Possible n00b question re: 2 wire vs 3 wire

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  • Lum
    Automated Home Lurker
    • Jun 2015
    • 2

    Possible n00b question re: 2 wire vs 3 wire

    I'm planning on retrofitting an existing house. It's a rented place and some of the wiring goes through brick and concrete so I'm not going to be running any more wiring.

    Currently my kit consists of fairly simple stuff. A Logitech Harmony smart hub for the AV gear, a nest thermostat and in the living room an Auraglow IR controlled light bulb. I've hacked about on the harmony such that my Synology NAS now runs scheduled tasks to control the light bulb, there's more detail here including my modified version of the HarmonyHubControl project which is /much/ faster.
    I also have a LimitlessLED/milight kit on its way, as well as a Z Wave USB dongle that I intend to use with the Synology NAS.

    Anyway, I want to fit a smart switch, but of course I need a neutral feed for that, however what I don't need is any physical switching between the lightswitch and the bulb. If I have the smart switch report back to my Synology NAS via Z-Wave, and then the NAS tell the bulb what to do, then I can reduce the number of wires going to the switch.

    Looking at my ceiling roses the wiring is as follows:

    Neutral terminal block:

    O - Neutral feed from ring main
    O - Neutral feed to rest of ring main
    O - Bulb

    Live terminal block

    O - Live feed from ring main
    O - Live feed to ring main
    O - Live feed to light switch

    Switched terminal block

    O - Switched live from light switch
    O - Bulb

    My plan is to rewire the ceiling rose as follows

    Neutral terminal block:

    O - Neutral feed from ring main (untouched)
    O - Neutral feed to rest of ring main (untouched)
    OO - Bulb + neutral feed from light switch (formerly switched live - will need black tape on the red wire)

    Live terminal block:

    O - Live feed from ring main (untouched)
    O - Live feed to ring main (untouched)
    OO - Live feed to light switch + Bulb

    Switched terminal block: no-longer connected.

    I then ignore the physical switch in any smart switch I buy, and treat the two wires in my light switch wiring as the live and neutral feed because they're now hardwired to the live and neutral in my house's lighting circuit.

    Only disadvantages I can see of this system are that if someone ever puts in a "dumb" light bulb then it will be permanently on, and by extension I have no actual physical control over the lighting, only wireless control. But I'm not too worried about this. I guess another slight advantage is that there's no 240V sparks in my switches, so less worry about gas leaks. Also any electrician that looks at my wiring is going to be rather confused, and if a standard switch is fitted without rewiring the ceiling rose, it'll connect live to neutral and throw the breaker, but my landlord's sparky is used to me by now, and I'll likely tell him what I've done just out of courtesy.

    Can anyone spot any problems with my plan? Here's a crappy MS Paint circuit diagram done on a touchpad which hopefully may make the idea more clear.
    Attached Files
    Last edited by Lum; 29 June 2015, 11:06 PM.
  • JimNoble
    Automated Home Jr Member
    • May 2005
    • 14

    #2
    This is a very bad idea. If you change the wiring this way it will create a potentially dangerous and/or deadly situation in that if a normal light switch is wired in and nobody has realised that the wiring at the ceiling rose has been altered, when the switch is "on" it will create a short between live and neutral.

    Do not do this.

    Jim

    Comment

    • Lum
      Automated Home Lurker
      • Jun 2015
      • 2

      #3
      I'm aware the the non-standard wiring will create a short if a standard switch is put back in, mentioned that in the OP. I'm also lucky that the wiring to the switch has two red wires, instead of standard T&E with a bit of red or brown tape to mark the black one as live, so the black tape will look unusual. I also won't be leaving it like this, as those switches and bulbs are expensive Hell I'll even stick a warning note in every light switch.

      That said, how would you suggest I get a neutral feed in to the light socket? I don't have access to the internal wiring and every plug socket in this house has already been spurred to provide additional sockets, so that option is out I guess I could just stick the smart switches in pattress boxes on the end of a normal 3 pin plug, but that's kinda horrible.

      Comment

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