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I have a 15 amp branch circuit where the first box from the breaker contains a switch for a ceiling light at the door leading to the garage. This box supplies the rest of the branch. On the same branch at the opposite corner of the room I am adding trailer circuits for multipoint switches located at each entry point to the room to control new recessed lighting fixturesenter image description here. These trailer wires end back at the garage door where I am replacing the first box with a multi gang box. This box will now contain the switch for the existing ceiling fixture, feed the rest of the branch, and also be the end point for the trailer wires where they connect to the load through the final S3 in each chain. This ends up making a big loop with sub branches branching off in the middle. I have included a diagram for clarity. The question is, how do I handle the neutral and ground connections in this box (Multi gang box combining B1 and B5). I am inclined to wire the neutrals and grounds as if they were still in separate boxes but everything I've looked at seems to indicate I should wire all the neutrals together and all the grounds together. Does anybody know the correct approach?

  • Are the grounds and neutrals connected in the first box (B1/B5)? If so, connecting the neutrals at B3 creates a loop. Is it possible to feed the "additional receptacles" directly from B2, instead of feeding through B3? – Tester101 Mar 24 '15 at 10:56
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What you will want to do in your case, instead of nutting all the neutrals together (which is technically a 310.10(H) violation!), is keep the neutral from the breaker at B1 and going to B2 and the existing light fixture separate from the neutrals coming in from B4 and going out to the two recessed-light circuits -- in other words, B1 and B5's neutrals are separate. Also, in boxes B4 and B5, keep the neutrals separated from each other as per Tester101's revised illustration -- again, NEC 310.10(H) applies.

One other tip -- the power feed to all the lights should come from the unswitched hot in B3. Otherwise, you wind up having to return the switched hots for the two four-way loops back through B4 and B5 from B3, leaving you without a neutral wire in those cables unless you switched the 14/3 for those runs out for 14/4. Using the netural from the three-way loop isn't an option because it'd create a large, annoying current loop that could interfere with the operation of timer or electronic switches that require the neutral at the switch box.

  • Thanks Three Phase, saw this post after I responded to the above. Yes, the power to the new lights is coming from the unswitched hot in B3, sorry I didn't make that clear. I am going to follow these suggestions and also add a divider in the B1/B5 ganged box to physically separate the two neutral/ground isolated feeds to avoid confusion for the next guy working on the wiring. Thanks for your help! – DYI Watts Mar 25 '15 at 15:53
  • One final question. Most of the discussion has been with a loop caused in the neutral wires, does the same issue apply to the grounds? I'm thinking the grounds can be tied together without problem since in normal operation these would not be carrying current (unless a fault exists) and therefor would not see the voltage potential differences that would occur with the neutrals. Thoughts? – DYI Watts Mar 25 '15 at 16:08
  • @DYIWatts -- I'd run the EGCs (ground wires) the same way as the neutrals to keep stray coupling to the EGCs down, although 310.10(H) does not appear to apply to equipment ground conductors for some reason? Also, are your boxes metal or plastic? – ThreePhaseEel Mar 25 '15 at 22:17
  • I'm using plastic boxes, same as existing wiring. Isolating the ground wires in the box would be more difficult since they are bare wires. I guess I could add dividers in all the gang boxes but seems like over kill. What is standard practice / code for handling multiple 3x/4x circuits in gang boxes? – DYI Watts Mar 26 '15 at 15:29
  • @DYIWatts -- plastic boxes make this easy, simply pigtail each ground off to its individual device. – ThreePhaseEel Mar 26 '15 at 22:08
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I'm guessing your wiring looks something like this.

Wiring Diagram

So if you also draw the grounded (neutral) conductors, it looks something like this.

enter image description here

Drawing it like this you can clearly see, if you connect the grounded (neutral) conductors in box 5 (B5) to the grounded (neutral) in box 1 (B1), you'll have a giant loop.

It shouldn't cause any problems, electrically speaking. Your electrons will just be able to take different routes back home. However, as ThreePhaseEel points out, paralleling conductors in this way would be a code violation. To avoid paralleled conductors, you should wire the circuit as shown in the second image above. Notice that the grounded (neutral) conductors are kept separate from box B3 on.

  • Thanks, this is exactly what I have and the loop created by the connection between B1 and B5 was my concern. If I left box B1 and B5 separate there would be no question, very straight forward. But for a clean appearance I wanted one box with a 3 switch face plate so I combined into one 3 gang box. I have connected the neutrals together with one wire, same for grounds so I can remove the connection easily if that turns out to be the best solution. I have it wired up now and all is working. Will the loop cause any problems? I know it can be a noise issue with audio/vidio, thoughts? – DYI Watts Mar 24 '15 at 16:46
  • I don't think it really matters. If it were me, I'd probably not connect it. Though not doing it may cause confusion later, if somebody else was poking around in the box. If you look at the diagram, you have loops between boxes B3-B4 and B4-B5 too. – Tester101 Mar 24 '15 at 16:57
  • @Tester101 -- technically, a looped neutral violates 310.10(H) on paralleling of conductors... – ThreePhaseEel Mar 24 '15 at 22:02
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    Tester, Three Phase, thanks for your comments. I was not comfortable with either approach, leaving neutrals and grounds connected due to the loop issue, and isolating in the same box due to confusion possibly caused down the line. I believe I came up with a solution that solves both. I can put a divider in the box and write "grounds/neutrals isolated to avoid loop" with sharpie on the divider. This solves both problems, removes the loop, and avoids confusion down the road. Thanks to all for your inputs! – DYI Watts Mar 25 '15 at 15:45
  • @DYIWatts Don't forget to keep the grounds and neutrals separate in B4 and B5 as well. – Tester101 Mar 25 '15 at 15:48
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All fed from one breaker... all neutrals together, all grounds together. That's how I was taught.

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