Wiring a GFCI outlet correctly depends on identifying the incoming supply and distinguishing it from any outgoing connections—not matching wire colours alone. The LINE terminals receive power from the circuit; the LOAD terminals can send power through the GFCI to downstream outlets, extending protection to them. A mix-up may prevent the device from working as expected or leave downstream outlets without protection from that GFCI. Because conductor colours and existing wiring can be misleading, treat this as an explanation of the connections, not a reason to work on unfamiliar wiring. If you cannot positively identify the cables or confirm that the work is permitted where you live, stop and call an appropriately qualified electrician.
A GFCI receptacle monitors the current leaving through the live conductor and returning through the neutral. If it detects an imbalance, it interrupts power. Its built-in TEST and RESET buttons operate the device’s protection mechanism; they do not make the GFCI a substitute for a correctly rated circuit breaker or fuse, which provides overcurrent protection.
The LINE connection is the source: the cable bringing power from the circuit. The LOAD connection is an optional onward connection. When the correct outgoing conductors are connected to the LOAD terminals, the GFCI can monitor and interrupt power to outlets farther along that circuit as well as to its own receptacle.
| Connection or part | Purpose | What to keep in mind |
|---|---|---|
| LINE terminals | Receive the supply from the circuit. | The device needs its supply connected correctly to operate. |
| LOAD terminals | Feed a downstream section through the GFCI. | Use them only when extending protection is intended and the correct cable has been identified. |
| GFCI face | Provides power at the receptacle and access to TEST and RESET. | A working face does not by itself prove that downstream outlets are protected. |
| Ground terminal | Connects the equipment grounding conductor where the circuit provides one. | Grounding is separate from GFCI operation. Never improvise a ground connection. |
The distinction matters because a GFCI can protect its own receptacle without using its LOAD terminals. Downstream outlets may still have protection from another device, such as an upstream GFCI, but that must be established rather than assumed. If downstream protection is intended to come from the new receptacle, the outgoing cable must be connected to the correct LOAD terminals and the installation must be tested.
Many GFCI receptacles mark their terminals “LINE” and “LOAD,” and the manufacturer may distinguish them with labels or a cover. Those markings are more useful than guessing from the terminal’s position. Follow the instructions supplied with the exact device: layouts and features differ, and the LOAD terminals may be covered until they are needed.
Wire colour can be a clue in a known, correctly installed system, but it cannot establish which cable is the supply or which one continues to other outlets. Older alterations, repairs, unusual circuits and local wiring conventions can all make a simple colour-based assumption unreliable. In New Zealand, conductor colours and common installation practices may differ from those shown in North American GFCI instructions.
A GFCI also needs the correct live and neutral conductors for the circuit it serves. Connecting a neutral from a different circuit, mixing neutrals, or disturbing a shared-neutral arrangement can cause tripping or create a hazardous fault. Circuits with multiple cables, unfamiliar splices, or more than one source of power need particular caution. Do not try to sort these out by trial and error.
Symptoms depend on the GFCI model and the rest of the circuit. A device may not reset, may not supply power, or may appear to power the receptacle while failing to protect the outlets that were meant to be downstream. Some newer devices are designed to block power or indicate a reverse-line/load connection, but that response is model-dependent. An apparent success is not proof that every intended outlet has protection.
Confusion can also arise when another GFCI or a GFCI-protected breaker already serves the circuit. An outlet that loses power may be downstream of a different protective device, not necessarily wired incorrectly at the outlet in question. Repeatedly resetting devices or swapping conductors without tracing the circuit can mask the actual problem.
Replacing or altering a receptacle means dealing with fixed electrical wiring. A switched-off breaker is not, by itself, proof that conductors are safe to touch: circuit labels may be wrong, and more than one supply can be present. Verifying that a circuit is de-energised requires suitable test equipment and the competence to use it correctly. A non-contact voltage pen or a test button is not a substitute for proper verification.
In New Zealand, a North American GFCI receptacle should not be treated as an automatic substitute for local socket-outlet or RCD protection. Installation requirements and the permitted scope of homeowner electrical work depend on the specific work and applicable rules. Ask an appropriately licensed electrician to confirm the right protective device and carry out fixed-wiring work. If you are elsewhere, follow the rules that apply in your jurisdiction.
Homeowners can use the following checks to decide what information to gather and when to hand the job to a professional. They are not instructions to open an energised receptacle or to connect conductors without proper training and authorisation.
If the GFCI is being installed where an ordinary receptacle was previously fitted, the number of cables in the box does not necessarily tell you which one is LINE. Likewise, a cable that appears to continue to another room may not be the only onward connection. Circuit tracing is a task for someone equipped and qualified to do it, not a visual guessing exercise.
Once an electrician has installed or inspected the device, use the TEST and RESET buttons as directed by the manufacturer. The TEST function should cause the device to trip; RESET should restore operation if the fault condition has cleared and the wiring is correct. If the buttons behave unexpectedly, stop relying on the outlet and contact the electrician who did the work.
If the purpose of using the LOAD terminals was to protect other outlets, those outlets need to be checked too. Identify which receptacles are meant to be protected and have their protection verified with suitable equipment. A plug-in tester may be useful in some situations, but its readings can depend on the circuit and grounding; it should not be treated as conclusive proof of correct installation.
GFCI protection does not repair damaged wiring, correct a loose connection, or guarantee protection against every electrical hazard. Keep any existing breaker protection in place, and report warm outlets, scorch marks, buzzing, or recurring trips rather than continuing to use the circuit.
The phrase “GFCI outlet” is most often used for a North American receptacle with built-in ground-fault protection. New Zealand homeowners are more likely to encounter RCD terminology. Although both types of protection respond to certain current imbalances, names, device designs, installation arrangements and local requirements are not interchangeable by default.
That difference matters when searching for wiring diagrams online. A diagram made for a particular North American receptacle may show terminal markings, conductor colours or an installation method that does not match a New Zealand home. Use it to understand the general idea of incoming supply versus protected outgoing circuit only; do not use it as a wiring plan for local fixed wiring. Ask a New Zealand electrician which protective device and arrangement suit the property and the work.
Yes, a compatible GFCI receptacle can protect downstream outlets when the correct outgoing conductors are connected to its LOAD terminals. The outlets must be on the intended circuit, and the completed installation needs to be tested. A receptacle’s own TEST and RESET buttons do not prove that downstream protection is working.
No. The LOAD terminals are used when the installation is intended to extend the device’s protection to downstream outlets. If no such protection is needed from that device, the terminals may remain unused as directed by the manufacturer.
No. Colours alone do not reliably establish which cable brings in the supply, particularly in older or altered wiring. Proper identification requires suitable testing and knowledge of the circuit; if there is any uncertainty, have an electrician trace it.
A missing supply, incorrect connections, a fault on the circuit, a downstream problem, or a defective device can all be possible causes. The symptom does not identify which one applies. Avoid opening the outlet or swapping wires to test guesses; arrange a qualified assessment.
They are related forms of protection against current imbalance, but their names, equipment and installation arrangements are not automatically interchangeable. Have a local electrician confirm the suitable device and requirements for a New Zealand property rather than following a foreign wiring diagram.
When wiring a GFCI outlet, the essential distinction is straightforward: LINE supplies the device, while LOAD can carry its protection onward to other outlets. Correctly identifying those connections, testing the intended protection and following local requirements are not tasks to replace with colour matching. If the circuit or device is unfamiliar, leave the wiring untouched and ask a qualified electrician to inspect it.
