A form of AC testing that applies voltage and measures the leakage/loss current of electrical insulation. It is a type of insulation testing used to evaluate the integrity of electrical insulation.
The magnitude of earth fault current for a given fault position within a winding demands upon the winding connections and method of neutral grounding. Earth fault protection for an electric motor is provide by instantaneous relay having a setting of approximately 30% of motor rated current in the residual circuits of two CTs and with ground wire.