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I have a 3-gang plastic box with six conductors that enter the box; three line-side, three load-side, and they pass through the three switches in pairs of two.

The load-side wires are all on the same branch circuit, and they all come from a common split point in another junction box upstream where all of the wires for H/N/G are tied together respectively.

To avoid confusion, they split, then they have routing to different boxes and then they all eventually meet up in this box again because of the involvement of 3-way switches.

The question: Am I required to connect all six incoming ground wires to each other in that 3-gang box, or can I make three pigtails on three wire nuts and connect each ground-in to it's respective ground-out with a pigtail for that pairing's respective switch's terminal in the same way I would if I had installed three separate 1-gang boxes next to each other instead of a single 3-gang box?

Whatever the answer for grounds is, does this also hold true for the neutral wires? Are multiple connected pairs of neutral wires acceptable in a multi-gang box on the same circuit?

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  • simple yes .....
    – Traveler
    Mar 15 at 0:16
  • 1
    the 3 neutral runs in the 3-gang box must be kept separate (see my answer), so tie them only pairwise in/out.
    – P2000
    Mar 15 at 5:15

3 Answers 3

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I'm a bit confused about the question. The basic rule is that inside any particular box all the grounds must be physically connected together. That can be "all in one wire nut" or "all in one Wago". That can also be "2 plus a pigtail in one wire nut" + "2 plus a pigtail in another wire nut" with that pigtail going between them. Or a number of other possibilities. Just think of it as: If every cable was chopped off right outside the box, would the ground wires sticking out of each cable outside the box all be electrically connected? If the answer is Yes, you're all set. If the answer is No, fix it.

Note the word electrically. If you have a metal box then the wires can connect (and at least one must connect) to the box itself. That box then extends ground to switch yokes and to self-grounding receptacle yokes. Which can significantly cut down on the number of ground wires needed.

To take it a step further, if you have metal conduit connecting a metal box to the panel (possibly with other metal boxes in between) then you don't even need ground wires! But wherever you do need ground wires - e.g., a non-metallic cable leaving one of the boxes to go elsewhere - the ground in that cable just has to connect to the box.

As far as neutrals, the general idea is the same. Except:

  • Neutrals don't touch the metal box - that's reserved for ground.
  • If there are multiple circuits in one box then the neutrals must be kept separate by circuit.

It is quite common to have a "neutral bundle" in a large switch box because dumb switches don't need the neutral. On the other hand, in a large receptacle box the receptacles will often provide the connection for neutral between cables, as well as using the neutral themselves.

As far as how the neutrals connect together, it gets complicated. Basically the neutrals need to stay together as long as the matching hot and/or switched hot and/or traveler wires are together and separate when they are separate. That generally means that all neutrals will be together until their partner hots split. A key thing to remember is that all wires within a cable or conduit need to balance the currents.

One example: Incoming power to a switch box. Two switches in the box. The switch cables run next to each other to another box that has both light fixtures attached (don't ask why - maybe one box that has a light for the left side of the room and a light for the right side of the room and you want to switch them separately). Since each cable must have balanced currents, that means that in the first box all the neutrals are together but then they split so that each switch cable has a switched hot (black wire connected to the switch) and a neutral (connected to the neutral bundle). In the light fixture box the neutrals must stay separate and each neutral must match the switched hot that is connected to a particular light fixture. But in that same light fixture box, all grounds (the two switch cables and the two light fixtures) are connected together, just like in the first switch box.

But alternatively, since the wires are following the same physical path, you could use:

  • Conduit with two switched hots and one neutral

or

  • A /3 cable with two switched hots (black and red) and one neutral

But if that same circuit split to two different light fixture boxes on opposite sides of the room (more typical) then it would be quite obvious that each one would need its own neutral and they would not be joined together because they couldn't be.

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  • 3
    It's starting to sound like short answer is "if the hots separate then the neutrals also separate." Mar 15 at 5:24
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    After re-reading through all of the answers after sleeping on this, this answer completely answers the question asked clearly and directly, without any other unnecessary information. Thanks. I'll mark this as accepted. Mar 15 at 14:32
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If spliced grounds must be connected together.

NEC 250.148 (A) Connections and Splices. All equipment grounding conductors that are spliced or terminated within the box shall be connected together. Connections and splices shall be made in accordance with 110.14(B) and 250.8 except that insulation shall not be required.

Neutrals need to be kept separate. There may be a direct reference, but these reach the conclusion.

200.4 Neutral Conductors. Neutral conductors shall be installed in accordance with 200.4(A) and (B).

(A) Installation. Neutral conductors shall not be used for more than one branch circuit, for more than one multiwire branch circuit, or for more than one set of ungrounded feeder conductors unless specifically permitted elsewhere in this Code. Informational Note: See 215.4 for information on common neutrals.

(B) Multiple Circuits. Where more than one neutral conductor associated with different circuits is in an enclosure, grounded circuit conductors of each circuit shall be identified or grouped to correspond with the ungrounded circuit conductor(s) by wire markers, cable ties, or similar means in at least one location within the enclosure.

If you connect neutrals together you create "parallel conductors"

310.10(G) Conductors in Parallel. (1) General. Aluminum, copper-clad aluminum, or copper circuit conductors for each ungrounded conductor, grounded conductor, or neutral conductor shall be permitted to be connected in parallel (electrically joined at both ends) only in sizes 1/0 AWG and larger and shall be installed in accordance with 310.10(G)(2) through (G)(4).

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  • 1
    In 310.10 it refers to "grounded conductor", that is code terminology for the neutral. Mar 15 at 2:05
  • Does this mean that if I have three switches on the same branch circuit that not only do I not need to connect every neutral wire under one nut, but I actually must splice them in three separate pairs? Mar 15 at 3:12
  • what's the relevance of 310.10(G) in OP's light switch case?
    – P2000
    Mar 15 at 4:42
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    @RyanMortensen yes, the whites need to be aligned with hots/travelers Mar 15 at 7:14
  • @P2000 if he connects all the whites in last switch box he creates parallels Mar 15 at 7:17
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Neutrals have to be kept separate by circuit and by run. If the neutral run for a circuit back to the panel fails, the circuit must fail. The return current should then not be carried by another neutral wire for a different circuit, as this may overload the wire. In your case, the neutrals are eventually all tied anyway and served by the same breaker. The factor that matters here is electromagnetic radiation and magnetic induction if current and return current are separated by some distance. The tight packing of conductors in cabling avoids this, as along as all the "forward" current is in the conductor running abutted to the "return" current conductor.

Thus, the neutrals in the 3-gang box should not be tied together otherwise it unbalances the currents.

Separating the neutral from their corresponding hot through separate cabling would cause this imbalance problem. Also tying the neutral at both ends would cause the currents on both to be substantially equal and thus they could be out of balance with respect to their corresponding lives. (E.g. one live carries 1A the other 0A but the neutrals -if tied- would carry 0.5A each, thus not balancing the live each is paired with, 1A and 0.5A are not balanced and neither is 0A and 0.5A. Keeping the neutrals untied would keep the neutral of the 0A live also at 0A, and the neutral of the 1A live at 1A.

Grounds must all be tied (firmly/positively electrically connected) together and bonded to each box, to avoid current induced voltages across exposed ground wires in the same box. Untied but touching bare wires then cannot generate heat over their weak interconnection in the event of a high current discharge.

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    would the expert who downvoted kindly explain their position?
    – P2000
    Mar 15 at 0:35

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