Low voltage power supply and distribution generally adopts hierarchical distribution. If only at the end of the line (switch) installed residual current circuit breakers, although leakage occurs, the fault line can disconnect, but the scope of protection; similarly, if only in the branch trunk (distribution box) or trunk (total distribution box) installed leakage breaker, although the scope of protection, if a certain electrical equipment leakage tripping, will cause the entire system of all power, not only affects the normal operation of the equipment without faults, and inconvenience to find the accident, obviously these protection methods are inadequate. Therefore, take line and load different requirements, at the end of trunk and branch lines and low-voltage lines were installed circuit breaker with different operation characters, form a hierarchical residual current  protection network. Grading protection, selection of the scope of protection at all levels should cooperate to ensure the leakage fault or personal electric shock accident in the end, the leakage protector does not operate; at the same time, when the breaker fails, the circuit breaker, accident remedial lower failure. The different levels of protection, can make each electrical equipment has more than two leakage protection measures, not only for the low voltage power network all at the end of the line for the electrical equipment to create multiple protection in direct contact with the safe operation conditions and provides personal safety and indirect contact, and can maximize the power to narrow the scope of failure and it is easy to find, and find the point of failure, to improve the safety level and reduce the electric shock accident, has a positive role in ensuring safe operation.