ASTM D495-14 PDF Download

ASTM D495-14 is a standard test method that aims to simulate the conditions experienced by solid electrical insulation when subjected to high voltage and low current dry arcs. The test method involves the intermittent occurrence of arc flashes between two electrodes placed on the surface of the specimen. The severity of the test increases gradually by decreasing the interval between flashes and increasing the current.

The standard identifies four general types of failure that can occur during the test. Inorganic dielectrics may become incandescent, leading to conductivity that is reversible upon cooling. Some organic compounds may burst into flame without the formation of a visible conducting path. Others may fail due to the formation of a thin wiry line called "tracking" between the electrodes. The fourth type of failure occurs through carbonization of the surface until there is enough carbon to conduct the current.

Materials often fail within the first few seconds after a change in severity stage, and it is emphasized that more weight should be given to the overlap between stages than to the elapsed time within a stage when comparing arc resistance. The standard also mentions possible methods for characterizing the remaining insulating value of the damaged area after failure.

It is important to note that the usefulness of this test method is limited by various qualifications and restrictions, and it is generally not suitable for material specifications. Alternative test methods are encouraged. The test method cannot provide conclusions about the relative arc resistance of materials in other types of arcs or different environmental conditions. However, it can be used for preliminary screening, detecting changes in formulation, and quality control testing after correlation with other simulated service arc tests.