An electrical fuse works by breaking the circuit when there is a fault in an appliance that causes too much current to flow. The wire within the circuit melts due to the heat generated when the current going through the circuit is too great.

As the current in a wire increases so does the heat generated. A fuse is simply a thinner piece of wire in the circuit. If the current gets too high the thin wire will melt and stop the current. The most commonly fuses used in the house are 3A, 5A and 13A.

Figure below shows the fuse wire in normal state and after being fused.