Question

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

Answer 1

The fuse is a device that protects the electric device from damage due to current of higher order than the rating of the device. The fuse is connected with the series to the device and carries the same current as that of the device.

Complete step by step solution:
The fuse is an electric component or the electric device that is used to protect the electric devices from the over current. The fuse does so by breaking the circuit when a current of higher order than the rated current tries to flow through the circuit.

The increase in current can be due two reasons: the short circuit or the overloading. The short circuit of the device invites a high amount of current through the circuit. The other reason for this is the overloading of the device, as a load of more than required capacity increases as the current through the circuit also increases.

The fuse element is connected in series to the circuit and the rating of the fuse must be the same as the current rating of the device to which the fuse is connected. As the amount of current increases the fuses blows of and cuts the circuit from the power supply. In this way the circuit is protected from any damage.

The fuse wire blows due to the heating effect of the electric current also known as the ${I^2}R$ effect. Here, $R$ is the resistance of the fuse wire and $I$ is the current through it.

Consider that when a fuse of current rating $3$ ampere is connected to the device with the same current rating. The fuse protects the device when the current through the device exceeds $3{\text{ A}}$ by blowing off itself. The case when the fuse of current rating $5$ ampere is connected to the device of $3\;{\text{A}}$, the fuse does not blow for current of more than $3\;{\text{A}}$, this damages the devices as a current of only more than $5$ ampere an blow the fuse.

Note: A circuit breaker works on the electromagnetism and switching principle and it can be used a number of times. A circuit breaker can be used as an ON/OFF switch and it gives an indication of the status.