The chemical composition of a wire’s insulation degrades at elevated temperature; this test provides data to establish curves describing the rate of degradation with respect to the exposure temperature.
Samples are divided into four groups; each group is exposed to a selected temperature for defined time intervals. The time intervals are determined by an estimate of the expected degradation rate of the insulation at the associated temperature.
Between each exposure cycle, the test samples are subject to a bend test and dielectric withstand test. Any samples failing the dielectric withstand are removed from the sample group and their time to failure is determined by the number of cycles until failure. This is repeated for the sample group until all wire specimens have degraded to failure.
The cycling procedure is repeated for all four test groups. After which, the average failure rate at each temperature can be graphed and a comparative relationship developed.
The evaluation should not be used to predict the lifetime of a wire insulation in application, but rather as a means to compare degradation rates at various temperatures or to compare degradation rates of different insulation constructions at the same temperature.