B type PR8HM is a kind of circuit breaker with complete update of residual current detection based on current A type RCCB. It can not only effectively protect AC, pulsing DC(A type) and the possible compound residual current(F type), but also smoothing DC and high frequency residual current(1K Hz). In a circuit considering of rectifiter, frequency inventer, etc. The leakage current caused in DC loop circuit can be effectively detectecd and protected.