The item is in accordance with standards of VDE 0664, CEE27 and BS4293 etc., applying to the circuit of AC 50/60Hz, 240V single phase, 415V three phases and below it for industrial and mining enterprise, building trade, commerce and family. To mainly prevent electric fire and personal casuatly accident caused by personal electric shock or leakage of electrified wire netting, this ELCB is a current-operated, fast leakage protector of pure electromagnetic type, which can break off fault circuit rapidly in order to avoid occurrence of accident. The item is precise in structure, less elements, without auxiliary power and high working reliability. The function of the switch won be influenced by ambient temperature and lighting.The mutual inductor of the item is used to test vector differential value of passing current, and produces are levant output power and add it differential value of protected circuit of personal electric shock is up to or over leakage operating current, the tripper will act and cut off so that the item will take effect of protection.