Miniature Circuit Breakers (MCB)

 A miniature circuit breaker (MCB) is an Electrical Switch that automatically switches off the electrical circuit during an abnormal network condition, resulting in overload and faulty conditions. We use an MCB in a low voltage electrical network instead of a fuse.

Earlier, we protected against over-current by using fuse wire (indeed, we used to sell it!). The principle was pretty simple - over-current would quite literally 'blow' the fuse wire by rapidly heating and melting it, thus breaking the electrical connection and, in doing so, protecting the rest of the electrical circuit.

Working & Operation of MCB

Under normal working conditions, MCB operates as a switch (manual one) to make the circuit ON or OFF. However, under overload or short circuit conditions, it automatically works or trips so that current interruption occurs in the load circuit.

The visual indication of this trip observes by automatic movement of the operating knob to OFF position. This automatic operation MCB can be obtained in two ways, as seen in MCB construction: magnetic tripping and thermal tripping.

Under overload conditions, the current through the bimetal causes it to raise its temperature. The heat generated within the bimetal itself is enough to cause deflection due to the thermal expansion of metals. This deflection further releases the trip latch, and hence contacts get separated.

In some MCBs, the magnetic field generated by the coil causes it to develop pull on bimetals such that deflection activates the tripping mechanism.

Under short circuit or heavy overload conditions, a magnetic tripping arrangement comes into the picture. Under normal working conditions, the slug is held in a position by a light spring because the magnetic field generated by the coil is not sufficient to attract the latch.

When a fault current flows, the magnetic field generated by the coil is sufficient to overcome the spring force holding the slug in position. And hence slug moves and then actuate the tripping mechanism.

A combination of magnetic and thermal tripping mechanisms is enforced in most miniature circuit breakers. An arc is created when the contacts start separating in both magnetic and thermal tripping operations. This arc is then pushed into arc splitter plates via arc runner.

These arc splitter plates are also called arc chutes, where an arc is created into a series of arcs and, at the same time, energy is extracted and cools it. Hence this arrangement achieves the arc extinction.

Types of MCB based on Tripping Characteristics

• Type B
• Type C
• Type D
• Type K

Type B

The MCB trips between 3 to 5 times of full load in type B.

Operating current 0.4 to 13 seconds.

Type of load: Resistive loads.

Response: React quickly to overloads.

Uses: Incandescent lighting, bulbs, heaters—residential applications.

Type C

In type C, the MCB trips between 5 to 10 times full load. Used in residential or industrial applications.

Operating current 0.4 to 5 seconds

Type of Load: Slightly inductive loads.

Response: React more slowly.

Uses Highly inductive loads such as motors, Air conditioners, fans, and household appliances.

Type D

The MCB trips between 10 to 20 times of full load in type D. This uses in industrial or commercial applications where there could be chances of the higher value of short circuit currents in the circuit.

Operating current 0.4 to 3 seconds.

Type of Load: Inductive loads.

Response: React more slowly.

Uses Very high inrush inductive currents such as small transformers, UPS, small motors, pumps.

Type K

In type K, the MCB trips between 8 to 10 times full load.

Operating current less than 0. 4 to 3 seconds.

Type of Load: Inductive loads.

Response: MCBs are slower.

Uses: Enhanced protection achieves without nuisance tripping.

BCH India is one of the leading manufacturers of MCB ( Miniature circuit breakers) in India. Our MCB helps to prevent damage to an electrical circuit. BCH Miniature Circuit Breaker is a high-performance device, able to disconnect Short circuit currents up to 10KA and conforms to Standards: IS/IEC 60898-1 ( 6A-63A), IS/IEC 60947-2 ( 0.5A-5A).

Visit to know more info: https://bchindia.com/product/miniature-circuit-breakers-mcb/