• 28/Sept, 2018

Everything you need to know about MCB’s

Demystifying the MCB for Electrical Safety

Every household, commercial establishment or industrial unit that uses electricity is most likely to have Miniature Circuit Breakers or MCB’s as they are popularly known. They are small devices and have replaced the fuse which was the only available choice earlier.

So, what is an MCB? Why do we need them? What purpose do they serve? The MCB is an electrical switch which is self-operating and is needed as a protection to human beings and electrical appliances from electrical shocks caused by current overload or short circuits. Under normal working conditions, a rated amount of current flows through an electrical network. However, in case of a fault where the current exceeds the rated limit, the MCB detects this excess flow and at once breaks the circuit. This is seen as the tripping of the MCB switch.

To understand how they work, we must be aware of the two operating mechanisms they employ. One is the thermal tripping effect and the other is the magnetic tripping effect. The thermal operation is achieved with a bimetallic strip. In case of a continuous over electric current flow, the bimetallic strip gets heated and deflects. This deflection releases the built-in mechanical latch which is connected to the operating mechanism causing it to open or trip the miniature circuit breaker contacts. Whereas, during a short circuit condition, the sudden rise of the electric current, causes an electro-mechanical displacement of the plunger associated with the tripping coil of the MCB. The plunger strikes the trip lever causing immediate release of the latch mechanism which opens or trips the circuit breaker contacts.

MCB’s are mainly defined in three categories based on their tripping characteristics and are simply named Type B, Type C and Type D. Each of these categories is based on the tripping over a range of fault current, as well as their distinctive characteristic curves. Characteristic curves describe the operational and tripping behaviour of an MCB in the event of an overload or short circuit.

Type B MCB’s are mostly used at residences and at light commercial applications like lighting and domestic appliances. They are designed to trip between 3 and 5 times the full load current.

Type C MCB’s have applications in the commercial and industrial sectors. They are connected mainly to inductive in nature machines, like induction motors and fluorescent lighting. This type of MCB trips between 5 and 10 times the full load current.

Type D MCB’s are appropriate for specialty applications of industrial and commercial machines where current inrush can be extremely high. Examples include transformers, large winding motors and X-ray machines. They are designed to trip between 10 and 20 times the full load current.


To conclude, choosing the right MCB is vital, and a must-have safety feature at all homes, offices, commercial buildings and factories. Switch to a smarter, better, reliable, and safer range of MCB’s brought to you by Finolex.


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