ASTM D3377-04(2009)

1.1 This test method covers the determination of the percent weight loss of cured solventless electrical varnishes when exposed to elevated temperatures for prescribed periods of time.

1.2 Results of this test method are based on 6-mm (¼-in.) thick specimens and will not be applicable to specimens appreciably thinner or thicker than 6 mm.

1.3 The values stated in SI units are to be regarded as the standard.

1.4 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.

Note 1—This standard resembles IEC 60216–2 “Guide for the determination of thermal endurance properties of electrical insulating materials. Part 2: Choice of test criteria” in a number of ways, but is not consistently similar throughout. The data obtained using either standard will possibly be technically equivalent.

The amount and composition of by-products produced by exposure of insulating varnishes to elevated temperatures can possibly:

Deteriorate other insulations in the system,

Cause cracking of insulation due to pressure, buildup in thick cross sections, or

Corrode other parts in the assembly.

Amount and rate of weight loss will possibly affect the thermal rating of a varnish.