What's going on in my light switch?

[naylorpd]

I've been wanting to control my lights by internet for a while, so unscrewed the light switch to see how deep the box was and, I thought, to confirm there was no neutral.

But to my surprise there were three T&E cables and the three neutrals were all connected together.

Two lives went to one side of the switch and one to the other. It's a one-way switch and one central light fitting.

But why three cables? One must be the incoming live & neutral, another the switched live & neutral to the light fitting. But the third? The next-nearest light switch is in the same wall but at least 3m away and is a complex 3-way switch arrangement - but I suppose the live feed to that has to come from somewhere...

Meantime, the backbox is only 30mm so will be a struggle to get a device in there with all the cable as well...not sure if I can change that as it looks like it may be screwed into a batten in the plasterboard wall.

Thanks

 

[brianmoooore]

Wiring is power in, power to the next light, and power to the light controlled by the switch. Fairly common way of wiring these days for two reasons - 1) For 'fancy' light switches that need a neutral, and 2) To accommodate 'fancy' modern light fittings that will only accept one cable, and only then with a struggle.
Box is 25mm, set 5mm back into the wall. 35mm would be better, but it could have been 16mm. Can't guarantee that you new switch will fit in, but I'd expect that it would.

 

[telectrix]

and flatten those top and bottom lugs.

 

[littlespark]

If there’s not enough space for the new switch, you could use a 10mm extension. Would bring the switch out from the wall a bit.

 

[timhoward]

This is what @littlespark referred to btw

https://www.NoLinkingToThis/p/schneider-electric-lisse-1-gang-spacer-white/5782j

 

[Rockingit]

 

[Rockingit]

Well that's a revelation that was worth the five mins in ACad - I never knew you can just do a standard copy/paste from objects in CAD straight into here!

 

[7029 dave]

Standard set up these days all new builds are wired this way, some call it 2 plate wiring.
However its not true 2 plate wiring has been about for decades, common in conduit systems with N at the light fitting.