The House I was installing some Home Automation yesterday kinda kicked my butt for the first two hours. The House is loaded with 3 way and 4 way switches. From my understanding with the Wire diagram I would need a Smart Switch for every switch but you don’t.
Just to give you a example a 3 way Switch has two light switches to control a load such as a Light fixture. A 4 way will have three or more switches to control a load.
The wire diagram for the three way showed one 3 way switch wired in to Live, Neutral, Traveler 1, Traveler 2 and Earth. The dead end or end of line switch showed it connected to Traveler 1, Traveler 2 and Earth. Problem with that is the second switch doesn’t get power and just doesn’t work. If you tie in the Neutral it freaks out and turns the circuit into a multi-vibrator and you end up with Rave Lights. For giggles I wired in the old switch back on the dead end / end of line and it worked. Even with the non-smart switch turned off the smart switch can still control it.
Later on the day I found the proper wire diagram. The one that came with the Switches was showing the Dimmer.
Keep in mind not all smart switches are alike. Some require all of the switches replaced. Some require only one at the Supply end to be changed.
To find the Supply Switch you have to do some investigating. You’ll need to pull the Switches from the box and take a look see. Using a non-contact AC probe you check the Switch with the Black Screw. Flip the switch and with the Light off you should get voltage on one of them. If you got voltage on that black screw and the light is off then that is your Supply Switch, that is also the Live/Hot line to power the Smart Switch.
This also works for the 4 way as well. The lights I was dealing with that were 4 way had a 3 way on the supply, a 4 way in the middle and a 3 way on the end of line.
Just remember to turn off the Breaker before wiring up the new switch.