Desert_AIP, on 14 Jan 2021 - 20:02, said:
If I wire the load sides of the switches together, so that either one can feed the load independently, would the switch in the "off" state be harmed when the other switch turned on?
Yes. The switch would have 120v coming into it from two different wires which puts 240v to the switch and it would instantly fry it's components.
Desert_AIP, on 14 Jan 2021 - 20:02, said:
I'm not trying to set up a three-way or remote situation, but use different technologies to operate the same load independently.
This is the solution however.
Safely hooking the switches up in parallel is
what 3/4 way switches do. So unless you want to swap both switches out for a matched pair of smart 3/4 way switches, you aren't going to be able to do that. However, as long as both switches have a hot and common wire, we can make it work just fine. This is because you are
going to set up a "remote" situation.
The thing you have to wrap your mind around is that only one switch will control the load and the non-load switch will simply trigger the switch with the load. Because the non-load switch is only acting as a remote for the load switch, the non-load switch will not have anything hooked up to it's local load wire. We only need to use the non-load switch's ability to communicate. There are two questions that have to be worked through IMHO. First, if the two switches are of different technologies, how will they communicate and trigger one another? Second, how do you keep the two switches "synched" together?
Question 1 - If by some miracle the two switches share some sort of communication protocol then use it, but because the two switches are of different technologies I think it is unlikely that they can communicate with each other. However, as long as they can both communicate with a common system like a MQTT broker or some other automation system, we can use that common system to handle everything. However, without some sort of common system that both switches can communicate with, I don't think you can get the switches to work as desired. If you don't want to run MQTT or some other automation system, then I think the best solution is to replace one of the existing switches to the other switch's technology so that the two switches will talk to each other directly (assuming the switch technology allows for this). Again, these switches do not need to be 3/4 way switches for this to work. Normal smart switches will work fine as long as they can communicate with each other.
Question 2 - Once you get the two switches speaking to the same automation system (or to each other), then you can start figuring out the logic to keep the two switches in sync. If the switches don't have status LEDs on them and you don't want dimming functionality, then you basically just need to set up a trigger to toggle the switch with the actual load anytime the switch without the load is toggled. This should be easy to set up, but is dependent on the particular system you are using. If the switches have LED status lights or dim, then you probably need to set a trigger up that toggles the opposite switch than what is actually pressed. This way both switches keep synced with each other. Again, the specifics on how to set this up are going to be dependent on which automation software you want to use to have the switches communicate with. And yes, this works even with dimming light switches as long as the switches and common automation software can receive and transmit the dimming status.
I do this "sudo" 3 or 4 way switches a lot with my lighting system. It's easier to find decent regular smart switches vs smart 3/4 way switches and a lot of times its cheaper to buy two regular smart switches vs a pair of 3/4 way smart switches. Even in locations that are wired for regular 3/4 way switches using traveler wires, you can just use 2 of the 3 wires to send hot and common to the 2nd switch to ensure it has power. The third wire is simply not used in this scenario.
The only downside to this strategy is that if the automation system goes offline for some reason, the switch without the load won't control the switch with the load. This is one reason that I like the Tasmota software (an alternative firmware for certain wifi devices) so much because it handles this common communication between the switches and ensures reliable operation as long as the switches have power and wifi connection (for the switch to switch communication). Even if my larger home automation system goes down, the switches will still communicate with each other and these sudo 3/4 way switches will still work as expected. That being said, any switch protocol that handles switch to switch communication would work the same way however. So even if the switches are Zigbee or something else, they would as expected without a larger automation system.
Hopefully that makes sense.