ASTM B738-13(2018)

Standard Specification for Fine-Wire Bunch-Stranded and Rope-Lay Bunch-Stranded Copper Conductors for Use as Electrical Conductors

ABSTRACT
This specification deals with bare fine-wire bunch-stranded and rope-lay bunch-stranded copper conductors made from round copper wires finer than No. 40 AWG, either coated or uncoated with tin or silver, for use as electrical conductors. The conductor types covered in this specification are designated Type B for bunch-stranded conductors, and Type R for rope-lay bunch-stranded conductors. On the other hand, the wire classifications are assigned as: Class R, stranded conductors using wire 42 AWG; Class S, stranded conductors using wire 44 AWG; Class T, stranded conductors using wire 46 AWG; Class U, stranded conductors using wire 48 AWG; and Class V, stranded conductors using wire 50 AWG. Wires shall undergo tests that shall evaluated their conformance to physical and electrical properties such as wire cross-sectional area and diameter, coating thickness, tensile strength, elongation, and DC resistance.
SCOPE
1.1 This specification covers bare bunch-stranded and rope-lay bunch-stranded conductors made from round copper wires finer than No. 40 AWG with diameters less than 0.0031 in. (.078 mm), either coated or uncoated with tin or silver, for use as electrical conductors. (Explanatory Note 1).  
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.  
1.2.1 Exceptions—The SI values for density and temperature are to be regarded as standard.  
1.3 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: 30-Sep-2018
• ICS: 29.050 - Superconductivity and conducting materials
• Technical Committee: B01 - Electrical Conductors
• Drafting Committee: B01.04 - Conductors of Copper and Copper Alloys

Relations

• Replaces: ASTM B738-13 - Standard Specification for Fine-Wire Bunch-Stranded and Rope-Lay Bunch-Stranded Copper Conductors for Use as Electrical Conductors
• Effective Date: 01-Oct-2018
• Refers: ASTM B49-20 - Standard Specification for Copper Rod for Electrical Purposes
• Effective Date: 15-Apr-2020
• Refers: ASTM B33-10(2020)e1 - Standard Specification for Tin-Coated Soft or Annealed Copper Wire for Electrical Purposes
• Effective Date: 01-Jan-2020
• Refers: ASTM B258-18 - Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors
• Effective Date: 01-Oct-2018
• Refers: ASTM B174-17 - Standard Specification for Bunch-Stranded Copper Conductors for Electrical Conductors
• Effective Date: 01-Apr-2017
• Refers: ASTM B298-12(2017) - Standard Specification for Silver-Coated Soft or Annealed Copper Wire
• Effective Date: 01-Apr-2017
• Refers: ASTM B49-17 - Standard Specification for Copper Rod for Electrical Purposes
• Effective Date: 01-Apr-2017
• Refers: ASTM B172-17 - Standard Specification for Rope-Lay-Stranded Copper Conductors Having Bunch-Stranded Members, for Electrical Conductors
• Effective Date: 01-Apr-2017
• Refers: ASTM B354-16 - Standard Terminology Relating to Uninsulated Metallic Electrical Conductors
• Effective Date: 01-Sep-2016
• Refers: ASTM B193-16 - Standard Test Method for Resistivity of Electrical Conductor Materials
• Effective Date: 01-Apr-2016
• Refers: ASTM B49-16 - Standard Specification for Copper Rod for Electrical Purposes
• Effective Date: 01-Apr-2016
• Refers: ASTM B49-15a - Standard Specification for Copper Rod for Electrical Purposes
• Effective Date: 15-Sep-2015
• Refers: ASTM B49-15 - Standard Specification for Copper Rod for Electrical Purposes
• Effective Date: 01-May-2015
• Refers: ASTM B172-10(2015) - Standard Specification for Rope-Lay-Stranded Copper Conductors Having Bunch-Stranded Members, for Electrical Conductors
• Effective Date: 01-Apr-2015
• Refers: ASTM B174-10(2015) - Standard Specification for Bunch-Stranded Copper Conductors for Electrical Conductors
• Effective Date: 01-Apr-2015

Overview

ASTM B738-13(2018) provides a comprehensive standard specification for bare fine-wire bunch-stranded and rope-lay bunch-stranded copper conductors for use as electrical conductors. Developed by ASTM International, this standard applies to conductors made from round copper wires finer than No. 40 AWG (American Wire Gauge), either uncoated or coated with tin or silver. The specification supports high-quality manufacturing, offering requirements for physical and electrical properties, construction, coating, and mechanical strength. The main goal is to ensure reliable performance and uniformity in applications where high flexibility and electrical conductivity are essential.

Key Topics

• Product Types and Classifications

  • Type B: Bunch-stranded conductors.
  • Type R: Rope-lay bunch-stranded conductors.
  • Classes R, S, T, U, V, categorized by wire diameters from 42 AWG through 50 AWG.

