Domestic electric circuits

In India, the electricity reaching our homes is AC (alternating current) at 220 V with a frequency of 50 Hz. It comes on three wires, each with its own colour:

The supply comes through a main fuse into the electricity meter, then through the main switch to the house. There are usually two circuits: a 15 A circuit for high-power appliances such as geysers and air coolers, and a 5 A circuit for bulbs and fans.

All appliances are connected in parallel, each with its own switch. So every appliance gets the full 220 V, and each can be switched on or off without affecting the others.

The earth wire. Over time, an appliance's wiring can wear out and current can leak onto its metal body. If you then touch it, the current could pass through you to the ground: a serious shock. The earth wire joins the metal body to a metal plate buried deep in the ground. Leaking current then takes this easy path to earth instead of through you.

When the current shoots up:

• a short circuit: the live and neutral wires touch directly, for example when insulation is damaged;
• overloading: too many appliances plugged into one socket, or a sudden rise in the supply voltage.

The wires can overheat and even start a fire. The fuse melts first and breaks the circuit.

"Can a 2 kW oven run on a 220 V, 5 A circuit?" I = P/V = 2000/220 ≈ 9 A: much more than 5 A. The circuit would be overloaded and the fuse would melt. It needs the 15 A circuit.