I'm new to the DIY community. I'm currently working on changing my switches to smart switches. I've done two single poles successfully but now I have some trouble with this one.

This is my bedroom light switch. I think it's a single pole as I don't see any other switches that control the same light. But there's two black wires and one yellow wire, which confused me. Can anyone let me know what they are and how I can wire them to a smart switch? I'm using lutron smart switch that has two black wire, one green/white wire, and one bare wire. enter image description here

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  • I'm using lutron smart switch that has two black wire, one green/white wire, and one bare wire. is a bit strange in 2 ways: "two" black wires (normally one black, one red, to distinguish line vs.load) and "green/white" (green indicates ground, white indicates neutral, the switch might be "either" but we need to know). Please list the specific MODEL NUMBER of the new switch. Oct 8, 2020 at 18:17
  • 2
    Oof... a shepherd's crook and a backstab for the black wires when the switch seems to have proper side clamps. Someone worked too hard, yet too lazy all at the same time. And, great pics! Especially well done for a first post!
    – FreeMan
    Oct 8, 2020 at 18:18
  • @manassehkatz-Moving2Codidact Lutron Caseta PD-6WCL is the new switch I'll be using.
    – Elsa Lee
    Oct 9, 2020 at 5:11
  • "I'm using lutron smart switch that has two black wire, one green/white wire, and one bare wire." According to the installation guide, the PD-6WCL has only 3 wires - 2 hot/switched hot and one green ground - not green/white - and no bare ground. Please upload a picture of the new switch showing the factory-attached wires. Oct 9, 2020 at 5:22

4 Answers 4


This is the same as your other single pole switches except it has one extra black wire that is sending power to someplace else.

One black wire brings the power into the box and the other black is connected to it on the switch, this is how it is getting power and sending to where it needs to go. The yellow should be the switched power or the the wire that is sending power to the fixture when you flip the switch on.

Does your new switch require a neutral (white) to operate correctly?

If not then; Just wire it up the same. If your new switch does not have screw terminals but only wire leads then you wire all the blacks together with a wire nut. You will need to tie the ground on the new switch to the screw at the back of the box that the green wires are attached to.

  • Thank you! The new switch doesn't require a neutral wire. It has a white wire but with green sleeve. In the instruction it says if I don't have a neutral wire, I'll tie the one with green sleeve and the bare wire with the green wire from the switch box together. When I was wiring the last two single poles, I took the green wire from the screw in the switch box and tied it with the green wire and bare wire from the new switch. Do I need to redo this?
    – Elsa Lee
    Oct 8, 2020 at 18:45

North American wiring is stuck with the colors in the pre-made cables, and are not color-co---- oh, wait. This is conduit.

Your wires are color-coded.

In your case, black is always-hot. It stops here for the switch, then goes onward to other points of use. They are using the switch itself as a splice block, which you might not be able to do with a smart switch with pigtails. Get a yellow wire-nut to splice the 2 blacks with the always-hot (probably black) from the smart switch.

Yellow is switched-hot. This goes to the (typically red?) wire on the smart switch that is intended to go to the lamp. The provided wire-nut will be fine, otherwise use a yellow or orange.

You do not have neutral in this box and you will need to use a smart switch which does not require a neutral wire. There is no way to tap the white wire passing through this box. Your best route is to change up to a smart switch that does not require neutral.

If the switch's instructions say what to do if you don't have neutral, go ahead and do that. (I suspect so given a green/white wire). If it requires you to attach it to ground, you notice there are no ground WIRES to attach to. Do not tamper with ground wires in the box. Obtain a #10-32 screw (any will do, but they sell green colored screws if you like the style) and fit it in the hole to the left of the existing ground screw. Wires to be grounded can be terminated there.

No need to wire ground to the new switch. That will happen via the mounting screws to the metal box.

If you really, really, really want neutral there...

and are willing to seriously "skill up" to get it, then you can figure out the 2 boxes that white wire is going from and to... open them up and figure out which of those runs will be easier to pull... and pull a new white wire. You can use the old white wire to pull in the new -- just lash it together with electrical tape at the "head" and at least 6" along its length.

