Miniature Circuit Breaker: Explained.

 Miniature Circuit Breaker:

In a miniature circuit breaker, there are mainly three mechanisms to make the switch off. They are bimetallic strip, one trip coil, and one hand operated on/off the liver. In an MCB, the current first enters through the inlet power terminal to the bimetallic strip. Then to current coil or trip coil then to moving contact then to fixed contact and lastly current leads through outlet power terminal.

All these are arranged in series. If overcurrent flows for a long time through this MCB, the bimetallic strip becomes overheated and hence it is deformed. This deformation of the bimetallic strip causes displacement of the latch point. The moving contact of the MCB has arranged through spring pressure with this latch point in such a way that a little displacement of the latch causes the release of spring and makes the moving contact move for opening the MCB. The current coil or trip coil is placed in such a manner that during short-circuit fault, the MMF of that coil causes its plunger to hit the same latch point and make the latch to be displaced. Hence during short-circuit fault, the MCB will open in the same manner again. When the miniatures circuit breaker or MCB is required to be switched off manually, the operating lever of the switches operated by hand. When we do so the same, the latch point is displaced and as a result, moving contact is separated from fixed contact and the MCB becomes in of position so whatever may be the operating mechanism. That means due to overload, due to short-circuiting fault or due to manual operation actually, the same latch point is displaced and the same deformed spring is released and this is ultimately responsible for the movement of the moving contact.

A miniature circuit breaker is always provided with arc splitters. During separation of moving and fixed contact, there may be a high chance of our and this arc goes up through the arc Runner and enters into arc splitters and is finally quenched.

When we switch on an MCB, we actually reset the displaced operating latch to its previous position.

 

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