The dielectric withstand test is a basic electrical stress test, conducted to ensure an insulation system will provide adequate service life. For the withstand test, the insulation under test must withstand a specified applied voltage that is higher than the service voltage across the insulation for a specified period without breakdown of the insulation.

The magnitude of the withstand voltage is usually far greater than that of the operating voltage and the amount of time applied is dependent on service age and other factors.

Dielectric withstand testing is a relatively easy test to perform. If no evidence of distress or insulation failure is observed by the end of the test, the specimen is considered to have passed. If the applied voltage results in sudden breakdown of the insulation material, however, a strong leakage current will flow and the insulation is determined to be unsuitable for service as it might pose a shock hazard.