You cannot tap the white wire as-is, because each end of it must have at least 6" of free length coming into this box, as well as come 3" beyond the wall surface... so it's about 12" shorter than it needs to be.

Read more on pulling wires into conduit before diving into this, however.

  • OP said: I'm using lutron smart switch that has two black wire, one green/white wire, and one bare wire. If it really has pigtails then (a) need to find out what green/white is and (b) can't just leave the bare wire flopping around - it will inevitably short on a screw. Oct 8, 2020 at 18:18
  • @manassehkatz-Moving2Codidact Good point about the green/white wire. I'm not too worried about bare ground wires, though. They're everywhere. Oct 8, 2020 at 18:26
  • @manassehkatz-Moving2Codidact and Harper Thank you both! the green/white wire is a white one with green sleeve. In the instruction, it says if I don't have a neutral, use it as a green wire and tie it together with the bare wire from the switch and the green wire from the box. If I have a neutral wire, take off the green sleeve, and use the wire as a neutral wire. When I did the other two switches, the green wire was like this - tied to the box with a screw. But I took them out, and tied them with the green sleeved one and the bare wire from the switch. Do I need to worried about this?
    – Elsa Lee
    Oct 8, 2020 at 18:55
  • @ElsaLee -- you should have a pigtail from the screw in the box to the new junction of grounding wires Oct 9, 2020 at 0:57
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    @ElsaLee Yeah, that ground wire isn't clipped to the back as a spare. It's clipped to the back because you're required to ground the box first. So yes, put that back onto the box, and if those boxes are like this one, use the other ground screw position to ground the extra wires to the box. Otherwise you'll need to add a pigtail ground wire to the box and tie all the grounds to it. Oct 9, 2020 at 2:00

Excellent pictures! That really makes it very clear. Ignoring the green and bare grounds, which all go together:

  • Coming up from the lower conduit, you have black (hot) and white (neutral)
  • Going out the upper conduit to the light, you have black (hot), white (neutral) and yellow (switched hot).

The black hots need to stay together. You need to identify which black on the new switch is "always hot" or "line in" and connect that to these two wires with a wire nut.

The yellow wire is the switched hot on the new switch - that should be the other black. Might be called "switched" or "load".

Neutral, as is often the case, is the complicated one. The problem is that the existing neutral passes through the box without stopping. In theory, you can snip it in the middle and wire nut it to the white wire from the switch. However, you are supposed to have several inches on each wire in the box - if the white wire doesn't have excess available then you would have to replace it.

But since the wire is apparently green/white with directions to connect to ground if neutral is not available then what is actually happening is:

  • The switch needs some sort of "back to the panel to match the hot" to function. (There are alternatives but they involve batteries (which people forget to replace) or don't play well with LED lights.)
  • The amount of current needed is low enough that UL allows use of ground when neutral is not available. There is no "blanket exception", but it is permitted in limited circumstances with properly designed devices. Basically, the ground wire is assumed to carry "no current" except when there is a fault, so deliberately putting current on ground is discouraged. However, ground is a fully functioning conductor (or should be) so it works.
  • The separate bare wire (which for a switch is also "grounded by metal screws to metal box", so the bare wire is not strictly needed in your particular case) is for grounding ESD and other safety issues. It is not the "return path for the current used by the switch electronics", even though in your case (connecting green/white to ground) it will actually go to the same place.

All in all, a strange, but sanctioned, work-around to the problem of "no neutral in the switch box", or in your case "neutral but not easily usable".

So follow the directions of green/white to a ground screw in the back of the box. Don't use the existing screw as it already has two grounds on it.

  • Thank you so much! The new switch does not require a neutral wire. I suppose I can just ignore the neutral wire here?
    – Elsa Lee
    Oct 8, 2020 at 18:48

I had the same switch wiring as you. To make it simple, the Yellow will go to LOAD and the 2 Black wires will go to LINE in your new smart switch or timer.

  • This answer does not explain anything the other answers did not Nov 15, 2021 at 2:37

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