GFCI Outlet trips when white and copper wire touch

gfci

I wired a bath renovation with all power routed through a GFCI outlet. With power on, and all switches off, when I touch the white wire and the bare copper wire in a fixture box, the GFCI trips (did it accidentally at first).

Here is what I have:

  1. Dedicated circuit from the breaker panel to the bath GFCI
  2. Load out of GCFI to 3 gang switch box
  3. In switch box, COPPER WIRE from the LINE in from GFCI and COPPER WIRES from 3 fixtures connected together with a pigtail out to ground the box
  4. In the switch box, WHITE WIRE from the LINE in from GFCI and WHITE WIRES from 3 fixtures connected together
  5. In switch box, BLACK WIRE from Line in from GFCI connected to 3 BLACK WIRES pigtails, one of each then connected to each switch
  6. In switch box, BLACK WIRE from each fixture connected to one pole of each of the switches

All fixtures work fine without tripping the GFCI. If I hook up a non-GFCI outlet to a fixture box, and plug in a 3-prong appliance, it works fine. I checked to ensure the Line/Load and polarity on the GFCI is correct, no visible bare wires anywhere, all connections are tight. Tried a new GFCI and the same occurs.

So, with all that, with all switches off, why would the GFCI trip if I touch white to copper in one of the fixture boxes? Seems to me there shouldn’t be ANY current in the white wire, let alone bleeding in the ground. Why would the GFCI trip if I touch the wire ends, but not trip when I hook up an outlet and appliance?

Maybe it's a predictable anomaly. But I thought GFCI's worked on change in resistance in the ground, and would think a direct connection of the white and copper to have low resistance versus an appliance. Ideas or explanations?

Best Answer

GFCI devices work by comparing the current incoming on the hot wire to the current leaving on the neutral wire. If there's a difference, it means electricity is leaving the circuit somehow (a "ground fault") and the GFCI cuts power*. The GFCI doesn't do anything with the ground conductor—in fact, you don't even need to have one at all. One way of upgrading a 2-prong outlet (without ground) to a 3-prong outlet is by inserting a GFCI device upstream or using a GFCI outlet.

So I'm guessing there is a small amount of current in your scenario, and when you touch the white and ground together, some of that current goes into the ground and doesn't return through the GFCI neutral. Do any of you lights have timers, nightlight, etc.?

(BTW I'm not sure it matters for this question but your description of how the wires up is a little confusing to me. LINE and LOAD are opposite sides of the GFCI device, but you use them interchangeably. If you want a downstream device to be protected by the GFCI it must be connected to the LOAD side. Anything on the LINE side is considered upstream and is unaffected by the GFCI.)

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