GFCI stands for Ground Fault Circuit Interrupter, while AFCI stands for Arc Fault Circuit Interrupter. Ground faults represent a high risk of electric shock, and arc faults can easily start a fire, which makes GFCI and AFCI receptacles fundamental for safety. Given their protection features, the NFPA 70 National Electrical Code has made both types of outlets mandatory for residential applications.
In terms of external appearance, these special outlets are characterized by the TEST and RESET buttons on their surface. With the TEST button you can verify if the protection mechanism is working correctly, and the RESET button is used to re-establish protection after it has fired off in response to a fault. Unlike normal circuit breakers, which have the main purpose of protecting wiring and equipment, GFCIs and AFCIs are intended to protect building occupants.
This article provides an overview of GFCIs, AFCIs and their applications. However, its purpose is to be informative, not to be used instead of the NEC when specifying an actual installation.
Improve the electrical safety of your building.
How GFCI and AFCI Outlets Operate
GFCI and AFCI outlets both respond to disturbances in electrical current, tripping when dangerous conditions are detected. These protection devices are characterized by a much faster response than circuit breakers and fuses.
Under normal conditions, when there is no ground fault, the current is equal in the live conductor and the neutral conductor. A GFCI measures the difference between both currents - any value different from zero indicates a current leak and the GFCI trips.
GFCIs have an extremely fast response, and can disconnect the power supply in just 1/40 of a second (25 milliseconds). The RESET button pops out when a GFCI trips, and it can be pushed to re-establish the connection after fixing the fault.
An AFCI responds to the current distortions that characterize dangerous electric arcs, especially those capable of starting a fire. In other words, AFCIs can detect changes in the waveform, and disconnect the power supply accordingly.
Some electric arcs occur normally and are not dangerous, and two examples are the sparks when flipping a switch or disconnecting a plug. AFCIs are designed not to trip when these brief electric arcs occur.
When Should a GFCI Outlet Be Used?
In general, the NEC requires GFCIs in moist or wet locations to protect occupants from electric shock. The following are some of the most critical applications:
- Laundry rooms
- Spa and pool areas, including underwater pool lights
- Crawlspaces below grade and unfinished areas
- Outdoor locations, garages and outbuildings
GFCIs are available as both receptacles and circuit breakers. A GFCI breaker protects the entire circuit, while a GFCI receptacle protects the loads connected to itself and any other receptacle wired downstream in the same circuit. In other words, if you have many receptacles in the same circuit and the first one connected is a GFCI, all are protected.
When Should an AFCI Outlet Be Used?
Since AFCIs contribute to fire protection, the NEC requires their use in all single-phase branch circuits rated at 15 amperes and 20 amperes. Previously, AFCI protection was only required for certain areas such as bedrooms, dining rooms and living rooms, but newer versions of the electrical code have changed the requirement to include the entire dwelling unit. Another difference is that the previous requirement was only for receptacles, but AFCI protection now extends to all circuits meeting the conditions established in the NEC.
Since AFCI protection is now required for the entire dwelling unit, AFCI breakers at the main electrical panel are normally more effective than individual receptacles. If you have an older property, and want to upgrade AFCI protection to meet the newer versions of the NEC, a professional assessment is strongly recommended.
How to Test GFCI & AFCI Outlets
GFCI and AFCI outlets are designed for simple testing, thanks to their characteristic TEST and RESET buttons. The testing procedure is very simple:
- Press the RESET button, in case the device has been tripped or is new.
- Connect a lamp to the outlet and make sure it is turned on.
- When you press the TEST button, the lamp should turn off. If the lamp stays on, there is an issue and you should contact a qualified electrician to check the GFCI or AFCI.
- When you press the RESET button, the lamp should turn back on.
Testing your GFCIs and AFCIs at regular intervals is highly recommended, for example once per month. Note that some are located in areas of your home that are not used frequently, such as guest rooms and outbuildings - make sure these are tested as well.
GFCIs and AFCIs make your home safer, reducing the risk of electric shock and helping prevent fires. However, this only applies if your electrical installation meets the requirements of the NEC in the first place. Installations in older buildings such as pre-war apartments are more likely to have electrical safety issues, since they were built under less stringent electrical codes.
If you want to improve the electrical safety of your property, the first step is a professional assessment of your current installation. There has been a notable reduction in casualties due to electrocution and fire ever since GFCIs and AFCIs were made mandatory by electrical codes.