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Insight - How MCB works

Written By: 

Arpit Jain
The heart of this mechanism is the solenoid which works on the principle of electro mechanism. As mentioned earlier one end of the coil is connected to the moveable contact by means of a thick wire for current to pass through it in the ON state. The coil of the solenoid is designed in such a way that when current passing through it is within the permissible value, the magnetic force produced is not enough to pull the plunger. When the current exceeds the permissible value, the magnetic force also increases and this magnetic force pulls the plunger inside towards the center of the coil.


When the plunger moves it also pulls the moveable contact and forces it to separate from the fixed contact thereby tripping the circuit. The moveable contact is connected to the knob by means of mechanical arrangement and forces the MCB knob to fall down. The plunger is connected to a spring from inside the electromagnetic coil and as the plunger moves towards the center of the coil, the spring gets loaded. After the MCB trips (i.e., the moveable contact separates from the fixed contact and the current stops flowing) the spring forces the plunger back to its normal state without disturbing the moveable contact.

Movable contact plunger arrangement




So Simply explained..was feeling the urge to know about the MCB mechanism .

does the frequency matters for a MCB? 



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i have MCB switch but i doesn't work

please tell that is it manadatory to connect Input supply to input terminal or we can connect it to output terminal also.