Domestic Electric Circuits

Electric power reaches our homes through a main supply carrying three wires. The live wire (red insulation) and neutral wire (black insulation) together carry the 220 V supply. A third wire, the earth wire (green insulation), is connected to a metal plate buried in the ground near the house: it's a safety measure, not part of the working circuit.

Inside the house, appliances are connected in parallel across the live and neutral wires, each with its own switch; this way every appliance gets the same 220 V and can be switched independently. Homes typically split these into two separate circuits: a 5 A circuit for lights and fans, and a 15 A circuit for higher-power appliances like geysers and coolers.

The earth wire is connected to the metal body of appliances like irons, toasters, and refrigerators. If a fault causes the live wire to touch the appliance's body, the earth wire gives the leaked current a low-resistance path straight to the ground, keeping the body's potential safely at zero instead of shocking whoever touches it.

A short circuit happens when the live and neutral wires touch directly (say, from damaged insulation), causing current to suddenly shoot up. Overloading can also happen from a voltage spike or from plugging too many high-power appliances into one socket. Either way, the fuse is what saves the day: it's a thin wire with a carefully chosen melting point, placed in series with the live wire, that heats up and melts the instant current crosses a safe limit, breaking the circuit before real damage is done.