Why is my earth conductor at the consumer unit showing 40°C when it's cold outside?

Finding your earth conductor warm or even hot at the consumer unit is genuinely unusual and worth taking seriously. In a healthy installation, the earth wire carries no current during normal use. It only carries current during a fault, and even then only for the fraction of a second it takes a fuse or breaker to operate. If it is sitting at 40 degrees Celsius continuously, current is flowing through it all the time, and that is not normal. The most likely explanations in plain English are these. A neutral-to-earth fault somewhere in the property. This means the neutral wire and earth wire are touching somewhere they should not be, perhaps inside a socket, a light fitting, or an appliance. Current then finds a path through the earth conductor and warms it up. A shared or borrowed neutral. In older properties or extensions, a previous electrician may have connected circuits in a way that puts neutral current onto the earth. This was never acceptable and is a serious fault. An appliance with a fault. Some faulty appliances bleed a small leakage current to earth continuously. If several appliances do this together, it adds up. A problem at the meter tails or the supply side. In some cases the issue lies before your consumer unit, in the meter or the service cable itself. This is the responsibility of your electricity network operator, but your electrician will identify it. What you can safely do yourself before calling an electrician. 1. Do not touch the earth conductor with bare hands if it feels hot rather than just warm. 2. Switch off and unplug appliances on circuits where you suspect a problem. 3. Note whether the warmth is present when everything is switched off at the consumer unit. If it is, the fault is on the supply side. 4. Do not attempt to disconnect or inspect the earthing conductor yourself. You should call a qualified electrician as soon as possible. This is not a job to delay. A continuously energised earth conductor is a fire risk and means your shock protection may not work correctly in an emergency. An electrician will use insulation resistance testing and loop impedance testing to find the fault quickly.