ASTM D3353-18(2024)

Standard Test Methods for Fibrous-Insulated Magnet Wire

ABSTRACT
These test methods cover the testing of fibrous-insulated electrical conductors, commonly referred to as magnet wire, which are used in electrical apparatus. The test methods are intended primarily for evaluation of the electrical insulating materials used. It is intended that these test methods be used, except where modified by individual specifications for particular applications. This elongation testing method covers the determination of the elongation of fibrous insulated magnet wire that results in a fracture of the conductor. The electrical resistance testing method covers the determination of the electrical resistance of fibrous insulated magnet wire conductors. The fibrous coverage testing method covers the determination of the quality of fibrous servings on round magnet wire or bare conductor. The measurement of dimensions test methods determine the dimensions of the bare or film insulated conductor and the fibrous-insulated magnet wire. The adhesion and flexibility test method covers the evaluation of the flexibility and adherence of varnished fibrous glass, and varnished or unvarnished fibrous polyester-glass insulating material on either bare conductor, or film-insulated magnet wire. The dielectric breakdown voltage test method covers the determination of the dielectric breakdown voltage in air of insulation on round, rectangular, and square wires at commercial power frequencies.
SCOPE
1.1 These test methods cover the testing of fibrous-insulated electrical conductors, commonly referred to as magnet wire, which are used in electrical apparatus. The test methods are intended primarily for evaluation of the electrical insulating materials used. It is intended that these test methods be used, except where modified by individual specifications for particular applications.  
1.1.1 These test methods apply to those magnet wires that are fiber-covered and in which the substrate is bare conductor or is coated with an underlying insulating film as covered by Test Methods D1676. Fiber-covered wires are produced by serving helically or wrapping fibers or fibrous-tape insulation uniformly around the wire in single and multiple layers. The served or wrapped materials are bonded or not bonded to the underlying wire.  
1.2 The test methods appear in the following sections:    
Procedure  
Section  
Measurement of Dimensions  
7  
Electrical Resistance of Conductors  
5  
Elongation  
4  
Adhesion and Flexibility  
8  
Fibrous Coverage  
6  
Dielectric Breakdown Voltage  
9  
1.3 This standard and IEC 60851 are similar if not equivalent in technical content.  
1.4 This standard and NEMA MW 1000 are similar if not equivalent in technical content.  
1.5 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.  
1.6 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 establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. See 8.4.1 and 9.4.1 for specific caution statements.  
1.7 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: 29-Feb-2024
• ICS: 29.060.10 - Wires
• Technical Committee: D09 - Electrical and Electronic Insulating Materials
• Drafting Committee: D09.12 - Electrical Tests

Relations

• Replaces: ASTM D3353-18 - Standard Test Methods for Fibrous-Insulated Magnet Wire
• Effective Date: 01-Mar-2024
• Referred By: ASTM D4881-05(2017) - Standard Test Method for Thermal Endurance of Varnished Fibrous- or Film-Wrapped Magnet Wire
• Effective Date: 01-Mar-2024
• Referred By: ASTM D1711-24 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Mar-2024

Overview

ASTM D3353-18(2024): Standard Test Methods for Fibrous-Insulated Magnet Wire establishes internationally recognized procedures for testing fibrous-insulated electrical conductors, commonly known as magnet wire, utilized in electrical apparatus. This standard is developed by ASTM and provides a framework for assessing various characteristics of the insulation and overall wire quality. The methods aim primarily at evaluating the performance of electrical insulating materials used in fibrous-covered magnet wire, regardless of whether the wire’s substrate is bare or coated with an insulating film.

The procedures detailed in ASTM D3353-18(2024) serve as a reference except where modified by specific product requirements, ensuring that magnet wire meets stringent criteria for safety, reliability, and efficiency throughout its applications.

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Key Topics

Test Methods Included

• Elongation: Measures ductility and the effect of insulation application on the conductor by determining elongation at fracture.
• Electrical Resistance: Determines the electrical resistance, a key factor for function and efficiency.
• Fibrous Coverage: Evaluates the quality of the fibrous serving, ensuring coverage integrity when wires are bent or handled.
• Measurement of Dimensions: Establishes dimensional specifications for bare, film-insulated, and fibrous-insulated wire, critical for proper fit and application.
• Adhesion and Flexibility: Assesses the flexibility and adherence of varnished or unvarnished fibrous insulation, including glass and polyester-glass.
• Dielectric Breakdown Voltage: Tests the insulation’s resistance to electrical breakdown at commercial power frequencies.

