I went to install 3 caseta luton dimmer switches in my bathroom, and found that I don’t understand the existing wiring which has a bank of 4 switches.

There are two dimmers and two on/off switches.

  1. dimmer - controls a bank of overhead LED lights
  2. dimmer - controls a second bank of overhead LED lights
  3. on/off switch controls pendant lights over bathtub
  4. on/off switch controls a fan over shower (that I don't want to touch)

I want to install the dimmers in #1-3, and leave the on/off for the fan alone. The issue is that their doesn’t seem to be any ground wires attached to the existing switches. The lutron dimmers are very simple, one green wire for ground and two black wires that usually connect to either existing wire, but the existing set up is confusing.

I’m hoping that someone might be able to clear this up for me. I’ve added two photos with description.

  1. is a Leviton P2W for first bank of overhead LED lights. Red wire (a) goes into the box, 2nd red wire (b) is dead (tag says use for 3-way switches), green wire (c) for ground? is cut off, black wire (d) is connected to black wire in #2 and #3 with orange connector (e)

  2. is a Leviton P2W for 2nd bank of overhead LED lights. Red wire (f1) connects to black wire (f3) with orange connector (f2), then goes into box. 2nd red (below picture) is dead like #1. black wire (g) is joined with orange connector (e) to black wire from #1, and black wire from #3.

  3. is a leviton on/off switch for pendant lights over bath tub. the black wire (h) goes to box, black wire on lower screw (i) goes to orange connector with #1 & #3, and 3rd black wire (j) comes from middle of switch, and goes to the middle of #4 switch.

  4. (see second photo) is a leviton on/off switch for the fan over the shower. black wire on top (k) screw goes to box, two black wires (L) on bottom screw, both go into box, 4th black wire (m) goes from middle of switch and connects to middle of switch on #3.

Overview of existing bathroom switches

insert of #4 switch that I don't want to change

2 Answers 2


OK, here goes:

What you have now

The power from the panel seems to come in in the middle of the bottom of the box. That black wire is always hot, and is connected to all of your switches via the orange nut you labeled e, which connects wires d, g, i. i connects to j via switch 3, and j (which is the same as m) connects to the always-hot (k) via switch #4. You shouldn't use the side screws and the backstabs at the same time (you shouldn't use the backstabs at all), especially since it looks like those screw terminals will accept two wires each.

a, f1 (f3), L, and h all look to be switched-hot, and will only be powered when the corresponding switch is in the 'on' position. L is a little troublesome since you said it only controls 1 fan, yet there seems to be 2 wires there. A clearer picture of switch 4 might help.

What you need for the new dimmers

Essentially, keep what you have. Each switch gets wired to the always-hot via a black wire. You can run a pigtail from each switch and nut them all together with the always-hot, or daisy chain the always-hot from one switch to the next. A lot of switches and dimmers come with pigtails already, so that's probably the easiest. If you do daisy chain, use the screw terminal for both wires, unlike how it's wired now.

All of your neutrals (white) get nutted together. There's a big bundle of neutrals already nutted together in the back of the box. Your new switches may require a neutral, in which case you'll need to tap into that big bundle. Given that there's already 5 wires in that nut, you'll probably have to separate it into 2 or more bundles and pigtail them to each other. Or use some large (8-port) push connectors instead of wire nuts. If your new switches don't require a neutral, leave that big bundle alone.

All of the grounds get nutted together as well. It looks like none of the switches currently has a ground attached (which is a no-no), so you'll need to add pigtails for those, and bundle them all together. Make sure at least one pigtail remains attached to the metal box, as well. Looks like you could pigtail the grounds for all 4 switches together with a pigtail to one of the screws on the box behind switch 4, as the rest of the grounds seem to be attached to the box already.

Finally, your switched-hots (a, h, f3, L) need to be connected. Get some electrical tape, and tape those wires with red or blue (or something other than white or green), so you can easily identify them in the future. Attach each to the corresponding switch. If there are multiple wires, use a pigtail and wirenut, or put both into the screw terminal (if the terminal supports it).

