Chapter 12 · Question 10

What is the function of an earth wire in a domestic circuit? Why is it necessary to earth metallic appliances such as an electric iron or a refrigerator?

Q10

What is the function of an earth wire in a domestic circuit? Why is it necessary to earth metallic appliances such as an electric iron or a refrigerator?

Answer Revealed

Direct Answer:

The earth wire provides a low-resistance conducting path for any leakage current from the metallic body of an appliance directly to the ground. In case of accidental contact between the live wire and the metallic body (due to damaged insulation or fault), the current flows through the earth wire to the ground instead of passing through the user's body. This keeps the potential of the appliance's metallic body equal to the earth's potential (zero), thereby preventing severe electric shocks. It is necessary to earth appliances with metallic bodies — such as an electric press, toaster, table fan, and refrigerator — because these appliances can become live and dangerous to touch if a leakage fault occurs.

Simple Explanation

The earth wire is your household's emergency exit for stray electricity. Imagine the live wire inside your fridge accidentally touches the metal body — without earthing, touching the fridge would send that current through you. The earth wire (green) connects the fridge body to a metal plate buried in the ground. If any current leaks to the body, it takes the easy path through the earth wire into the ground instead of through you. It is mandatory to earth every appliance with a metal body — iron, toaster, fridge, fan — because their bodies can become live and deadly.

Exam-Ready Structure

Earthing is a critical safety mechanism in domestic electric circuits designed to protect users from electric shocks due to leakage currents. 1. Earth wire characteristics: The earth wire has green insulation cover and is connected to a metal plate buried deep in the earth near the house. It provides a low-resistance conducting path to the ground. 2. Function: The earth wire is connected to the metallic body of appliances (electric press, toaster, table fan, refrigerator, etc.). If the insulation of the live wire gets damaged or there is a fault causing the live wire to touch the metallic body, the current flows through the earth wire directly to the ground instead of passing through the body of a person who touches the appliance. 3. Safety principle: The earth wire ensures that the potential of the appliance's metallic body remains equal to the earth's potential (essentially zero). This prevents the user from receiving a severe electric shock, even if they touch the appliance during a leakage fault. 4. Why earthing is necessary: (a) Any appliance with a metallic body can become live due to insulation failure, ageing of wires, or manufacturing defects. (b) Without earthing, touching such an appliance would allow current to flow through the person to the ground, causing a potentially fatal electric shock. (c) Earthing provides a safe alternative path of much lower resistance than the human body, so almost all leakage current flows through the earth wire, not through the person. 5. This is why three-pin plugs include an earth pin — the top, thicker pin connects the appliance body to the earth wire in the socket.

Key Points

Earth wire: green insulation, connected to a metal plate buried deep in the earth
Provides a low-resistance conducting path for leakage current to the ground
Keeps metallic body of appliance at earth potential (zero), preventing electric shock
Necessary for all appliances with metallic bodies: iron, toaster, fridge, fan, etc.
Without earthing, a leakage fault makes the appliance body live and dangerous to touch

What is the function of an earth wire in a domestic circuit? Why is it necessary to earth metallic appliances such as an electric iron or a refrigerator?