and Use
4.1 The purpose of this guide is to provide end-product manufacturers and other users with technical information and methods
recommended towards the achievement of successful application of crimped wire terminals.
4.2 For any given use, there is generally a choice of terminal types available, employing different mechanical design, materials,
and installation tooling. Although terminals available to choose from may be similarly rated, typically according to wire sizes and
combinations, their electrical contact performance in the end product may vary substantially. For many applications, the
end-product reliability and user safety is substantially influenced by the choice of terminal and the quality of the completed
termination. This guidance document contains specialized information on selection, assembly, and quality control of crimped wire
terminals, covering aspects considered to be necessary to achieve reliable long-term operation in the intended application. This
information is not generally found in commercial literature or textbooks. The methods discussed utilize connection resistance as
the primary measure of termination quality, and change of connection resistance with time as the measure of termination
deterioration. The methods are based on a foundation of modern electrical contact theory and practice.
5. Connection Resistance Considerations
5.1 The required performance of a crimped wire termination depends on the application, and it must be determined by the user
or end-product manufacturer based on the effect that connection resistance may have on the reliability or safety, or both, of the
end product. To satisfy the more demanding application requirements, it is necessary to establish adequate initial metallic contact
at the wire-to-connector interface and maintain that contact over many decades of service without maintenance or inspections.
Available from Underwriters Laboratories Inc. (UL), http://www.ul.com. (UL), UL Headquarters, 333 Pfingsten Road, Northbrook, IL, 60062, http://www.ul.com.
B942 − 21
5.2 A crimped wire termination is intended to be a permanent electrical contact. Current passes through a multitude of contact
interfaces among the wire strands and from some of the strands to the connector body.
5.3 In many applications, substantial connection deterioration can be tolerated because there are no harmful consequences of
increasing connection resistance. Crimp termination failures in other applications have potentially severe consequences, however,
which may be avoided by use of stringent acceptance criteria and quality control methods that assure high quality connections.
5.4 A crimp termination is conceptually visualized as compressed into a virtually solid mass of metal, with wire and terminal in
intimate contact at the interfaces. Because of an effect generally called “spring-back,” this is often incorrect. Spring-back is the
elastic recovery of the distorted metal back towards its original shape. While the crimping dies are closed on the terminal, the
surfaces are in contact. Spring-back then occurs when the crimping die is removed.
5.5 If the outer terminal springs back more than the wire strands, then the normal force and the real area of contact at the contact
interfaces within the termination are substantially reduced. When this occurs, there may be little or no residual compressive force
at the contact interfaces within the termination. This degrades the mechanical integrity of the termination and also makes it more
susceptible to corrosive deterioration. Spring-back causes open spaces to develop where intimate surface-to-surface contact is
expected, allowing ingress of moisture and atmospheric contaminants, thereby accelerating oxidation and corrosion related
deterioration.
5.6 The selection and setup of the correct die set for the particular terminal are critical factors. For a given terminal and wire fill,
there is a narrow range of compression within which satisfactory results will be obtained. Inadequate crimping generally results
in shortened service life. Over-crimping may also be harmful, due to crack formation in the crimp barrel, severing of wire strands,
or excessive deformation of the wire.
5.7 The typical connection resistance of crimped wire terminations when initially made will be low, about the same order of
magnitude as the bulk resistance of the terminal. A newly-made termination of #16 AWG stranded copper wire, for example, is
-4
expected to have a connection resistance of less than 10 Ω (0.1 milliohm).mΩ). Deterioration at the metallic contact interfaces
within the crimped termination may occur after initial installation, causing increasing connection resistance with time in service.
Termination deterioration may be due to oxidation, corrosion, mechanical and/or thermal effects, any of which may occur within
the normal and expected conditions of use in a particular application.
5.8 Increasing connection resistance of terminations in a particular end-product may influence reliability or safety, or both,
depending on the particular function and current for each crimped termination in the circuit. Within a given product, there may
be crimp terminations having substantially different reliability and safety requirements.
5.8.1 An example is a portable heater intended for retail sale and residential use. There are eight crimped wire terminations in the
unit’s internal wiring that are in series with the heating element, which draws 12 A. There are also seven crimped wire terminations
associated with neon indicator lights (less than 0.01 A), and another four in the heater’s blower motor circuit (1.2 A). (Note:
thereThere may be more than one subcircuit terminated within a single crimp fitting.) The influence of connection resistance on
reliability and safety for each of the crimped termination types in this example heater is outlined in Table 1. Adverse consequences
of connection resistance increase are generally more severe with higher circuit current.
5.8.2 A second example is a temperature sensitive control or safety device, on which the effective operating set point may be
substantially offset due to self heating (I R) at its wire terminals. For instance, a manually-reset thermal safety device may
erroneously trip due to connection heating, causing malfunction of the product or system in which it is installed.
TABLE 1 Example—Crimp Terminations within a Portable Electric Heater
Maximum Allowable
Circuit Application within Maximum Current, No. of Terminals/ Consequence(s) of Exceeding
Connection Resistance,
Heater Assembly Amps No. of Different Types Maximum Allowable Resistance
Ohms
Main power 13.2 2/1 0.005 damage to wire insulation
Heater element power, general 12 4/2 0.005 damage to wire insulation
Temperature limit switch (heater element power) 12 2/1 0.001 offset of trip point, product malfunction
Blower Motor 1.2 2/1 2.0 motor may fail to start
Indicator Lights nil 7/3 >10 000 indicator light malfunction
B942 − 21
5.9 Factors Influencing Connection Resistance:
5.9.1 Acceptably low initial resistance of crimp terminations is very easily achieved. To assure that it will remain acceptably low
in the intended application is the greater challenge, since the rate of deterioration (resistance increase) in service is sensitive to
many variables of the terminal/wire/tooling system.
