Odd 3 Way Smart Switch Wiring


(Mark) #1

I am working on installing a 3 way smart switch, but the wiring in my house has me very confused as to how they wired it. My house is only 2 years old.

I have a single box, with one 4 wire romex coming in (black, red, white, bare). I was assuming this is the add on switch due to having only one incoming wiring, however, when I used my multi meter to test, this has the live power coming into it (black wire). I’m not really sure how the circuit works like this?

In the second box, I have the same 4 wire romex coming in, however the black wire is hooked a bundle of wire, and isn’t used in this circuit. The red and white wires (travelers are used), and the black wire is connected to a 3 wire romex (white, black, bare), which I assume is going to the light fixtures. The white wire here appears to be used as a neutral and is connected to another bundle of wires.

From what I can tell, I have a line-switch switch load configuration, but they have used one run of 4 wire romex vs 2 runs of wires to complete this.

I realize the first box doesn’t have a common wire, however, I do have very easy access to an outlet on this circuit that I think I can get a common wire from.

Can anyone help me confirm if my review of the wiring configuration is correct?


(Tony Fleisher) #2

Your explanation of the second box is a bit confusing. The black wire is either used or not used…it can’t be both. Perhaps some pictures or diagrams would help.


(Bryan) #3

This part makes sense as a switch on the end of a run. I’d expect the black conduct of the 3-wire to be hot if the light is one. Also, either the red or the white (possibly with black tape wrapped on it) should be hot at any given time (one or the other). What happens is that power to the light is fed via the black connected to either the red or the white based upon the switch position.

If the light was off and the black was hot, then I’m not sure. Pictures will help so that we can see which terminals the wires are connected to. I couldn’t make any sense of the 2nd box you described, particularly without switch connection descriptions.

Also, just so you don’t confuse others in further describing, don’t count the bare (ground) as a “wire”. Romex with a white, black, red and bare is a 3-wire.


(MarkTr) #4

Based on your description, this is pretty straightforward 3-way wiring per this diagram (my 2010 new construction home is wired the same way). If you’re not confident in your understanding from this explanation, you may want to hire an electrician.

Correct, this is where you will install the add-on. In the “dumb” configuration, the black wire is hot, and sends current back over either the red or white wire depending on the position of the switch.

There are three romex cables you need to worry about in this box: line in (2-wire, connected to your big line and neutral wire nut bundles), 3-way switch (3-wire, connected to line and switch), and light (2-wire, connected to neutral and switch). You also have one or more additional outlet circuits connected to line in - since you’re going to leave these connected, it doesn’t actually matter which is line and which is another branch.

If you’re using GE switches, your master switch goes in this box. Disconnect the black wire of the 3-wire bundle and cap it with a wire nut. Connect the switch’s line and neutral to the appropriate big bundles. You may need to make a short jumper to connect line to the wire nut, since the old switch didn’t connect there, but if you only have two wires to join to the switch (line and outlet) you can just insert both into the switch. The light gets connected to the switch’s load. Red from the add-on goes to the Traveler port and white goes to the neutral bundle.

In the add-on switch box, connect white and red to neutral and traveler respectively, and cap the black wire with a wire nut.


(Mark) #5

That is a perfect explanation, thanks mark!!