This is the upstairs light switch and I think it is this one that is wired to the ceiling light?
The wiring looks the same at the other switch, there is a red and black cable at the bottom of the switch and a red cable at the top of it. There is also a red / green cable and a green cable going to an earthing point on the metal back box.
OK I’ve read that article again and I don’t like any of the options, as it requires adding a new wire between the switches which isn’t going to be possible or re-wiring the live to the other upstairs switch also probably not possible.
Or maybe using two Dimmer 2 modules one for each switch as show in the last example on the article, which is more cost.
Or I do a hack? There is a 3 pin plug socket directly below the upstairs wall light switch. Wonder if I could pinch a perm live feed from that to power the Dimmer 2 and install it behind the upstairs wall light switch.
Your Leccy mate is right, mixing circuits is not a good idea. The lighting would be on a power circuit, probably 30A, instead of typically 5A for a lighting circuit.
Does not sound like you have RCDs, but mixing would cause problems in future if you upgrade the Consumer Unit. (I put separate MCBOs on my consumer unit, and the landing light tripped the circuits every time. I found that the Downstairs switch was taking Live from the Downstairs circuit, but the light was using Neutral from the Upstairs circuit. So turning on the light meant that the there were different Live and Neutral currents in each circuit and the so MCBOs would trip).
Repurposing the wires as in your post should be fine, your Live lighting would all be off the Light MCB, and you probably have a single common Neutral bar.
Octoplayer (not a qualified Electrician, but Fellow of Inst of Physics)
Success, I’ve actually done the wiring today rather than just thinking about it
I am still currently using the original bog standard UK toggle / latching light switches, I may change to 3 position retractive / momentary switches later for dimming and double click scene activations etc.
20 - 1 - enables the dimmer to work with a toggle switch (default is 0 for a momentary switch)
26 - 1 - enables the dimmers S2 switch to also control the dimmer (default 0)
The upstairs light switch only started working again after setting parameter 26.
Now both light switches work to turn on / off the light.
I also had to force a calibration for the bypass device as before I did this, the lights would turn on and then turn themselves off again. That is done using parameter 13.
So pretty happy its working now, as without pinching that perm live from the junction box above the bathroom ceiling from the lighting ring there, this would not have been possible without running an extra new wire between the two switches.
My sparky friend did say “Taking it from a lighting circuit is fine”.
As it was I could just drop down a new short wire from the bathroom ceiling in the loft down the stud partition wall to the upstairs hallway light switch for the new perm Live to run the Fibaro Dimmer 2 module.