ASTM B267-07(2023)

Standard Specification for Wire for Use In Wire-Wound Resistors

ABSTRACT
This specification covers round wires and ribbons with controlled electrical properties made from magnetic and nonmagnetic class 1a-11 alloys. The wires and ribbons, which may have insulated coverings or enamel coatings, are recommended for use in wire-wound resistance units like precision resistors and other similar applications, but not for use as electrical heating elements. Each bare wire should conform to the requirements for nominal resistivity, elongation, thermal electromotive force with respect to copper, and the temperature coefficient of resistance contained in this specification. The nominal resistance per unit length for a round wire is calculated from the nominal resistivity and nominal cross-sectional area.
SCOPE
1.1 This specification covers round wire and ribbon with controlled electrical properties for use in wire-wound resistance units and similar applications, but not for use as electrical heating elements.  
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3 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.  
1.4 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-Oct-2023
• ICS: 29.050 - Superconductivity and conducting materials
• Technical Committee: B02 - Nonferrous Metals and Alloys
• Drafting Committee: B02.10 - Thermostat Metals and Electrical Resistance Heating Materials

Relations

• Replaces: ASTM B267-07(2018) - Standard Specification for Wire for Use In Wire-Wound Resistors
• Effective Date: 01-Nov-2023

Overview

ASTM B267-07(2023) is the globally recognized standard specification for round wire and ribbon used in wire-wound resistors. Published by ASTM International, this document ensures consistent quality and performance in wires made from magnetic and nonmagnetic alloys, designated primarily for use in precision resistors and similar resistance units. The standard covers the physical, mechanical, and critical electrical properties required for wires and ribbons, whether bare, enameled, or wrapped with insulated coverings. It does not apply to wires intended for use as electrical heating elements.

This standard plays a crucial role in defining the requirements for nominal resistivity, elongation, temperature coefficient of resistance, and thermal electromotive force (EMF) relative to copper-all essential factors in the manufacturing and reliability of wire-wound resistors.

Key Topics

• Alloy Classes: ASTM B267 describes 15 classes of alloys, both magnetic and nonmagnetic, including nickel, copper, and iron-based materials, widely used in precision resistor applications.
• Electrical Properties: Requirements include controlled nominal resistivity, consistent temperature coefficient of resistance, and limited thermal EMF with respect to copper, ensuring reliability and stability in circuit performance.
• Mechanical Properties: The standard specifies minimum elongation values for wires, guaranteeing mechanical strength and durability during winding and operation.
• Dimensions and Tolerances: While dimensions are secondary to electrical resistance per unit length, the standard outlines permissible resistance variations based on wire diameter, enhancing quality control.
• Surface Finishes and Coatings: Guidelines exist for types and dimensions of enamel coatings and insulated coverings-including cotton, silk, nylon, and glass-ensuring insulation integrity, high dielectric strength, and appropriate maximum operating temperatures.
• Marking and Labeling: Specific labeling requirements ensure traceability regarding alloy class, resistance values, and coating type.

Applications

ASTM B267-07(2023) wire is engineered for use in wire-wound resistance units where stable electrical properties are essential. Practical applications include:

• Precision Wire-Wound Resistors: Essential in consumer electronics, instrumentation, measurement equipment, and industrial controls that demand accurate, stable resistance values.
• Resistor Arrays and Networks: Suitable for complex electronic assemblies where consistent resistor performance is critical across varied environmental conditions.
• Resistance Measurement Devices: Ideal for reference standards and calibration applications, thanks to tight controls over resistivity and temperature coefficients.
• Circuit Protection and Control: Applied in specialized resistive elements within control circuits, where predictable thermal EMF and mechanical properties ensure reliable operation.
• Custom Resistor Fabrication: Used by resistor manufacturers as a base material for customized resistance components with specific electrical characteristics.

Note: This standard is not applicable to wires designed for electrical heating applications, focusing instead on stability and precision rather than thermal power handling.

