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Wiring problem

Discussion in 'Electrical Engineering' started by David B, Dec 12, 2012.

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  1. David B

    David B Guest

    Hello,
    I'm trying to change some light switches for PIW switches so they come on
    when my disabled brother walks into the room.
    My problem is that the PIW switches require a live in, a live out and a
    neutral and light switches in the UK only have a live in and a neutral.

    Can I connect the live out to the neutral as well as the neutral to the
    neutral as shown inn my diagram here:

    http://www.flickr.com/photos/[email protected]/8267477718/in/photostream

    The crossed out line is what don't have and want to replace with the dashed
    line.
    Being as the switch controller is drawing such a low current will this make
    any difference to the outcome? Will they now be in series rather than
    parallel and would this matter?

    Thank you

    David
     
  2. David B

    David B Guest

    Obviously one drawback would be that the bulb would be live at all times,
    but would that matter? Would it only have 0.2W passing through the
    filament when the switch was off?

    D
     
  3. Tom Biasi

    Tom Biasi Guest

    The unit should work if wired they way it was before you crossed out stuff.
    The 'live out' is the output from the device.
     
  4. David B

    David B Guest

    Yes, that's how it should be wired. The problem is I can't wire it like
    this without a lot of rewiring between the light and the switch.
    Will it still work the way I've drawn it (even though there will be a
    constant low current going through the bulb?

    D
     
  5. Tom Biasi

    Tom Biasi Guest

    You are not supplying neutral to the device the way you drew it.
     
  6. David B

    David B Guest

    I am, through the filament of the bulb, so it would be like having a 0.25A
    fuse in line which should make no difference to the device.

    D
     
  7. Tom Biasi

    Tom Biasi Guest

    The bulb filament would act like a resistor and the device may not
    function properly. AND, do you wish to violate all your electrical codes?
     
  8. Rich.

    Rich. Guest

    What you've drawn will not work. Once the contact for the live in/out wires
    close, you will be cutting out power to the PIW device. This will cause the
    contacts to again open. This cycle will repeat and in turn giving you a
    blinking bulb effect.

    With the style of wiring in your house, what you need is a PIW up at the
    light fixture. Once installed you would just keep the wall switch on all the
    time, except possibly when he's asleep.
     
  9. You can get a few light fittings with a PIR built in, although they're
    not particularly pretty looking (tend to be a plain circular dome), e.g.
    http://cpc.farnell.com/eterna/cf28pir/ceiling-light-with-pir-28w/dp/SR08250?Ntt=SR08250

    Another option, if you can easily get to the wiring above the ceiling,
    and if the switch drop cable is in conduit or behind capping and can
    be used to draw a new cable through, is to replace the cable with
    triple-and-earth, so you can get a neutral supply to the switch point.

    (And before anyone suggests it, no you can't use the earth as a neutral
    return in the twin-and-earth cable.)
     
  10. Tom Biasi

    Tom Biasi Guest

    I hate when that happens in a public bathroom.
     
  11. JW

    JW Guest

    Even worse if you're at home, it's dark, and you're standing up!
     
  12. J.B. Wood

    J.B. Wood Guest

    Hello, and this isn't rocket science. The motion detector (MD)
    electrical circuit should be connected to the AC power source which in
    your case would be live in (hot) and neutral so that the MD internal
    circuits are continuously energized. The live out goes to the
    controlled device (lamp). I can certainly understand why you might have
    a light switch in a box without a neutral but I would avoid trying to
    kluge something together. It would probably be in violation of your UK
    electrical codes. Sincerely,
     
  13. Don Kelly

    Don Kelly Guest

    Memory! it's what we old people have to do when the hose and the aiming
    control are obscured by the belly-depend on aural feedback. If the
    hearing aid batteries have gone dead-sonar is also dead. Sit down to be
    sure.
     
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