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