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Changing light fitting - finding switch live

Discussion in 'Electrics UK' started by Bixer30, 4 Dec 2020.

  1. Bixer30

    Bixer30

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    Apologies in advance if this is an annoyingly common question...

    Changed 4 light fittings today and 3 of them work absolutely fine. The 3 all conveniently had the switch live marked/sleeved accordingly (blue wire with an additional brown sleeve) so I connected that to live and connected any other brown/live wires to a terminal block. Voila.

    Changing the 4th however and this one doesn't have it labelled, so I'm struggling to work out which is the switch live. Unfortunately I don't have any testing equipment.

    From the ceiling there appear to be 3 of each - 3 earth, 3 blue/neutral and 3 brown/live.

    So far I've been connecting all 3 blue/neutrals to the neutral terminal of the light fitting (and obviously all 3 earth to earth), and then one by one trying to connect one of the brown/live wires to the live terminal and then connecting the other 2 to a terminal block. With one of them connected the light doesn't power on at all, with one it does, but as soon as you turn the light switch it cuts out at the fuse board and with the third the light just stays on permanently and the light switch does nothing either way.

    Am I right in thinking that one of the blue/neutrals is likely actually the switch live? This has been the case with two of the other light fittings (a blue wire but with a brown sleeve), so I suppose it would make sense. If that is the case, would it be completely dangerous to try each of the blues one by one in the live terminal, leaving all 3 brown/lives connected to the separate terminal block - or without testing equipment is this best left to a competent electrician to identify for me?
     
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  3. EFLImpudence

    EFLImpudence

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    Yes, of course. Otherwise how could it work?

    You need to determine which of the three cables goes to the switch.
    Is there any way you can tell this - by their direction, grouping or slightly different colour?

    You really need a multimeter to do electrical work. Do you have one?
     
  4. Bixer30

    Bixer30

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    No obvious way to tell. There are three separate groups of cables so to speak all within their own grey outer sleeve (with an earth, live and neutral within each), but they're all identical and it's not possible to tell from the ceiling which one goes to the switch.

    Unfortunately I don't have a multimeter.

    Would my trial and error method be ill-advised? Basically on the off chance I first accidentally connect a regular neutral wire to the live terminal etc. I have a wago terminal block which I've connected the 3 lives to for now.

    Of course I won't try anything potentially dangerous and happy to just call an electrician for this final fitting if that's the best option!
     
  5. EFLImpudence

    EFLImpudence

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    What can I say? Trial and error is not advisable.

    Buying a meter might be quicker than getting an electrician.
     
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  7. sparkwright

    sparkwright

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    You can get a multimeter for less than a tenner.

    One of the blues would have been on it's own - I take it you have no idea which one then?

    Are any any of the copper ends on the blue wires 'doubled over'?
     
  8. Bixer30

    Bixer30

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    Unfortunately not, I naively thought they’d be labelled/marked correctly like on all the other 3 fittings so just took the previous fitting off without checking, but alas.

    Unfortunately no discernible markings/differences on any of the blue wires at all, no.
     
  9. Taylortwocities

    Taylortwocities

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    Ah well, you need to invest in a test meter. As above, a tenner will get you a basic one.

    You really need some basic equipment to do any DIY job. Working on a car, you’ll need some spanners. Doing electrical work you’ll need a test meter.
     
  10. mattylad

    mattylad

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    How about trying this then?

    Assuming this is a normal single radial lighting circuit, you could still identify it by trial and error.
    Read this completely through a few times until you can understand and follow the process and above all - do this safely - tell others in the house what you are doing.

    • Turn off the lighting MCB at the Consumer Unit.

    • Try the lights in several other rooms near this one - they should not work. (This confirms a single circuit and the correct MCB).
    • Connect all the Green/Yellow wires together

    • Connect all the browns together in the ceiling rose and to one side of the light. (They are all considered the live wires).

    • Mark the blue wires with 1, 2 & 3 stripes using a pen. (so you know which one you test with)

    • Individually separate each of the blue so they cannot touch each other or you. (tape the individual ends to prevent accidental touching)

    • Leave this rooms light switch off. (better still, remove the blue wire from it and tape it). (to prevent accidental switching and causing a fault).

    • Connect 1 blue wire into the other side of the light. (individually tape the others).

    • Turn on the lighting MCB at the Consumer Unit.
    • If the fitting lights you have identified the incoming neutral, to confirm this try some of the other rooms light switches where some should not light.

    • If it does not light, turn off the lighting MCB at the Consumer Unit and swap the blue one for one of the others.
    • Turn on the lighting MCB at the Consumer Unit.
    • if it still does not light then the third will be the incoming neutral and can be confirmed by trying that in the light in the same way as the above line.

    • You have now identified the incoming neutral. (note it's number)

    • To identify the outgoing neutral for the other lights:

    • Turn off the lighting MCB at the Consumer Unit.
    • Connect one of the other blue wires to the incoming neutral.
    • Turn on the lighting MCB at the Consumer Unit.
    • Try the light switches in the other rooms.
    • If they do not light then the 2nd blue wire is the switched live, if they do light then the other blue wire is the outgoing neutral.

    • So if the other rooms do not light:
    • Turn off the lighting MCB at the Consumer Unit.
    • Swap the 2nd blue wire for the third one.
    • Turn on the lighting MCB at the Consumer Unit.
    • Try the light switches in the other rooms.
    • The rest of the lighting circuit should be OK now.

    • To connect up correctly:

    • Turn off the lighting MCB at the Consumer Unit.
    • Disconnect the 3 brown wires from the one side of the light and leave them all connected together in the rose.

    • Put the third blue wire (now identified as the switched live) in one side of the light.

    • Connect the incoming & outgoing neutrals together and to the other side of the light.

    • Reconnect the blue wire into the switch, leave it turned off.

    • Turn on the lighting MCB at the Consumer Unit.

    • Try all light switches - they should all work correctly now.

    • Identify the switched live with some brown sleeving or brown tape.
    • Congratulate yourself on another DIY job done.
    This sounds long winded but in reality it should only take a few minutes.
    Please wait until others have read it and confirm that this will work or of I have made a cock-up in the process. I am sure some will be horrified at not buying a tester to do it :)
     
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