MCB Miniature Circuit Breaker

The smallest size circuit breakers are usually available for a single phase and are normally used in residential or commercial buildings. They are either installed in a consumer unit for residential building or a distribution board (DB) in the commercial building. The breaking capacity (kA) of an MCB for the short circuit is relatively low and the overload current cannot be adjusted.

In residential application the MCB is used as the main circuit breaker or individual circuits. The main breaker will need to be able to handle the combined load of the individual circuits which is usually around 100A. The individual circuit is selected according to the circuit load such as the plugs, air-conditioning, water heaters, etc.

The selection criterias are the number of poles, the rated current (In), and the breaking capacity (Icu)

• In or the rated current is maximum operating current before the breaker trip under normal operating condition. The normal operation current should be designed to operate within 80% of this figure.
• Icu or the breaking capacity (kA) is the maximum short circuit current the device can withstand while still able to safely disconnect the circuit. It is the most important selection criteria, if the MCB experience a higher short-circuit current than it’s breaking capacity then the breaker will fail and will likely catch fire or in the worst case, explode.