1.1 This test method covers the determination of the dielectric breakdown voltage of insulating oils of petroleum origin. This test method is applicable to liquid petroleum oils commonly used in cables, transformers, oil circuit breakers, and similar apparatus as an insulating and cooling medium. The suitability of this test method for testing oils having viscosities of more than 19 cSt (mm /s) (100 SUS) at 40°C (104°F) has not been determined. 1.2 This test method is more sensitive to the deleterious effects of moisture in solution than is Test Method D877, especially when cellulosic fibers are present in the oil. It has been found to be especially useful in diagnostic and laboratory investigations of the dielectric breakdown strength of oil in insulating systems. 1.3 This test method is recommended for testing filtered, degassed, and dehydrated oil prior to and during the filling of power systems apparatus rated above 230 kV, and for testing samples of oil from the apparatus after filling. It is also finding increased usage for testing oils from transformers in service. 1.4 This test method is not recommended for, and should not be used for, acceptance tests on oil received from vendors in tank cars, tank trucks, or drums. 1.5 Both the metric and the alternative inch-pound units are acceptable. 1.6 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.