Related Standards

• ASTM B63: Standard Test Method for Resistivity of Metallically Conducting Resistance and Contact Materials.
• ASTM B77: Standard Test Method for Thermoelectric Power of Electrical-Resistance Alloys.
• ASTM B84: Standard Test Method for Temperature-Resistance Constants of Alloy Wires for Precision Resistors.
• ASTM B268: Specification for Ribbon for Use in Wire-Wound Resistors (for flat/ribbon forms).

These related ASTM standards provide supporting methods for testing and evaluating the electrical, thermal, and physical characteristics of resistance wire, ensuring comprehensive control over quality and conformance in resistor manufacturing.

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Keywords: ASTM B267, resistance wire, wire-wound resistors, precision resistors, resistor alloys, controlled resistivity, temperature coefficient, thermal EMF, electrical insulation, enamel coatings, wire standards, electronics manufacturing.

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: B267 − 07 (Reapproved 2023)
Standard Specification for
Wire for Use In Wire-Wound Resistors
This standard is issued under the fixed designation B267; 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 3. Significance and Use
3.1 This specification on wire and ribbon contains the
1.1 This specification covers round wire and ribbon with
generic chemistry and requirements for resistivity, temperature
controlled electrical properties for use in wire-wound resis-
coefficient of resistance, thermal emf versus copper resistance
tance units and similar applications, but not for use as electrical
tolerances, and mechanical properties of bare wire, as well as
heating elements.
the wire enamels and insulations of alloys normally used in the
1.2 The values stated in inch-pound units are to be regarded
manufacture of wound resistors.
as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only
4. Alloy Classes
and are not considered standard.
4.1 Fifteen classes of alloys are covered by this specification
1.3 This standard does not purport to address all of the
as listed in Table 1.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to become familiar
5. Elongation
with all hazards including those identified in the appropriate
5.1 The wire shall conform to the requirements for elonga-
Safety Data Sheet (SDS) for this product/material as provided
tion as prescribed in Table 1, when tested on a 10 in. (254 mm)
by the manufacturer, to establish appropriate safety, health,
length.
and environmental practices, and determine the applicability
of regulatory limitations prior to use.
6. Resistivity
1.4 This international standard was developed in accor-
6.1 The bare wire shall conform to the requirements for
dance with internationally recognized principles on standard-
nominal resistivity as prescribed in Table 1.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
6.2 Actual resistivity shall not vary from nominal resistivity
mendations issued by the World Trade Organization Technical by more than 65 % for Alloy Classes 1 to 4 inclusive, and
Barriers to Trade (TBT) Committee.
610 % for Alloy Classes 5 to 11 inclusive.
7. Nominal Electrical Resistance per Unit Length
2. Referenced Documents
7.1 The nominal resistance per unit length for round wire
2.1 ASTM Standards:
shall be calculated from the nominal resistivity and the nominal
B63 Test Method for Resistivity of Metallically Conducting
cross-sectional area.
Resistance and Contact Materials
B77 Test Method for Thermoelectric Power of Electrical-
NOTE 1—When ribbon or flat wire is produced by rolling from round