• Wire and Coating Options

  • Copper wires may be used bare or coated with tin or silver.
  • Coated wires must meet requirements for thickness and adherence as specified for tin (ASTM B33) or silver (ASTM B298).

• Physical and Mechanical Requirements

  • Assessment of wire diameter and cross-sectional area.
  • Coating thickness standards.
  • Tensile strength and elongation properties depending on whether the wires are annealed or unannealed.
  • Maximum allowed length of lay for different conductor constructions.

• Electrical Properties

  • DC resistance values provided for different conductor types and constructions.
  • Testing to ASTM B193 for electrical resistivity.
  • Density and temperature values in SI units for consistency.

• Inspection and Testing

  • Visual and mechanical inspection for quality and workmanship.
  • Testing procedures for both coatings and mechanical strength.
  • Compliance verification for DC resistance and elongation.

• Ordering, Packaging, and Marking

  • Requirements for identifying size, type, and class of conductor.
  • Packaging must protect conductors in shipping and handling.
  • Product marking to facilitate traceability and compliance verification.

Applications

Fine-wire bunch-stranded and rope-lay bunch-stranded copper conductors are widely used in electrical and electronic applications that demand high flexibility, strong electrical performance, and reliability. Typical application areas include:

• Electronics: Internal wiring for circuit boards, connectors, and small devices.
• Electrical Equipment: Power supply cords, communication cables, and assemblies requiring fine, flexible conductors.
• Instrumentation and Control Systems: Internal and signal wiring in precision instruments.
• Automotive and Aerospace: Lightweight, flexible cables in confined or dynamic spaces.
• Medical Devices: Leads and wiring where space and bending cycles are critical.

This standard ensures that such conductors meet rigorous criteria for both structure and performance, promoting safety and consistency across industries.

Related Standards

ASTM B738-13(2018) references several related standards to ensure comprehensive coverage of manufacturing and testing requirements:

• ASTM B33: Specification for Tin-Coated Soft or Annealed Copper Wire for Electrical Purposes
• ASTM B49: Specification for Copper Rod for Electrical Purposes
• ASTM B172: Specification for Rope-Lay-Stranded Copper Conductors
• ASTM B174: Specification for Bunch-Stranded Copper Conductors
• ASTM B193: Test Method for Resistivity of Electrical Conductor Materials
• ASTM B258: Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires

Compliance with ASTM B738-13(2018) ensures interoperability and quality across a global supply chain, aligning with internationally recognized best practices in copper conductor production.

Keywords: fine-wire copper conductor, bunch-stranded copper conductor, rope-lay conductor, ASTM B738-13, electrical conductor standard, tin-coated copper wire, silver-coated copper wire, flexible electrical conductor.

