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Hoping someone can help me with this. I have searched the whole dang internet multiple times and can’t find the answer to my question, so I am posting it here. I have added two 120V-20A circuit breakers to my panel, and ran 12/4 MC to a string of five “2-gang” boxes (the first box will host a pair of GCFI’s, different than what I drew). I’ll use commercial 20A receptacles in down-stream 2-gang boxes. Total length of the run is under 100’.

Here’s where I need help (just a review and approval if I’m good). My plan is to use:

  • Black/White wires from 12/4 to power the first circuit “A” on the left side of the box.

  • Red/Blue (blue taped white) wires to power the second circuit “B” on the right side of the box.

  • Tie all grounds together (Line/input ground wire, 2-gang chassis, “A” outlet, “B” outlet and Load/output ground wires).

  • I’ll send line power to the tops of the outlets (inputs) and take load power from the bottoms of the outlets (outputs) to feed the next box ... lather, rinse, repeat. I have installed a string of 5 boxes over about 60’, but may possibly add 3 more for a total of 8 boxes within a single workshop under 100’ of 12/4.

Please see pic. It’s all surface-mounted MC and boxes, strapped with Minerallac 125 Jiffy Clip one-hole clamps with holes above the MC, and fastened within 11” of each box, 12” everywhere else. I will pull a permit and have the work inspected because I have an affinity for doing things right.

My rationale for “assuming” this is correct is that it’s how I would run 12/2 to a string of 1-gang boxes/outlets. My main confusion is whether or not I should be bonding all of the neutrals in each 2-gang box, but think it’s not required because the neutrals are all bonded together in the panel. Is there a safety requirement in the code that requires the bonding of the neutrals in each receptacle box? And if so, can you please point me to the code so I can read/learn/understand?

PleaseCheckMyPlan

2-GangBoxWithMCin&out

Thank you so much for your time and assistance with my question! I love this stuff and wish I would have chosen to become an electrician. My problem is that I’m an anal perfectionist beyond comprehension. I guess a little OCD is a good thing when dealing with electricity. :-)

Thanks again, Rich

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You gotta keep em separated!

You need to keep the neutrals separated throughout the circuit for a couple of reasons. First off, if you want to put GFCI on this, the GFCI will tell you if you cross or join the neutrals by stubbornly refusing to stay un-tripped, so keeping them separated is a good policy that way. More importantly, though, neutrals rely on being protected by the overcurrent devices of their partner hot wires, as they don't have fuses or overcurrent breakers of their own. As a result, if you tie the neutrals together, and one of them opens, you'll potentially put 40A down a 12AWG wire, which is going to get rather toasty and melty...

And yes, you have the wrong cable for the job

While reidentifying neutrals to hots in a cable works, you can't take a wire smaller than 4AWG that's not white, grey, or striped with one of those two colors and legally use it as a neutral. To be fair, if one was working under significant duress, tape-flagging a hot to a neutral is by no means the worst thing you can do, but it sounds like you'll have to order in some 12/2/2 MC and do this over.

5
  • holy crap, that was fast! Thank you very much for your super fast and informative response! Now I need to figure out how to give you kudo’s for your time and response! I am so glad I discovered diy.stackexchange.com! Thanks again, Rich. Oh bummer ... I got a dreaded new guy rejection: “Thanks for the feedback! Votes cast by those with less than 15 reputation are recorded, but do not change the publicly displayed post score.“ Dec 19 '20 at 2:14
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    @riffin-rich -- we thank people around here by upvoting and/or accepting their answers :) Dec 19 '20 at 2:15
  • not sure if you saw my edit, but I’m typing this note so you know I tried to thank you by upvoting but couldn’t because I got a dreaded new guy rejection: “Thanks for the feedback! Votes cast by those with less than 15 reputation are recorded, but do not change the publicly displayed post score.“ I’ll close this as “answered” now. Thank you again. Rich Dec 19 '20 at 2:22
  • Question for the smarter people here at SE. If the OP took the tour, that gives someone 100 points, Would that enable him to vote? Dec 19 '20 at 13:15
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    @George Anderson, no clue what you’re talking about but I’d be happy to take the tour. This forum is amazing. Dec 19 '20 at 17:21
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Can't do that. You have the wrong cable for this job.

White (in a cable) can be re-identified as hot, but other colors cannot be re-identified as neutrals unless they are 4AWG or larger - neutrals have to be white or gray (they can be white or gray striped with other colors for identification purposes.) Three CONTINUOUS white stripes (the whole length of the wire) on any color but green is also acceptable.

NEC 200.6(A) (read it and weep, since you obviously already bought and cut the wrong cable for the job.)

The use of white tape, paint, or other methods of identification isn't permitted for grounded conductors 6 AWG or smaller.

12/2/2 is a cable that would work. That's commonly black/white/red/white-with-a-red stripe. Black/white/red/gray would also work.

The only way I can see to "save this" would be to get a 20A 240V GFCI, and then you could use the one neutral, and two of the three hots to run a MWBC (Multiwire Branch Circuit - the GFCI HAS to be done by a 240V GFCI breaker for that to work correctly) rather than needing to buy new cable. If you have some other place where 12/4 would actually be useful, just get new cable.

