Why is my double socket showing signs of burning around the screw terminals?

Question

Accepted Answer

Burning marks around the screw terminals of a double socket are almost always caused by a loose or poorly made connection creating high resistance, which generates heat and can start a fire. Turn off the circuit at the consumer unit immediately and do not use the socket. This is a serious electrical fault. A qualified electrician must inspect and replace the socket before it is used again. Do not attempt to retighten the screws yourself and continue using it. What you are seeing around those screw terminals is called arcing or thermal damage, and it tells you that electricity has been finding it difficult to flow cleanly through that connection. When a connection is loose or made poorly, the resistance at that point rises sharply. High resistance creates heat, and over time that heat discolours the plastic, scorches the insulation on the wires, and in the worst cases can ignite the back box or surrounding materials. This is one of the more common causes of electrical fires in UK homes.

The most likely reasons this has happened are:

A loose screw terminal that was never tightened properly when the socket was installed or last worked on.

A wire that has partially pulled out of the terminal over time, perhaps due to movement in the wall or cables under tension.

Overloading the socket with high-demand appliances such as electric heaters, kettles, or washing machines, which causes sustained high current through the connection.

Corroded or oxidised wire ends, particularly common in older properties where the cable insulation has become brittle.

A socket that is simply old and worn, where the terminal clamp no longer grips the conductor firmly.

What you should do right now:

Stop using the socket immediately.

Go to your consumer unit and switch off the circuit breaker or remove the fuse for that circuit. If you are unsure which one controls that socket, switch off the main switch.

Do not switch it back on or use the socket for any reason.

Call a qualified electrician who is registered with a competent person scheme such as NICEIC, NAPIT, or the Electrical Safety Register.

Do not try to open the socket and retighten the screws yourself. The damage may extend into the wiring behind the wall, and there could be carbon tracking on the plastic that you cannot see, which can continue to cause problems even after re-tightening. The entire socket accessory and possibly the cable end must be replaced by a professional.