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:B738 −13 (Reapproved 2018)
Standard Specification for
Fine-Wire Bunch-Stranded and Rope-Lay Bunch-Stranded
Copper Conductors for Use as Electrical Conductors
This standard is issued under the fixed designation B738; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Cross-Sectional Areas of AWG Sizes of Solid Round
Wires Used as Electrical Conductors
1.1 This specification covers bare bunch-stranded and rope-
B298Specification for Silver-Coated Soft orAnnealed Cop-
lay bunch-stranded conductors made from round copper wires
per Wire
finer than No. 40 AWG with diameters less than 0.0031 in.
B354Terminology Relating to Uninsulated Metallic Electri-
(.078 mm), either coated or uncoated with tin or silver, for use
cal Conductors
as electrical conductors. (Explanatory Note 1).
1.2 The values stated in inch-pound units are to be regarded
3. Classification
as standard. The values given in parentheses are mathematical
3.1 For the purposes of this specification, the following
conversions to SI units that are provided for information only
classifications have been assigned (Explanatory Note 2):
and are not considered standard.
3.1.1 Type:
1.2.1 Exceptions—The SI values for density and tempera-
3.1.1.1 Type B—Bunch-stranded conductors.
ture are to be regarded as standard.
3.1.1.2 Type R—Rope-lay bunch-stranded conductors.
1.3 This international standard was developed in accor-
3.1.2 Class:
dance with internationally recognized principles on standard-
3.1.2.1 Class R—Stranded conductors using wire 42 AWG
ization established in the Decision on Principles for the
(0.0025).
Development of International Standards, Guides and Recom-
3.1.2.2 Class S—Stranded conductors using wire 44 AWG
mendations issued by the World Trade Organization Technical
(0.0020).
Barriers to Trade (TBT) Committee.
3.1.2.3 Class T—Stranded conductors using wire 46 AWG
(0.00157).
2. Referenced Documents
3.1.2.4 Class U—Stranded conductors using wire 48 AWG
2.1 ASTM Standards:
(0.00124).
B33Specification for Tin-Coated Soft or Annealed Copper
3.1.2.5 Class V—Stranded conductors using wire 50 AWG
Wire for Electrical Purposes
(0.00099).
B49Specification for Copper Rod for Electrical Purposes
3.2 Detailed information on Type B Conductors is found in
B172Specification for Rope-Lay-Stranded Copper Conduc-
Table 1 and Table 2. Detailed information on Type R Conduc-
torsHavingBunch-StrandedMembers,forElectricalCon-
tors is found in Table 3 and Table 2.
ductors
B174Specification for Bunch-Stranded Copper Conductors
4. Ordering Information
for Electrical Conductors
4.1 Orders for materials under this specification shall in-
B193Test Method for Resistivity of Electrical Conductor
clude the following information:
Materials
4.1.1 Quantity of each size, class, and type,
B258Specification for Standard Nominal Diameters and
4.1.2 Conductor size—circular-mil area, dc resistance (7.1)
or AWG (5.2.1),
This specification is under the jurisdiction of ASTM Committee B01 on
4.1.3 Class and type (Section 3),
Electrical Conductors and is the direct responsibility of Subcommittee B01.04 on
4.1.4 Whether coated or uncoated; if coated, designate type
Conductors of Copper and Copper Alloys.
of coating (6.1); if silver coated, the minimum thickness of
Current edition approved Oct. 1, 2018. Published October 2018. Originally
silver (6.1.2), and whether tarnish protection is desired (11.3),
approved in 1984. Last previous edition approved in 2013 as B738–13. DOI:
10.1520/B0738-13R18.
4.1.5 Maximum length of lay (5.2.4), if required,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4.1.6 Temper (6.2),
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
4.1.7 Separators, if required (5.2.2),
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 4.1.8 Package size (11.1),
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B738−13 (2018)
TABLE 1 Classification of Type B Bunch-Stranded Conductors
6. Physical Properties
A
Class Wire Diameter, in. Conductor Sizes, AWG
6.1 Wire Coating—When coated, the coating of the wires of
R 0.0025 (No. 42 AWG) 24,26,28,30,32,34
the stranded conductor, before stranding, shall conform to the
S 0.0020 (No. 44 AWG) 26,28,30,32,34,36
requirements of 6.1.1 or 6.1.2.
T 0.00157 (No. 46 AWG) 28,30,32,34,36,38
U 0.00124 (No. 48 AWG) 30,32,34,36,38,40
6.1.1 Tin coating shall conform to the coating requirements
V 0.00099 (No. 50 AWG) 32,34,36,38,40
of Specification B33.
A
Sufficientquantitiesofwiresofthesediametersshallbeusedtoformconductors
6.1.2 Silver coating shall conform to the minimum thick-
having cross-sectional areas approximately equal to the AWG conductor sizes
ness requirements of the purchase document. Minimum thick-
listed.
ness shall be determined using the method for determining
plating thickness described in Specification B298.
6.1.3 The finished diameter and mass of the coated wires
used shall be substantially equal to those of the uncoated wires
4.1.9 Specialpackagemarking,ifrequired(Section10),and
of the same class.
4.1.10 Place of inspection (Section 9).
6.2 Temper—Unless otherwise specified, all coated conduc-
4.2 In addition, Supplementary Requirements shall apply
tors shall be furnished in the annealed temper. Uncoated
onlywhenspecifiedbythepurchaserintheinquiry,contract,or
conductors may be furnished either annealed or unannealed as
purchase order for direct procurement by agencies of the U.S.
ordered (see 4.1.6).
Government.
NOTE 1—The term unannealed as used in this specification means
cold-worked conductor as produced on commercial wire-drawing ma-
