The earth leakage switch is mainly composed of three parts: detection components, the middle of amplification, operation of the implementing agencies. ① detection components. By the zero sequence transformer, the detection of leakage current, and send a signal. ② amplification link. Will be weak leakage signal amplification, according to the device different (amplification components can be used mechanical devices or electronic devices), constitute an electromagnetic protector phase electronic protection. ③ executive body. Upon receipt of the signal, the main switch from the closed position to switch to the open position, thus cutting off the power supply, is the protection circuit out of the grid trip parts.