Molded case circuit breaker is also known as a modular circuit breaker. All parts are sealed in a plastic housing, and the auxiliary contacts, the undervoltage release, and the shunt release are modular. Because of the very compact structure, the molded case circuit breaker is virtually out of repair. Most of them are operated by hand, and large capacity can be selected by electric separation. Due to the application of electronic over current tripping device, circuit breaker can also be divided into class A and class B two, class B has three good protective characteristics, but because of the price factor, the thermal magnetic trip is a product of higher market share. MCCB is the contact and interrupter, release and operation mechanism are installed in a plastic shell, is generally not considered suitable for maintenance, protection switch branch, over-current release with thermal magnetic and electronic two, general pyromagnetic circuit breaker is non selective circuit breaker, overload long delay and only two instantaneous short circuit protection, electronic MCCB overload long delay, short time delay, instantaneous short circuit and ground fault protection function four. Part of the electronic molded case circuit breaker, the new product also has regional selective chain function. Most molded case circuit breakers are operated manually and partly with motor operated mechanisms.