How to Test a GFCI Outlet, and Where Your Home Needs One
The U.S. Consumer Product Safety Commission (CPSC) says to test every GFCI at least once a month, after installation, and after a power failure. A GFCI is the outlet with TEST and RESET buttons, or a breaker with a test button. The CPSC fact sheet also dates when the National Electrical Code (NEC) began requiring GFCIs in each location, which shows where an older home may have none.
1. What a GFCI is watching for
CPSC defines a ground fault as an unintentional electrical path between a power source and a grounded surface. It usually happens when an appliance or cord is damaged so that live parts are no longer covered. If your body becomes that path, for example one hand on a faulty hair dryer and the other on a metal faucet, you can be shocked, burned, or electrocuted.
A GFCI constantly compares the current going out on a circuit with the current coming back. According to the CPSC fact sheet, if the two differ by as little as 0.006 amperes (6 milliamps), the device cuts power before the shock can affect your heartbeat. CPSC also notes a GFCI works even on an older two-slot receptacle.
CPSC adds that a GFCI can also prevent some electrical fires and reduce the severity of others by interrupting current. It also warns that blackouts and other power disturbances can sometimes damage a GFCI's ability to work, which is one reason to retest after an outage.
2. The monthly test, step by step
CPSC says to test every GFCI after installation, at least once a month, after a power failure, and according to the manufacturer's instructions. If you do not have the instructions, CPSC's procedure is:
- Plug a lamp into the outlet and turn the lamp on.
- Press the TEST button. The light should go out. If it does not, the GFCI is not working or was not installed correctly, and CPSC advises calling a qualified electrician.
- Press RESET. The light should come back on. If it does not, replace the GFCI.
2.1. Testing a GFCI breaker
Some homes have GFCI protection built into a breaker in the panel. CPSC's Home Electrical Safety Checklist (July 2008) says to test those monthly too: push the test button, and the breaker handle should go to the middle or off position. To reset, move the handle to off and then on. The checklist also says GFCIs can fail without showing any sign of failure.
3. Why one outlet can protect several others
A receptacle-type GFCI protects whatever is plugged into it and, according to CPSC, other outlets "downstream" on the same branch circuit. That is why a bathroom outlet with no buttons can still go dead when the GFCI in the next room trips.
When you press TEST, check nearby plain outlets with a lamp. Any that also go dark are downstream of that device, and a label on each tells the next person where to reset.
4. Where your home probably has, or lacks, protection
CPSC says GFCI circuits are designated by the NEC, which typically applies only to new construction and major renovations, and that coverage has increased over the years. This list is from CPSC's fact sheet dated September 2010; later NEC editions (revised every three years) may require more locations:
| Location | NEC requirement since |
|---|---|
| Underwater pool lighting | 1968 |
| Outdoor receptacles | 1973 |
| Bathrooms | 1975 |
| Garages | 1978 |
| Kitchens | 1987 |
| Crawl spaces and unfinished basements | 1990 |
| Wet bar sinks | 1993 |
| Laundry and utility sinks | 2005 |
The dates work as a rough audit. A kitchen last wired in 1980 predates the 1987 requirement, and a house from the early 1990s may lack a GFCI at the laundry sink (2005). Local codes and past remodels vary, so look and test; the dates only say where to look first.
5. Your options for adding protection
CPSC describes three types (receptacle, circuit breaker, and portable):
- GFCI receptacle. Replaces a standard outlet and protects downstream outlets on the same circuit. CPSC notes it can even replace an old two-slot outlet, as long as you apply the supplied "No equipment ground" label so no one assumes the outlet is grounded.
- GFCI circuit breaker. Installed in the panel to protect the wiring and every outlet, light, and appliance on that branch circuit, and it also protects against overload. CPSC says a qualified electrician may install it.
- Portable GFCI. Plugs into a receptacle like any cord-and-plug device. CPSC suggests one for electric garden equipment and for electric tools such as drills, saws, and sanders for DIY work.
CPSC says receptacle types may be installed by consumers only with adequate knowledge and skills to follow proper wiring practices and the device's instructions, and that when in doubt you should contact a qualified electrician and not install it yourself.
6. Twice-yearly check
CPSC's Home Electrical Safety Checklist recommends inspecting electrical products in your home every six months, for example when you move in or change your clocks. The GFCI test itself is monthly.
7. Key takeaways
- CPSC says a GFCI interrupts power when outgoing and returning current differ by as little as 0.006 amperes.
- CPSC says to test every GFCI at least monthly, after a power outage, and after installation: lamp on, press TEST (light off), press RESET (light on).
- One GFCI receptacle can protect downstream outlets, so map and label which outlets go dead during a test.
- NEC dates in CPSC's 2010 fact sheet (bathrooms 1975, kitchens 1987, laundry sinks 2005) show where an older home may lack protection.
- Portable GFCIs plug into an outlet, and CPSC suggests them for power tools and yard equipment.