1) The fuse consists of a thin wire of low melting point. When the current in the fuse exceeds 20 A, the wire will heat up and melt.
2) The circuit then becomes open and prevents the flow of current into the household circuit. So all the electric devices are saved from damage that could be caused by overload.
3) Thus we can save the house holding wiring and devices by using fuses.
4) In this way a small fuse prevents a great damage to costly electrical appliances in the circuit.