Plastic shell circuit breakers, also known as device type circuit breakers, have all components sealed in a plastic casing. Auxiliary contacts, undervoltage release devices, and shunt release devices are often modularized. Due to its very compact structure, molded case circuit breakers are basically impossible to maintain. It mostly adopts manual operation, and for large capacity, electric opening and closing can be selected. Due to the application of electronic overcurrent release devices, molded case circuit breakers can also be divided into two types: Class A and Class B. Class B has good three-stage protection characteristics, but due to price factors, Class A products using thermal magnetic release devices have a higher market share. Plastic shell circuit breaker is a type of circuit breaker that integrates contacts, arc extinguishing chambers, release devices, and operating mechanisms into a plastic casing. It is generally not considered for maintenance and is suitable for use as a protective switch for branch circuits. There are two types of overcurrent release devices: thermal magnetic and electronic. Generally, thermal magnetic plastic shell circuit breakers are non selective circuit breakers, with only two protection methods: overload long delay and short circuit instantaneous. Electronic plastic shell circuit breakers have four protection functions: overload long delay, short circuit instantaneous, short circuit instantaneous, and ground fault. Some newly launched electronic molded case circuit breakers also have area selective interlocking function. Most molded case circuit breakers are manually operated, and some are equipped with electric motor operating mechanisms.