Prok dv's make digital microprocessormicrocontroller based earth leakage relays (elr) with core balance current transformer (cbct zct) are used to detect leakage currents in electrical power systems. Elr transmits a signal to activate the trip coil of the mccbacbocbcontactor in the event of earth leakage resulting in automatic isolation of the load. Elr have been widely used and accepted because of field adaptability and are economic.