Diagrama de cableado de un GFCI

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.

Trace it yourself

Start at the panel and follow the line conductor to the device. It lands on the line terminal, top left of the device box. That conductor is live whenever the breaker is on — nothing the device does changes that.
Inside the device, the internal contact runs from the line terminal down to the load terminal. Armed, it is closed; tripped, it is open.
From the load terminal, follow the conductor out to the downstream device and across the lamp to the neutral, and home.
Now trip it. The contact opens. Everything from the load terminal on goes dead. The line terminal, and the conductor feeding it, stay copper.
Say what a meter would read from the line terminal to neutral with the device tripped. Then say it for the load terminal. If the two answers are different, you have understood the device.

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.

What goes wrong

Line and load swapped

Symptom: trip it and the downstream outlet dies — but the device's own face stays live. (Newer devices refuse to reset at all when wired this way.)

The device's face receptacle is fed from the load side internally, on the protected side of the contact. Land the supply on the load terminals and you have fed the face straight from the panel, around the protection. The downstream outlet, now on the line terminals, is the only thing the contact still controls.

Downstream: on · Face: on

Trip it. Watch which load goes dead and which stays live, then read the diagnosis below. The copper highlight is the live path, not a wire colour.

Why it behaves like that

Follow the supply: it lands on the load terminal and feeds the face directly, no contact in the way. The contact now sits between the load terminal and the line terminal, where the downstream hangs — so tripping opens the downstream but not the face. On the job the tell is a device that "trips" but whose own outlet still runs a lamp. Every GFCI is marked line and load on the back; the supply goes to line, always.

En la obra

The device tells you everything it needs on its own back: line, load, and a test button. Nearly every GFCI complaint on a job comes from ignoring one of those three, and every one of them is provable before the cover goes on.

Common mistakes

Supply on the load terminals. The fault drawn above. The face is fed around the protection, so the device "trips" and its own outlet stays live. Newer devices simply refuse to reset — which is the manufacturer saving you from yourself.
Splitting a hot and neutral pair. The device compares the current going out with the current coming back. Send the load's return anywhere but through the device's own neutral and the comparison is meaningless: it trips on nothing, or protects nothing.
Landing a downstream neutral on the line side while its hot is on the load side. It will sit quiet until something actually draws current, then trip the moment a load runs — the worst kind of fault to find with the wall closed.
Treating the test button as proof of the wiring. That button tests the device's own internals. A plug-in tester's button injects an imbalance through the bond, which is what proves the circuit.
Putting it somewhere nobody can reach to reset it. The book has something to say about that, and so does the customer at 11pm.

What the inspector looks for

That the outlets the book wants protected in that location actually are, and that the downstream ones are marked as protected.
Line and load correct — usually proved by asking you to trip it in front of them.
The protected circuit's neutral coming from the device's load side only, and not shared with anything else.
Accessible for reset, without moving furniture or standing on something.
The enclosure and cover the book requires for the location. Outdoors, whether the cover has to work with a cord plugged in is a real question with a real answer in the book.

Check it before you call it done

Breaker off. Live-dead-live at the box.
Supply to LINE, the run onward to LOAD, and each hot kept with its own neutral. Never split a pair between the two sides.
Energise. Press TEST: the device's face and everything downstream must go dead together. Press RESET: all of it comes back.
Plug-in tester at the device and at every outlet downstream, using its GFCI button at each one. Every single one must trip the device.
If an outlet stays live when you trip the device, it is not on the load side. Find it now, not after the drywall.
Label the protected outlets. That label is the only thing telling the next person where the reset is.

Preguntas frecuentes

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.

Ver también

Glossary: AFCI vs GFCI — shock versus arc, two different jobs.
Duplex receptacle wiring
All wiring diagrams

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