How a GFCI works

A ground fault circuit interrupter compares the current flowing out on the live conductor with the current returning on the neutral. Any difference is leakage — some of it flowing through a person or through damaged insulation to earth. The device trips when the difference exceeds its sensitivity.

Where it is required

Wet and damp locations such as kitchens, bathrooms and wash areas

Outdoor socket outlets

Construction and temporary supply points

Circuits supplying equipment where water or earthed metalwork is present

RCD, RCCB and GFCI

These names describe devices that all respond to earth leakage current. The differences lie in sensitivity, whether they include overcurrent protection, and which standard they are made to. What matters on site is that the sensitivity and type suit the application and the earthing arrangement.

Testing

A GFCI should be tested with its test button at regular intervals, and its trip time verified with a tester at commissioning. A device that fails to trip is no protection at all — this is a routine check, not a one-off.