This test method differentiates among solid electrical insulating materials for use at commercial power frequencies with respect to their voltage endurance under the action of corona (see Note 1). In general, this test method is more meaningful for rating materials with respect to their resistance to prolonged a-c stress under corona conditions than is dielectric strength. Note 1-The term "corona" is used almost exclusively in this test method instead of "partial discharge", because it is a visible glow at the edge of the smaller electrode. This is a difference in location, not in kind. Partial discharges also occur at the edges of electrodes, and in general corona describes an electrical discharge irrespective of its location. The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 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. For specific hazard statements, see Section 7.