Electrical appliances in homes are normally earthed so that

Step 1: Analyze the question We are asked why household appliances are earthed (connected to the ground through the third pin of the plug).

Step 2: The concept Most appliances have a metal casing. If the live wire becomes loose or its insulation fails, it can touch this casing and make it "live" at a dangerous voltage. Earthing connects the metal casing to the ground through a low-resistance wire.

Step 3: How it works

• If a fault occurs, a large current flows through the earth wire to the ground instead of through the person touching the appliance.
• This large current also blows the fuse or trips the circuit breaker, which disconnects the appliance from the supply.
• The casing stays at about the same potential as the earth (zero potential), so there is no significant potential difference between the casing and a person standing on the ground. Hence, no dangerous shock.

Step 4: Check each option

• A. A person touching the appliance is safe from electric shock. This is the main purpose of earthing, so it is correct.
• B. Both a.c. and d.c. can be used. Earthing has nothing to do with the type of supply. Wrong.
• C. Maintained at a higher pd than the earth. This would be dangerous, and the aim is the opposite. Wrong.
• D. Maintained at a lower pd than the earth. Earthing keeps the casing at the same potential as the earth, not lower. Wrong.

Answer: A

Exam tip: Remember "Earth = Escape route". The earth wire gives fault current an easy path to the ground, so people are protected. The three wires are: live (brown), neutral (blue), earth (green/yellow). Questions on earthing almost always point to safety from electric shock.