  • Thanks for the great feedback! So, what I did was connect the first three Lutron Caseta dimmers (in diagram d, g, i) to connector (e) as you outlined. The jumper wire (j) from the 4th switch I didn't change, I connected to the (i) screw on #3 to connect them together, and I then connected the ground wires from all 4 switches to a single copper ground cable and connected it to the back of the metal box. This all worked perfectly. Thanks again for the advice!
    – Walt
    Oct 25, 2017 at 13:15

We gotta do something about that mess

There's no way to avoid the fact that this many wires will be a huge mess in this box. It's already a huge mess and efforts were made to keep it neat.

Your #1 problem is just what you're running into - wires are not well-marked. You've done yourself a huge favor by identifying everything before you tore it all apart. But now let's mark every single wire before we go any further. Get some colored tape.

Color coding

Wires themselves are color-coded thusly.

  • Green for ground (mandatory)
  • White or gray for neutral (mandatory).
  • Hot - any other color. It's convenient to use black for always-hot, or a second color if you have 2 circuits in there, which mercifully you do not.

Wires can also be marked with black or colored tape. If a wire is a hot color, marking it with tape is only an identifier. If in cable, marking a neutral with a hot color makes it a hot. This probably won't come up in your case, just don't do that. Putting white, gray or green on a hot colored wire does NOT make it a neutral or ground (unless the wire is quite large, like #00 or larger). So feel free to use white or green to mark a hot.

Anytime you mark a wire, take the time to mark it on both ends - otherwise you'll lose your mind later.

Mark those hots

This is what's really happening. Notice it's fairly straightforward when you untangle the wires.

enter image description here

Right now, you have supply coming in, and 4 loads going out. Supply neutral is simply nutted with the 4 load neutrals in a big 5-bundle. Grounds all go to those plentiful and convenient ground screws in the back of the box - you'll be adding more to those, as many of your switches will want ground and some will NEED ground. The screws that hold it down, are not good enough as a ground path.

Then your supply "hot" goes to every single switch. It looks like in some cases, like #3, it uses both a screw and a backstab to make the connections. The screw-backstab are connected together internally. If you have a non-contact voltage tester (or a contact one), this will be the terminal that is always hot, even when all the switches are off. This is the same wire. I recommend you color-code this one black. Which it already is in most cases. Mark it with black tape otherwise. Be very clear which cable this comes from, I would even go ahead and mark the black wire with black tape to make it clear.

Then, off each switch, is a "switched-hot" wire going to the load. This is the one you want to carefully mark. This wire is only energized when the switch for that load is on. I want you to use your colored electrical tape to mark every single one of them something other than black. When you get pigtails on the switches, mark them too. Now it looks like this

enter image description here

Every single wire has a color, and the color matches its purpose.

This is the key to not losing your mind in a box like this.

Adding those smart switches

It's going to get more messy with the smart switches. Some of them will need neutral. That neutral bundle already has 5 wires in it, we'll ned to add one more - a short pigtail, maybe 6" or so. That pigtail will go to another new wirenut which will take all the neutrals from the smart switches. You can get special connectors designed to take as many as 8 wires, if you can't get 6 in a wire nut.

The smart switches may also dangle unused pigtails, but you're familiar with that.

End up looking like this

enter image description here

  • As this is a metal box, you won't need the ground wires. Oct 26, 2017 at 20:26
  • @JoelSpolsky yes you will. The metal box only grounds the switch yoke if a) you remove the little paper squares which capture the screws, and b) the switch yoke is able to bottom out hard on the metal box without paint, rust or schmutz getting in the way. In this case, the drywall is proud of the box, so the yoke's drywall ears will catch and prevent them from bottoming. The screws themselves are not a valid ground path. Oct 26, 2017 at 20:37
  • Thanks Harper. I had already followed @mmathis suggestions before you had posted, but I very much appreciate the time you took with your suggestions. I was wondering if there was anything incorrect with what they had suggested, and if you think I need to open it back up and make changes? thanks Walt
    – Walt
    Nov 1, 2017 at 22:00
  • 2
    @Walt his stuff looked ok, honestly I didn't look THAT close, the alphabet soup was giving me a headache, and I thought trying to painstakingly distinguish every wire was too error-prone and not a good approach. I'm really into my colored tape :) Nov 2, 2017 at 3:01
  • Much clearer than my answer, +1!
    – mmathis
    Nov 3, 2017 at 14:20

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