Can multiple z-wave and non-z-wave switches share a neutral in a 2 or 3 gang box?


#1

I am building a house, and I am trying to see if I can start out with z-wave and home automation. My electrician hasn’t ever installed any z-wave switches, and after watching a video on how to install a z-wave GE 12724 dimmer he said, “Well what happens when I have a 2 or 3 gang box and all of the switches share the same neutral?”

I am not sure I even understand his question, but It seems he isn’t sure how things will work if he has a mult-gang box with multiple z-wave dimmers, or some z-wave, some traditional. Can anyone give me feedback for him?

Thanks,
Lani


(Michael Stroh) #2

I connected the neutrals switch to switch and the last one in the line to the wire in the box. The GE switches I bought had two holes on the back for each screw on the side so it was pretty easy.

I am NOT an electrician, I don’t know if this is right or wrong but it worked without a problem in my setup.


#3

I believe it is fine, the Neutral is just powering the Z-Wave Switch’s other functions…

I can atleast say that I have 2 Z-Waves in a gangbox, and both share the same Neutral. No issues, one is a of/off switch for the light, and the other is the smart fan control for the fan. Works great.

I’ve seen others wire up 4 in a gangbox just all jumping off the one neutral.


#4

@stroh interesting, i didn’t think of doing that… I wonder if that is proper… it would surely make me stuffing 4 wires into a nut atleast easier. (as i wouldn’t have to doing it with your way. :stuck_out_tongue:)

Anybody know if that is proper?


(Bobby) #5

Have 4 switches in one box they all share the same neutral and hot (installed by a professional, after having similar concerns)


(Eric) #6

Look at it this way, the neutrals are usually tied to ground in the breakerbox, which is ALMOST the same thing as tying them together in the switchbox.

Neutrals are all the same neutral voltage, wiring them together and adding a fat pigtail to wirenut back to breakerbox is typical. If you can get all the device neutrals and the return neutral on one big wirenut then that is also fine.

I am not an electrician. I’m an EE so I can argue with supreme confidence leading to certain doom.


(Guillaume G) #7

I installed a Z-wave switch today in a 4-switch box and I had the same concern. I initially followed carefully the instructions and separated the neutral of the Z-wave switch from the other neutral wires, and I ended up with “funny results”. I then changed the set up and tied all the neutral wires together (non Z-wave and Z-wave) and it worked like a charm. I think you only need to separate the neutrals if you have more than one hot line coming into your box.


#8

I can’t speak to the initial question (I don’t comment on specific wiring just from verbal descriptions), but I’m really glad you brought this up. Having only one gang box doesn’t necessarily mean there’s only one hotline. Some people have an estheticissue about limiting the number of holes in the wall and they will put multiple separate circuits into one box. This makes the wiring more complicated.

So before starting any project, always photograph the existing wiring, including the screw connections. And test every segment of every line so you know exactly what it’s doing.

People do all kinds of random things, and US code generally does not mandate wire colors. US code also allows for striping, which is putting a bit of color tape on the on the end of a wire, and it won’t necessarily be the end you’re working with. :scream:

So don’t guess, don’t just follow wire colors, don’t just follow a diagram on the Internet. Test the circuits in front of you. It’s the only way to be sure.


(Guillaume G) #9

I couldn’t agree more JDRoberts! I happen to have many of those 4 gang boxes in my house, sometimes with one hot wire, sometimes with two. I just take my time, follow and test every wire to identify the cabling.

On a slightly different - but related topic- has anyone tried to install a Z-wave outlet as a replacement of an outlet that is mounted in series with another couple of outlets? If the outlet you are trying to replace with the Z-wave one is not the last one in the series, there are actually 4 wires instead of 2 and with my limited knowledge about home electricity, I decided to go another route (i.e. purchase a plug in smart outlet). But I’m curious if there is a way to do what I initially attempted?


#11

You can tie all neutrals that are returning to the same breaker together. If any neutrals are going to a separate breaker, they need to be kept separate.

You should have only one breaker in a gang, but sometimes you’ll find separate breakers run to one box.


(Eric) #12

Neutrals don’t wire to the breaker. For typical residential service. They ALL wire to the neutral bus bar which is a solid block of aluminum/whatever, with screw-held hole terminals for neutrals and grounds. Breakers interrupt the individual hot lines. You can see the neutral bar inside the breaker panel under the cover.

