The final distribution in residential building (Tertiary power distribution) is closest to the load, and thus has the following characteristics: Good operation between circuit breakers and reasonable distribution circuits could effectively make short circuit breaking quickly to avoid a loss of power failure causes distortion. Because close to the load, thus operating more frequently required components have reliable mechanical and electrical life. Terminal distribution circuit breakers are applied directly with a load, if the protection is unreasonable, easily burning appliances, and there is a big fire hazard threat to personal safety. Residential building three distribution mainly through isolation protection, overload protection, short circuit protection, residual current protection, fire protection, lightning protection and other ways to achieve safe, reliable endpoint protection.