Examination of the leakage current resulting from a gradual or stepwise increase in d-c test voltage permits significant conclusions in the determination of the service suitability of rotating machine insulation. Dielectric absorption effects have an appreciable influence on the leakage behavior. Therefore, in attempting to use the results of such tests there is considerable merit in conducting the test in such a manner that the various components of the leakage currents are either known or their influence on the test results controlled.