ASTM D4881-05(2017)

Standard Test Method for Thermal Endurance of Varnished Fibrous- or Film-Wrapped Magnet Wire

SIGNIFICANCE AND USE
4.1 Individual varnishes behave differently when applied to the same fibrous- or film-wrapped magnet wire when exposed to elevated temperatures. Likewise, a varnish does not always behave the same when applied to different types of fibrous or film-wrapped magnet wires and when exposed to elevated temperatures.
FIG. 1 Jig for Forming Wire
SCOPE
1.1 This test method covers the determination of thermal endurance of rectangular and square fibrous- or film-wrapped magnet wire coated with an insulating varnish.  
1.2 The values given in SI units are the standard. The values given in parentheses are for information only.  
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 establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. A specific precautionary statement is given in Section 5.  
Note 1: There is no similar or equivalent IEC Standard.  
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-Aug-2017
• ICS: 29.060.10 - Wires
• Technical Committee: D09 - Electrical and Electronic Insulating Materials
• Drafting Committee: D09.01 - Electrical Insulating Products

Relations

• Replaces: ASTM D4881-05(2012) - Standard Test Method for Thermal Endurance of Varnished Fibrous- or Film-Wrapped Magnet Wire
• Effective Date: 01-Sep-2017
• Refers: ASTM D3353-18(2024) - Standard Test Methods for Fibrous-Insulated Magnet Wire
• Effective Date: 01-Mar-2024
• Refers: ASTM D1711-24 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Mar-2024
• Refers: ASTM D3353-18 - Standard Test Methods for Fibrous-Insulated Magnet Wire
• Effective Date: 15-Mar-2018
• Refers: ASTM D1711-15 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2015
• Refers: ASTM D1711-14a - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2014
• Refers: ASTM D1711-14 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-May-2014
• Refers: ASTM D1711-13 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2013
• Refers: ASTM D1711-11a - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Aug-2011
• Refers: ASTM D3353-10 - Standard Test Methods for Fibrous-Insulated Magnet Wire
• Effective Date: 01-Jan-2010
• Refers: ASTM D1711-08 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-May-2008
• Refers: ASTM D2307-07a - Standard Test Method for Thermal Endurance of Film-Insulated Round Magnet Wire
• Effective Date: 01-Oct-2007
• Refers: ASTM D2307-07 - Standard Test Method for Thermal Endurance of Film-Insulated Round Magnet Wire
• Effective Date: 01-Jan-2007
• Refers: ASTM D2307-05 - Standard Test Method for Thermal Endurance of Film-Insulated Round Magnet Wire
• Effective Date: 01-Sep-2005
• Refers: ASTM D3353-04 - Standard Test Methods for Fibrous-Insulated Magnet Wire
• Effective Date: 01-Apr-2004

Overview

ASTM D4881-05(2017) is the internationally recognized standard test method for determining the thermal endurance of varnished, fibrous- or film-wrapped magnet wire. Published and maintained by ASTM International, this standard applies to both rectangular and square magnet wires that are coated with an insulating varnish. As the insulation performance of varnished magnet wire is paramount in ensuring the reliability of electrical equipment, this test method provides a consistent framework for evaluating how these materials hold up under prolonged exposure to elevated temperatures.

Key Topics

• Thermal Endurance Measurement: The standard sets out procedures to assess the duration for which varnished magnet wires can maintain their insulating properties at high temperatures.
• Variety of Varnish and Wire Types: Recognizes that different varnishes and substrate combinations may perform uniquely under heat stress, making direct testing critical for material selection.
• Test Set-Up: Outlines the preparation of magnet wire specimens, including the use of glass yarn ties and specific varnish application techniques, ensuring repeatability and reliable results.
• Safety Considerations: Emphasizes the need for precautions when handling varnishes, particularly at temperatures above their flash points, and the importance of adequate ventilation.
• Reporting Requirements: Specifies detailed information to be recorded and reported, including varnish and wire identification, temperature index, and correlation coefficient.
• Standard Referencing: Relies on related terminologies and concepts as provided in ASTM D1711 and processes found in ASTM D2307 and D3353.

Applications

The ASTM D4881-05(2017) standard is widely used in the electrical and electronics industries where the reliability of magnet wire insulation is critical. Applications include:

• Motors and Generators: Assessing the suitability of magnet wires in high-temperature operating conditions.
• Transformers: Ensuring long-term insulation stability in power and distribution transformer windings.
• Automotive and Aerospace: Testing the performance of magnet wire in environments requiring high thermal tolerance.
• Electrical Apparatus Manufacturing: Supporting quality control processes by providing a standardized assessment of insulating varnish performance.

