Usage category of molded case circuit breakers

A molded case circuit breaker used for terminals does not require excessive consideration of selective coordination with lower level molded case circuit breakers (when a lower level short circuit occurs, the upper level molded case circuit breaker should not act impulsively, be cautious, and wait for a short delay time before acting, otherwise the entire building will run out of electricity). This type of circuit breaker is defined as Cat A.
Molded case circuit breakers used for backbone nodes, such as frame molded case circuit breakers, often need to be carried first during short circuits. After withstanding 100-1000 milliseconds, if the lower level molded case circuit breaker fails to cut off the circuit due to some reason, the higher level brother will take action again. This definition is Cat B.
Class B molded case circuit breakers require an explicit declaration of a parameter Icw for short-term withstand current, where w should mean Withstand.

Molded case circuit breakers, also known as device type molded case 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 basically impossible to repair. By manual operation, electric opening and closing can be selected for large capacity. Due to the application of electronic overcurrent releases, 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 releases have a higher market share. Molded case circuit breaker is a type of circuit breaker that installs the contact, arc extinguishing chamber, release, and operating mechanism in a plastic casing. It generally does not consider maintenance and is suitable as a protective switch 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 four protection functions: overload long delay, short circuit short delay, short circuit instantaneous, and ground fault. Some newly launched electronic molded case circuit breakers also have a region selective interlocking function. Most molded case circuit breakers are manually operated, and there are also some with electric motor operating mechanisms.