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In my garage I have wiring for a 220 V outlet. It is a four-wire setup (two hots, one neutral and one ground). It is set up on a 20 ampere, double breaker in the circuit breaker box. I want to remove that outlet and install two 110 V receptacles in its place. I plan to run each of the hot wires to the hot side of outlet 1 and 2 inside one electrical box. My plan was to split the neutral inside the box, and run it to the neutral side of outlets 1 and 2, and do the same thing with the ground.

I have researched this issue, but I've come up with conflicting answers. This answer seems to suggest that this would be acceptable since it is already on a 20 ampere, double breaker:

Can two circuits share a neutral?

  • Is the neutral also a 20A wire - or something less? – chux Dec 28 '17 at 19:31
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    It's all 12 gauge wire. – Kevin Bright Dec 28 '17 at 20:07
  • Also related: diy.stackexchange.com/questions/42183/… – canadianer Dec 28 '17 at 21:02
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    So long as you have both ground and neutral, and the neutral is rated for the breaker capacity it should be OK. 240V circuits prior to about 1975 often had a single wire that served as both ground and neutral, and this would not be legal, except as grandfathered for a (3-pin) 240V outlet. – Hot Licks Dec 29 '17 at 4:43
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    When you do this leave a note in the breaker box explaining what you've done. If the breakers are ever moved around in the box such that the two hots are on the same phase then the neutral can be carrying excess current that is not protected by a breaker; only the hots are protected by a breaker. Remember, you have to not just make it safe today; you have to take into account the safety of ignorant people making changes in the future. My house was miswired in this fashion and it was quite the archaeological deduction process to figure out how it got that way. – Eric Lippert Dec 29 '17 at 15:07
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Yes, you can certainly do this. It is referred to as a Multi-Wire Branch Circuit. The two hot legs share the neutral. It is quite common.

Note: Make sure you pigtail the neutral and ground wires, do NOT daisy chain them through the receptacles.

Here is a pertinent National Electrical Code reference:

210.4 Multiwire Branch Circuits.

(A) General. Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors of a multiwire branch circuit shall originate from the same panelboard or similar distribution equipment.

Informational Note No. 2: See 300.13(B) for continuity of grounded conductors on multiwire circuits.

(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Informational Note: See 240.15(B) for information on the use of single-pole circuit breakers as the disconnecting means.

(C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.

Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.

Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

Good luck!

  • Excellent answer. Thanks for the NEC reference. However, I wanted to add that if this is done incorrectly you will get odd voltages. I see this a lot in older homes where a circuit will have 5-20V when off. In most cases I believe following through with your second paragraph will minimize this. – mreff555 Dec 28 '17 at 19:38
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What ArchonOSX says.

However, MWBCs are falling out of favor because of the GFCI or AFCI requirement in so many places. For instance, your garage requires GFCI protection.

Putting GFCI protection on an MWBC is annoying. Puttng it in the service panel requires an expensive 2-pole GFCI - handle-tying regular breakers will not do, because GFCI devices can't share a protected neutral.

You can use GFCI deadface or liveface* modules... But this must happen after a half-circuit splits off permanently. That is to say, hot1 goes east, hot2 goes west, neutral splits, and you can put a GFCI liveface/deadface on each branch after the split, and daisy-chain outlets from there.

If you're installing 2 GFCIs in a single box, make sure it is a deep box. If metal, I recommend to change to either a deep 4" or a deep 4-11/16" square box ** followed by a 2-gang mud ring, not a domed box cover. The 4" domed box covers provide for a neater installation, but you must bend off the mounting-screw ears on a GFCI (or any Decora) device, making it not reusable. If you can change to 4-11/16 boxes, ask the electrical supply if you can see the domed cover, and see if it has clearance for the GFCI ears.

* otherwise known as a GFCI+receptacle combo device.

** those are cheaper at real electrical supply - big-box gouges you on the fat boxes. Also big-box will not have the covers you'll need for the 4-11/16 boxes.

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    Thanks. I hadn't thought about he GFI issue. For wiring purposes, I can just swap out my existing 20 amp outlets for two GFI 20 amp outlets, right? – Kevin Bright Dec 28 '17 at 19:21
  • Yeah, that should do it. Attach to LINE terminals only, no use of LOAD terminals at all. Hence my advice on getting fat GFCIs to fit. And once they're installed you could add additional outlets by coming off the LOAD terminals of either one. – Harper Dec 28 '17 at 21:42

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