Fibaro Dimmer - location in 3-wire setup

As part of my renovation I am having a complete re-wire of the lighting circuits done. I need to provide specs for the electrician as he is not experienced with Z-Wave. I am planning Fibaro Dimmer 2 modules behind dumb momentary switches throughout and have therefore specified 3-wire wiring at the switches (I believe this is called “switch loop-through” rather than “ceiling rose loop-in”)?

This will facilitate installation of the modules behind the switches. However, there are one or two locations where I need to install 2 modules in a single width backbox or 3 in a double-width backbox. I imagine this is tight from a heat and physical space point of view. However I can’t get my head around whether I can install one of the modules in the ceiling space with this wiring topology. Will the wiring in the ceiling effectively be “2-wire” - i.e., switched live and neutral - and therefore I am undoing all my good work in getting 3 wires available at the switch?

Would appreciate advice on the normal way to get around this (@RobinWinbourne - you must have come across this problem before?). Do I just ask the electrician to create a much bigger wall space behind the switch - feels a bit clumsy?

You will definitely struggle to fit two modules in a single box / 3 modules in a double box… not so much a heat issue, more just physical space.

I’ve nearly completed work on my mothers new-build. We divided the house up into zones and star wired all lights and switches to a series of hubs positioned in cupboards throughout the house.

All modules go in the hubs rather than behind switches / light fittings.

Wow I am in complete awe of this. I can see that with the quantity of modules/tech you are putting in you had no good alternative than these hubs/wiring looms.

I’m in a different place - I have only about 20 circuits to automate and all but about 3 I can manage with 1 module per switch. I also don’t have convenient places for hubs like this as it’s not a new build.

So…

  1. I interpret from your answer that I was basically right that if I have 3 wires at the switch, I don’t have 3 wires at the light fitting…

  2. So in parts of the lighting design where I need more modules than can fit behind the switch, I need to wire to a junction box rather than the switch. This junction box contains the modules and feeds the switch and the light fittings as well as the next part of the radial circuit.

Does this sound right?

I am going to study your project for other ideas - thanks!

3 wires at the switch does not mean you won’t have 3 wires at the fitting.

Typically in the UK, lights are always wired the same (radial circuit goes to the lights with live and switch live dropping to the switches), but more modern circuits also drop a neutral leg to the switch which is capped off for future use… essentially jut=st a spare wire core between fitting and switch.

You should be able to connect a module behind the fittings in either scenario.

In another of my properties, I had hollow stud walls, so i located the modules inside the walls behind the removable switch boxes, rather than inside the boxes.

That’s really helpful. So I can get the electrician to wire the circuits as is traditional in the UK (ceiling rose to ceiling rose radial circuit, with 2C+E to the switches) BUT simply replace the 2C+E to the switch with 3C+E to the switch - so I have a neutral in the switch as well. Then the extra conductor for neutral is simply terminated without connection if there’s no module behind the switch.

For some reason I’d had in my head that the radial circuit would need to run switch to switch, with the lights connected as a 2C+E off the switch (i.e. the reverse of the usual arrangement) which would give no neutral at the light fitting. Your version is far superior…

Did I understand you right?

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correct… it’s fairly standard these days, your electrician won’t have any issues.

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