Why is my earth wire carrying AC voltage when the main switch is off?

Finding voltage on your earth wire when the main switch is off is understandably alarming, and it should be taken seriously. Here is what is happening and what you should do. What the earth wire is supposed to do The earth wire in your home is a safety conductor. Under normal conditions it carries no current and sits at zero volts. Its job is to give fault current somewhere to go safely, which in turn trips the breaker or blows the fuse before anyone gets hurt. Why it might be showing voltage There are a few common reasons this happens. 1. A faulty appliance is leaking current onto the earth. Even with the main switch off at the consumer unit, some supplies such as a smart meter tail or a neighbour sharing a TNC-S supply may still be energised. 2. There is a wiring fault inside the property, such as a live or neutral conductor touching the earth conductor inside a socket, light fitting, or junction box. 3. Your property is connected to a TNC-S (PME) supply. In this arrangement the supply neutral and earth are combined at the cutout, so if the supply neutral loses its connection, the earth conductors in your home can rise to a dangerous voltage relative to true earth. 4. Voltage is being coupled in from a neighbouring circuit, especially in older properties where cables run close together for long distances. What you can safely check yourself Unplug every single appliance and turn off every circuit breaker inside the consumer unit, not just the main switch. Then check whether the voltage is still present. If it disappears, the fault is likely with one of your appliances or a circuit inside your home. If it remains with everything disconnected, the issue is coming from the supply side and you must not investigate further yourself. When to call an electrician You should call a qualified electrician straight away if the voltage persists with all circuits off. A live earth is classed as a dangerous fault. It means your metalwork, your sinks, your boiler casing, and anything connected to the earthing system could be at a hazardous potential. Do not continue to use the property normally until the fault has been investigated and cleared.