Resistance Alloys wire, the cross section departs from that of a true rectangle by an amount
depending on the width-to-thickness ratio and the specific manufacturing
B84 Test Method for Temperature-Resistance Constants of
practice. The conventional formula for computing ohms per foot and feet
Alloy Wires for Precision Resistors
per pound is to consider the cross section as 17 % less than a true rectangle
when width is more than 15 times the thickness and 6 % less than a true
rectangle in other cases. This is not valid in view of modern rolling
equipment and practices, but still is widely used as a basis of description.
This specification is under the jurisdiction of ASTM Committee B02 on
Ribbon actually is made to a specified resistance per foot, and no tolerance
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
is specified for thickness. An alternative and a closer approximation would
B02.10 on Thermostat Metals and Electrical Resistance Heating Materials.
be that for ribbon rolled round wire, the electrical resistance would be
Current edition approved Nov. 1, 2023. Published November 2023. Originally
calculated on a cross 6 % less than a true rectangle.
approved in 1952. Last previous edition approved in 2018 as B267 – 07 (2018).
DOI: 10.1520/B0267-07R23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 8. Temperature Coefficient of Resistance
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
8.1 The change in resistance with change in temperature,
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. expressed as the mean temperature coefficient of resistance
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B267 − 07 (2023)
TABLE 1 Classes of Alloys and Requirements
Mean Temperature Coefficient of Resistance, α ppm for Maximum Thermal emf
m
Elongation in 10 in., min, %
B
°C Over Temperature Range,Δ T versus Copper, mV/°C
Resistivity,
Alloy Alloy Composition,
Over 0.002 in.
0.0009
Ω·cmil/ft
A
Class approximate, % D
Temperature 0.002 to 0.001
in. in
(μΩ·m)
ΔT α ΔT mV/°C
m C
D D
Range, ΔT Diameter
in. in in. in
and Finer
Diameter Diameter
1 2 3 4 5 6 7 8 9 10 11 12
1a nickel base, nonmagnetic 800 (1.330) 0, ±20 +25 to −55 0, ±20 +25 to +105 +0.003 −65 to +250 10 5 3
1b nickel base, nonmagnetic 800 (1.330) 0, ±10 +25 to −55 0, ±10 +25 to +105 +0.003 −65 to +150 10 5 3
1c nickel base, nonmagnetic 800 (1.330) 0, ±5 +25 to −55 0, ±5 +25 to +105 +0.003 −65 to +150 10 5 3
2a iron base, magnetic 800 (1.330) 0, ±20 +25 to −55 0, ±20 +25 to +105 −0.004 −65 to +200 10 5 3
2b iron base, magnetic 800 (1.330) 0, ±10 +25 to −55 0, ±10 +25 to +105 −0.004 −65 to +150 10 5 3
3a 80 nickel, 20 chromium 650 (1.081) +80, ±20 +25 to −55 +80, ±20 +25 to +105 +0.006 −65 to +250 15 5 3
3b 80 nickel, 20 chromium, 675 (1.122) +60, ±20 +25 to −55 +60, ±20 +25 to +105 +0.006 −65 to +250 15 5 3
stabilized
4 60 nickel, 16 chromium, 675 (1.122) +140, ±30 +25 to −55 +140, ±30 +25 to +105 +0.002 −65 to +200 15 5 3
balance iron
5a 55 copper, 45 nickel 300 (0.499) 0, ±20 +25 to −55 0, ±20 +25 to +105 −0.045 −65 to + 150 15 5 3
5b 55 copper, 45 nickel 300 (0.499) 0, ±40 +25 to −55 0, ±40 +25 to +105 −0.045 −65 to +150 15 5 3
E E E E
6 manganin type 290 (0.482) 0, ±15 0, ±15 −0.003 +15 to +35 15 5 3
7 77 copper, 23 nickel 180 (0.299) +180, ±30 +25 to −55 +180, ±30 +25 to +105 −0.037 −65 to +150 15 5 3
8 70 nickel, 30 iron 125 (0.199) +3600, ±400 +25 to −50 +4300, ±400 +25 to +104 −0.040 −50 to +100 15 5 3
9 90 copper, 10 nickel 90 (0.150) +450, ±50 +25 to −55 +450, ±50 +25 to +105 −0.026 −65 to +150 15 5 3
10 94 copper, 6 nickel 60 (0.100) +700, ±200 +25 to −55 +700, ±200 +25 to +105 −0.022 −65 to +150 15 5 3
