Why does my neutral wire show voltage to earth even when the main switch is off?

Finding voltage on a neutral wire when you think everything is switched off can be alarming, and it is right to take it seriously. Here is what is actually happening and what you should do. What the neutral wire is supposed to do In a standard UK wiring system, the neutral wire completes the circuit back to the transformer at the substation. Under normal conditions it should be at or very close to 0 volts relative to earth. A small reading of 1 or 2 volts is often just measurement noise or a tiny imbalance in the supply network, and is not dangerous. Anything above roughly 5 to 10 volts, however, deserves attention. Why it might show voltage when the main switch is off The most common reasons are listed below. 1. Back-feed from a shared or looped neutral. If your neutral conductor is shared with another circuit, or looped through from a neighbour on the same network, switching off your main switch does not remove the return path from their supply. 2. A faulty or open neutral connection. A broken neutral somewhere in your supply causes the remaining voltage to appear on conductors you expect to be dead. 3. An RCD or consumer unit with internal leakage. Older or damaged RCDs can allow a small voltage to appear across their load-side terminals. 4. An appliance with a live-to-neutral fault still plugged in. Some faulty equipment can push voltage back down the neutral before it reaches your board. 5. Capacitive coupling. Long cable runs next to live conductors can induce a small phantom voltage, particularly noticeable on high-impedance meters. What you can safely check yourself Do not touch any wires. You can note what reading your electrician should investigate, but do not open the consumer unit or touch any terminals yourself. When to call an electrician Call a registered electrician if the reading is consistently above 10 volts, if circuit breakers or RCDs are tripping for no obvious reason, if you notice a buzzing or humming from the consumer unit, or if lights flicker when heavy appliances switch on. These are signs of a potentially dangerous wiring fault. Use an electrician registered with NICEIC, NAPIT, or another Part P competent person scheme.