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Im currently trying to upgrade two three-way light switches in the kitchen to some new smart three-way switches. The issue I have run into though is that there appears to be two common wires on one of the switches? The other switch has just one common but this one appears to have two. See picture below.

Picture shows the old switch with the wires already disconnected.

Old switch with wires disconnected

Any idea which one is which here? I believe the two wires on top are the traveler wires but not sure about the bottom two.

  • Can you post photos looking into the back of the box the switch came from by the way? Also, what make and model are the smart-switches in question? – ThreePhaseEel Feb 17 at 0:00
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Notice how the two terminals are brass? Those are travelers. You'll save yourself a world of confusion if you get a 5-color pack of electrical tape and mark the traveler wires yellow. Every 3-way switch circuit is different. Colors are totally inconsistent in 3-way switches, the next one you see might have red and white travelers.

It's not unusual to have 2 wires on the common terminal; that is simply the supply being split off to also supply something else. That is more clear if it uses a pigtail, and feel free to convert it to a pigtail if you prefer.

You have to be especially careful with smart-switch 3-ways. Every 3-way switch configuration is different. There are many cases where the smart switch is not going to work in that box or even that application. Move slowly, document carefully, and if you get stuck on one, ask us a question and post pictures of what's going on inside both switch boxes.

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    Good mention on the smart switches not working in every application+ – JACK Feb 17 at 1:09
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    Thank you for the advice! I did as you said and made a pigtail and everything is working great now! – Quiver Feb 17 at 18:04
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In your photo the the round holes you've circled at the top are the backstabs for the travelers for the switch. They're quick connection terminals that are known to be unreliable. You want to shepherd hook the wire and hook it around the brass screw terminals and tighten the screws. It's a good idea to tape the travelers with some yellow tape for future identification. The bottom black screw is the common terminal along with two backstabs for continuing the feed if needed. You wouldn't want to use the backstabs so you'd pigtail the feed with a wire nut and connect to the black screw. Hope this helps.

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    +1. Do not use backstabs. Every time you press the switch, it rocks the wire. They will break eventually, especially as the copper ages. Might not be your problem but someone else's. Do them the favour. Pigtail all connections; makes it easier to understand and less prone to breakage... and you'll have a little extra left over in case you need it. – J.Hirsch Feb 17 at 16:33
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I’ll second the motion NOT to use the quick push-in connectors. It’s asking for trouble down the line.
Quick way to get your 3-way wires right: the hot feed wire will always go to a common (differently colored) switch screw. The common screw on the other switch will always feed the light(s).

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Sometimes there are multiple light wires in one switch box. Then a tail can be used or both can be put on the common screw, depends on the local code and/or if it was followed.

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. – Daniel Griscom Feb 18 at 13:32
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Always identify screw color 2 brass = travelers (x2), and black screw is common for the switch leg or for the lack of better terms the hot wire that supplys power to the lighting array and the opposite switch has the constant hot and of course the travelers from the aformentioned switch. And always after the screw color id, always replace one wire at a time for beginners.

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. – Daniel Griscom Feb 19 at 0:58
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If you look carefully the bottom screw should have com beside in small lettering. The other two are travelers.

Smart switches are wired differently. Here is a video that explains it. Worth the watch. https://m.youtube.com/watch?v=qi6o8v3rJug

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  • We prefer answers that can stand on their own, rather than things that depend on a video link that might break at any time. – ThreePhaseEel Feb 23 at 0:00

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