The residual current circuit breakers are mainly provided when the electric equipment has the leakage fault, and when the residual current circuit breaker is installed, the overcurrent protector is additionally installed. When fuse is used as short circuit protection, the selection of its specifications should be adapted to the breaking and breaking capacity of the leakage protector. The current widely used leakage protection device and a power supply switch (automatic air breaker) assembly leakage breaker together, this new type of power switch with short circuit protection, overload protection, leakage protection and undervoltage protection performance. When the utility model is installed, the circuit is simplified, the volume of the electric box is reduced, and the management is convenient. Leakage circuit breaker type nameplate its meaning is as follows: use should pay attention to, because of leakage circuit breaker with multiple protective performance, when tripping, should distinguish the specific failure: when the leakage circuit breaker with short circuit breaking, shall open cover check whether there is serious loss of contact or pit; when the line overload trip, not immediately close again. The circuit breaker equipped with thermal relay as overload protection, when there is greater than the rated current, double sheet metal bending of the contact must be separated, bimetal natural cooling can be restored after re closing contact. When the trip caused by the leakage fault, we must find out the cause, after the fault can be re closed, strictly prohibit closing. The breaking trip occurs leakage breaker, L a handle in the middle position, when closed, will need to handle and pulled downwards (off position), the operating mechanism is to carry on dunks, closing. Residual current circuit breaker can be used for large capacity (greater than 4.5kw) power lines, not frequent operation of switching equipment.