Leakage protector the main component is a magnetic ring inductor, the fire wire and the zero line using parallel winding method in the magnetic ring winding a few times, there is a secondary coil in the magnetic ring.
When the same phase of the firewire and zero line in normal operation, the current generated by the magnetic flux just offset, in the secondary coil will not induce a voltage. If a line has a leakage, or not connected to the zero line, in the magnetic ring through the current of the fire line and zero line will be unbalanced, and produce a magnetic flux through the magnetic ring, in the secondary coil induced voltage, through the electromagnet to make the release action tripping.
Principle of choice
Because of the direct contact with the electric shock of the hazard is relatively large, causing serious consequences, so we should use the higher sensitivity of the leakage circuit breaker, electric tools, mobile electrical equipment and temporary lines, should be installed in the circuit of the action current of 30mA, the action time of 0.1s within the leakage circuit breaker. For residential houses with more household appliances, it is best to install them behind the incoming energy meter.
If once electrocuted is easy to cause secondary injuries (such as working at height), should be installed in the circuit with an action current of 15mA, action time within the US leakage circuit breaker. For electrical medical equipment in hospitals, earth leakage circuit breakers with an action current of 6mA and an action time within US should be installed.
Reference: Baidu Encyclopedia - Earth Leakage Circuit Breaker