Can a neutral be shared beween the line and load side of a GFCI if it's on the same circuit?

Question

All neutrals are crimped together on this circuit. Not daisy chained. So I have one hot and one neutral from panel (line) and one hot downstream (load). And additional no neutral wire for going downstream (load). A clump of neutrals are in the back of the box, all crimped together. Can't I just add a jumper between the line and load neutral screws of the GFCI? I am stumped; I've studied this for over a year. The circuit is in my kitchen, 20 amps. Feeds aquarium, gas stove, vent, and fridge. So, as of now, only the aquarium is protected. Nothing downstream. I really would like to get the entire circuit protected without having to put in a new GFCI breaker. Thanks, Jim

Answer 1

This is a common issue that arises from the previous meaning of the word LOAD.

You're used to talking about the cables in a box as "Line" meaning the supply cable from the service panel, and "Load" referring to the cable(s) that go onward to other points-of-use.

With GFCI, you have to throw that definition out. In fact, I use the word "Onward" to refer to those onward cable(s).

GFCI has hijacked the word "LOAD" to mean extending GFCI protection to also protect certain specific onward outlets or points-of-use. You should never, ever use the LOAD terminals on a GFCI unless you mean to do precisely that.

Usually people go after the LOAD terminals merely because their old receptacle had wires on 4 screws and they don't know where else to put the extra 2 wires. This results in protecting downline loads inadvertently - they have no idea what effect that has, and have no idea how to fix it when it starts tripping. Don't do that.

When you actually, really do want to protect a downline, you must take that particular downline's hot and neutral wires both, and put both of them on LOAD. You would never put just one on LOAD.

So you say you have a kitchen circuit that feeds aquarium, gas stove, vent and fridge. Let's go through those loads.

• Aquarium - oh yes, you want that on GFCI!
• Gas stove - Is it grounded? A steel box that is grounded is vanishingly unlikely to have the kind of problem GFCIs help with. It might be a source of nuisance trips though.
• Vent - is hardwired and does not need to be on GFCI. Again if grounded, GFCI is of little use here.
• Refrigerator -- is a human-safety nightmare for GFCI. It's a steel box, grounded, all the mains electric is in the bottom back where it's totally inaccessable, and you're really not likely to drop it in the sink. So it's simply not a use case for GFCI at all. GFCI does not help fridges. However, a GFCI nuisance trip can take out a fridge, and now you have a huge human safety problem in food spoilage. Fridges do not need to be on GFCI. Further, fridges are notorious for tripping GFCIs themselves. Putting this on GFCI is a bad idea.

But if you have any other loads, evaluate them on a case by case basis and decide whether to attach their hot + neutral to GFCI LINE or LOAD.

Answer 2

Harper’s excellent answer does omit one thing: why you have to separate the neutrals. A GFCI functions by comparing the current flowing through its hot and neutral LINE terminals. If the current differs by more than (typically) 5ma, it’s assumed that current is flowing to ground, perhaps through a person, and cuts the circuit.

If you were to simply keep the neutrals joined and connect the neutral only to the LINE side, there would be no current seen flowing on the neutral and any draw from the LOAD hot (over the threshold ) would cause a trip.

If you were to connect the same neutral bunch to both LINE and LOAD, then the direct connection would allow some neutral current to bypass the GFCI and, again, trip it.

For a single-phase GFCI to function correctly on the LOAD side, you must connect only one matching set of hot and neutral. Any other connection will prevent the GFCI from functioning.

Answer 3

Jim commented: "I probably will join the red and black circuits together with a pigtail and land it and the neutral on the GFCI/AFCI breaker."

Jim, please do not blindly pigtail red and black together. That can potentially short out the two legs of your 240V service. When red is at +120V, black is at -120V and vice versa. The hazard in a shared-neutral setup is that if the two hots are in opposite phase and the shared neutral line is somehow interrupted, you end up with 240V with the appliances in both circuits in series, which if the load impedances are mismatched (e.g., microwave on one circuit, laptop on the other) results in a hugely uneven voltage distribution (e.g., microwave will get 12 volts and laptop will get 228).

Use a multi-tester and measure the voltage across red and black. If it measures 240V, they're in opposite phase -- you can't simply connect the two as if they're the same circuit.

And to your original question, if you add a jumper from line to load, the GFCI circuitry will interpret that as a current leakage and trip (and not even reset).