Question

What is the current through an electrical appliance of rating 5 kW, 200 V and can you use a fuse which is rated 8 A ?

• A. 25 A, yes
• B. 2.5 A, yes
• C. 25 A, no
• D. 2.5 A, no

Answer 1

The correct option is C 25 A, no

Fuses are safety devices that are to be built into our electrical system. 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.
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.
In this case, let us consider a device of power 5 kW, that is, 5000 W and 200 V.

The current through the appliance is given as $I=P/V.$

That is, $I=\frac{P}{V}=\frac{5000}{200}=25A$.

The fuse of 8 A cannot be used because the current through the appliance is

greater the fuse rating. When the 25 A current flows through the fuse it will

blow off and it will not be able to fulfill it purpose.

Hence, a fuse is rated 8 A cannot be used with this appliance.