GFCI Protection

A ground-fault circuit interrupter (GFCI) shuts off power in a fraction of a second when it senses electricity leaking to ground, which might be through your body. It’s one of the cheapest, most effective electrical safety devices on a jobsite, and it has saved thousands of lives since it became required.

• Construction
• General Industry

What a ground fault is

Electricity normally flows out on the hot wire and back on the neutral wire. A ground fault happens when current finds another path to ground: through a damaged cord, a wet tool, a nicked wire touching a metal case, or a person. Water, sweat, damp soil and metal surfaces make ground faults much more likely and much more dangerous.

What current does to your body

It’s the current (measured in milliamps, mA) flowing through your body that does the damage. A standard 20-amp circuit can push 20,000 mA, far more than enough to kill.

Effects vary with the path through the body, how long the current flows, and whether your skin is wet. The “can’t let go” range is especially dangerous because the shock keeps going.

How a GFCI works

A GFCI constantly compares the current going out on the hot wire with the current coming back on the neutral. If they differ by about 5 milliamps (4 to 6 mA for personnel-protection GFCIs), some current is leaking somewhere it shouldn’t, and the GFCI cuts the power in about one-fortieth of a second. That’s fast enough to prevent most electrocutions, although you may still feel a painful shock and could be hurt by a fall from a ladder when it jolts you.

What a GFCI does not do

• It does not protect you if you touch both the hot and neutral wires at the same time, because no current is leaking to ground.
• It does not protect you from overhead or underground power lines.
• It does not protect against overloads or short circuits. That’s the job of the circuit breaker or fuse.
• It does not replace a proper equipment ground. Keep ground pins on plugs and use grounded or double-insulated tools.
• It can’t help if it’s broken, bypassed or plugged in downstream of the problem.

Types of GFCIs

When GFCIs are required

Construction (29 CFR 1926.404)

Employers must protect workers using temporary power in one of two ways:

• GFCIs on all 120-volt, single-phase, 15- and 20-amp receptacle outlets that aren’t part of the building’s permanent wiring, or
• An Assured Equipment Grounding Conductor Program (see below).

Most contractors simply use GFCIs everywhere because it’s easier and safer. Many company safety programs require GFCIs even when plugging into a building’s permanent outlets, and for 240-volt temporary equipment.

General industry (29 CFR 1910.304)

During construction, remodeling, maintenance, repair or demolition work, 125-volt, single-phase 15-, 20- and 30-amp receptacle outlets that aren’t part of the permanent wiring must have GFCI protection (or the employer must use an assured equipment grounding program for other receptacles).

The electrical code

The National Electrical Code (NFPA 70) requires GFCI protection in many permanent locations, including bathrooms, kitchens, garages, outdoors, basements, laundry areas and near sinks, and on temporary wiring at construction sites. Each new edition tends to expand where GFCIs are required. See National Electrical Code.

The Assured Equipment Grounding Conductor Program

Instead of GFCIs, a construction employer can use a written program to make sure every cord, receptacle and tool is properly grounded. It requires:

• A written description of the program, available at the jobsite
• A competent person to run it
• Daily visual inspection of cords, plugs and equipment before use, with damaged items removed from service
• Tests for grounding continuity and correct wiring: before first use, after repairs, after any incident that might have caused damage, and at least every 3 months (every 6 months for fixed cord sets and receptacles not exposed to damage)
• Records of the tests, often by colored tape on each cord showing the test period

It’s more work and depends on people doing every test, which is why GFCIs are the more common choice.

Test it before you use it

1. Plug in a light or tool and turn it on.
2. Push the TEST button. The power should shut off and the light or tool should stop.
3. Push RESET. The power should come back on.

• Test portable GFCIs before each use, and permanent GFCI receptacles at least monthly.
• If it doesn’t trip, or won’t reset, don’t use it. Tag it out and replace it.
• Use a plug-in GFCI tester for outlets you can’t test with the button, but remember the built-in TEST button is the manufacturer’s test.

When a GFCI keeps tripping

A GFCI that trips is doing its job. It’s telling you something is leaking current. Common causes:

• A damaged cord or plug, or water in a connection
• A tool with worn insulation or moisture inside
• Too many cords and tools on one GFCI, which can add up small leakage currents
• Very long extension cord runs
• Rain getting into outlet boxes without in-use (bubble) covers

Unplug everything, then plug in one item at a time to find the problem. Take the faulty tool or cord out of service.

Jobsite tips

• Put the GFCI at the power source, not at the tool end of the cord, so the whole cord is protected.
• Keep connections off the ground and out of puddles, and use weatherproof covers.
• Use hard-service, three-wire extension cords and inspect them daily. See Extension Cords.
• Generators used on construction sites also need GFCI protection or an assured grounding program. See Portable Generators.

At home

Many older homes don’t have GFCIs where they’re needed today. GFCI receptacles are inexpensive and can be added in kitchens, bathrooms, garages, basements and outdoors. Use a portable GFCI for outdoor power tools and holiday lights. See Home Electrical Safety.

Last updated: October 1, 2026