I dunno, all my houses are not fresh, so new breaker panels could be different. I don’t think so.


(Ray) #13

Just to clarify about neutral. @Michael_D is correct. You CANNOT tie two separate circuit breaker neutrals together unless it’s a double-pole breaker that supplied opposite line phases.

The problems with tying separate circuit breaker neutrals together are -
if of one of circuit neutral is loose. You now have 30amps returning with a single neutral that is rated for 15amps.

GFCI/AFCI plugs will detect an imbalance on the current that’s passing via the neutral and hot and will trip.
There could also be a current loop effects causing EMI and heating metal.
But it’s not a code violation to have two line hot in a single gangbox.


#14

Yeah my wording is misleading. They don’t physically return to the breaker but it helps to think of every circuit as completely separate


(Eric) #15

I appreciate your explanation - I have to relearn this every time BEFORE my house burns down. Good thing I’m not an electrician but then again I would know the NEC


(BrianP) #16

Outstanding post/advice. Just last night I wired up a few Linear WD500Z-1 dimmer units in a 3-gang box with 1 toggle and 1 fan control. Everything worked as expected (or so I thought). When I finished my work, I flipped the breaker back on only to discover a second AFCI breaker tripping. Puzzled by this as I had triple-checked all my wiring.

Slept on it overnight and then worked on it again this morning. Discovered that there are indeed 2 breakers feeding this single gang box. 15 amp for the toggle + fan, 15 amp for the dimmer switch. As a result, there were in fact 2 neutral bundles in the back of the gang box. I traced the line wire from my z-wave dimmer to the back of the gang box and located the neutral that was coming in with that hot wire. That neutral went to the other neutral bundle… not the one I had connected the z-wave neutral wire to. So, I moved the z-wave neutral to the other neutral bundle and voila, the circuits were connected properly, thus the AFCI breakers were no longer tripped.

I post this detail in the hopes it helps someone else out.

This post saved me countless hours of debugging.

Thank you.
Brian


(Pundit Sharp) #17

I had exactly this scenario today - 2 z-wave switches together in the same box, the two switches are on separate breakers.

At first I had an issue with one of the switches in the box - it’s an auxiliary switch and it wasn’t operating at all. The gang box has two neutral bundles in - which seems reasonable because of the separate breakers When I connected the aux switch to the other neutral bundle, it started working, yay.

Here’s where thing get confusing now - the other switch in the box had been previously connected and working fine, supposedly with the “wrong” neutral being used. After I swapped the neutrals and bundled everything back together, the second switch stopped working and smelled like the magic smoke that makes electronics work properly, if you get my drift. So now I have a permanently fried switch, and a doubt in my mind as to why it fried:

  • Could the neutral I connected it to have caused it to fry?
  • Or as I was squeezing it back into the box, did something perhaps short behind it and cause it to fry?

Any thoughts?


(Ray) #18

Just a little confused. Are both addon switches? I am assuming the master switch was working and you couldn’t get the addon switch from another circuit but in the same gangbox to work. By using the neutral of the master switch. The addon started to work.
You realized the master was using the wrong neutral and fried it by bring it to the right neutral bundle?
I don’t think using the wrong neutral will fried your switch but more likely it’s not a neutral bundle your are connecting that switch to. Possible wire came undone/shorted as you described above.


(Pundit Sharp) #19

You have it pretty much spot on. Two switches, one master and one add-on that belong to separate circuits. Master had been installed earlier and was working fine. The add-on wasn’t working properly until I swapped the neutral bundles that the master and add-on were connected to. Then the add-on started working, but when I turned the power back on to the master switch, something happened and it got fried.

I guess it’s just one of those unfortunate things. Space is pretty tight in the gang box, so I perhaps something touched somewhere it shouldn’t have when stuffing it all back in.


(Pundit Sharp) #20

Sooooo…my replacement switch arrived on Tuesday and I had some time yesterday afternoon to look at things.

It turned out what I thought was the second neutral bundle wasn’t actually one (good call there @Navat604). For the aux switch it appeared like a neutral, but for the master switch on the other circuit, the potential difference between it and the line of the circuit was 240V…no wonder the switch curled up and died!

Lesson learned, check the voltage difference on every wire BEFORE you connect it up. :fearful: