Question

What is the role of fuse, used in series with any electrical
appliance? Why should a fuse with defined rating not be replaced
by one with a larger rating?

Answer 1

Fuses are safety devices that are to be built into our electrical appliances. If there were no fuses and we operated too many appliances on a single circuit, the cable carrying the power for that circuit would get extremely hot, short circuit, and possibly start a fire. To prevent electrical overloads, fuses are designed to trip or blow, stopping the flow of current to the overloaded cable.
Fuse is a piece of wire of a material with a very low melting point. When a high current flow through the circuit due to overloading or short circuit, the wires gets heated and melts. As a result, the circuit is broken and current stops flowing.
The fuse must always be connected to the mains and it must be of correct value. For example, a 15-ampere fuse should trip when the current through it exceeds 15 amperes. A 20-ampere fuse should blow when the current through it exceeds 20 amps.
If the amperes of the fuse are greater than the amperes of current flowing through the appliance, in case of an overload or short circuit, the protective fuse will not melt to break the circuit and instead, the current will flow to the appliance and breaks it down.
Therefore, the fuse should be built with right rating to protect the electrical appliances from damage.