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I tried installing a smart dimmer switch and add-on into a two-way switch configuration, but after a few hours of messing around I think that the circuit isn't wired properly for a smart switch. Right now the light ( a LED panel wired directly into the circuit ) is way too bright at night so I wanted to put in a smart dimmer.

With the default switches in, it looks like this:diagram of switch wiring

Green: ground, black: load/line, blue: neutral, red: traveller, numbers indicate "bundles" -- 1 is all the wires going to/from the breaker, 2 is the set of four wires going from switch to switch, and 3 goes off somewhere else, probably to the next bedroom as all the ceiling lights are on the same circuit.

Basically, instead of being wired "switch -> switch -> light", the light sits in between the two switches. Based on what else I've seen in this ( newly built! ) townhouse, I think this was the electrician saving themselves some money by using less wire to get this set up =. It works fine for dumb switches, but after spending three hours it seems there's no way to hook up a smart dimmer + add-on that will allow them to control the light.

As far as I can tell, the smart switches are only built to handle the "switch -> switch -> light" setup. The second switch only connects to neutral, ground, and traveller; so in the second box that leaves the load/line wire unconnected and means the circuit is incomplete.

Is there a way I can put in a smart dimmer & add-on that will allow me to control this light? In the second box where the add-on switch goes can I use a wire nut to connect the neutral & line, or will that mess with the add-on switch that needs to be connected to neutral?

Could I use a Shelly dimmer right in the light fixture box?

Or am I just out of luck until I completely re-wire this switch circuit?

EDIT

I took a better look inside the ceiling light fixture, and here's an updated diagram: enter image description here

I labeled the inputs into the light fixture as A and B, because I can't tell which one corresponds to switch 1 and which to switch 2. Oh, and the triangle labeled "WN" are wire nuts, because I figured that was the easiest way to show how

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    That wiring, as drawn, doesn't make any sense. Also you state "1 traveler" so either you have changed the wiring, or this is not standard 3-way wiring. Can you review the connections inside the lamp?
    – Harper - Reinstate Monica
    Jul 23, 2021 at 18:12
  • Was the line hot at switch 1 originally connected to the common terminal or to one of the other terminals? There are two different ways to wire a pair of 3‐way switches to control a load, one called 2-wire control and the other called 3-wire control. The 2-wire is traditional in the US, but sooner or later in the US and in Canada we will start to see the 3-wire, because it has certain advantages. In the 2-wire the two switches are connected to each other only by the two travelers. In the 3-wire the commons are also connected to each other.
    – Jim Stewart
    Jul 23, 2021 at 20:06
  • @Harper-ReinstateMonica took a better look inside the light fixture, updated the post to include a new diagram
    – Sean Hagen
    Jul 23, 2021 at 21:12
  • Oh, that makes a lot more sense. White has to be used as neutral for the left half, and can't be used as switched-hot for the right half. That's why the color change at the lamp.
    – Harper - Reinstate Monica
    Jul 23, 2021 at 21:46
  • So would it be possible to re-wire the three boxes ( switch 1, switch 2, and light fixture ) to get this to work? One of the switches is an add-on switch and only needs neutral, traveler, and ground and it just communicates with the "main" switch using the traveler. So switch 2 gets neutral, ground, and traveler from the light fixture, light is hooked up to live, neutral, and ground, and main switch is doing the actual work of turning the light on and off ( and dimming ).
    – Sean Hagen
    Jul 23, 2021 at 22:07

1 Answer 1

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Your diagram does not use standard switch symbols so it is impossible to determine where the common pole (C) is and the normally open (NO) and normally closed (NC) contacts are.

enter image description here

Figure 1.

You can see in Figure 1b that switching SW4 will short-circuit the live and neutral.

If you can redraw your circuit we may be able to help further.

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  • Re-did the diagram, and also took another look inside the light fixture and got a better understanding of how that's wired.
    – Sean Hagen
    Jul 23, 2021 at 22:07

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