MCB | Working principle and Application


What is MCB?

Miniature circuit breaker, commonly known as MCB. This device-operated switch-cum-circuit is a safety device. After overload and short circuit occurs it disrupts the circuit. And mcb is used for this purpose. It is used as an alternative to fuses for home applications. Where power is cut off when there is a short circuit in the fuse. But this does not happen in MCB. After a short circuit in the line, after correcting it, the MCB again turns on the electricity.


Creative Features of MCB

Each MCB has the following parts:

Outlet Cover

The outer cover keeps all the internal components firm and protects them from dust. It is made of insulating material such as plastic or ceramic.


A pair of contacts can be found inside the MCB. One of them is stationary and the other is movable.


Knobs are used to turn MCBs on and off.

Mechanical action

A latch is arranged inside MCBs to hold the contacts under spring tension in the ON position.

Bipolar Strip

The dipole strip delays overload protection by sensing a longer flow of current than its rated current.


The solenoid provides instantaneous protection against short circuits by releasing the mechanical latch. When the solenoid is activated. The current through the coil then exceeds a particular value. Is usually more than 3 times its rated current. It is not activated by solenoid overload.

Arc Chute

Arc chute is used for division and mitigation of arc.

Operation of MCBs

Miniature circuit breakers perform four important tasks:


Miniature circuit breakers can be manually turned on and off. This functionality is highly useful, especially during maintenance. An internal latch is arranged such that it automatically holds fixed contacts as soon as the knob is pushed into the ON position. When closed, the pressure exerted by our finger on the knob leaves the latch and opens the contacts.

Excessive protection

When there is an excess load on one side of an instrument. So it consumes more electricity. This current flows through the dipole strip and heats it. The dipole strip that malforms on heating will lower the latch, which will open the contact and disconnect the equipment from the supply.

Short Circuit Protection

During a short circuit, a sudden increase in current makes the MMF powerful enough to project towards the latch and release it, opening the contacts.

Arc Quenching

When the contact is opened for load. Then an arc is formed between the permanent and moving contacts.The contacts are designed such that the arc between them protrudes outward through the runners and reaches the arc splitters or arc chutes. Arc splitters or arc chutes are an arrangement to increase the length of an arc, to split and to extinguish it.

MCB Construction View

The operation of the MCB is influenced by the temperature of the environment, particularly the deflection of the dipole strip. Therefore it is very important to choose the appropriate MCB based on your ambient temperature.

Miniature circuit breakers are single, two, three or four-pole. And in two, three, four-pole versions, equal number of equal pole MCBs are added. Their knuckles are combined. So that the defects cleared by any pole can open all the poles simultaneously.

Operating principle

In case of overload, a current greater than the rated current is driven through the MCB. As the dipole flows through the strip, it becomes hot and deflects by bending and releasing the mechanical latch. The deflection time of the dipole strip depends on the amount of current flowing through the strip. The higher current will be faster the deflection of the dipole strip.

During a short circuit, a transient current flowing through the solenoid leads the plunger to the latch. This action instantaneously leaves the mechanical latch and opens the contacts immediately.


MCBs are utilized in the protection of lights, refrigerators, Air conditioners etc. as another for fuses.

Advantages of MCBs over fuses

  • Small circuit breakers can act faster than fuses during short circuits.
  • they will be reset after the clearance of fault. But fuses must be rewired or replaced.
  • Secure disruption of short circuit current and arc quenching.
  • The knob makes the operation of a miniature breaker much easier than a fuse.
  • Tihey'll be turned off whenever we would like. Therefore, Circuit isolation during maintenance is far easier compared to fuses.

Tripping of MCB and possible faults

Whenever a short circuit, overload or a short fuse may occur. Once they are short, the breaker is not properly selected within the mean ampere rating. the explanation for tripping should be identified and faults must be cleared before turning ON them again.

When it trips, first of all, we've to test whether there are any visible faults like short circuits or overloads. Even fused LED lamps can trip an MCB. If there's no visible fault within the circuit protected by it, wait till it cools down and switch it ON again. If it trips again immediately, meaning there's a brief circuit within the circuit or equipment it protects. If it trips again after some minutes, then there's an opportunity that the circuit or equipment is overloaded. Clear the fault within the equipment OR gate and switch on the MCB. raise expert advice if required.


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