GFCI wiring diagram
Light: on
Trip it and watch: the downstream device dies, but the line conductor into the GFCI stays energized. Reset re-feeds the load. The copper highlight is the live path, not a wire colour.
A GFCI feeds and protects everything on its load side, and drops that load the instant the current leaving on the hot stops matching the current returning on the neutral. The supply lands on the line terminals; the downstream devices hang off the load terminals; the sensing electronics sit between them.
How this circuit works
In normal use the hot and neutral currents are equal and opposite — every electron that leaves comes back the way it should. The device is happy and the load side is fed. The moment a path opens that lets current return some other way, the balance breaks, and the GFCI opens its internal switch on the load side. That is the trip.
The lesson worth burning in is the one the diagram makes obvious when you trip it: the load goes dead, but the line conductor into the device is still energized. A tripped device is not a safe-to-touch device. Reset it and the load comes back live.
Questions people ask
What does "line" and "load" mean on a GFCI?
Line is the pair of terminals fed from the supply. Load is the pair that feeds devices further down the circuit. Wire the incoming supply to line and the downstream receptacles to load, and the one GFCI protects everything on the load side as well as itself.
How does a GFCI decide to trip?
It continuously compares the current going out on the hot with the current coming back on the neutral. In a healthy circuit they match. If some current is finding another way back — through a person, for instance — the two no longer balance, and the device opens the load side in a fraction of a second.
Why is the device still hot after it trips?
Because tripping only opens the load side. The line side is fed straight from the supply and stays energized right up to the device. Toggle the diagram to tripped and you will see the downstream device go dead while the line conductor stays copper. Never assume a tripped GFCI means a dead circuit — meter it.
Does the whole circuit lose power when it trips?
Everything on the load side does. Anything wired to line, and the supply itself, does not. That split is exactly why the line/load distinction matters, and why getting the two backwards leaves downstream devices unprotected.
Related
- Glossary: AFCI vs GFCI — shock versus arc, two different jobs.
- Duplex receptacle wiring
- All wiring diagrams
Learn one thing a week
Now and then a new diagram, drill, or reference sheet goes up. Leave your email for a short heads-up when it does — no spam, no selling it on, one click to leave.