Molded Case Circuit Breakers

Molded case circuit breakers (MCCB) are electrical switches that are designed to trip during a short circuit or overload to protect against electrical faults and equipment failure. Overload protection is accomplished through a thermal operation with a slight time delay. When an overcurrent passes through an MCCB, a bimetallic strip is heated and bends. The bending causes a mechanical latch to release, opening the MCCB contacts, halting the flow of current. When the overcurrent is removed, the contacts close and the MCCB is reset. Short circuit protection is accomplished through an electromagnetic operation that is instantaneous. A current coil is tripped causing the mechanical release of the latch that opens the contacts that halt the flow of current. When the overcurrent is removed, the MCCB can be reset.

Molded case circuit breakers are similar to miniature circuit breakers (MCB) in methodology, however the main difference between the two is in the capacity. MCBs current rating is under 100 amps with an interrupting rating under 18,000 amps while MCCBs current rating is 1,000 amps with an adjustable trip function that allows an interrupting range from 10,000 amps to 200,000 amps.