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I have a Leviton 7299-NW GFCI/switch combo

enter image description here

The diagrams in a response to the question "How do I wire a GFCI/switch combo?" is helpful. But I want to see a diagram for a situation where the power enters at the light and the device is wired so that the light is ground fault protected. Provided the cable between the light and the device is a 14/3 (with red wire), I would also need to be able to do the following:

The white wire in the cable from the breaker box which runs to the light box would have to be pigtailed together in the light box with the light's white wire and the returning white wire that runs in the cable between the light and the device. At the device end, the white line wire would have to be pigtailed in with the LINE white-silver neutral screw and the LOAD white-silver neutral screw. So that one white neutral wire is shared by the line and load of the GFCI/switch. Is this permissible?

Simply put: How can I wire the device, GFCI/switch, to ground fault protect light if the power enters at the light?

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  • Unless code has changed recently, I don't even think it is a code requirement for luminaires to be GFI protected in bathrooms. I am sure @Tester101 will be able to verify this or not.
    – maple_shaft
    Mar 8, 2013 at 12:40
  • Is there only a switch installed currently? How was the circuit wired, before you decided to add the comobination device?
    – Tester101
    Mar 8, 2013 at 13:53
  • @maple_shaft This would likely be covered by 110.3(B). NEC 2008 110.3(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.. AKA, RTFM n00b.
    – Tester101
    May 28, 2013 at 14:47

4 Answers 4

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Unfortunately, you can't. For a GFCI outlet to protect other devices they have to come after the GFCI outlet in the circuit. The power (hot and neutral wires) have to enter the outlet on the terminals labeled "line," and leave the outlet on the terminals labeled "load." This way the GFCI outlet can measure the power running to your light on the black wire and returning from your light on the white wire, which is the whole purpose of the GFCI. If those two measurements aren't the same, it turns off. Putting a jumper (what you're calling a "pigtail") between the Line and Load terminals on the device end would effectively bypass the GFCI functions inside the outlet altogether. Connecting the neutral wire coming from your breaker box in the same wire nut with the neutral feeding your light AND feeding the GFCI device will give the electrons leaving your light a direct path back to your breaker box, meaning that they never flow back through the GFCI. It will trip and refuse to reset as long as the light is on, assuming it works at all.

If you want that light to be GFCI protected, you will have to re-run the wire from your breaker box so that it enters the box for the GFCI first. Alternatively, you could splice a second cable to the line in your light box and run it over to the device and then use the black and white from the existing 3 conductor wire to take the power back from the device to the light (with the black wire connected to one pole of the switch and a black jumper from the gold "load" terminal on the outlet to the other terminal on the switch). Either way, you have to run additional wiring. It just depends whether it's easier to add a new cable between the device and the light or to run a new cable from the breaker box to the device.

Put another way, if you want to protect things "downstream" using a GFCI outlet, you have to have at least 4 conductors present in the box, and you only have 3.

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You can't. You also can't put the LINE and LOAD neutrals together.

The GFCI has to get the power FIRST (both supply hot and neutral tied to LINE only), so that if any power goes missing on the return(neutral) leg, it shuts off power. You send the Load hot out the through the switch to the light and return the light neutral to the GFCI's LOAD neutral.

You could protect the light by adding a GFCI upstream to where the power originates or add a GFCI breaker to your panel for that circuit.

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  • Thanks! Does it matter what else is on the circuit when I add a gfci breaker at the box? The house alarm is on the circuit along with other various things (typical 1950's not so well designed circuit).
    – user11933
    Mar 19, 2013 at 4:18
  • The only thing that matters to a GFCI is that the current leaving is the same as the returning current. A full circuit has more potential leakage paths than a point-of-use GFCI.
    – HerrBag
    Mar 19, 2013 at 4:56
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The easiest way to accomplish this would be to install a GFCI breaker, that way the entire circuit is protected. Why do you need to have ground-fault protection on a light though - there shouldn't be a shock hazard to humans with most lights.

Keep in mind that if this circuit protects the living areas (bedrooms) of your house, code might require an arc-fault (AFCI) breaker be installed.

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  • Thanks! The light/fan is in the shower stall so it needs gfi. An electrician came to run new power source to the light switch box or see if a GFCI in the breaker box would work. He put in the combo gfci/switch. It kept blowing. That combo device cannot be put in that box as it is wired. He must have wired it wrong, so it is blowing. Question: What should concern me about what else is on the circuit besides the shower light/fan I want to gfci protect with a gfci breaker? Are there possible things running on the circuit that makes a gfci breaker unsatisfactory (like the house alarm)?
    – user11933
    Mar 19, 2013 at 3:53
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You're going to have to run two 14/2 cables, instead of a single 14/3. Since you want to GFCI protect the light, you'll have to run an extra grounded (neutral) conductor between the GFCI device and the light fixture.

Circuit diagram

Without this additional grounded (neutral) conductor, the GFCI will trip every time you turn the light on. If you connect the circuit like this...

enter image description here

The GFCI receptacle will sense an unbalanced load on the load side whenever the light is switched on.

As previously noted, protecting the entire circuit by way of a GFCI breaker may be the best option.

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