MCB or Miniature Circuit Breaker

What is MCB?

 it is device which protect conductor or electrical installation from short circuit or overload. Now-a-day instead of fusethey are used both residential and industrical wiring.These can be single pole, double pole or triple pole. It sustained overloading of 150% or above.

It consists of Frame,Trip Unit, Operating mechanism and contacts.
(a) Frame : it is a moulded case gives mechanism and contacts.
(b) Trip Unit : It is most important unit which  activates the operating mechanism when overload or short circuit occurs.
(c) Operating mechanism : MCB has operate in three positin, ON,OFF and Tripped. Trip occurwhen current draws from circuit and come to OFF position.
(d) Contact : contacts basically make ON or OFF. When it tripped an electrical arc occur.

Different type of rating of MCBs are current rating, voltage rating and interrupting rating. Interrupting rating is that much current where MCB tripped the circuit, MCBs are specify by 5A,10A,16A,32A,60A,120A etc with 10 to 65 KA interrupting capacity.

Operation Of Miniature Circuit Breaker 

The MCB is a high fault capacity thermal and magnetic current trip free automatic switching device.There are two main operartions i.e. thermal operation with inverse time characteristics for overload protection and hammer trip assisted magnetic operation for short circuit operation.

Connect single phase MCB in series with phase wire whereas the neutral wire is to connected from main distribustion board to plug point.

The  thermal operation is achievied with a bimetallic strip,which deflects when heated by an overcurrent flowing through it. The latch mechanism is released and caused the contact to open.

when short circuit fault occurs,the rising current energises the solenoid operating the plunger to strick the trip lever causing immediate release of the latch mechanism.

Advantage of MCB

1. Automatic switch off in case of overload or short circuit.

2. Quick identification of fault circuit even in dark.

3. Supply restored by switching ON again- No fuse to replace or rewire.

4. Automatic switch back to OFF it over load persists of faulty appliance is connected.

5. prevent the passage of full fault current during short circuit.

6. Total operating time is reduced to less than 5 m sec.

 Disadvantage of  MCB

1. The cost of M.C.B is greater than fuse.
2. The cost of on M.C.B distribution board is greater than rewire able fuse board.
3. The risk of overloading of circuits due to unqualified persons operating than is
completely removed.