11 98 copper, 2 nickel 30 (0.050) +1400, ±300 +25 to −55 +1400, ±300 +25 to +105 0.014 −65 to +150 15 5 3
A
Alloy Classes 1a to 8 inclusive are designed to provide controlled temperature coefficients. Values shown for other classes are for information only. All values are based
on a reference temperature of 25 °C.
B
Alloy Classes 1a, 1b, 1c, 2a, 2b, 3a, 4, and 6 are designed to give a low emf versus copper. Values shown for other classes are for information only. Maximum indicates
the maximum deviation from zero and the plus or minus sign the polarity of the couple.
C
The maximum temperature values listed apply to the alloy wire only. Caution should be exercised pending knowledge of the maximum temperature of use for the coating
material involved.
D
If metric sizes are desired, 1 in. = 25.4 mm.
E
Alloy Class 6 (manganin type for resistors), has a temperature-resistance curve of parabolic shape with the maximum resistance normally located between 25 °C and
m
30 °C. Thus, Columns 5 and 7 cannot indicate 25 °C as a limit but α may be expressed as a maximum of +15 ppm for 15 °C to the temperature of maximum resistance
and a maximum of −15 ppm from the temperature of maximum resistance to 35 °C. All of the information included in this note is based on measurements made in
accordance with Test Method B84.
A
TABLE 2 Dimensions of Enamel Coated Wire
Nominal Bare Wire Size Light Coated Wire Medium Coated Wire Heavy Coated Wire
Outside Diameter, Outside Diameter, Outside Diameter, Outside Diameter, Outside Diameter, Outside Diameter,
B&S Gauge No. Diameter, in.
min, in. max, in. min, in. max, in. min, in. max, in.
28 0.0126 0.0130 0.0134 0.0134 0.0139 0.0139 0.0144
29 0.0113 0.0116 0.0120 0.0120 0.0125 0.0125 0.0130
30 0.010 0.0103 0.0107 0.0107 0.0112 0.0112 0.0116
31 0.0089 0.0092 0.0096 0.0096 0.0100 0.0100 0.0103
32 0.008 0.0083 0.0086 0.0086 0.0090 0.0090 0.0093
33 0.0071 0.0073 0.0076 0.0076 0.0080 0.0080 0.0083
34 0.0063 0.0064 0.0067 0.0067 0.0071 0.0071 0.0074
35 0.0056 0.0057 0.0060 0.0060 0.0064 0.0064 0.0067
36 0.005 0.0051 0.0054 0.0054 0.0057 0.0057 0.0060
37 0.0045 0.0046 0.0049 0.0049 0.0052 0.0052 0.0055
38 0.004 0.0041 0.0043 0.0043 0.0046 0.0046 0.0049
39 0.0035 0.0036 0.0038 0.0038 0.0041 0.0041 0.0043
40 0.0031 0.0032 0.0034 0.0034 0.0037 0.0037 0.0039
0.00275 0.0029 0.0031 0.0031 0.0033 0.0033 0.0035
0.0025 0.0026 0.0028 0.0028 0.0030 0.0030 0.0032
0.00225 0.00235 0.0025 0.0025 0.0027 0.0027 0.0029
0.002 0.0021 0.0022 0.0022 0.0024 0.0024 0.0026
0.00175 . 0.0019 0.0019 0.0021 0.0021 0.0023
0.0015 . 0.0016 0.0016 0.0018 0.0018 0.0020
0.0014 . 0.0015 0.0015 0.0017 0.0017 0.0019
0.0013 . 0.0014 0.0014 0.0016 0.0016 0.0018
0.0012 . 0.0013 0.0013 0.0015 0.0015 0.0017
0.0011 . 0.0012 0.0012 0.0014 0.0014 0.0016
0.001 . 0.0011 0.0011 0.0013 0.0013 0.0015
0.0009 . 0.0010 0.0010 0.0012 0.0012 0.0014
0.0008 . 0.0009 0.0009 0.0010 0.0010 0.0012
0.0007 . 0.0008 0.0008 0.0009 0.0009 0.0010
0.0006 . 0.0007 0.0007 0.0008 0.0008 0.0009
0.0005 . 0.0006 0.0006 0.0007 0.0007 0.0008
A
To convert from inches to millimetres multiply by 25.4.
B267 − 07 (2023)
based on the reference temperature of 25 °C, shall be within the 13. Enamel Coatings
limits specified in Table 1, Columns 4 and 6, over the
13.1 Enamel coatings shall include any baked-on film of
corresponding temperature ranges specified in Columns 5 and
insulating material, such as varnish enamel, polyurethane,
7. The mean temperature coefficient of resistance referred to
vinyl acetal, etc. and shall conform to the requir
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