5. Materials and Manufacture
chines.
5.1 The material shall be copper of such quality and purity
6.3 Tensile Strength and Elongation—The stranded
that the finished product shall have the properties and charac-
conductor, in its finished form, shall conform to the following:
teristics described in this specification. Material meeting the
Tensile Strength, min. Elongation, min,
requirements of Specification B49 is such a material.
Finished State psi MPa 10 in. %
5.2 Construction: Unannealed 40 000 275 .
Annealed . . 10
5.2.1 Cross-Sectional Area—The cross-sectional area,
number, and diameter of wires for a variety of strand construc-
7. Electrical Properties
tions in general use are shown in Table 2.
7.1 DC Resistance—The dc resistance in Ω/1000 ft of the
5.2.2 Separators—If a separator is required to be furnished
bunch-stranded conductor shall not exceed the appropriate
with the conductor, it shall be specified by the purchaser at the
values specified in Table 5. The dc resistance inΩ/1000 ft of
time of the order as to the requirements for the kind and
the rope-lay bunch-stranded conductor shall not exceed the
thickness of material and its application details.
appropriate values specified in Table 6 (Explanatory Note 3
5.2.3 Joints:
and Note 4).
5.2.3.1 Necessary joints in wires shall be made in accor-
dance with accepted commercial practice.
8. Test Methods
5.2.3.2 Joints shall be so constructed and so disposed
throughout the conductor that the diameter or configuration of
8.1 Coating—Teststodetermineconformanceofthecoating
the completed conductor is not substantially affected, and that
totherequirementsofSpecificationB33orSpecificationB298
the flexibility of the completed conductor is not adversely
shall be performed on the individual wires before stranding
affected.
(see 6.1.1 to 6.1.3).
5.2.4 Lay:
8.2 Tensile Strength and Elongation:
5.2.4.1 Conductors of the same size and description fur-
8.2.1 Tests to determine conformance to the tensile strength
nished on one order shall have the same lay.
and elongation requirements of 6.3 shall be made on the
5.2.4.2 The direction of the lay of bunch-stranded conduc-
finished stranded conductor.
tors shall be at the option of the manufacturer unless otherwise
8.2.2 Determine tensile strength, T , expressed in pounds
s
specified by the purchaser.
per square inch as follows:
5.2.4.3 Unless otherwise specified by the purchaser, the
length of the lay of bare or coated bunch-stranded conductors L
T 5
s
shall conform to the requirements of Table 4. A
5.2.4.4 Thedirectionofthelayoftheouterlayerofrope-lay
where:
stranded conductors shall be lefthand, unless otherwise speci-
L = maximum load on the stranded conductor during the
fied by the purchaser.
tension test (see Explanatory Note 6), lbs, and
5.2.4.5 The length of the lay of the outer layer of rope-lay
A = original cross-sectional area of the stranded conductor,
stranded conductors shall be not less than 8 or more than 16
in. (see 8.2.3).
times the outside diameter of the completed conductor. The
length of the lay of the wires composing the bunch-stranded 8.2.3 The original cross-sectional area of the stranded con-
members shall be not more than 30 times the diameter of the ductor shall be considered to be the cross-sectional area of the
member. individualwirecalculatedfromthenominalwirediameter(see
B738−13 (2018)
A
TABLE 2 Construction Requirements of Bunch-Stranded and Rope-Lay Bunch-Stranded Conductors
CLASS R CLASS S CLASS T CLASS U CLASS V
Minimum Number Minimum Number Minimum Number Minimum Number Minimum Number
Nominal
Size, of Wires 0.0025 in. of Wires 0.0020 in. of Wires 0.00157 in. of Wires 0.00124 in. of Wires 0.00099 in.
Area,
AWG in Diameter in Diameter in Diameter in Diameter in Diameter
cmil
(No. 42 AWG) (No. 44 AWG) (No. 46 AWG) (No. 48 AWG) (No. 50 AWG)
B C
Type B Type R Type B Type R Type B Type R Type B Type R Type B Type R
2580 16 . . . 665 . . . . . .
1620 18 . . . 413 . . . . . .
1020 20 . 168 . 259 . . . . . .
640 22 . 105 . 168 . . . . . .
404 24 65 . . 105 . 168 . . . .
253 26 41 . 65 . . 105 . 168 . .
159 28 26 . 40 . 65 . . 105 . 168
100 30 16 . 25 . 40 . 65 . . 105
64 32 10 . 16 . 25 . 40 . 65 .
40 34 7 . 10 . 16 . 25 . 40 .
25 36 . . 7 . 10 . 16 . 25 .
16 38 . . . . 7 . 10 . 16 .
10 40 . . . . . . 7 . 10 .
A
This table shows a variety of strand constructions useful and generally adequate to meet the needs encountered. It is not intended that the constructions listed in this
tablebeexclusiveofotherconstructionsthatmayappeardurableincertainapplicationsemployingthesamenumberofwires.Theconstructionsshowninthistableprovide
for a finished, noncovered, stranded conductor approximately of the area indicated. When specified by the purchaser, usually to provide additional area to compensate
for draw-down during subsequent processing, the number or size of wires composing the uncovered conductor may be increased as required.
B
Type B Bunch-Stranded Conductors.
C
Type R Rope-Lay Bunch-Stranded Conductors.
TABLE 3 Classification of Type R Rope-Lay Bunch-Stranded
supplied package. Use a white card (as a background) to
A
Conductors
ascertain if any base metal is exposed through a break in the
B
Class Wire Diameter, in. Conductor Sizes, AWG
coating. Detection of any base metal constitutes rejection.
R 0.0025 (No. 42 AWG) 20,22
8.6 Examination for Workmanship of Finished Uninsulated
S 0.0020 (No. 44 AWG) 16,18,20,22,24
T 0.00157 (No. 46 AWG) 24,26
Stranded Conductor—Avisual inspection with 10× magnifica-
U 0.00124 (No. 48 AWG) 26,28
tionandawhite
...