--- title: "Mains Electricity: a.c., Earthing and Fuses" description: "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 wh" canonical: https://lightmysky.com/learn/science/mains-electricity-a-c-earthing-and-fuses-mt_jKTotBL78P source: https://lightmysky.com/learn/science/mains-electricity-a-c-earthing-and-fuses-mt_jKTotBL78P.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # 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. Subject: Science · Area: Energy · Ages 14 to 15 Page: https://lightmysky.com/learn/science/mains-electricity-a-c-earthing-and-fuses-mt_jKTotBL78P ## Ready when they can - 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 ## Lesson: Mains, plugs, and fuses 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. **Example.** 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. **Tip.** 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. **Recap.** Live brings power, neutral returns it, earth guards you, and the right fuse cuts the danger. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Electrical Power and the Cost of Running Appliances](https://lightmysky.com/learn/science/electrical-power-and-the-cost-of-running-appliances-mt_099G0drIbk) - [Assessing Hazards and Risks](https://lightmysky.com/learn/science/assessing-hazards-and-risks-mt_r66rs2EVkZ) ## Opens up - [Transformers and the National Grid](https://lightmysky.com/learn/science/transformers-and-the-national-grid-mt_ExV4Kc_7_P)