Applicability

• Relevant for fiber-covered wires produced by helically serving or wrapping layers of insulation, bonded or unbonded.
• Applicable to round, rectangular, and square wire, including those with film insulation under the fibrous cover.

Safety and Compliance

• Emphasizes the responsibility of users to implement safety, health, and environmental practices.
• Developed according to international standards development principles and aligns with WTO Technical Barriers to Trade (TBT) guidance.

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Applications

ASTM D3353-18(2024) is crucial for various industries and sectors where fibrous-insulated magnet wires are deployed, such as:

• Electrical Machinery and Equipment: Used in the winding of motors, transformers, generators, and inductors.
• Manufacturing Quality Control: Ensures wire meets product specifications for insulation performance, resistance, and dimension.
• Material Evaluation and R&D: Supports the development and assessment of new insulation materials or application methods for magnet wire.
• International Trade and Compliance: Facilitates global trade by aligning with IEC 60851 and NEMA MW 1000, promoting product compatibility and acceptance in multiple markets.

These test methods help manufacturers, testing laboratories, and end-users ensure that magnet wire will perform reliably under operational stresses such as mechanical bending, electrical loading, and chemical exposure.

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Related Standards

ASTM D3353-18(2024) complements and, in several aspects, aligns with the following standards:

• IEC 60851: Methods of Test for Winding Wires – International procedures closely related to this ASTM standard.
• NEMA MW 1000: Magnet Wire Standard – North American counterpart providing equivalent test criteria.
• ASTM D1676: Test Methods for Film-Insulated Magnet Wire – For testing underlying film insulation.
• ASTM D149: Test Method for Dielectric Breakdown Voltage – Referenced for high-voltage testing equipment and procedures.
• ASTM B193: Test Method for Resistivity of Electrical Conductor Materials – Provides supporting tests for conductor resistance.
• ASTM D1711: Terminology Relating to Electrical Insulation – For consistent definitions and terminological clarity.

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By following ASTM D3353-18(2024), organizations enhance the safety, reliability, and marketability of fibrous-insulated magnet wire, supporting high standards in electrical applications worldwide. Key terms: fibrous-insulated magnet wire, electrical insulation, magnet wire testing, ASTM D3353, fiber-covered wire, dielectric breakdown, adhesion, flexibility, wire dimensions.

