Smart Dimmer switch wiring suggestions..

Discussion in 'Electricians' Talk' started by BanDwagon, Sep 29, 2021.

  1. BanDwagon

    BanDwagon New Member

    I would like to install a smart dimmer switch in my living room for the ceiling light. The Missus has recently had a 9 bulb chandelier style fitting with LED filament bulbs in it installed and I want to be able to alter the brightness of the whole thing via Alexa without having to buy 9 smart bulbs.

    In preparation of purchasing the switch and to familiarise myself with the job ahead I opened up the existing single switch (I have attached a picture of the wiring set up inside which is of three cables (A, B, C) old style T&E black and red with a bare copper earth).

    Using a digital multimeter I was able to ascertain that the one of the 2 red wires (A) at the top is hot, i.e. has 240V running into the switch from it. I believe that means it is coming from the fuse box - or from somewhere else with power.
    The other red wire (B) at the top was dead.
    The red wire at the bottom (C) i marked with a piece of black tape as I believe it is the wire running to the ceiling rose and delivering power into the light fitting.

    The three black wires are all connected together in a plastic connector. I believe they are the neutral wires.

    The 3 bare copper wires are twisted together, a green and yellow sleeve covering them and secured in the metal box with a screw.

    I removed red wire C and discovered that removes power to a vestibule ceiling light, 2 ceiling lights in the hallway and a bedroom ceiling light. I assume that means that black wire C is the return cable for all those parts of the circuit too...

    My questions are these:

    1. Is this a recognised/recommended method of wiring ceiling light switches? As I understood it, this setup should ideally be up in the ceiling rose?

    2. My new smart dimmer switch needs a neutral connection. Will connecting the Black wire from Cable A do the trick for that? (Whilst keeping B & C connected to it as well)

    3. The box is 25mm deep, would I be as well to replace the box with a deeper one to accommodate the wires and the additional depth of the dimmer switch gubbins?

    Thanks in advance for any assistance you can offer!

    Attached Files:

  2. terrymac

    terrymac Screwfix Select

    Perfectly ok for neutrals at ceiling rose ,or behind switches.
    To be certain all the blacks are neutrals you need to test with a meter . But I would be surprised if they are not .
    Back box depth may or may not be enough ,but nowt wrong in fitting a deeper one ( if needs it).
    BanDwagon likes this.
  3. MGW

    MGW Screwfix Select

    I used a spacer at switch rather than a deeper box, @terrymac has given you the answers you asked for, however I have found two problems with electronic switches.
    1) Lamps flashing when off, your not likely to have this problem if the switch uses a neutral.
    2) Shimmering when switched on. The latter is an interaction between switch and lamp, some lamps have a capacitor inside to stop it, but there is nothing on the spec of light bulbs to tell you which do and which don't have the capacitors.

    I found one tungsten bulb stopped the problems, however I did not really want one odd tungsten bulb, so I hunted for bulbs that would work, the G9 bulbs were a real problem, G9-comp.jpg as could not find smart versions, and the small bulb shown allowed the cover to fit, but the large one did not, however the capacitor in the large bulb was nearly as big as the small bulb so clear why the small bulb had a shimmer. But net result is a draw full of good bulbs which will not work with electronic switches.
  4. BillyBobToo

    BillyBobToo Active Member

    Is there any reason why you couldn't fit a capacitor at the switch or in the rose position?
  5. MGW

    MGW Screwfix Select

    Yes the capacitor is fitted after the rectifier, and the rectifier is inside the bulb. That is if referring to the smoothing capacitor, there is often also a current limiting capacitor and a load capacitor.

    The load capacitor to stop flashing when switched off is often fitted in the ceiling rose.

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