Mini Circuit Breakers

Miniature circuit breakers (MCB) 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 MCB, a bimetallic strip is heated and bends. The bending causes a mechanical latch to release, opening the MCB contacts, halting the flow of current. When the overcurrent is removed, the contacts close and the MCB 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 MCB can be reset.

Miniature circuit breakers have a current rating less than 100 amps and have an interrupting rating less than 18,000 amps. They come in different types according to their tripping or overcurrent characteristics. The three main types, B, C and D can be selected based on their response to different electrical surges in different settings.

Type B trip if the current flowing through is between three and five times the recommended rated load. These are the most sensitive and are best for low voltage settings where current surges are likely to be small.

Type C trip if the current flowing through is between five and ten times the recommended rated load. These are best for industrial and commercial environments where surges are likely to be higher. 

Type D trip if the current flowing through is between ten and twenty times the recommended rated load. These are the least sensitive and are best for heavy-duty industrial and commercial devices where very strong surges occasionally occur.