5.9.1.1 Terminal variables include the physical configuration, the materials of construction (including plating) and their properties,
and the surface finish.
5.9.1.2 Conductor variables include the material, hardness, plating material and thickness, stranding, and surface cleanliness. If
wire strands are to be pre-tinned, it is especially important to specify and control the thickness, since most tinning materials are
self-annealing at room temperature. If the tinning is too thick, loss of contact force due to self-annealing (or creep/stress relaxation)
may result in premature failure.
5.9.1.3 Tooling variables include selection of the tooling (dies and associated crimping tool or machine), its setup, its operation,
and its wear and maintenance.
5.10 The rate of deterioration is also influenced by the environmental and mechanical conditions of the application.
5.10.1 Deterioration due to corrosion and oxidation can occur in ordinary environment, and is generally accelerated by high
temperature and high humidity. Corrosive agents are present in the normal atmosphere as well as in special industrial and
household situations.
5.10.2 Temperature variations in service may cause deterioration due to differential thermal expansion effects (causing fretting and
thermal ratcheting), while extreme high temperature can result in metallurgical changes (dezincification of brass, annealing) and
loss of contact force (creep, stress relaxation). The specific operating conditions in many common applications impose harsh
thermal conditions, such as in the engine wiring harness of an automobile, or at the terminal of a heating element.
5.10.3 Deterioration may also occur due to mechanical vibrations (causing fretting) and due to mechanical motions and stresses
that cause conductor strand breakage.
6. Specification of Required Crimp Termination Performance
6.1 The sensitivity of each particular circuit to connection resistance of its crimp terminations must be assessed, and a maximum
allowable connection resistance must be specified. Connection resistance is a series resistance, and, in a newly-made wire
termination, is generally negligible, of the order of less than 0.001 Ω. With time in service, however, or if poorly made, connection
resistance may exceed 1 Ω.
6.1.1 Relatively high series resistance of one or more crimp terminations in a circuit may have an adverse effect on the circuit’s
functionality. For example, some battery chargers will malfunction (improperly regulate the charging cycle) if a series resistance
of the order of 0.1 Ω or more is introduced in the output circuit.
6.1.2 Resistive heating (I R) at a high resistance termination may have an adverse effect on both the functionality and also on the
safety of the product.
6.1.2.1 An example of thermally-induced malfunction due to excessive crimp termination resistance is at a manually reset
over-temperature cutout device in a portable electric heater. Normally, with connection resistance of the order of 0.0001 Ω, at 12
amps, 12 A, the I R heating from the two crimp terminations on the device (0.03 W) results in a negligible temperature increase
at its temperature sensing element. If the connection resistance increases to 0.01 Ω at one of the terminations, the resulting heat
generation (1.4 W) causes sufficient temperature rise at the over-temperature device to activate it, incorrectly shutting off the heater.
6.1.2.2 A safety problem arises if self-heating at a termination causes damage to the electrical insulation or is extreme enough to
pose a direct fire hazard. For example, if the connection resistance of a crimp termination carrying 12 A increases to 0.1 Ω, (14
W heat generation), the temperature on the wire would become high enough to destroy the insulation on the adjacent section of
wire and present a fire ignition hazard if any combustible materials are in contact with it.
B942 − 21
6.2 The minimum life requirement must be determined and specified. This is the time that must pass before a termination can
deteriorate to its allowable maximum connection resistance.
6.2.1 When there is no safety consequence of failure, the specified crimp termination minimum life may be set as low as the
expected (or guaranteed) life of the system of which it is a part.
6.2.2 When there may be safety consequences of failure, it is recommended that the required life be considered as indefinite. In
terms of connection resistance, that requires that there be no reasonable possibility that the resistance will increase to its allowable
maximum no matter how long it remains in service. This is achievable, in that crimp terminations can be reliably manufactured
that will demonstrate essentially zero resistance increase under most service conditions. If it cannot be done with a crimp
termination, due to the specific challenges of the particular application, then it is recommended that a more suitable termination
type should be utilized.
7. Crimp Termination Evaluation for Initial Selection
7.1 Potential suitability for the application, for commercially-available terminals, may be determined by the manufacturer’s
information together with listing or certification by a recognized testing laboratory based on an existing standard (UL 486-A, for
example). It must be understood that listing or certification by a testing laboratory does not guarantee or imply suitability for any
particular application. For non-critical (no safety risk on failure) and non-demanding (large tolerance for connection resistance
increase) applications, however, this level of assurance of performance may suffice.
7.2 For resistance-sensitive or critical applications, available life test data pertinent to the intended application should be reviewed.
Life test results may be available from the terminal manufacturer, from the listing or certifying laboratory, or from present or past
users of the particular terminal(s) being considered. The information should be reviewed for relevance of the applied conditions
to those of the intended application, for data quantifying the change of resistance resulting from the applied test conditions, and
for statistical significance (sample size, see Practice E122).
7.3 When considering a specific candidate terminal for a resistance-sensitive or critical application, if the available test data does
not provide a suitable basis on which to assure satisfactory performance in the intended application to a sufficient level of
confidence, then additional testing is required. (See Section 10.) If additional testing cannot be undertaken, by either the supplier
or potential user, then consideration of an alternate terminal (manufacturer or model) or alternate terminating means is
recommended.
7.4 It is recommended that, for resistance-sensitive or critical applications, the final step in the selection process should include
verification testing using the actual termination system (terminal, wire, tooling, and manufacturing procedure) that will be used in
product manufacturing. Once the performance of this combination is confirmed by test re
...