MCB (Miniature Circuit Breaker) Introduction, Functions, Operation, Advantages, Disadvantages, Applications.

MCB (Miniature Circuit Breaker)

Introduction

It works as a protective device because in case any fault occurs, they operate automatically and break the faulty circuit form the system.

MCB is an electro-mechanical device.

It operates when device the current reaches a pre-determined value and disconnects the faulty circuit to prevent the fault current to increase.

Fig. MCB

Functions of MCB

Operates on 5 % to 20% excessive over loads.

It breaks the circuit even for small overload current flow.

It can be revived in the circuit without any additional requirement.

Direction indication of faulty circuit is known as switching knob.

In case of fault occurrence, it trips down due to braking the circuit to OFF position and can be reclosed to ON position in the circuit after rectifying.

Operation of MCB

MCB is high capacity current trip free automatic switch device, which trips magnetically.

There are two operations of MCB

1. Thermal operation.
2. Hammer Trip.

Thermal operation

It has a bimetallic strip which deflects when heated by over current flowing through the circuit. Thermal trip has inverse time current characteristics greater the inverse current, shorter time is required operation of MCB thereby releasing the latch mechanism a
causing the contacts to open.

Hammer Trip

If short circuit fault occurs, the increase in current energize the solenoid which operates the plunger to strike the trip level thereby causes release of latch mechanism to open contacts. It assists magnetic operation for short circuit protection.

Advantages of MCB

1. Its operating time is less.
2. It is more accurate and efficient as compared to conventional fuse.
3. Reset operation can be operated manually after fault rectification without additional cost.
4. The tripping of circuit after fault occurrence i.e. overload or short circuit can be easily identified from the position of the switch.
5. It shows dual behavior; for normal operation it behaves as switch for control purpose and as protective device for any fault and circuit.
6. They're available in plug in design in which they can be easily replaced during energized condition, thus easy replacement.

Disadvantages of MCB

In case of any equipment problem or damage, entire unit needs to be replaced, thereby increase in cost.

Specifications of MCB

1. Number of poles: 1, 1+ neutral, 2, 3, 3+ neutral, 4 poles.
2. Voltage rating: 2401 415 volts A.C., 220 volts D.C
3. Current rating:0.5 Amp to 63 Amp
4. Range: 25-63 Amps,30mA, 40 mA.
5. Short circuit breaking capacity: 9kA (IS 828 at 240/15 volts).
6. Rated frequency: 50, 60 Hz.
7. Electrical Life: more than 50,0X0 operating cycles.
8. Mechanical life: more than I, 00,000 operating cycles.
9. Protection class: P.30 (AS 2147).
10. Connecting conductor size: 35 sq.mm
11. Any installation position.

Applications of MCB

It can be installed at homes, shops, offices, distribution boards, power loads, for protection of individual circuit and complete wiring system of main circuit in the building.

Difference between MCB and Conventional Fuse

MCB	Conventional Fuse
It instantly switches off the supply automatically in case of short circuit, overload or earth fault. It prevents damage and risk of fire.	If fuse wire of suitable rating is not used, then in case of short circuit over load the wire does not melt resulting in accidents and damage to the circuit
It needs no maintenance and repairs.	It needs maintenance and repairs.
It can be installed on board for elegant look	It is not compact and is large enough to hide.