As required by the electrical code, every house must have ground-fault circuit-interrupter (GFCI) outlets in locations where moisture is present, and if you have a bad GFCI outlet in one of those places, the consequences could be dire. A ground-fault circuit-interrupter is designed to protect you from electrocution, and if you think a GFCI is working when it isn't, you aren't getting that protection when you think you are. Doing something as simple as operating a hair dryer with wet hands could result in a severe electrical shock.
A GFCI is designed to trip when it detects a ground fault, which is a current surge that happens when electricity finds a path to ground through faulty circuitry or through your body. This function is different from that of a circuit breaker, which trips when it detects a short circuit. A ground-fault shock hazard exists in the bathroom, kitchen, laundry room, basement and crawl space as well as exposed outdoor areas and covered areas that have plumbing, and GFCIs are required in these places. The 2020 version of the National Electrical Code also requires GFCI protection for HVAC equipment and indoor and outdoor service equipment in a dedicated space that isn't movable, like a pool pump, for example.
Self-Testing vs. Manual-Testing GFCIs
To do the job it's supposed to do, a GFCI outlet must be able to trip, and unless you have a self-testing receptacle, you should periodically check this function by using the test button. Self-testing outlets have an LED on the lower part of the receptacle, and as long as it's green, the outlet is good. The outlet needs to be replaced if this light turns red.
Self-testing GFCI outlets are becoming more common, especially in newer homes, but most houses have manual ones without the LEDs. All GFCIs can be tested manually whether they are self-testing or not. You'll see two buttons on the face of the outlet, and the test button is the top one. If the buttons are color-coded, the test button is the black one. The red button is the reset button.
How to Test a GFCI Outlet
You can use a two-prong voltage tester to test a GFCI outlet you suspect is bad, but it's better to use a three-prong tester. This inexpensive device will tell you if a wiring problem is causing the outlet malfunction or if the outlet is bad. The procedure for testing the outlet involves three simple steps.
Step 1: Push in the Test Button
If the power is on and the GFCI outlet is good, you'll hear a little click, the test button will stay in and the power from the outlet will go off. When the button won't stay in, that's an indication that either the power is off and there's no electrical current flowing through the outlet or that the outlet is bad or improperly wired.
Step 2: Check for Power
Plug a voltage tester into the receptacle and check the LEDs. If the tester lights stay off, check the circuit breaker and reset it if it has tripped. If the breaker is on, look for other tripped GFCIs on the same circuit and reset them. If the current is flowing, a wiring problem with the outlet will be indicated by which lights come on, and if no lights come on, the outlet is probably bad. Call an electrician to correct faulty wiring or to replace the outlet as this is not suitable for DIY work.
Step 3: Push in the Reset Button
If the test button clicked and stayed in, cutting power from the receptacle, you should be able to restore power by pushing in the reset button. You'll hear another click when you press it, and it should stay in. If it doesn't, that's another possible indication that no electrical current is flowing through the circuit. If you've checked the breaker and other GFCIs and found no problems, however, it means the outlet is bad and needs to be replaced.
Do GFCI Outlets Go Bad?
Like any other type of electrical equipment, a GFCI outlet has a expected lifespan — typically about 15 years — after which there's a possibility of failure, so GFCIs in older homes are often suspect. Overloading a GFCI receptacle by plugging in too many appliances via a plug multiplier can cause it to fail prematurely, as can loose electrical wiring, which can cause arcing that overheats and melts the plastic. All electrical outlets — not just GFCIs — can be damaged by overuse or improper use, such as pulling plugs out forcefully, which weakens the internal clamps and creates a loose connection that causes the outlet to trip repeatedly.
A GFCI outlet can also go bad because of where it's located. If an outdoor outlet is continually exposed to moisture, the contacts could rust or weaken. The cause of a bad GFCI outlet may also be something that affects all the circuits in the house, such as a power surge from a faulty line transformer, or it could be another device on the same circuit as the GFCI.
How to Tell If a GFCI Is Bad
When a GFCI trips, it won't supply power, so your hair dryer or power saw won't work, and if a tripped GFCI is at the beginning of a circuit, it will cut power to the entire circuit, so other outlets and lights on the circuit won't work either. The difference between a bad GFCI outlet and a good one that has simply tripped is that you can reset the good one, but you won't be able to do that if the circuit has lost power. That can happen if there is another tripped GFCI on the circuit or a short circuit caused the circuit breaker controlling the circuit to trip. You need to investigate these possibilities before deciding you have a bad GFCI.
GFCI Troubleshooting Tips
A GFCI outlet will go bad in a wet location if it isn't properly protected from the elements. All outdoor GFCIs should be in electrical boxes rated for weather exposure and should have covers that protect them from rain and snow. If you're wiring a GFCI yourself, be sure to do it correctly. The terminals are not interchangeable as they are on standard outlets, and the GFCI won't function the way it's supposed to if it isn't wired correctly. When in doubt, it's always safer to have an electrician do the wiring.
Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker.com.