Build it · interactive puzzle

Wire a GFCI Outlet: Build-It Puzzle

A GFCI receptacle cuts power in a fraction of a second when current leaks to ground, the kind of leak that runs through a person. It only does that job if it's wired right: the cable from the panel on LINE, and the cable to downstream outlets on LOAD. This puzzle is a cut-open wall with a box, two cables and a GFCI. Drag each wire to a terminal, ground it, push the device in, screw it down and plate it. Then turn the breaker on and press RESET and TEST. Wire it wrong and it fails the way a real one does.

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What is the difference between LINE and LOAD on a GFCI?

LINE terminals take the cable that brings power from the panel. LOAD terminals feed outlets further down the circuit and give them GFCI protection. If you aren't protecting anything downstream, leave the LOAD terminals taped.

How to play

  • Drag the GFCI from the pegboard out in front of the box. You see its back: LINE terminals at one end, LOAD (taped) at the other.
  • Drag each wire's bare end onto a terminal hole. Tap the yellow tape to peel it before you use the LOAD terminals.
  • Drag the ground pigtail on, then tap the device to fold the wires in and push it into the box.
  • Fit the mounting screws, then the cover plate. The breaker can't come on until the plate is on.
  • Tap the breaker handle (or the Breaker button), then press RESET and TEST. The plug-in testers show what each outlet is getting.
  • No mouse? The list under the figure does every move with buttons.

What the puzzle teaches

  1. LINE is the cable from the panel; LOAD feeds the outlets after this one. The LOAD terminals ship covered with tape.
  2. Black (hot) goes to the brass screw, white (neutral) to the silver screw, bare (ground) to the green screw.
  3. A modern GFCI locks out if LINE and LOAD are reversed: no power at the face, and RESET won't stay in.
  4. Outlets wired to the LOAD terminals are protected: TEST cuts them too. Outlets spliced through with the line still work but aren't protected.
  5. With hot and neutral swapped the outlet still works, but polarity is reversed: a plug-in tester shows HOT/NEU REVERSED.
  6. A GFCI protects people even without a ground, but a ground in the box should be connected. A plug-in tester shows OPEN GROUND when it isn't.
  7. A GFCI trips when the current out on the hot and back on the neutral differ by about 5 milliamps. Press TEST once a month.

Parts on the list

  • GFCI receptacle, 15 A or 20 A to match the circuit
  • Ground pigtail (6 inch bare or green conductor) and a wire nut
  • Mounting screws (usually captive on the device)
  • Cover plate
  • Non-contact voltage tester and a plug-in receptacle tester

This is a learning puzzle, not a substitute for training. Before working on a receptacle, turn the breaker off and confirm the circuit is dead with a voltage tester. Follow the device's instructions and your local electrical code, or hire a licensed electrician.

FAQ

Frequently asked questions

What happens if you reverse LINE and LOAD on a GFCI?

A modern GFCI detects it and locks out: the face has no power and the RESET button won't stay in. Turn the breaker off and swap the cables so the one from the panel is on LINE.

Which wire goes on the brass screw?

The black (hot) wire goes on the brass screw and the white (neutral) on the silver screw. The bare or green ground goes on the green screw.

Will a GFCI work without a ground wire?

Yes: it trips on a current imbalance, not through the ground. Codes allow it as a replacement on an ungrounded circuit when it's labelled 'No equipment ground'. If a ground is in the box, connect it.

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