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: D3353 − 18 (Reapproved 2024)
Standard Test Methods for
Fibrous-Insulated Magnet Wire
This standard is issued under the fixed designation D3353; 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 mine the applicability of regulatory limitations prior to use.
See 8.4.1 and 9.4.1 for specific caution statements.
1.1 These test methods cover the testing of fibrous-insulated
1.7 This international standard was developed in accor-
electrical conductors, commonly referred to as magnet wire,
dance with internationally recognized principles on standard-
which are used in electrical apparatus. The test methods are
ization established in the Decision on Principles for the
intended primarily for evaluation of the electrical insulating
Development of International Standards, Guides and Recom-
materials used. It is intended that these test methods be used,
mendations issued by the World Trade Organization Technical
except where modified by individual specifications for particu-
Barriers to Trade (TBT) Committee.
lar applications.
1.1.1 These test methods apply to those magnet wires that
2. Referenced Documents
are fiber-covered and in which the substrate is bare conductor
2.1 ASTM Standards:
or is coated with an underlying insulating film as covered by
B193 Test Method for Resistivity of Electrical Conductor
Test Methods D1676. Fiber-covered wires are produced by
Materials
serving helically or wrapping fibers or fibrous-tape insulation
D149 Test Method for Dielectric Breakdown Voltage and
uniformly around the wire in single and multiple layers. The
Dielectric Strength of Solid Electrical Insulating Materials
served or wrapped materials are bonded or not bonded to the
at Commercial Power Frequencies
underlying wire.
D1676 Test Methods for Film-Insulated Magnet Wire
1.2 The test methods appear in the following sections:
D1711 Terminology Relating to Electrical Insulation
D5423 Specification for Forced-Convection Laboratory Ov-
Procedure Section
Measurement of Dimensions 7
ens for Evaluation of Electrical Insulation
Electrical Resistance of Conductors 5
E8 Test Methods for Tension Testing of Metallic Materials
Elongation 4
[Metric] E0008_E0008M
Adhesion and Flexibility 8
Fibrous Coverage 6
2.2 Other Standards:
Dielectric Breakdown Voltage 9
IEC 60851 Methods of Test for Winding Wires
1.3 This standard and IEC 60851 are similar if not equiva-
NEMA Standards Publication No. MW 1000 on Magnet
lent in technical content. 4
Wire
1.4 This standard and NEMA MW 1000 are similar if not
3. Terminology
equivalent in technical content.
3.1 Definitions:
1.5 The values stated in inch-pound units are to be regarded
3.1.1 For definitions of terms used in this test method, refer
as standard. The values given in parentheses are mathematical
to Terminology D1711.
conversions to SI units that are provided for information only
3.1.2 Definition of Term(s) Specific to this Standard:
and are not considered standard.
3.1.2.1 serving—a uniform wrapping of fibrous insulation
1.6 This standard does not purport to address all of the
around a magnet wire of bare conductor.
safety concerns, if any, associated with its use. It is the
3.1.2.2 fibrous coverage, of served-magnet wire—that char-
responsibility of the user of this standard to establish appro-
acteristic which allows a fibrous served magnet wire to be
priate safety, health, and environmental practices and deter-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
These test methods are under the jurisdiction of ASTM Committee D09 on Standards volume information, refer to the standard’s Document Summary page on
Electrical and Electronic Insulating Materials and are the direct responsibility of the ASTM website.
Subcommittee D09.12 on Electrical Tests. Available from International Engineering Consortium, 549 West Randolph
Current edition approved March 1, 2024. Published March 2024. Originally Street, Suite 600, Chicago IL 60661–2208.
approved in 1974. Last previous edition approved in 2018 as D3353 – 18. DOI: Available from National Electrical Manufacturers Association (NEMA), 1300
10.1520/D3353-18R24. N. 17th St., Suite 1752, Rosslyn, VA 22209, http://www.nema.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3353 − 18 (2024)
wound around mandrels in a prescribed manner without
B = original length
causing observable openings in the fibrous coverage.
4.6 Report the Following Information:
4. Elongation
4.6.1 Bare conductor dimensions,
4.6.2 Bare conductor material,
4.1 Scope—This test method covers the determination of the
4.6.3 Type and build of film insulation,
elongation of fibrous insulated magnet wire that results in a
4.6.4 Type of fibrous-insulation,
fracture of the conductor.
4.6.5 Number of servings,
4.2 Significance and Use—The elongation determined by
4.6.6 Direction of servings,
this test method provides a general measure of the ductility of
4.6.7 Type of varnish,
the conductor and the effect of the processing to which it has
4.6.8 Whether or not bench marks are used, and
been subjected during the insulating operation.
4.6.9 Individual and average elongation.
4.3 Apparatus—The equipment shall have a minimum sepa-
4.7 Precision and Bias:
ration sufficient to attach and measure the length of the test
specimen between grips, and be capable of elongating the
