The library
Everything about ground-fault protection, in 32 guides
Each guide names its source — the National Electrical Code section, the UL standard, the OSHA rule, the IEC document — so you can go to the document instead of trusting us. Start with a question at which protection do I need, look a room up at where GFCI is required, or read from the top.
Basics
What the device does, who invented it, how it decides to trip.
- What a GFCI actually does
The current-balance test, 4 to 6 mA, why it is not a breaker, the TEST and RESET buttons.
- How a GFCI works inside: the coil, the window and the 25 milliseconds
The sensing coil, the 4–6 mA window, the 25 ms trip, and why the neutral matters.
- A short history of the GFCI: from a Berkeley laboratory to every bathroom
Invented at Berkeley in 1961; into the Code for pools in 1968 and outdoors in 1973; self-test since 2015.
- GFCI, AFCI and surge protection: three devices, three faults
Three devices, three faults: current leaving the circuit, arcing inside it, and a spike riding in on it.
- Class A, Class B and special-purpose GFCIs
Class A trips at 4–6 mA; Class B at up to 20 mA for old pool lighting; special-purpose 20 mA for industrial gear.
- Self-test GFCIs: what changed in 2015 and what the light means
Since June 2015 every UL-listed GFCI receptacle tests itself and refuses to reset when it has failed.
At home
Outlets, breakers, where the Code wants them, how to wire and test them.
- GFCI outlets and receptacles: the device on the wall
The device on the wall: line vs load, protecting the outlets downstream, 15 vs 20 A, TR and WR marks.
- GFCI breakers vs GFCI receptacles: which one, where
Protection in the panel or at the point of use — when each is the right answer.
- Where the NEC requires GFCI protection, room by room
Room by room: bathrooms, kitchens, garages, outdoors, basements, laundry, sinks — NEC 210.8.
- Wiring a GFCI outlet: line, load, and the mistake that leaves a room unprotected
Which wires go where, what the load terminals do, and the mistake that leaves a room unprotected.
- GFCI in older homes without a ground wire
Two-wire houses: a GFCI is the Code's answer, with the label that goes on it (NEC 406.4(D)(2)).
- GFCI for pools, spas and hot tubs: Article 680
NEC Article 680: pumps, lights, the receptacles near the water, and the 2020 change for pump motors.
- GFCI in kitchens, bathrooms and laundry rooms
The three rooms where it is required at every receptacle, and the sink rule.
- GFCI outdoors, in garages, basements and crawl spaces
Damp places: the receptacles, the freezer question, and why a garage door opener is no longer exempt.
On the job
Construction sites, shops, wash-down floors, generators.
- GFCI on construction sites: the OSHA rule and how contractors meet it
OSHA 1926.404(b)(1): GFCI protection or an assured grounding program for every temporary receptacle.
- Does a GFCI trip on a generator or an inverter?
Bonded and floating neutrals, NEC 445.20, why it trips at plug-in and why it will not reset.
- GFCI for food service and wash-down floors
Wet floors, hose-down, stainless equipment: what the Code and the health inspector expect.
- Portable GFCI cords and plug heads: protection that travels with the tool
Protection that travels with the tool: plug-head, in-line and rewireable devices, and when each is right.
Around the world
RCDs, RCBOs, 30 mA, types AC, A, B and F.
- GFCI vs RCD
5 mA vs 30 mA, 120 V vs 230 V, UL 943 vs IEC 61008 / 61540, RCD types AC, A and B.
- RCD types AC, A, F and B: what each one can see
What waveform each type detects, and why a variable-speed drive needs Type B.
- RCBOs and RCDs in consumer units: how the European panel does it
The European panel: an RCD protecting a group of circuits vs an RCBO on each.
- RCD cords for export equipment
The plug for each country, 30 mA and Type A as the defaults, the approval marks, the cordage.
Troubleshooting
Trips, resets, tests, and what the buttons are telling you.
- Nuisance tripping: a checklist before you replace the device
A ten-step checklist, from unplugging everything to the device itself, before you buy another one.
- When a GFCI won't reset: the four reasons
No power to the device, a fault still present, a failed self-test, or a dead GFCI — how to tell.
- A GFCI that trips with nothing plugged in
Moisture in a downstream box, a nicked cable, a shared neutral: the fault is in the wiring.
- How to test a GFCI cord
The button test, why a plug-in tester needs a ground, how often, and the three ways a test fails.
- How often to test a GFCI, and how
Monthly by the maker's label; before every use on a job site; what self-test changed.
Portable protection
The protection World Cord Sets builds: on the cord, in the plug, or wired to yours.
- Manual reset or automatic reset?
What happens after a trip or a power cut; tools and heaters vs refrigeration and pumps.
- Plug-head, in-line or rewireable: where the protection sits
Where the protection sits, what each form covers, the three ratings to match when you rewire.
- Which NEMA plug does my GFCI cord need?
5-15, 5-20, 6-15, 6-20, L5 and L6 in one table, with what fits what.
Reference
The standards, the words, the numbers.
- The standards behind every rule on this site
The documents behind every rule on this site, and what each one governs.
- GFCI and RCD glossary
Every term on the datasheet, with the standard behind it.