Explain a domestic electric circuit with a neat diagram. How do the fuse, circuit breaker and earthing protect us?
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open with one line. A domestic circuit brings mains electricity (220 V, 50 Hz AC) from the meter to every appliance in the home.
2 · Describe the path.
Pole or cable → kWh meter → main fuse and main switch → distribution board with MCBs.
Live, neutral and earth wires run to each room.
Appliances are in parallel, each with its own switch on the live wire.
3 · Draw the circuit. [Diagram: meter, main fuse, distribution board, live and neutral lines with a bulb, fan and socket in parallel, green earth wire to an earth plate]
4 · Explain the fuse. A tin-lead wire with a low melting point, in series with the live wire; it melts on a short circuit or overloading.
5 · Explain the MCB. An automatic switch that trips on excess current; reset it after fixing the fault.
6 · Explain earthing. The metal body is joined to an earth plate in moist ground, so leakage current flows to the earth and the user is safe.
7 · Real-life link. The MCB box near the door and the long earth pin on the iron box plug are these devices at work.
8 · Close. Parallel wiring with these safety devices keeps the home working and safe.
Scoring tip: Draw the switches and the fuse on the live wire, not on the neutral: examiners check this.
