I've got a handful of these on the way. It goes behind a regular wall switch, and this particular model works without a neutral by trickling current through the load. I shouldn't need the bypass device because my load is greater than 20W.

It isolates the wall switch from the mains, only sending a low voltage via Sx through the switch(es), and the device can be programmed to respond to your manual switches however you want. It will also operate on a schedule or you can trigger it via app or other means.

Anyway, wiring it to 1 or 2 switches in the same box is pretty straightforward. My problem is I want to use it with a 3-way switch, and I'm struggling to find a wiring diagram for that. I'm not even sure it is possible given my wiring situation, which is why I'm here.

To be sure I've got this part right: the line comes into one switch, two travelers go to the other switch, then the line goes out to the lights. Pretty common, correct?

Given that, is it possible to use only 1 of these devices behind one of the switches, but still have both switches act as inputs to the device? I'm thinking not, and I would need a third wire from switch to switch since one would have to send 110 and I would need two more for a low voltage switch circuit.

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Posted by mchias1

Member since Dec 2009

801 posts

Posted on 5/10/22 at 6:13 am to Korkstand

The easiest way I had wired one was put it after the last manual switch. It kind of acts as a third switch in line. Set it up to toggle from the manual light switches.

The "hard" part is figuring out how to supply it 120.

edit: Just saw a youtube video saying these don't support 120 as the switch voltage input like the other shellys. You'd still put it after the 2nd manual switch.

Do you have 3 wire romex going to your switches? If you only have 2 wire, I'm not sure this can be done.

With 3 wire, you'd remove the line voltage from the switches and use them as dry contacts to send the switch signal back to the shelly.

This post was edited on 5/10/22 at 7:17 am

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Posted by Korkstand

Member since Nov 2003

28703 posts

Posted on 5/10/22 at 10:28 am to mchias1

quote:
Do you have 3 wire romex going to your switches? If you only have 2 wire, I'm not sure this can be done.

2 wire, and yeah I'm thinking I can't do it this way because one conductor has to carry 110 from switch to switch.

I think I can get it done by putting one shelly in each box. As you said I will wire the one which controls these lights after the second switch, and then in the first box I have another circuit that I can use to run the shelly and I will just use it with the first switch to signal the other shelly.

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Posted by kengel2

Team Gun

Member since Mar 2004

30693 posts

Posted on 5/10/22 at 11:13 am to Korkstand

quote:
how to modify your circuit

remove the switch that is crossed out

tie line to a traveler as shown with ugly purple line

the other traveler is useless and may be removed from the second switch (optional, make sure to cut off exposed copper to be safe)

Your two 3-way switches are now one 2-way. Wire in a Shelly as shown in the directions.

What if you still want two switches? Put a Shelly in the first box, but don't connect the relay to anything. It will send a signal to your software and then your software can trigger the light.

Found this:

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Posted by mchias1

Member since Dec 2009

801 posts

Posted on 5/10/22 at 11:44 am to Korkstand

That's another option, but would need a Shelly in each box.

I did a similar thing with smart light switches. One switch I connected to the load then other just had power run to it. When either switch changed state it told the other one to change state as well.

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Posted by Korkstand

Member since Nov 2003

28703 posts

Posted on 5/10/22 at 11:49 am to kengel2

Thanks, that confirms the solution I arrived at above.

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Posted by kengel2

Team Gun

Member since Mar 2004

30693 posts

Posted on 5/10/22 at 12:33 pm to Korkstand

Those look pretty cool. I like that they talk to the wireless network directly.

How big are they? I'd be worried about putting them in a single gang box and then having enough room for the switch and wiring.

Let us know how they work.

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Posted by Korkstand

Member since Nov 2003

28703 posts

Posted on 5/10/22 at 1:14 pm to kengel2

quote:
How big are they? I'd be worried about putting them in a single gang box and then having enough room for the switch and wiring.

I think they're about the diameter of an Oreo and maybe twice as thick. Space might be an issue in some boxes, but they're designed to go in there so maybe just cram it in.

Shelly also makes switches to be used with these in case you don't want to or can't use a standard switch. They are thin to save space and only for low voltage of course, and I think they have momentary ones so you can program double or triple taps to set different scenes or whatever.

The first two I'll be doing are 2 gang and 3 gang boxes so I should have plenty of room with my standard switches.

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Posted by Korkstand

Member since Nov 2003

28703 posts

Posted on 5/10/22 at 4:48 pm to kengel2

quote:
How big are they?

They just came in. They're pretty small! About 1-11/16" x 1-1/2" x 1/2"

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Posted by Korkstand

Member since Nov 2003

28703 posts

Posted on 5/11/22 at 12:26 pm to mchias1

quote:
would need a Shelly in each box.

So I took the plates off and turns out I've got a 4 way switch. I completely forgot there is a 3rd switch for these lights.

So now I think I need to use *three* of these units, like so:

1 in the box with the 3 way switch and line. Line will tie direct to one traveler wire, other traveler unused, switch wired to low voltage input. Power for the unit will come from a different circuit in this box

1 in the box with the 4 way switch. Always-hot traveler ties direct to next traveler, other traveler unused, switch wired to low voltage input. Power for this unit will come from a different circuit in this box.

1 with the 3 way switch which connects to the lights, to actually control them. Always-hot traveler to line input on device, out to lights, switch wired to low voltage input.

This might actually work out nicely since there are two switch inputs. There is another switch I wanted to automate anyway in one of the boxes, and the other I hadn't planned to automate but it actually might be kind of nice since it's a main entry to the house.

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