Hi - I’m doing some rewiring and got to thinking about this. Latest NEC code requires all junction boxes (JBs) to have a neutral in them, but does not require a live. In the case of a two way switch you’ll have both neutral and live in your JB by default. But for a 3 way switch you’re likely to end up without live in one of the JBs. Can smart switches deal with this? To be clear - one of the travelers for the 3 way/4 way would always be hot - but it would toggle between when is hot and which isn’t as the switch gets toggled.
Thank you!
If by 3 way switch you mean an intermediate cross over so that you have 3 switches in a hallway which all control the same light?
In that case the intermediate cross-over switch will always have at least 1 live.
The problem is, it changes between the two. Every 2 way switch, including cross over intermediates have 1 live, 1 dead port. How they work is toggling between the two.
If the light is on, then all switches in their current position are connecting up the same live. If you change any one switch the light goes out as that switch has by logical expansion switched over to it’s “dead” feed. The really interesting thing is, it doesn’t matter how many 2 way switches you configure like this, switch ANY one of them will change the state of the light.
In practical terms, if you are just trying to power a smart device, you might be better considering a parasitic device and by 2 coils, put one on each “in” live. One will always be live and power will be flowing through ONE of them when the light in on.