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Take power from a light switch

Discussion in 'Electrics UK' started by Lol999, 4 Sep 2020.

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  1. 333rocky333

    333rocky333

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    Single red and bare earth in grey sheathing is pretty rare I would have thought, i wonder if the 2 black cores are snipped off
     
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  3. JohnW2

    JohnW2

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    So would I. In fact, I personally have never seen single+earth cables, other than in photos!
    That's possible, but it wouldn't alter what I said - that the black conductor at the light must come from somewhere and (given the light works) must be connected to something 'useful' (probably a neutral feed, and certainly not a black conductor that has been snipped off at the switch!) at that somewhere - presumably a JB which, one would imagine, would also have the two conductors from the switch and also a L+N feed.

    Kind Regards, John
     
  4. AndyPRK

    AndyPRK

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    It could also be singles to the light.
     
  5. bernardgreen

    bernardgreen

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  6. Colin Brenton

    Colin Brenton

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    I've certainly seen at least one property wired with 'red and earth' cable looped from switch to switch, and another run of same from each switch to the light(s). A double insulated single-core neutral looped from light to light, completing the circuit.

    It confused me when I first met it, but seemed to be actually quite a good design. I'd estimate the age as late 1960's, so there may have been copper shortages at that time...???

    No doubt a pain to plan and install, though!
     
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  7. AndyPRK

    AndyPRK

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    Exactly
    It was most useful for 2 way switching.

    Then you only needed twin between the switches
     
  8. JohnW2

    JohnW2

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    It could be. However, assuming what we have been giold is true, that still would does not alter what I've been saying ...

    ... we are told that one of the two conductors (other that 'earth') at the light is black. Whether what is at the switch are single+earth cables or T+E with one conductor 'snipped off' (and not visible), there is certainly no black conductor connected to anything at the light switch, and nor (per what we have been told) is there a second red conductor at the light.

    Since both switch and light 'work', both of the conductors attached to each of them must 'go somewhere' (and 'meet' each another and a L+N supply) - so surely a 'JB', or something being used as a JB - and, if that somewhere can be found, it should have all the OP needs to install an additional light and switch.

    Kind Regards, John
     
  9. JohnW2

    JohnW2

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    As I said, I've personal never seen it used, although I've 'always' been aware that it is sometimes used.

    It might, in some senses, be "quite a good design", but it may (because of convenience of cable routing etc.) sometimes tempt people to not run the cable such as the conductors are in 'corresponding pairs' - and if they succumb to that temptation, they will end up with potential 'electromagnetic pollution' of the surrounding area.

    Having the L and N conductors taking power to something, or having the L and S/L conductors from a switch, in the same cable means that the electromagnetic fields generated by the conductors will almost completely cancel out, and therefore not radiate into the environment. If the L & N, or L & S/L, are physically separated, that 'cancelling' does not happen, so radiation occurs.

    Kind Regards, john
     
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  11. AndyPRK

    AndyPRK

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    It’s not unusual for the signal neutral to leave the CU and go direct to light points.
    And the single live to go wherever necessary.
    Granted it seams a Stretch in a shed etc.

    In the 60s and 70s they didn’t care about the EMC implications. Even much later
     
  12. JohnW2

    JohnW2

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    True. One could have power feed, switch and light all in series (in a 'ring') with separate single conductors between them (in a 'ring') - just as with an experiment on a classroom bench. However, with AC that is just about the 'worst possible scenario' in terms of EMC radiation, so I would say 'not recommended'!

    If the situation is like that (or, indeed, in any other situation), I suppose the OP could continue with that 'not recommended practice' and get a permanent L from the switch and an N from the light!

    Kind Regards, John
     
  13. Harry Bloomfield

    Harry Bloomfield

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    This place had lots of single + earth used in it, in what I would guess was the mid 60's - all long since replaced.
     
  14. JohnW2

    JohnW2

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    In the mid-60s (or earlier) you were presumably lucky to have single + earth (rather than 'single without earth') cables in lighting circuits!

    Kind Regards, John
     
  15. AndyPRK

    AndyPRK

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    Yeah mid 60s didn’t have an Earth. Just double insulated singles.

    An expert could accurately date the op’s install with the green cpc sleeving.

    I’m going for the early 70s
     
  16. RF Lighting

    RF Lighting

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    I don’t know if it’s a regional thing, but it certainly isn’t rare in my area. I’d say that most houses I go to are wired in singles up until maybe the early 90s when it seemed to fall out of favour. The property I was working in on Friday is wired in it.
     
  17. RF Lighting

    RF Lighting

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    Between 1966 and 1977

    1966 is when CPCs were first used on lighting circuits, and 1977 is when the colour for earth changed from green to green and yellow.
     
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