Why does my earth wire get warm?

Earth wires should be cold under normal use — current should never flow through them except during a fault (when it flows only for milliseconds before the circuit trips). If an earth wire feels warm, something is wrong. Common causes: there's a wiring fault somewhere causing current to continuously leak to earth; neutral and earth have been connected at the wrong point; or a damaged appliance is continuously leaking current to earth through its casing. This is a safety issue. A warm earth wire means current is flowing where it shouldn't be — this can cause the earth conductor to overheat, break down insulation, and potentially cause a fire or leave metalwork with a dangerous voltage on it. Switch off the circuit and call an electrician. Do not continue using the affected circuit.