What causes a GFCI outlet to smoke and melt?

Answer 1

Anything electrical that smokes and melts does so because it is conducting more current than it was designed to handle. If the circuit, including the breaker, conductors, and the GFCI have been properly installed and are in good working order this will not happen.

My first guess is that the GFCI has come apart internally, causing a short, but not causing enough current to trip the breaker. A GFCI will not trip in an over current condition. It trips when there is a measured difference in current on one conductor than the current on the other. So a dead short, which should trip the breaker, will not trip the GFCI.

My second guess is that the breaker is the wrong size for the circuit or the breaker has malfunctioned. In either case you likely have more than the outlet smoking. You likely have conductors back in the wall melting and smoking as well. If you suspect this may be the case you should call for emergency services (911 in most of the US and I believe 999 in the UK) because wires back in the wall might smolder for a long time, even after electricity is turned off, and flame up at a later time, possibly while you are asleep.

In any case you need at the very least a new GFCI. Do not use a device that has obvious damage.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.

Answer 2

A GFCI outlet might smoke and melt due to an electrical overload or short circuit in the wiring, causing excess heat buildup. This can be a result of faulty wiring, a malfunctioning appliance plugged into the outlet, or water contacting the outlet. It is a serious safety hazard and should be addressed immediately by a qualified electrician.