Miniature Circiut Breaker (MCB) is one of the most widely used terminal protection devices in building electrical terminal distribution devices. It is used for short circuit, overload and overvoltage protection of single phase and three phase below 125A, including four kinds of single pole 1P, two pole 2P, three pole 3P and four pole 4P. In the design of civil buildings, the low-voltage circuit breaker is mainly used for overload, short circuit, overcurrent, voltage loss, undervoltage, grounding, leakage, automatic switching of dual power supply and motor infrequent starting protection, operation and other purposes