MCB Types and Characteristic Curves

MCBs or Miniature Circuit Breakers are electromechanical devices providing a resettable protection against two types of overcurrent situations: Overload and Short Circuit.

An MCB is a better alternative to a Fuse since it does not require replacement once an overload is detected. Unlike fuse, an MCB can be easily operated and thus offers improved operational safety and greater convenience without incurring large operating cost. 

Miniature Circuit Breaker

ENTEK MCBs are of following types

1   Single Pole

2   1 Pole (with N)

3   2 Pole (DP)

4   3 Pole (TP)

5   3 Pole with N (TPN)

There are two arrangement of operation of miniature circuit breaker. One due to thermal effect of over electric current and other due to electromagnetic effect of over current. The thermal operation of miniature circuit breaker is achieved with a bimetallic strip. 

Whenever continuous over electric current flows through MCB, the bimetallic strip is heated and deflects by bending. This deflection of bimetallic strip releases mechanical latch. As this mechanical latch is attached with operating mechanism, it causes to open the miniature circuit breaker contacts. 

But during short circuit condition, sudden rising of electric current, causes electro-mechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing immediate release of latch mechanism consequently open the circuit breaker contacts. This was a simple explanation of miniature circuit breaker working principle.

MCB Characteristics

ENTEK MCB Characteristic Curves

Type B characteristic curves.

Type C characteristic curves. 

The classification of Type B, C is based on fault current rating at which magnetic operation occurs to provide short time protection (typically less than 100ms) against short circuits. It is important that equipment having high inrush currents should not cause the circuit-breaker to trip unnecessarily, and yet the device should trip in the event of a short-circuit current that could damage the circuit cables. 

Type B devices are generally suitable for domestic applications. They may also be used in light commercial applications where switching surges are low or non-existent. Type B devices are designed to trip at fault currents of 3-5 tomes rated current. For example a 10A device will trip at 30-50A. 

Type C devices are the normal choice for commercial and industrial applications. Type C devices are designed to trip at 5-10 times In (50-100A for a 10A device).