Class 10 > Unit # 15: Current Electricity > Domestic Main Supply

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Functions of Live, Neutral, and Earth Wires in Domestic Main Supply

Q.9 State the functions of live, neutral and earth wires in the domestic main supply.

Electrical Power Transmission to a House

"Electricity is supplied to domestic buildings through a three-wire cable system consisting of the Live wire, Neutral wire, and Earth (Ground) wire, maintaining a standard potential difference of $220\text{ V}$."

The specific functions and characteristics of each supply cable are as follows:

1. Live Wire ($L$ - Brown/Red Insulation):

   The live wire operates at a high potential (typically $220\text{ V}$ relative to earth). Its primary function is to carry electric current from the power mains source to domestic appliances. All switches and fuses are connected in series with the live wire for safety isolation.

2. Neutral Wire ($N$ - Blue/Black Insulation):

   The neutral wire is grounded to the Earth at the local power substation or distribution transformer to keep its electrical potential close to zero volts ($0\text{ V}$). Its function is to complete the electrical circuit by providing a return path for the electric current flowing back from the appliances.

3. Ground Wire or Earth Wire ($E$ - Green/Yellow Insulation):

   Normally, no current flows through the earth wire. It is connected to a heavy metal plate buried deep underground near the building. Its primary safety function is to provide a low-resistance path for leakage current to flow safely into the earth if a live component touches the metallic casing of an appliance, protecting users from lethal electric shocks.

Connections in Domestic Main Supply

The human body is a good conductor of electricity. If a person accidentally touches an exposed live wire, electric current will flow to the ground through their body, which can be extremely dangerous or fatal. To prevent hazards and ensure efficient operation:

• Parallel Connection: All domestic appliances and equipment are connected in parallel across the live and neutral wires so that every appliance receives the same potential difference ($220\text{ V}$) and can operate independently.
• Mains Distribution: Cables from the street mains enter through an electricity meter, pass into the main distribution board protected by high-rating fuses (approx. $30\text{ A}$), and branch out to individual room circuits.
• Independent Protection: Each appliance has its own direct connection to the live wire equipped with a dedicated switch and fuse. If one appliance's fuse blows due to a fault, it does not affect the operation of other electrical appliances in the home.

Fig: Standard domestic main supply wiring showing Live, Neutral, and Earth connections.