An appliance with a metal covering, rated at 2 kW, 220 V, is to be connected in a circuit. Given below are four diagrams (P, Q, R & S) depicting different…

Given,

• Power rating (P) = 2 KW = 2000 W
• Voltage rating (V) = 220 V

(a) The safest circuit is S.

(b) There are two criteria to choose the circuit S :

1. It is earthed so that in the case short circuit all the excess current can flow to earth without harming the person.
2. The current in the supply should be less than or equal to the current rating of the fuse.

So, current in the circuit = $\frac {\text P}{\text V} = \frac {2000}{220}$ = 9.09 A

Circuit P

As the circuit is not earthed so it is not safe.

Circuit Q

• Circuit is earthed properly.
• Current in the circuit is 9.09 A but it has fuse which has current rating of 8 A so it will get damaged and hence someone can be hurt.

Circuit R

• Circuit is not earthed properly so it is not safe.
• Current in the circuit is 9.09 A and it has fuse which has current rating of 10 A.

Circuit S

• Circuit is earthed properly.
• Current in the circuit is 9.09 A and it has fuse which has current rating of 10 A.

So circuit S satisfy all the necessary criteria for a safe circuit.