1- Miniature Circuit Breaker (MCB):

MCB is an electromechanical protection device. It is used for switching of electrical circuit with safety as short circuit and overload. Mechanical function is used for tripping as When any fault is occurred in electrical circuit then mechanical function is activated and circuit is opened.
It is available in different types like as equipment capacity, types of fault etc.

2- Circuit diagram of MCB:

3- Working principle of MCB:

Normal working

When current passes through MCB under capacity then circuit works without interruption. MCB has a bimetallic strip which is connected in series. If the passing current is normal then bimetallic strip will not heat and MCB will not trip.
MCB has two type protection systemd one is thermal and other is magnetic. Thermal protection works on overload condition and magnetic protection works of short circuit.

Overload or Thermal protection:

For overload protection the bimetallic strip is used in MCB. When over current passes through bimetallic strip then it becomes heat and starts bending. After reaching maximum limit of bending, the mechanical latch is got down resultant MCB is switched Off.
For resetting, the MCB is turned ON manually

Short circuit or Magnetic protection:

For Short circuit or heavy overload current protection the magnetic coil is used in MCB. During short circuit condition the heavy current passes through magnetic coil then a magnetic flux is produced and mechanical latch is attracted which is connected with tripping leaver resultant the leaver is got down and MCB is switched Off.

4- Types of MCB:

1. According to Phase:
   • single phase
   • three phase
2. According to Pole:
   • Single Pole MCB
   • Double Pole MCB
   • Triple pole MCB
   • Four pole MCB
3. According to current ratings:
   • 5A, 10A, 16A, 20A, 25A, 32A, 40A, 63A

5- Why MCB is used:

For general purpose of utilization of electricity we have required many equipments, lighting or power circuits. During utilization these equipments will have to switch on or switch off as per requirement.
If the current is low then we can use switch. If the current is above 5A then we will have to use MCB which can be used 5A to 100A in single phase or three phase. Excepting switching MCB has two type protection, thermal and magnetic.If the overload condition then thermal protection is used. If the short circuit or heavy load condition then magnetic protection are used.
So in this way we can safely operate us equipment with the help of MCB.

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