# 2-way switches - “Hotel type”

I’m having difficulty with terminology and wonder whether someone can help.

I have an apartment with many two-way switches - that is, there are two switches at different end of the rooms that switch on one light. I’m keen to automate them (preferably with Zigbee) , but I’m not sure what type of module I should be searching for. I’d appreciate some advice on maybe the Sonoff range which would help me get started.

I also use Lightwave switches, but they were simpler as you replaced both switches with a ‘Master’ and a ‘Slave’

I understand there is a control wire that passes between the switches (or have I got that wrong too!) - so how do you identify which wire it is?

This is, I guess, what you have now…

This is a way to automate with use of the original switches:

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I have done this and it is a little tricky. I did ALOT of research on it and carefully saved what I learned as it is very valuable! First image below is the before and after concept. I didn’t have a neutral to work with either (at either switch) so I had to use a Shelly 1L. Spend a few minutes studying both of these - especially the first one, which as you can see when either switch is changed position the light changes to the other state than what it was before (off to on or on to off) - that is how the circuit is completed - extremely clever (the circle with the X is the light fixture):

If you examine the above closely, you will notice the connectors for the switch on the left goes from “2 1” to “1 2”. That is NOT a mistake, it is just shown that way so the diagram does not have to show wires crossing over each other (just for readabilty). Note, do not put anything back into the wall until you have fully tested the whole setup to make things easier. Even with being very careful, I reversed the wires for the switch on the left as I thought the diagram was incorrect. That was no big issue as that switch just did not work properly, it was no harm done.

“Traveler” leads are the ones that go from one switch to another (and yes you will have those). Then, the next thing you need to figure out is which “traveler” leads are which - otherwise how do you know which to connect to which? I found a youtube video which works perfectly and shows you how to figure out which traveler wires are which. I had to watch this several times - and then re-watched it while actually going through the steps (thank god for the pause button!). It is a very clever way to do it however - but you should have a voltmeter (I am crazy I did it without a voltmeter by just connecting the wires to a light bulb!). (Notice, a volt meter is pretty cheap you can get one online for like \$10 on amazon, you don’t need a fancy one like they have in the video, just one that lights up when there is juice. Later when I have bought shelly’s online they even threw into the box a very inepensive one that also can work as a screwdiver (picture below)!)

Anyway, although your voltage is higher than the 110 we have over here in the US, I believe the general concept/principle of how they are wired remains the same. (For some way over here if there are two switches and one light fisture they call them “three way switches”. I think that is because there are three wires going to each switch.)

Lastly, when you have everything set up, the shelly should have both switches set to “Edge” for them to properly operate as they used to - but also through the Shelly as well. Seamless and works perfectly for me!

BOOM!

Good luck, let us know how it goes!

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They are typically called three way switches. Plenty of on line resources explaining them. The circuit schemat, like the ab5, are pretty easy understand. The reality is that the wires can be routed several different ways. Think of it this way: the power can come in at any of the three locations; one switch, the light fixture or the other switch. So the wires at each switch might be used in different ways. Usually one or both are connected to " travelers," not the typical hot and neutral you see in, say, an outlet.

To complicate things more, switches connected to travelers often don’t have a neutral wire in the box, so you have no way to power a smart switch. You need to draw out the circuit for your situation to choose the right hardware and how to install it.

Assuming this your standard 2 way wiring and without neutral.

Then you can use this no neutral hack without adding new cables

At least in the US, that would be a questionable assumption. There really is no one “standard” way to wire these. In fact it would be rare to have the hot (“Phase” in the diagram) at one switch and the neutral at the other. Generally the power “in” would be at one of the three locations, either a switch or the light fixture. Until recently, two-conductor “travelers” to the switches would be common. There’s always a spool of 2-conductor cable handy when wiring a house. You might have to go out to the truck to get 3-conductor.

With smart switches becoming more common, code in the US now requires a neutral at each location, with some exceptions, which means the use of two-conductor cable for travelers isn’t going to be common going forward. But there are still a lot of them already in use.

Agreed - the wiring in your diagram is the same as my “before” with the two travelers. The elegance of the solution I offered is that no diodes or neutral are needed, and also no rewiring or changes to the switches. Regardless of the solution used, the youtube video I supplied is a good way how to check the wiring so it can be figured out which traveler is which. That is not to say the solution I offered is any better than the other solution, every situation is different. The idea with the diodes is clever, but what surprises me is that when either switch is flipped, during that very tiny time period while a switch is changing state there isn’t there a break in the circuit for powering the sonoff (and if so it could be that time period is so short that it doesn’t make any difference)? @frog0 when can we get to hear back from you on what you decided to do?