GFCI Circuit neutral sharing

Question

I'm running two 120 volt circuits to GFCI's with three wires each (Hot, Neutral, Ground) and then extending the load terminals out to a remote location. I've run four wires through conduit. Is it possible to share the neutral from the two load terminals on the GFCI's so that I can have two hots, one ground and one neutral for the two remote non GFCI outlets?

Answer 1

Two confused adding machines

GFCIs work by measuring the difference in the current through their hot and the current through their neutral -- if it's more than the trip threshold, then the current must be going somewhere it shouldn't, so they trip to cut off that unwanted current flow.

This means that your plan is doomed to failure -- neither GFCI will reset because the current will divide differently between the GFCI-neutrals than it will between the loads. You'll have to pull a 5th wire into the conduit beyond the GFCIs to serve as a 2nd neutral -- I'd use a grey or striped wire here to distinguish it from the existing neutral so you don't mix them up by accident and wonder why your GFCIs have tripped.

Or, use a breaker form factor

Alternately, you could use regular receptacles and a two-pole GFCI circuit breaker in your panel instead of the regular breaker that's there right now. This works, but may be a bit more expensive, depending on what you have for a panel and how much extra wire you're saving.

Answer 2

It doesn't matter. You say you've already run the wires, that means what you do will be defined by the colors of the wires you ran. Any green/bare wires can only be used for ground, any white/gray wires must be neutral and cannot be re-marked to be a hot. And all other colors can only be hot.

If you ran black red white gray, for instance, then your only option is to run two ungrounded circuits (which you can get away with if they're downstream from a GFCI). And remember, the metal shell of conduit is a grounding path, so it may be grounded after all.

Also, if the remote location is an outbuilding, you cannot run two circuits of the same voltage unless one of them is switched.

If you ran black red white green, only one 120V circuit with GFCI protection will be possible. You cannot run a Multi-wire branch circuit without GFCI protection, because you ran two separate cables to the GFCIs, and combining two separate cables to make a MWBC is not allowed.