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!
Master Electrician. I would highly recommend you either hire or find someone with experience to physically come out and help you. You know enough to be dangerous and far too often I find people giving very dangerous advice. Lutron Cassetta family of smart switches are my go to for any smart lighting. You can find solutions slightly less expensive, but the flexibility and reliable quality I have with Lutron.
It’s all over the map depending on the product line. As Engineers-rock pointed out, there are product lines that allow one switch wired into the circuit and everything else has to be battery-powered remotes. (Which in the case of Lutron Caseta look almost exactly like their switches and can be mounted on a wall behind a switchplate.) One nice feature is that you can directly pair the remote with a switch, so it works even if your hub is offline, assuming the remote and switch are close enough to each other to communicate directly.
Another product line you might want to look into is the Jasco/GE Embrighten switches. They make “Add-on” switches that work with their smart switches that can be wired in a box with neutral and 2 travellers coming in from the smart switch’s box. If you look at the wiring diagram (https://byjasco.com/media/manuals/46200-QSG-v1.pdf) you’ll realize that the add-on switch is not actually switching anything, but is acting as a remote for the smart switch, while being powered by the smart switch.
There are other switches, an example, I believe, are the Aqara switches, where you’re expected to integrate the switch and button of your choice with a hub and the whole affair is the lowest common denominator “have something happen; have hub tell switch to switch” that should work with any smart switch.
For the sake of completeness, I’ll mention that many (most?) smart switches will work with the existing 3-way switches so long as you put the smart switch nearest the breaker (so it always gets power on the terminal it expects to). See https://help.inovelli.com/en/articles/8269832-red-series-dimmer-switch-wiring-schematics for Inovelli’s instructions for doing that with their Red Series devices, as an example. The user experience may vary, however.
The smart switch must be on a live line wire otherwise once it was turned off the “smart” part of the switch would stop working. In 3/4 way switches - there is only one “main” that is connected to the line and that is where the smart switch must be (also note, not every smart switch is 3/4 way compatible). Different smart switches can handle different configurations on the other switches. Many require a companion switch or some sort of jumper wiring to be done. Innovelli is the only one I’ve seen reliably work with existing dumb switches reliably w/o tweaking. If there is no line coming into the 3 or 4 way box via traveler, then you’ll have to buy a battery powered remote that pairs with the switch (Caseta has one, I’m sure there are others).
Don’t overthink it. Place a smart switch (dimmer/three or four way) in the location that has constant power (and a neutral of course). The other locations just regular three way switches, nothing ‘smart’ is needed there. Use your favorite home automation ’service’ to control everything. In my case Alexa. I have switches I haven’t physically touched in months.
If desired, you can still physically turn on/off from any (three way) location, just set to whatever dimmer level the main happens to be at. If you want to dimming level either touch the main, or call out something like; ‘Alexa dim hallway to 80%’
Leviton now only has a real switch at the connection to the device, everything else is a remote. This allows changing all the travelers into hot and neutral, and ideally a ground. Their previous generation Z-wave didn’t do this, and the box controlling the switch was left without a neutral. The electricians stole the neutral from another switch on a different circuit in the same box. I ended up crawling through the attic to connect a neutral from the same circuit at a ceiling light box on a single switch. What a pain. Even worse, there were two different 120V in the same box without tying the breakers together.
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.