[Exact] Function of MCB Explained with examples

Hey, we are going to discuss the detailed explanation of the MCB Function. MCB means Miniature Circuit Breaker. In this article, your all doubts will be clear about the function of MCB. MCB is a very commonly known and widely used electrical protective equipment used from low voltage to high voltage circuits.

MCB can be called an Interrupting Device because it interrupts the current flow in a circuit when a fault or error occurs. It also can be called an electromechanical device because is its construction and working depend on the mechanical arrangements operated by electricity.

Exact Function of MCB

MCB can provide only two functions to protect an electric circuit. Don't be confused about that, because most of the people have so many doubts and wrong arguments about MCB Function. Don't worry we will discuss in later. So, the two important Functions of MCB are,

1. Overcurrent Protection

2. Short Circuit Protection

Read Also: Wiring Diagram for House with MCB Rating Selection Guide

Overcurrent Protection by MCB

Now, we will discuss how an MCB provides  Overcurrent Protection. MCB has an arrangement of a Bimetallic strip which is connected with the Latch Mechanism of the MCB. The latch mechanism is associated with spring pressure, and it is used to turn on or off the MCB.

So when in normal conditions current always flows through the bimetallic strip and the magnetic coil but it does not affect the latch mechanism, because, in normal conditions rated current flows through the bimetallic strip, it does not become hot and no physical changes also occur.

But when overcurrent flows through the bimetallic strip, it starts to become hot, and after some time the bimetallic strip will deflect by bending and it will hit the latch mechanism of MCB to turn off or trip the MCB.

So, when an overcurrent fault occurs, MCB takes some time until the bimetallic strip becomes enough heated for bending and to hit the latch mechanism to turn off the MCB. This time depends upon the overcurrent flowing through the circuit, and current ratings of the MCB.

So, remember that during an overcurrent fault, MCB cannot give instant protection, it takes some time.

Read Also: Why RCCB cannot give protection against Overload and Short Circuit Faults?

Shortcircuit Protection by MCB

Now, we will discuss, how an MCB provides protection against short-circuit faults. For short circuit protection, MCB has a solenoid coil or tripping coil. As I told you before, in normal conditions, current always flows through the bimetallic strip and the magnetic coil or solenoid coil but no effect occurs to trip the MCB. During overcurrent fault, only the bimetallic strip is affected and it trips the MCB after taking some time but the solenoid coil does not do anything.

In an overcurrent fault, no effect occurs in the solenoid coil, because it is designed for extremely high current because we know that during a short circuit fault, extremely high current flow and that time we need to trip the circuit instantly.

So, when a short circuit fault occurs, a very high current flows through the solenoid coil and it produces a magnetomotive force(MMF) which causes the plunger to hit the latch mechanism of the MCB to trip the MCB instantly.

So, remember that during short-circuit fault, MCB provides instant protection.

Read Also: [Exact Reason] Why MCB for Air Conditioner (AC) frequently Tripping?

MCB can provide overvoltage or surge voltage protection?

Now we will discuss, whether can an MCB provide protection against overvoltage or surge voltage or voltage fluctuations. In simple words, NO. Don't be confused with Overvoltage and Overcurrent protection, both are different.

MCB is a current-controlled device, which means when overcurrent or high current flows through it due to a short circuit or any other fault, it will trip and interrupt the circuit. But if there is high voltage or voltage fluctuation occur it does not do anything. Of course, if the high current flow due to that overvoltage, it will trip the circuit.

Read Also: MCCB Full Form | MCB and MCCB Difference

MCB can provide protection against Neutral Fault, Earth Fault, or Ground Fault?

MCB cannot give protection against Neutral faults, Earth faults, or Ground faults because it cannot sense if there is any neutral fault or earth fault that occurs in an electrical circuit. MCB only provides protection against the Overcurrent fault and Shortcircuit fault.

Read Also: [Main] Difference Between Neutral and Earth Explained

MCB can give protection against Electrical Shock?

The sudden convulsion of muscles with pain in the human body due to the flow of current through the body is called electrical shock. Only a few milliamperes of current flow through the human body creating electrical shock. So when anyone gets an electrical shock only a few milliamperes extra current will flow in the circuit which does not make any affect the operation of the MCB. So MCB cannot give protection against electrical shock.

Read Also: [Know] Which RCCB should You use to Prevent Electrical Shock

Advantages of MCB(Miniature Circuit Breaker)

1. MCB provides protection against major important faults in any electrical circuit that is overcurrent faults and short-circuit faults.

2. During short circuit faults MCB provides instant protection which is a very good advantage of MCB.

3. MCB has ARC preventive arrangement in its construction, so during manual turn on or off no spark will occur.

4. MCB is more sensitive than a fuse and its operation is also very fast.

5. Instant power supply resume is possible with an MCB just manually turn on the MCB. 

Read Also: Proper RCCB connection Diagram with MCB.

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