In all the domestic, commercial and industrial applications miniature circuit breakers are widely used. Conventional fuses are replaced by these circuit breakers. It combines the features of good HRC fuse and a good switch.
Under normal operation conditions, it can be operated as a switch to make the circuit ON or OFF. In case of induction motor it will be used to give 3 phase supply to the motor. During overload or any other type of fault, it is operated, it is operated automatically and isolate the faulty circuit from the supply. The tripping mechanism is actuated by magnetic and thermal sensing devices provided within the MCB.
In case of induction motor protection circuit the functions of thermal overload relay and contactors are done solely with the help of MCB. Thus two separate elements are not required. Various current ratings (Typically include 5, 10, 15, 20, 30, 40, 50, 60 A etc) at voltage ratings of 240 V / 415 V are commercially available.
The tripping mechanism and the terminal contacts are assembled in a moulded case, moulded out of thermosetting powders. They ensure high mechanical strength, high dielectric strength and virtually no ageing. The current carrying parts are made out of electrolytic copper or silver alloy depending upon rating of breaker. The breaker has unit construction from which multiple pole breakers can be made by assembly of single pole breakers.