ASTM D4881-97

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Designation: D 4881 – 97 An American National Standard
Standard Test Method for
Thermal Endurance of Varnished Fibrous- or Film-Wrapped
Magnet Wire
This standard is issued under the fixed designation D 4881; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope plied to the same fibrous- or film-wrapped magnet wire and
aged at elevated temperatures. Likewise, a varnish may not
1.1 This test method covers the determination of thermal
behave the same when applied to different types of fibrous or
endurance of rectangular and square fibrous- or film-wrapped
film-wrapped magnet wires and aged at elevated temperatures.
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 appro-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. A specific precau-
tionary statement is given in Section 5.
NOTE 1—There is no similar or equivalent IEC Standard.
2. Referenced Document
2.1 ASTM Standards:
D 1711 Terminology Relating to Electrical Insulation
D 2307 Test Method for Relative Thermal Endurance of
Film-Insulated Round Magnet Wire
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 varnish, electrical insulating, n— a liquid resin sys-
tem that is applied to and cured on electrical components
FIG. 1 Jig for Forming Wire
providing electrical, mechanical, and environmental protec-
tion.
5. Safety Precautions
3.1.1.1 Discussion—There are two types of electrical insu-
lating varnishes—solvent-containing and solventless. Solvent-
5.1 Do not use varnish at temperatures above the flash point
containing types are solutions, dispersions, or emulsions of a
when inadequate ventilation, possibility of flames or sparks
polymer or a mixture of polymers in a volatile, nonreactable
exist. Store varnish in sealed containers. These precautions
liquid. Solventless types are liquid resin systems free of
shall also apply to the handling of the reagents and solvents
volatile, nonreactable solvents.
called for in this test method.
3.1.2 Refer to Terminology D 1711 for definitions of other
6. Test Specimens
terms.
6.1 Construction of Test Specimens:
4. Significance and Use
6.1.1 Cut two 250-mm (10-in.) lengths of wire for each
4.1 Individual varnishes may behave differently when ap-
specimen to be made.
6.1.2 Form each length in a fixture as shown in Fig. 1.
6.1.3 Prepare a test specimen by placing the two formed
This test method is under the jurisdiction of ASTM Committee D-9 on
wires together back to back and wrap tightly with glass yarn
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.01 on Electrical Insulating Varnishes, Powders, and Encapsu-
over the middle 6-in. (150-mm) section. The glass yarn shall
lating Compounds.
have a gap between turns and there must be intimate contact of
Current edition approved Sept. 10, 1997. Published February 1998. Originally
the two wires.
published as D 4881 – 88. Last previous edition D 4881 – 93.
Annual Book of ASTM Standards, Vol 10.01. 6.1.4 Prepare ten specimens for each test temperature.
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