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  • thank you for your reply. Bad news doesn’t get better with time, so I appreciate your blunt truth now. I just discovered my affinity for perfection and doing things right is flawed by the amount of $285. LOL. FWIW, I tried to get 12/2/2 but it wasn’t available at each of the 4 nearby supply houses or their warehouses and they each said “at least a month” so I’m going to let it ride while labeling each box with “blue/white is Circuit B neutral.” Bottom line, if my inspection bounces, I’ll pull it, order 12/2/2, and give my electrician my remaining 12/4. He’s a good guy. Thank you! Dec 19 '20 at 2:44
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    I think you would have done better to use EMT (even if it meant learning to use a bender) or metal flex conduit (which is pretty much exactly empty MC you pull wires into) if you could not get the right MC cable. Have fun, stay safe.
    – Ecnerwal
    Dec 19 '20 at 2:50
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    Crazy, but I actually had a bender in my hand and thought it would be cool to learn how to use it, but I didn’t want to further delay my project to run surface-mounted power around my basement. I’ve been without my power tools too long since moving into this house. That’s also why I didn’t consider ordering/waiting for 12/2/2 ... I assumed I could reallocate/tape-over the blue wire to indicate the second neutral. Sad because I know better than to Ass-U-Me. Glad I verified 2 independent circuits nonetheless. Dec 19 '20 at 3:41
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Harper's Law: Buy the wire LAST after all research is finished.

In the future use FMC or EMT.

Really, since you want a metal-jacketed system with an arbitrary combination of wires inside, you would have been better off selecting Flexible Metal Conduit.

However, noting your installation style in the photos, the better system still would be EMT (Electrical Metal Tubing). EMT is a nice compromise between hard pipe and "easy to work with". It cuts with a hacksaw (why is your wire stripper tapered? To ream the burrs off EMT!) and uses very cheap fittings and the same 4x4 metal boxes.

But EMT does something even cooler for you: provides ground. You can get the kaboodle done with 2 spools of wire (white+black) and a 5-pack of colored tape ($5)... I myself do enough of it I just invested in 10 spools of wire. (none green since EMT is ground).

You use stranded THHN wire which is a pleasure to work with. Although it's a nightmare to land on side screws, so either pigtail with solid wire, or use "Screw-and-clamp" type receptacles.

Further, with EMT conduit, when you need another circuit, you just pull it into the conduit! You future-proof with pipe instead of wire. Mind you there's a 4-circuit practical max, and circuits 30A or above need special derating.

You must mark wires to indicate which circuit they're part of. However, in THHN wires, functional remarking is not allowed (can't buy just white and mark all the hots with black tape). Which means, you're free to use tape markings to distinguish circuits. So green-taped white and green-taped black are simply Green Circuit, they didn't become grounds because that's not allowed.

For now, recover with GFCI receps everywhere.

Can't use blue as neutral. No remarking is ever allowed on anything #6 or smaller except neutral to hot, and even then only in cable (not EMT). To spare the wire you've already laid, wire it as a Multi-wire branch circuit (MWBC) sharing neutral. Cap off the blue wire.

People always pooh-pooh "just putting a GFCI recep at every recep". That's understandable since it entirely wastes the GFCI downline protection feature. However, let me make the case for it.

  • It plays well with MWBCs.
  • It assures a GFCI trip at one socket doesn't waylay the whole circuit. Think about this when wiring a bathroom light - you don't want a GFCI trip killing the light.
  • Nobody ever has trouble finding the reset.
  • It eliminates the Code violation from failing to apply the "GFCI Protected" labeling, which you're requires to apply, but 99% of people refuse to. (or tear it off because the provided blue stickers are "ugly").
  • It means never getting written up for no GFCI protection and having to argue with the inspector about the GFCI actually existing upstream (and the inspector is correct because the sticker is missing!)
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  • Thank you! @Ecnerwal suggested MWBC but I didn’t understand it. Been reading and think I do now: In each box, I can put Black into outlet A, Red into outlet B, bond all neutrals and bond all grounds (box chassis and outlets) and repeat for all receptacle boxes downstream. Since Black & Red are 180 degrees out of phase, I’d never have more than 20A returning on the neutral. Pulling 20A on each circuit yields 0A on Neutral because they cancel each other out. And GFCIs keep “me” from becoming ground if the neutral breaks. 2-Pole breaker IS necessary - correct? Thank you! Dec 19 '20 at 22:47
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    @riffin-rich Yes, you have it!! 2 handle-tied breakers will suffice if there are no 240V loads on the MWBC, but a 2-pole is the easiest to acquire. Neutrals need to be pigtailed anywhere shared, because neutral can't be dependent on a device being present. (severing neutral would give imbalance current nowhere to go, sending one leg above 120V and the other below.) Dec 19 '20 at 23:15
  • I’ve drawn-up another pic — will upload it momentarily ... hoping for confirmation to ensure I’ve got all the details correctly. Thanks again! Rich Dec 20 '20 at 1:49
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Don't bond the neutrals from the two circuits in the boxes. Treat them as two entirely separate circuits (because they are). This way if one neutral breaks the circuit stops working and you don't overload the one neutral wire with loads from both circuits. You probably wouldn't be able to get the GFCIs working right anyway if the neutrals on the two circuits were connected downstream.

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  • Thank you very much. I can’t upvote you because I’m too new. I’m typing this note so you know I tried to thank you by upvoting but couldn’t because I got a dreaded new guy rejection: “Thanks for the feedback! Votes cast by those with less than 15 reputation are recorded, but do not change the publicly displayed post score.“ Thanks again! Dec 19 '20 at 2:20

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