4.7.1 This test method has been in use for many years, but
specimen to its breaking point, at a constant rate. The equip-
no statement of precision has been made and no activity is
ment shall be such that the error of the length measurement will
planned to develop such a statement.
be 1 % or less. Suitable, non-slip grips are required that will
4.7.2 No information is presented on the bias of this
not damage the specimen in the region of elongation. Drum or
procedure in Section 4, for measuring the percent elongation,
capstan type grips have been found to be unsatisfactory.
as no material having an accepted reference value is available.
NOTE 1—See Test Methods E8 for a discussion of machines, gripping
5. Electrical Resistance of Conductors
devices, and rates of stressing.
4.4 Procedure: 5.1 Scope—This test method covers the determination of the
4.4.1 Remove the fibrous insulation without distorting the
electrical resistance of fibrous insulated magnet wire conduc-
conductor for wire sizes 0.0253 in. (0.6426 mm) (AWG 22) tors.
and finer. Do not remove the fibrous insulation from sizes
5.2 Significance and Use—Accurate control of resistance is
larger than 0.0253 in. (0.6426 mm) (AWG 22).
necessary to meet apparatus design parameters. Resistance is
4.4.2 Standard Method: Insert the test specimen into the
expressed in terms of ohms per unit length corrected to 20 °C
grips resulting in an original length of 10 6 0.1 in. (254 6 2.5
(68 °F) and is a function of conductor dimensions, resistivity,
mm) to be stretched. Elongate the wire at a constant rate of 12
and temperature. Resistance is affected by the processing
6 1 in./min (305 6 25 mm/min) until the conductor breaks.
operation.
Determine the length at break by measuring the final distance
5.3 Apparatus—The types of apparatus utilized for measur-
between the grips. Discard the results for any specimens that
ing resistance and length are specified in Test Method B193.
break within ⁄4 in. (6 mm) of the grips. When breaks occur
frequently in this manner, a need for modification of the
5.4 Procedure—Remove the insulation on both ends of the
equipment or technique is indicated.
test specimen for electrical contact. The cleaning operation
4.4.3 Bench Mark Method: Rectangular, square, or round
must not affect the conductor dimensions. Determine the
wire larger than 0.0651 in. (1.654 mm) in diameter is allowed
electrical resistance of the test specimen.
to be tested using bench marks. Measure the original length
NOTE 2—While balancing the bridge, care must be taken to prevent
between bench marks to ensure the distance between the bench
excessive heating of the specimen as a result of prolonged current, and to
marks is 10 6 0.1 in. (254 6 2.5 mm). Insert the wire specimen
avoid changes in temperature due to air drafts or to variations in ambient
into the grips and locate the bench marks centrally and not
conditions.
more than ⁄2 in. (12.7 mm) from either grip. Elongate the wire
5.5 Report the Following Information:
specimen at a constant rate of 12 6 1 in./min (305 6 25
5.5.1 Bare conductor dimensions,
mm/min) until the conductor breaks. Match the broken ends of
5.5.2 Bare conductor material,
the specimen, place together, and measure the final length to
5.5.3 Type and build of film insulation,
the nearest 0.1 in. at break between the bench marks. In order
5.5.4 Type of fibrous-insulation,
to minimize the effect of local variations in the wire under test,
5.5.5 Number of servings,
test three specimens of the sample. Discard the results for any
5.5.6 Direction of servings,
specimens that break within ⁄4 in. (6 mm) of the grips or the
bench marks. When breaks occur frequently in this manner, a 5.5.7 Type of varnish,
need for modification of the equipment or technique is indi- 5.5.8 Test temperature,
cated.
5.5.9 Specimen length,
5.5.10 Apparatus used,
4.5 Calculation—Calculate the elongation as follows:
5.5.11 Resistance reading, and
Elongation, % 5 @~A 2 B!/B# × 100 (1)
5.5.12 Resistance ohms per unit length corrected to 20 °C
where:
(68 °F).
A = length at break, and
5.6 Precision and Bias:
D3353 − 18 (2024)
5.6.1 This test method has been in use for many years, but as in stranded or litz wire, or where the insulating material is
no statement of precision has been made and no activity is readily distorted as in the case of some organic fibers.
planned to develop such a statement.
7.2 Significance and Use—Knowledge of the dimensions of
5.6.2 No information is presented on the bias of this
the bare conductor, overall dimensions of fibrous–insulated
procedure in Section 5, for measuring the electrical resistance
magnet wire, and average insulation addition to the dimensions
of the conductor, as no material having an accepted reference
are necessary for specification and use purposes. Bare conduc-
value is available.
tor dimensions are one of the basic parameters used in the
design of electrical machinery and the breakdown voltage is
6. Fibrous Coverage
related to the thickness of the insulation.
6.1 Scope—This test method covers the determination of the
7.3 Apparatus:
quality of fibrous servings on round magnet wire or bare
7.3.1 Micrometer, apparatus for measuring the dimensions
conductor.
of bare conductor and fibrous–insulated wire shall consist of
