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  • Writer's pictureClaire Huang

How Miniature Circuit Breakers (MCBs) Work

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

Overload Protection

The bimetal strip plays an important role in protecting against a continuous overload. The bimetal strip is made up of two metals with different temperature coefficients. This thermal strip is located in the lower right side of Entek's MCBs (Miniature Circuit Breakers) and is part of the current path in the MCBs (Miniature Circuit Breakers) inner circuit structure.


When the current exceeds the rated value, the increased current flow heats the bimetal strip causing it to bend. The copper wire connected to the bimetal strip therefore pulls the trip bar and makes the contacts open.


Short Circuit Protection

The solenoid located in the upper left is the heart of this mechanism. When current passing through it within the permissible value, the magnetic force produced is not enough to pull the plunger. However, when there is a short circuit, the magnetic force pulls the plunger. The plunger functions as a hammer, it pushes the trip bar and makes the contacts open.

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