Miniature Circuit Breakers.

MCB's or miniature circuit breakers are electro mechinical devices which protect an electric circuit from an overcurrent.
The overcurrent, in an electrical circuit, may result from short circuit, overload or faulty design. 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 offer improved operational safety and greater convenience without incurring large operating cost.