Fuse are seen frequently in household electrical circuits.
Fuse is a electrical device that has a conductor with low resistance,when the current load is very high that melts the conductor due to heat generated and circuit opens thereby saving other devices in the same circuit from short circuit.
Fuse uses electrical and thermal properties of the conducting material.
Generally fuses are reusable,we just have to change the conductor (copper wire ) inside them.
MCB - Miniature Circuit Breaker, does the same operation as fuse but they just trip.They can be reset easily by setting them on.
Fuses protects against power overloads.
circuit breaker offers protection against power overloads and short circuits.
MCB is a switch which automatically turns off when the current flowing through it passes the maximum limit.
There are two contacts one is fixed and the other moveable.
When the current exceeds the predefined limit a solenoid forces the moveable contact to open (i.e., disconnect from the fixed contact) and the MCB turns off thereby stopping the current to flow in the circuit. In order to restart the flow of current the MCB is manually turned on.
This mechanism is used to protect from the faults arising due to over current or over load.
To protect against fault arising due to over heating or increase in temperature a bi-metallic strip is used.
MCBs are generally designed to trip within 2.5 millisecond when an over current fault arises. In case of temperature rise or over heating it may take 2 seconds to 2 minutes for the MCB to trip.
more : http://www.engineersgarage.com/insight/how-mcb-works