ASTM D149 checks solid electrical insulation materials by determining their breakdown voltage under controlled laboratory conditions. A successful test is a common cause of assurance that the insulation will perform well under service. Nevertheless, the electrical failures still take place in the systems that operate with materials tested and approved according to ASTM D149. Such disconnection does not mean there is something wrong with the standard, but instead a lack of understanding of what the ASTM D149 does and does not look at. These limitations can be identified by engineers to close the divide between the laboratory and the field.
ASTM D149 Measures Short-Term Electrical Strength
ASTM D149 is used to apply a steadily increasing voltage until dielectric breakdown is experienced to show the maximum electrical stress that the material will sustain in the short run. The test only records instantaneous failure characteristics, but not long-running operation with the operating voltage.
Laboratory Conditions Do Not Reflect Service Environments
The criterion demands a standard of temperature, humidity, and specimen preparation. In real service, insulation is exposed to variable temperatures, water intrusion, vibration, and contamination, as well as mechanical forces. These components increase degradation processes which ASTM D149 cannot replicate, and enable insulation to be lost even though it had seemed to be strong enough to start breaking down.
