Insulation testing can discover any sorts of issues that come up because of aging, physical stress, dirt, corrosion, past electrical stresses and other issues which deteriorate the insulation elements inherent in an electrical unit. Which elements should be tested depend on the unit under test, but the testing can performed at voltages from 1 kV to 15 kV and over. Insulation testing is non-destructive and should not damage the unit under test.