Quite fresh here, have been with HA for a while and finally wanted to do some more than just installing light switches. I have a few Tapo 2 Gangs and some other controllers but I actually want to install a relay on a 2-way light circuit.
I’ve opened both light switches and have drawn up a basic diagram of the cables that I’ve found and am quite confused as to where the shelly or alternative would go and what I am to do with the existing cables. I think one switch is the end of the circuit, however I assume the relay needs to go between the main switch and the light. I’m also a bit confused as to the common line - it feels like it goes in a loop between the switches but is that even possible?
I’ve watched a bunch on youtube and gone through 15-20 threads but can’t seem to understand or find something that is like this one.
Thanks, I took some pictures of both switches, I did mistake a brown for a blue wire on L2 on the main switch.
Please have a look and I’ve also drawn up 2 diagrams, one of how I currently understand the circuit is and the second is of another person’s relay installation that supposedly works. (The green wire is a new one).
Unfortunately I am only allowed 1 media per post so it has to be a large one -
Look, your circuit drawing doesn’t make any sense. It’s missing electricity, you know… If you put some wires and switches together on your desk, it’s not going to get powered from thin air.
Your images are ok, but it’s difficult to confirm the wiring.
I expect your wiring is like the top one circuit here:
Hi, yes, I was thinking the same and I saw that diagram earlier - it feels exactly that way, just the colours are slightly mismatching from what people say they “should” be.
So switch 1 has in L2 - Black with sleeve which goes to switch 2 L2, and a brown, I assume the live.
In L1 there is a gray with a sleeve going to switch 2 L1, and a blue with a sleeve, I assume that means its a live switched.(I thought it meant neutral switched).
And common into common.
So if that is the case, would it make sense to be able to wire up the live of switch 1 into a sonoff or shelly’s “L In”, and wire up the live switched to the “L Out”, and then connecting the two switches via their Commons to the S1 and S2 of the relay?
I understand these are very newbie questions and appreciate the help.
I don’t like the blue wire there. This wiring is not done by any code I know.
Sometimes I find wirings where neutral is switched instead of phase.
What country?
Do you have voltage tester?
You need electrician or someone with tester and skills to verify your wiring. You need confirmation that it’s switching phase and not neutral.
If so, that wiring scheme is good for any smart relay that works without neutral, but I strongly recommend Shelly. You don’t need to operate on the second (3-wire) switch at all and you don’t need to add extra wiring between the switches.
Ideally you would bring neutral there as well.
You’ll need to trace which cable on the COM that’s wired to the light bulb and the other one would be incoming live. Turn off the breaker, disconnect both COM cables, connect to wire connector (wouldn’t want those coppers just exposed), then turn on the breaker and test them with test pen. Obviously PROCEED WITH CAUTION or just get an electrician to do this.
From the picture the light could be wired on the 2nd switch.
You’ll need to add another live cable going to the shelly relay
or replace both switches with retractive if you don’t want to add new cable.
Also, zbmini2 is good alternative since it doesn’t look like you have neutral behind the switches.
UK installations frequently use 2 core wire for the switch drop.
Brown is live in, and the blue is used for switched live.
The regulations allow it as long as there’s a brown sleeve on the blue wire to indicate that it’s not a neutral.
That’s great info, thanks. I ordered a voltage tester pen and a relay that has a S1, S2, L In and L Out. I’ll first test to 100% make sure the blue is the switched live and I think I’ll try to put the relay in, as I am feeling a bit more confident now after another day of reading up on electrics.
Will report back with results, if my flat is still around that is
Thanks to everyone who helped! After about two days of researching all the ways a switch works, how circuits work, how 2-way switches go and more I felt confident enough to do it.
So yes, it actually was very simple but only if you understand what the cables mean and do. The Voltmeter really helped to solidify my understanding of the switched live wire.
I ended up going with the diagram I made and Karosm sent. The Live(brown) went into L In, the Switched Live (blue with brown sleeve) into L Out, I cut off a small piece of the Common(Com) cable that was connecting the two switches and connected switch 2 Com into S1 and the small piece I put into switch 1 Com into S2 on the relay.
I first tested it without the switches connected, managed to pair it to SmartThings hub and was elated when I was able to turn the lights on and off, then I connected the COMs into the relay. The 2 way switches still work as expected, just now I have extra control with the relay.
I used the Sonoff ZBMini L2 as it didn’t need a neutral and could directly pair to ST Hub.
