What is MCB ?

 A miniature circuit breaker (MCB) automatically switches off the electrical circuit during an abnormal condition of the network means in overload condition as well as faulty condition. Nowadays we use an MCB in a low voltage electrical network instead of a fuse. ... MCB is much more sensitive to overcurrent than a fuse

MCBs or Miniature Circuit Breakers are protective electromagnetic devices that act as a switch in a circuit. They automatically open the circuit whenever they sense the current passing over the circuit has crossed a certain limit or value. The device can also be used as a normal on and off switch manually. 

MCBs are also known as time delay tripping devices which trip and shut down the system whenever there is an overcurrent flowing for a longer period of time and there is a danger to the entire circuit. However, in the case of short-circuits, these devices can trip and stop the power supply within 2.5 milliseconds.

In an electrical system ‘Fault’ is the condition which arises due to the malfunctioning of some component or wrong electrical practice. A fault may lead to a very dangerous situation such as explosion & fire if not cleared timely, not only this, the amount of time for which fault remains in the system, it continuously deteriorates the system health causing high energy losses resulting in increased thermal stress upon the system. Faults are hazardous to the system & require to be cleared at the earliest thus, there is a need for such a device that not only is capable of clearing the fault but also has a lower opening time in order to save the let-through energy & minimize the thermal stress.

type of curve/applications the MCB is of 3 types:

B Curve: This type of MCB has a lower short circuit trip zone and can be used for Resistive/ Lighting loads, for example, lights, heaters, etc.

C Curve: These MCBs have a higher short circuit tripping zone and can be useful for the inductive type/motor loads, for ex: AC, Refrigerator, etc.

D Curve: These MCBs have a very high short circuit tripping zone and are generally used for the loads which draw a very high starting current such as Sodium Lamps. 

2 kinds of fault which disturb the system often are:

Overload: An overload is a fault condition that arises in a system when a circuit draws a higher current than its rating. For example from a 6A socket if we draw 10A current the condition is said to be overload.

Short Circuit: This is a condition in which an extremely low resistance path is created due to an accidental or intentional connection between 2 or more conductors which leads to the sudden increase of current to its peak value and voltage getting minimized to an extremely lower magnitude.