Three-way upgrade: Need help to ID Master vs. Add-on and other fun

NOTE: Updating this after successfully completing the switch installs thanks to the responses from several members below. I’ve tagged one response in this thread as the “solution” so this thread would be marked as solved, but really it was the input of multiple members below that led to my success. If you’re a newbie like me scan the entire thread for the best results before you begin.


I’m going to be replacing the two switches in a three-way setup in my kitchen. Using GE switches (12722 Smart Switch, and 12723 Add-on Switch).

What’s the easiest way to ID (using GE install instruction terms) which is the current load switch (add-on switch), and which is the current line switch (primary switch)?

Below is a shot of the switch that I thought was going to be the one I would replace with the add-on switch, but once I had the switch in sight I realized I wasn’t 100% sure whether it was the one to replace w/the add-on switch or not.

Pics below of the switch that I opened up, and the GE install instructions, for easy reference.

I’ve replaced many standard switches in my home, and put in one connected switch (standard single switch) but this is my first foray into three-way w/SmartThings and don’t want to fry a switch along the way. :slight_smile:

My switch:


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Good pictures! Many people don’t realize you need to include where the wires attach to the screws in the “before pictures.” :sunglasses:

There are tools for doing this. If you happen to live near a Home Depot, many offer a free class on installing a light switch which will get you familiar with the tools and how to use them. They won’t cover networked switches, but since the GE switches are also sold it Home Depot, often times the instructor can get you answers on those as well.

Other than that, I’m going to leave it up to the electrical experts like @Navat604 and @dalec to answer. :sunglasses:

Thanks…I have a line tester so I can confirm if a line is hot or not, and have neutral and ground in the box so the necessary connections are available.

Just need help to ID master or not, and oh yeah, confirm which is the traveler.

This kinda makes me wish I had fewer three-way switches. :wink:

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OK this isn’t for the faint at heart, but I will try to explain testing method. Use what is called a Wiggins tester home depot sells it. It isn’t just a light that goes on in the presence of power. That will only tell you if there is power in the wire.

  1. Now you test the wire at the bottom of the switch and check that wire by putting one probe on it and the other to a neutral wire usually white. You try to avoid using the ground. If you test it now and you find no voltage present switch the switch if it becomes alive it is chances are it is the load side to the light.

  2. If you find voltage on the wire all the time it is the feed.

  3. If for some strange reason there isn’t power to either bottom contact on the switch look for markings for power, some switches are strange depending where it came from. Once you ID the line and load the other two colored wires on the switch are the travelers or T1 & T2.

So you find the line or hot and the load or wire to lamps. But remember for this to work you MUST have a white neutral wire… Good Luck

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I am not a licensed electrician so please take my advice as just that - friendly advice.

Turn off your breaker, remove both switches then cap the bare wire ends. Turn breaker back on then use your tester to see what black has power. The box that has a black wire with power is your ‘master.’ No black at the other box should have power at this point.

Now, you usually can make any box the master in a 3-way by nutting the black hot and load together in the box where power enters then placing an add-on there (with no line or load connected to it) then put the master at the other location. But, there are about 8 or 9 different ways 3-ways can be wired so it can get complicated. If you search this forum you will find MANY threads covering it all.

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Well lots of friendly advice to get you setup. It really isn’t that difficult once you identify what you have in which box. You didn’t take a photo of the wires coming in at both boxes which helps us identify and direct you what to wire. So you might get a nice photo of both boxes with clear shots of all its current wiring so you know what you started with and what is currently working before you make the any changes and post it up for us. Then:

  • You need to identify which box has the incoming breaker power typically will be the romex bundle with black, white, ground. Verify that with your meter. This box typically will also have the romex bundle with black, white, red, ground. and this one will serve as the traveler connection. (this will be the primary switch location) One of the other romex bundles will go out to the load (lights) from this box as well. All three bundles need to be labeled so you know how you will be terminating.

  • The other switch box will have hopefully just be the single bundle romex of black, white, red, ground. If you see only that one romex bundle then that should be the add-on switch location. You will only need two wires for the new conversion so we will be abandoning one of the wires and cap it off.

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Thanks, @joelw135 & @Nezmo & @dalec.

One thing, Joel, I can’t find anything like “wiggins” on Home Depot or Amazon sites…could it be under another name?

You shouldn’t need it. Just your own meter.
Wiggy is just another kind of meter. They literally vibrate with voltage detection. This is one at HomeDepot Klein or Ideal.
Electricians use them all the time but you don’t need it.

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Thanks, @dalec.

Pic of second switch (which I think is the master.

The switches are wired differently than each other (at least in terms of color of wires) - hopefully that helps.

  • The first (potential Master switch) has the red wire in the single slot at the top, two black wires at the bottom.

  • The other switch has a black wire in the single slot at the top, and black and red wires at the two bottom slots.

Is the red wire the likely traveler wire?

First (maybe Master) switch:

Potential secondary switch (the pic I posted previously):

Pic of what I could see in the box behind the “potential Master switch”:

Surprised at how messy it is in there. This is a three switch box. Other two switches (a single and another three way) are to the right.

I’m also noticing that neither switch is grounded (this is the first time I’ve gotten into this switch box, as it was put in when we did a remodel about 12 years ago so all the switches were already upgraded). Should I be calling my general contractor to get him to send someone out to fix this? Makes me wonder if none of the new switches in the areas where we had new electrical installed were grounded.

Dumb switches do not use ground. Ground is nutted-off in the box. A dumb switch simply interrupts the line side of the circuit. Ground is needed on smart switches as they are always ‘live’ so the radio can function (thus the need for a neutral too).

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I just did two of these last weekend. The GE instructions are a little hard to understand until you do your first one. Here is a link to a pretty good GE video that I watched as well …

As long as you figure out which wire (line) is connected to the breaker, the rest is pretty easy.


I did forget to post test results of the wires in the first picture.

The red wire (top of switch) is only hot when the switch is on.

The two black wires (bottom of switch) are both hot when the switch is off.

Which means?! :slight_smile:

This isn’t 100%, but generally the switch closest to the device (light or outlet) will be your new GE addon and the switch furthest from the device will be your new GE primary.


Thanks for the pictures but you need very detailed pictures so you know exactly which wires are going to what on your switches. I am trying to trace the wires exactly from each box going to what on the switches and I still can’t tell. Take a look at the pictures at this posting for examples of the details needed to help you quickly

Forget the red for now.

You need to determine where the romex bundle with the hot coming in from breaker. Trip the breaker. Then disconnect your wires from the 3-way switches (remember you have great pictures to put everything back incase you need to). Flip the breaker back on, the power will only be showing up on one of the romex blacks. That romex black label as your LINE and the white is NEUTRAL for the primary GE switch.


With respect, while this can be true, it’s not a rule you should go by. You must test and understand your wiring before doing anything.

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Absolutely! Just trying to help if @Danabw can’t use a voltmeter.

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Good advice but remember, as I pointed out above, you can locate your master anywhere.

Not true. The master switch needs to have power, neutral and load at the box. The slave 3-way doesn’t have those three.

Right, so you can nut the blacks together in the box that the line comes in from the breaker and then locate your master in the other location. I have done this many times - even in a 4-way.

I stand corrected. :grinning: You can use what I call in the above post the abandoned spare conductor going out to the add-on switch to pass the power to the other box.

However I find the biggest issue for me has always been where is the power coming in at. More than once I have had the power come in at the light fixture box and not the switch box leaving no neutral for the smart switch.