3 way switch wiring

I've wired a ton of switches over the years, and several 3 ways. I just bought a half a dozen ZOOZ Zen 21s and i have to say i really like that you can wire one smart switch and one dumb switch. All of my previous installations with smart 3 way switches required the use of a add on switch.....for an extra 20 bucks!

It has been a while since i had wired a 3 way in and as i was doing this i thought i'd jot down my notes in the event someone else might find it useful.

There are multiple ways to wire a 3 way.

  • Power from the breaker and wires to the light in the same box
  • Power from the breaker, wires to the light in the other 3 way switch box
  • Power at the light

I know it can be a little daunting to try and identify which wires are which, and when connecting the switch this time took a more systematic approach.

  • With power off...remove the switches from the box
  • Remove the black wires from each switch...keep track of the location of each wire ( top of the switch or bottom)
  • Turn the breaker back on...BE CAREFUL...there are now exposed live wires.
  • Check all of the black wires and identify which one the hot wire is...this is your line wire from the breaker.
  • Turn power back off.
  • Connect up the wires on that switch only..we'll call it 3 way #1 ( the one that has the line wire)
  • Turn the breaker back on.
  • When you switch the light switch on and off...if the light comes on then you have the power and the light ( line / load) in box #1, and by default the other black wire on that switch is the load wire ( the light). If the light doesn't come on ....then the load wire is in the other box...call it 3 way switch 2...box # 2
  • If the load wire is in the other box. ( 3 way #2, Box #2) ....check for the hot line of the wires that were disconnected. When you find the hot line ( thats the line feed from 3way#1), then the other black by default SHOULD be the load wire ( light)

the reason this is important is the smart switch needs to be powered at all times - meaning it has to be in the box that has the line from the breaker.

I haven't had a chance to see how this identification works when the power is at the switch however and as a discipliner...this is assuming that the red was wired properly as the traveller.

The wiring diagram that comes with the zooz has the re-wiring schematics for both scenarios above...and easy enough to follow.

Again....if you're not comfortable working with hot wires...get an electrician. I also appreciate that with a little more time and thought you can probably identity all of the wires when they are still connected to the switches BUT as both 3 ways will have a hot line ( based on how a 3 way works) i found this much easier.

Hope this helps someone in the future when looking to add smart 3 way setups.



So, what you are saying is you can have a smart 3 way switch as the leader while using a normal 3 way as the follower?

When I started installing smart switches in my house ( 8 years ago) a 3 way setup required a smart switch and ad “add on “ switch that was designed to work with the smart switch.
The last couple of 3 way switches I’ve installed from Zooz no longer require the add on…..rather they use the existing dumb 3 way…..but it is wired peculiar.