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I have a four-gang box that I'm installing new dimmers in. Currently all of the neutral (white) wires coming into the box are connected together (and not to the dimmers). The new dimmers require connections to the neutrals.

There are three bundles of wires coming into the box, two of them having their own triads of hot, neutral, and ground. The third bundle has two triads of hot, neutral, and ground wires.

Schematic of junction box

In this third bundle, it's unclear which neutral is paired with which hot. Does this matter when connecting my new dimmer or can the dimmer be connected to any random pair of neutral and hot wires?

  • 1
    If there are multiple circuits, it would matter if the circuits were protected by GFCI or AFCI devices. – Tester101 Aug 28 '14 at 16:48
  • Are there different circuits in the box, or is it all one circuit? In other words. If you turn off one breaker, does it kill power to the box, or do you have to turn off multiple breakers? – Tester101 Aug 28 '14 at 16:54
  • @Tester101, One breaker kills power to the box. – drs Aug 28 '14 at 16:57
  • @Tester101, are GFCI or AFCI devices ever used for ceiling lights? – drs Aug 28 '14 at 16:58
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    If it's a single circuit, it shouldn't matter. There should be one hot and one neutral bringing power to the box, and everything else branches off of that. – Tester101 Aug 28 '14 at 17:01
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This is a single circuit, and the neutral is common to all branches of this circuit. In this case, all neutral wires in this box must be connected together.

Similarly (and this is regardless of single or multiple circuits/breakers) all grounds must be connected to each other, as well as to the box itself.


In the case of your switches, they simply need a neutral to operate the electronics in the switch itself. All you need to do is wire the neutral to each switch. You'll probably have to add pigtails, and probably additional wire nuts (purely for convenience).

Just to illustrate, using your schematic, I added the neutral lines (my changes highlighted in yellow):

enter image description here

The number and placement of wire nuts is not important, other than you need to pay attention to the number and size of wires when choosing wire nuts (they have a rating that will say how many wires of a given gauge they support).

2

All of the neutral wires that are connected together should belong to a single circuit.

You can generally tell if it is a single circuit if you only have to turn off 1 breaker.

If this is the case, then you should keep all the neutrals together.

If it is not the case, then you should isolate the neutrals that belong to a different circuit.

To connect a dimmer that requires a neutral, you would pigtail the hot and the neutral to the hot and neutral of the dimmer.

It doesn't matter which pair of neutrals and hots you use as long as they belong together on the same circuit.

enter image description here

  • If the breaker your turning off is a 2 pole breaker or one with a tie bar you have a multi wire circuit the neutrals that are all tied together (as long as there is only one group) you can take a pigtail from the group and connect it to the neutrals on the switches. Be sure that the hots and switch legs stay with their respective switches. Always turn the breaker off and check for voltage with at least a non contact voltage tester that you have checked on a live circuit before working in the box. – user24125 Aug 29 '14 at 5:23
  • I've updated the question to clarify what I'm asking. I want to wire up new dimmers that use the neutral wires and am wondering if it matters which pair of hot and neutral wires are connected to the same dimmer. Currently all the neutrals are tied together. – drs Aug 29 '14 at 13:08
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If all the hots are currently (no pun intended) tied together, and all the grounds are also currently tied together, and if one breaker shuts off everything in the box, then that's a simple branch circuit with two "twig circuits" (my own term, don't bother looking it up on Wikipedia). In such a case, all the neutrals in that box will still need to be tied together or you'll lose power to something else, probably nearby.

  • I've updated the question to clarify what I'm asking. I want to wire up new dimmers that use the neutral wires and am wondering if it matters which pair of hot and neutral wires are connected to the same dimmer. Currently all the neutrals are tied together. – drs Aug 29 '14 at 13:08
  • OK, that sounds (without a picture or sketch) like two individual circuits that share a neutral. The two circuits might originate at different breakers, or they might originate at the same breaker. The best idea is to find out which circuit controls what else around that area, and tap (for your dimmer) from the one that makes the most sense. Since your neutrals are all common, you're probably fine to just add your dimmer's neutral to the same bundle. It'd be a good idea to verify that whole neutral situation, though, to be sure it's "right". – TDHofstetter Aug 29 '14 at 15:26
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The real question you should be asking; is how to hook up your new dimmers.

You will have to add the neutrals for each of the new dimmers to the neutrals that are already there.

If you are using wire nuts and you have more than 4 wires to connect you will have to daisy chain to more than one wire nut. To do this you take three of the wires and an additional length of white wire in one nut. Then if you have more than three more wires to add you take two of them in addition to the previous length of wire, and another length of wire in a wire nut. When you get down to the last few wires just take the last length of wire and wire nut them together.

( It could be easier if your dimmers had "screw and clamp" connections; which is doubtful. )

You could wire it differently than I said above as long as all of the neutrals are connected together.

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Firstly, I am going to assume that the original wiring was done by a licensed electrician. So called common wires (or neutral if you prefer) simply completes the circuit back to the panel. If multiple circuits are going to a box all the grounds would be bound together, but the commons would be on a separate circuit so it sounds like you have just one circuit. In your question you have used the word dimmers in the plural. If this is on the same light you can't do that unless you are using a special set of dimmers designed to communicate electronically together and would come as a set with directions. So I'll assume that the dimmers are controlling one light each and therefore are a single pole light dimmer. The common white wire NEVER gets connected to a single pole switch. Because there is no 3/1 cable (red, white and black wire with a ground) I am eliminating the possibility that you are dealing with a 3 way switch because at least one 3/1 cable is required unless your house is conduit which is usually wired with all black hots and tape markers. 3-way switches, which are used when there is one other location that you can turn the light on from, have many possibilities as to how they are wired depending on where the live hot wire is located i.e. the one that is always hot and leads directly back to the breaker panel. If there is a 3-way circuit you should hire an electrician as they're tricky when you haven't done them before. However, single pole switches under current electrical code are simple because they must be wired in line with the hot wire so the hot wire in is the black wire coming from the panel and the hot wire out goes to the light. The only time that a switch should be connected to a white wire is if the wires are a switch leg which only occurs when the power goes directly to the box that the light fixture is attached to and the switch leg runs down to the single pole switch as a two wire bundle one white and one black. If this were the case both wires would be connected to black at the light box and the white wire should be recoded by either black tape or permanent marker for the last two inches at each end. So I think that the answer to your question is ignore the white wires and determine which hot wire goes to your light and which hot wire goes to the breaker panel and connect each to the appropriate screw on the switch. Don't forget to connect the ground wire to the switch again assuming that this is plastic sheathed wire (NM or non-metallic) and plastic boxes. Metal conduit wiring is grounded through the switch body and it is perfectly kosher to bring NM wire to metal box with the proper cable clamp and then connect the ground to the box with a screw. Then all devices would be grounded through their body.

  • 1
    your answer doesn't address the question: the dimmers require a neutral, but you don't address how to connect them. – longneck Nov 11 '14 at 17:39

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