3-way wiring for smart switch


I’m trying to replace my existing 3-way switches with smart switches. My current setting is line-switch-switch-load with the neutral only connected to light. If I try to replace the second switch (connected with load) with a smart switch, should I do the following?

  1. Disconnect the line cable from first 3-way switch.
  2. Pull a line cable to the smart switch from supply. I do see hot line in the box of this second switch, but it is only used by another circuit. I’m assuming I can use the same HOT line for this smart switch as well.
  3. Connect the neutral cable (that is currently going straight to light bulb) with the smart switch neutral terminal.

Am I getting this right? I’m attaching the picture of the switch in question (second switch of line-switch-switch-load circuit).

  • List item

Pictures of both boxes will help. Make sure we can see all the wires coming into the box.


As a new user, I can only attach one picture in a post. So I’ll reply three times. The blue cables are acting as travelers. Black is line and yellow is load. There are two yellow cables connected together because they are two separate bulbs. I’m trying to replace the “load switch” with the smart switch.

Wiring Diagram:

Load Box:

Line Box:

Are you in the US? I haven’t seen wire colors like yours and typically Romex wires are used which are black, white, and red. In your load box I see white wires in there. Are any of them neutral? Also what is that yellow wire hooked up to? You may have both line and load in the box and that yellow wire is the same you see in the other switch.

You can use one of your blue wires to “send” neutral to your other switch.

Yes, I’m in US. The house was built in 1999.

I can answer the questions. The White wire is Neutral. Yellow wire is connected to the load (light bulbs). Let me try to explain the wiring here, if the picture isn’t that clear.

Load Box: This switch has three cables: Two blue cables as travelers that are in turn connected to the other switch in the same way (as travelers). The third cable with this switch is the yellow cable, that is connected to the load. There is a black cable in this box (line), but it is not connected to this switch. It’s connected to something else. There is also a white cable in the box, but not connected to this switch. It’s acting as the neutral wire.

Line Box: This is the box on the other end of the house. This switch also has three cables. Two blue as travelers (connecting to load Box switch) and one cable is black (line). This box also has white cable that is neutral.

Now, what I’m trying to do is replace the switch in “load Box” with the smart switch. The smart switch requires four cables: traveler, load, line and neutral. The switch I’m replacing already has traveler and load. So my questions are:

  1. Can I use the black cable in this load box and connect to this new smart switch? As mentioned earlier, this black cable is not connected to the current switch.
  2. If I connect the line to the smart switch, should I disconnect the line (black cable) from the other existing switch?
  3. I currently have two travelers (blue). Should I just replace one of them with the neutral?


What is make and model of your smart switch? I ask because wiring is different. For example if GE, you will have a master and an Aux. if Inovelli or Zooz you will only have master and can use existing switch as “aux”. But all of this said wiring will have to be tweaked more with GE and less with Inovelli or Zooz.

The reason I was asking for clear box pictures is because the wires in back of box that aren’t hooked up to the switch are important. With 3 way switches, the common screw on the switch is really the only important one where one switch will have line and other will have load. Often load and line are in same box but one is being “sent” to the other to make the 3 way work. I suspect that is true in your “line” box. But with out pictures of box with switch(s) out of way its hard to provide guidance.

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Thanks Michael. I think we are on the right track. Here’s the link to the smart switch I just bought.

TOPGREENER Smart Wi-Fi Switch, Control Lighting from Anywhere, in-Wall, Single Pole or 3-Way, No Hub Required, Compatible with Alexa and Google Assistant, TGWF15S, 2 Pack https://www.amazon.com/dp/B07D8YR75X/ref=cm_sw_r_cp_api_5K05BbKYMJC6R

The Q&A section does state that it can work with the existing 3-way switch and an aux or add-on isn’t really needed. Having said that, line and neutral are my biggest questions while replacing. You’re correct that I do have the line cable in my box but it’s not connected to the load switch. Same goes with neutral. So I’m assuming I could use those line and neutral and connect to this smart switch. But at the same time, what do I do with the other switch? Remove the line from there?

These switches are Wi-Fi and not zwave or zigbee so I am not familiar how you will connect these to The SmartThings hub. You do have a SmartThings hub correct?

Yes, I do have the SmartThings hub. But you’re correct. These switches are just WiFi enabled. I still thought of checking with the community because it’s a great place for such questions.