LMCB1 series mini circuit breaker are composed of the moulded case, operating mechanism, contact system, arc-extinguishing system, tripping mechanism, etc. The case is made of the special plastic of high fire-resistance and shockproof, which contributes their capacity of high resisting fire & impact and light in weight. The parts of the operating mechanism employ high strength plastic products, which assures the flexible, relaible operation and obtains minimum moment of inertia as well. Hereby, the time from the moment that the short circuit fault occurs to that of the tripping is very little. The tripping mechanisim is composed of the two parts of bimetal sheet overload counter time limit tripping mechanism and short circuit instantaneous electromagnetic mechanism. The contact arc-extinguishing system employs the special arc-conducting angle and gangway arc-extinguishing chamber, so they have distinct current limiting characteristics.