A ground fault circuit interrupter (GFCI) is a type of electrical outlet or circuit breaker that monitors the flow of electricity through a circuit. If it detects a sudden leakage of current to the ground (typically 5 milliamps or more), it switches off power within milliseconds, stopping dangerous electric shocks before they can cause serious harm.
GFCIs are essential in areas where water is present because water conducts electricity. UK building regulations require them in bathrooms, kitchens near sinks, outdoor sockets, and anywhere near potential moisture exposure. You'll recognise a GFCI outlet by its TEST and RESET buttons in the centre.
How they work. A GFCI compares the incoming and outgoing current in both wires of a circuit. Under normal operation, these values match exactly. If electricity escapes through an unintended path (such as through a person standing in water), the incoming and outgoing currents no longer balance. The GFCI detects this imbalance instantly and trips, cutting power.
Types available. You can install GFCIs as individual outlet units or as circuit breakers that protect an entire branch of your home's wiring. Portable GFCI adapters are also sold as travel options or temporary solutions.
Common misconception. GFCIs don't prevent all electric shocks, only ground fault shocks. They won't help if you touch both live wires simultaneously. They also require a proper earth connection to function.
Testing and maintenance. Press the TEST button monthly to confirm your GFCI is working, then press RESET to restore power. If a GFCI trips repeatedly without obvious cause, have an electrician investigate, as this suggests a genuine fault in your wiring.