What a Ground Fault Circuit Interrupter (GFCI) Is

Electrician installing GFI plug in kitchen.
••• Pamela Moore/E+/Getty Images

A ground fault circuit interrupter is an electrical device installed to protect against severe electric shocks. GFCI’s could also reduce electrocutions and minimize electrical burns and shock injuries. A GFCI, not to be confused with an AFCI, integrates a ground fault protection in receptacles where electrical equipment is near water or might be in contact with water.

Ground fault circuit interrupter also detects ground faults and interrupts the flow of electric current. A GFCI is not and might not be used to replace a fuse and does NOT protect against circuit overloads, short circuits, or shocks.

How a GFCI Works

A normal 120-volt outlet has two vertical slots and a round hole just below them or to the sides. Usually, the left slot is larger than the right, and it corresponds to the neutral while, the right slot is called hot. The round hole is the ‘ground’. When the outlet is working properly the electricity is flowing from hot to neutral, and that’s when the GFCI enters into action.

The GFCI measures the amount of current flowing from hot to neutral, so the circuit can trip and shuts off. When properly installed, a GFCI can detect variations as small as 4 milliamps, and it trips quickly, less than a second, cutting off electricity.

Where to Install a GFCI

A GFCI is required by the National Electrical Code and is required in:

  • Underwater Pool Lighting
  • Outdoors and this will include fountains
  • Escalators and elevators
  • Bathroom Receptacles including hot tubs
  • Garages
  • Kitchen (Above the countertop), although not needed on refrigerators in the kitchen
  • Crawl Spaces and unfinished basements
  • Wet Bar and Utility Sinks
  • Laundry Receptacles
  • Healthcare facilities
  • When needed for fairs and outdoor activities

Portable GFCI protection could also be required whenever electrically-powered equipment is used in garden-related works and when using electric tools in and around the house.

Three Types of GFCI’s

GFCI’s can be found in three different ways. The most common one is the GFCE receptacle, very similar to a common wall receptacle, very cheap and easy to install. The portable GFCI can be plugged into a standard outlet providing the protection needed while the temporary one is an attachment plug that can be used to provide the desired protection but will not substitute the requirements of a permanent one. When used outdoors the portable and temporary one shall be waterproof and indicated to use outdoors by the manufacturer.

Sometimes you will need to install a new GFCI where an old unprotected receptacle was installed. These receptacles can be replaced with one of the following:

  • Another non-grounding type receptacle.
  • A GFCI-receptacle, if marked “No Equipment Ground.”
  • A grounding-type receptacle, if GFCI protected and marked “GFCI Protected” and “No Equipment Ground.”

What To Do If the GFCI Trips

In some cases, GFCI’s will trip but does not mean that there is something wrong with the installation. If the GFCI is installed in circuits longer than 100 feet, could be one of the reasons your interrupter is tripping. Another issue can occur when the circuit has many splices, fluorescent lighting fixtures or permanently installed electric motors as this can cause the GFCI to trip.

Before installing a GFCI, the loss of power might be considered when using the protection with freezers, garage door controls, and others. Be aware that during the installation the lines and/or loads are properly landed to ensure that the device will work properly, if not, the GFCI will not reset, so make sure the connections are right. 

The GFCI is not the same as the ACFI. The AFCI is used to address fire hazards, while GFCI is installed to prevent shock hazards. We expect soon to have combination devices including both AFCI and GFCI protection in one single piece.