By following this thermal endurance test method, manufacturers, suppliers, and quality assurance professionals can make informed decisions when selecting varnish and wire combinations, ultimately improving product durability and safety.

Related Standards

For comprehensive quality assurance and to support the implementation of ASTM D4881-05(2017), the following standards may also be relevant:

• ASTM D1711 - Terminology Relating to Electrical Insulation: Provides essential definitions and terms used throughout electrical insulation testing.
• ASTM D2307 - Test Method for Thermal Endurance of Film-Insulated Round Magnet Wire: Offers related procedures for round wire types.
• ASTM D3353 - Test Methods for Fibrous-Insulated Magnet Wire: Covers evaluation methods for fibrous-wrapped insulation.

Note: There is currently no direct equivalent to this ASTM standard under IEC standards. Organizations operating in global markets may use this ASTM method as a reference point in the absence of international alternatives.

---

Keywords: ASTM D4881, thermal endurance, varnished magnet wire, fibrous-wrapped wire, film-wrapped wire, electrical insulation testing, insulating varnish, thermal endurance test, ASTM International, magnet wire performance.

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: D4881 − 05 (Reapproved 2017)
Standard Test Method for
Thermal Endurance of Varnished Fibrous- or Film-Wrapped
Magnet Wire
This standard is issued under the fixed designation D4881; 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 3.1.1.1 Discussion—There are two types of electrical insu-
lating varnishes: solvent-containing and solventless. Solvent-
1.1 This test method covers the determination of thermal
containing types are solutions, dispersions, or emulsions of a
endurance of rectangular and square fibrous- or film-wrapped
polymer or a mixture of polymers in a volatile, nonreactable
magnet wire coated with an insulating varnish.
liquid. Solventless types are liquid resin systems free of
1.2 The values given in SI units are the standard.The values
volatile, nonreactable solvents.
given in parentheses are for information only.
3.1.2 Refer to Terminology D1711 for definitions of other
1.3 This standard does not purport to address all of the
terms.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Significance and Use
priate safety and health practices and determine the applica-
4.1 Individual varnishes behave differently when applied to
bility of regulatory limitations prior to use. A specific precau-
the same fibrous- or film-wrapped magnet wire when exposed
tionary statement is given in Section 5.
to elevated temperatures. Likewise, a varnish does not always
NOTE 1—There is no similar or equivalent IEC Standard. behave the same when applied to different types of fibrous or
film-wrapped magnet wires and when exposed to elevated
1.4 This international standard was developed in accor-
temperatures.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
5. Safety Precautions
Development of International Standards, Guides and Recom-
5.1 It is unsafe to use varnish at temperatures above the
mendations issued by the World Trade Organization Technical
flash point without adequate ventilation, especially if the
Barriers to Trade (TBT) Committee.
possibility exists that flames or sparks are present. Store
2. Referenced Document
varnish in sealed containers.
2.1 ASTM Standards:
6. Test Specimens
D1711 Terminology Relating to Electrical Insulation
D2307 Test Method for Thermal Endurance of Film- 6.1 Construction of Test Specimens:
Insulated Round Magnet Wire 6.1.1 Cut two 250-mm (10-in.) lengths of wire for each
D3353 Test Methods for Fibrous-Insulated Magnet Wire specimen to be made.
6.1.2 Determine the thickness dimensions per Test Method
3. Terminology
D3353.
6.1.3 Form each length in a fixture as shown in Fig. 1.
3.1 Definitions of Terms Specific to This Standard:
3.1.1 varnish, electrical insulating, n—aliquidresinsystem 6.1.4 Prepare a test specimen by placing the two formed
wires together back to back and wrap tightly with a minimum
that is applied to and cured on electrical components providing
electrical, mechanical, and environmental protection. of6turnsofglassyarnoverthemiddle6-in.(150-mm)section.
The glass yarn shall have a gap between turns and there must
be intimate contact of the two wires.
This test method is under the jurisdiction of ASTM Committee D09 on
6.1.5 Prepare ten specimens for each test temperature.
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.01 on Electrical Insulating Products.
6.2 Varnishing the Test Specimens:
Current edition approved Sept. 1, 2017. Published September 2017. Originally
6.2.1 Adjust the consistency of a solvent-containing varnish
approved in 1988. Last previous edition approved in 2012 as D4881 – 05 (2012).
DOI: 10.1520/D4881-05R17.
to give a 0.025 6 0.005-mm (0.0010 6 0.0002-in.) cured film
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
on each side of a 0.13-mm (0.0
...