A wide variety of synthetic electrical insulating materials are available for application in electric machinery and apparatus. Included in these materials are the silicones, fluorocarbons, wire enamels, new films, rubbers and varnishes. As there is a growing tendency to either rely solely on these materials as electrical insulation, or to employ them with the old familiar materials in novel combinations, there is a corresponding increase in the problems associated with the selection and evaluation of insulations. Frequently an insulation system or combination of insulation materials must be evaluated rather than one insulating material. Many of the specifications regulating the use of insulation materials were written before the advent of the newer synthetics and were based upon experience gained with the old materials over a long period of time. Difficulties arise, therefore, when an effort is made to classify these new materials or combinations for insulation purposes under the USA Standards as Class A, Class B, Class F or Class H insulations. This Test Procedure has been prepared to outline useful procedures for the evaluation of systems of insulation for form-wound rotating electric machines. It is expected that the several insulating materials, or components, making up any insulation system to be tested will first be screened in accordance with specific test procedures for each type of material.