Mains Electricity: a.c., Earthing and Fuses
Mains supply is alternating, changing direction many times a second, unlike the direct current from a cell. The live, neutral and earth wires each have a job, and a fuse or breaker cuts the circuit when the current climbs too high.
What a learner can do afterwards
- States the difference between alternating and direct current and names the mains voltage and frequency
- Describes what each of the three wires in a plug does and why the live one is dangerous even when a switch is off
- Chooses a suitable fuse rating for an appliance from its power and explains how earthing plus a fuse work together
1 · Read
A cell pushes current one way only, which is direct current. Mains supply is alternating current: it swaps direction 50 times a second in the UK, at about 230 V. That swapping lets transformers step voltage up and down.
A plug holds three wires with three jobs. Live brings the 230 V in and is the dangerous one. Neutral completes the circuit back to the supply, and earth is a safety path that normally carries nothing. A wrongly wired switch may break neutral instead, leaving the appliance live even when it looks off.
A 2300 W kettle at 230 V draws 10 A, so it needs a 13 A fuse. If a fault joins live to the metal case, the earth wire carries the surge away and the surge melts the fuse, cutting the circuit. Test a suspect fuse with a multimeter: a good one reads near zero, a blown one reads open.
Pick the next standard rating above the normal current: 3 A for small appliances, 13 A for heavy ones like kettles. Never fit a bigger fuse to stop blowouts, because oversizing lets dangerous currents flow until wires overheat. A correct fuse that keeps blowing means the appliance has a fault.
Live brings power, neutral returns it, earth guards you, and the right fuse cuts the danger.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.