What is the purpose of a ground fault circuit interrupter (GFCI), and where are they required by code?

The purpose of a Ground Fault Circuit Interrupter (GFCI) is to protect people from electrical shock. A GFCI constantly monitors the current flowing through a circuit. If it detects that the current flowing out to a device or appliance differs from the current returning by a small amount, typically 5 milliamperes, it quickly interrupts the circuit, cutting off the power. This difference indicates that some of the current is leaking to ground, which could be through a person touching a live wire or a faulty appliance. The GFCI trips much faster than a standard circuit breaker, typically in a fraction of a second, preventing serious injury or death from electrical shock. Building codes, such as the National Electrical Code (NEC), mandate the use of GFCIs in areas where there is a high risk of electrical shock, particularly where water is present. These areas typically include bathrooms, kitchens (especially countertop receptacles), garages, outdoor receptacles, unfinished basements, and near swimming pools or spas. The specific requirements vary depending on the jurisdiction and the edition of the code, but the general principle is to protect people in areas where they are likely to come into contact with water or other conductive surfaces while using electrical appliances or equipment. GFCIs are installed as either receptacle outlets or circuit breakers, depending on the application and the extent of protection needed.