ASTM D495-14 Standard Test Method for High Voltage, Low Current, Dry Arc Resistance of Solid Electrical Insulation

In the ASTM D495-14 standard developed by the American Society for Testing and Materials (ASTM), a test method that includes the differentiation of the resistance of similar materials to the action of a high-voltage, low-current arc near the insulation surface when a conductive path is formed that causes the material to become conductive as a preliminary. is offered. However, the use of this test method is severely limited by some restrictions. Generally, this test method is not used in material specifications. Where possible, it is recommended to use other testing methods.

Because the time required for testing is short, this test method is designed to detect the effects of changes in formulation and for quality control testing after correlation with other types of simulation services.

This test method is not applicable to materials that do not form conductive paths under the influence of an electric arc, or that melt or form liquid residues that push conductive residues out of the active test area, thereby preventing the formation of a conductive path.

The high-voltage, low-current arc resistance test described in ASTM D495-14 is intended to approximately simulate the service conditions present in alternating current circuits operating at high voltages. To more easily distinguish materials with low arc resistance, the initial stages of this test method are mild, while the later stages are more intense. The arc occurs intermittently between two electrodes resting on the surface of the sample, in either normal or reverse orientation.

Four general types of failures are observed in practice:

• Many inorganic dielectrics become incandescent and can conduct current thereupon. However, after cooling, it returns to its previous insulating states.
• Some organic compounds ignite without forming a visible conductive path in the substance.
• Some organic compounds appear to fail with tracking, meaning a thin wire line is formed between the electrodes.
• The surface becomes carbonized until enough carbon is available to carry the current.

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