6.2 Significance and Use—The results of this test are
accurate hand or bench micrometers. The micrometer spindle
indicative of the quality of the fibrous servings applied to the loading shall not be greater than 8 oz/ ⁄4-in. diameter anvil (225
wire. High quality serving is required since it will permit the
g/6.36 mm diameter anvil) for 0.0651 in. (1.654 mm) (AWG
wire to be stressed by bending without exposing the conductor 14) and finer. For all round wire sizes larger than 0.0651 in.
or underlying film.
(1.654 mm) and for all rectangular and square wire sizes, the
micrometer spindle loading shall be 3 lb 6 1 oz/ ⁄4-in. diameter
6.3 Apparatus:
anvil (1360 6 28 g/6.36 mm diameter anvil).
6.3.1 Means for chucking and rotating mandrels while
maintaining suitable wire tension.
NOTE 4—Other instruments such as electronic micrometers or light
6.3.2 Mandrels, to be specified. wave micrometers have been found suitable for measuring the bare or film
insulated conductor diameter.
6.4 Procedure:
NOTE 5—Spindle pressures specified above have been established based
6.4.1 Wind the wire, with only sufficient tension to form it
on experience with copper.
around a mandrel of a diameter to be specified, without
7.3.2 Mandrel, tapered (Fig. 1).
twisting or stretching and at a speed not to exceed 40 rpm. Ten
7.3.3 Weights, suitable (Table 1).
turns closely spaced along the mandrel shall constitute a test
7.3.4 Calipers, precision, with vernier reading to 0.001 in.
specimen.
(0.025 mm).
NOTE 3—Commercially, it is normally specified that the bare conductor
7.4 Specimens:
or underlying film is not exposed when the specimen is wound around a
7.4.1 When using the micrometer technique, the test speci-
mandrel having a diameter ten times the diameter of the bare conductor.
mens shall consist of at least 3 in. (76 mm) straight lengths of
6.4.2 Examine the test specimen for exposed bare conductor
wire free of kinks or obvious defects. Carefully remove the
or underlying film with normal vision.
specimens from the spool or container at 1 ft (0.3 m) intervals
6.5 Report the Following Information:
without more than 1 % stretch for straightening.
6.5.1 Bare conductor dimensions,
7.4.2 When measuring the diameter using the tapered man-
6.5.2 Bare conductor material,
drel technique, the specimen shall be of sufficient length to
6.5.3 Type and build of film insulation,
wind a minimum of 25 turns on the tapered mandrel and shall
6.5.4 Type of fibrous-insulation,
be free of kinks or other obvious defects. Carefully remove the
6.5.5 Number of servings,
specimens from the spool to avoid damaging or stretching.
6.5.6 Direction of servings, and
7.5 Procedure:
6.5.7 List the smallest mandrel diameter that does not
7.5.1 For round wire, using a micrometer, measure the
expose the bare conductor or underlying film.
overall diameter at four places approximately 45° apart around
6.6 Precision and Bias:
the specimen. The average of the high and low values is
6.6.1 No information is presented about either the precision
considered the overall specimen diameter.
or bias of Section 6 for evaluating fibrous coverage since the
7.5.2 For round wire, using the tapered mandrel technique,
test result is nonquantitative.
attach one end of the specimen to the small end of the mandrel,
pass the wire over a pulley as indicated in Fig. 2 and attach the
7. Measurement of Dimensions
free end of the wire to the load specified in Table 1. Closely
7.1 Scope: wind a minimum of 25 turns onto the tapered mandrel at the
rate of approximately 12 rpm. Measure the length of the
7.1.1 These test methods determine the dimensions of the
bare or film insulated conductor and the fibrous–insulated winding along the mandrel with a vernier caliper and divide
this distance by the number of turns along the mandrel. The
magnet wire.
7.1.1.1 The micrometer technique is applicable to wires quotient is the average overall diameter of the wire.
where compressibility of the conductor or insulation is not a 7.5.3 For rectangular wire, measure the overall thickness
factor. and width for each of three specimens. On square wire, mark
7.1.1.2 The tapered mandrel technique is suitable for mea- one side to insure that the measurement will be taken on the
suring the diameter of wires where compressibility is a factor same sides on both the insulated wire and bare conductor. The
D3353 − 18 (2024)
FIG. 1 Tapered Mandrel
A
TABLE 1 Copper Wire Tension
Nominal Bare Diameter Tension to Produce 7500 psi (52 MPa)
AWG Size in. mm lb kg
22 0.0253 0.6426 3.8 1.75
23 0.0226 0.5740 3.0 1.50
24 0.0201 0.5105 2.4 1.10
25 0.0179 0.4547 1.9 0.85
26 0.0159 0.4039 1.5 0.70
27 0.0142 0.3607 1.2 0.55
B
28 0.0126 0.3200 0.45
B
29 0.0113 0.2870 0.35
B
30 0.0100 0.2540 0.27
A
Wire tensions for materials other than copper have not been established.
B
For weights less than 1 lb (0.45 kg) use specified kilogram values.
average of the three thicknesses and width measurements shall 7.6 Report the Following Information:
be the overall thickness or width, or both.
7.6.1 Individual bare conductor dimensions,
7.5.4 Remove the fibrous insulation without distorting the
7.6.2 Bare conductor material,
conductor and measure the diameter or thickness and width as
7.6.3 Number of strands for litz wire,
in 7.5.1 or 7.5.3. In the case of stranded o
...