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HELP! Replacing 3 gang light switch.

Discussion in 'Electrics UK' started by lateintheday, 23 Mar 2015.

  1. lateintheday

    lateintheday

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    I've been a bit silly and need help asap please. I'm helping my mate sort out his recently deceased parent's house ready for selling, they were heavy smokers and he's had the walls painted but left the brown stained light switches and plug sockets!

    I've swapped most of the light switches now, like for like. But his living room one I've messed up on, I unscrewed it without making note of where the wires went!

    So it's a 3 gang switch 1 way. 1 switch does one ceiling light in the room, another switch does 2 wall lights in the room, and last switch does outdoors garden light.

    The weird thing is, there's only 2 pairs of cables for the switch so I really can't get my head around how it can control 3 separate lights.

    There was 2 red wires strapped between points on it too! I literally have no idea how to put this back together. Here's a photo of the old switch I've got on my desk here and the 2 straps, the new switch has the same connection points (only difference is new switch says L rather than COMMON)...

    [​IMG]


    Here is a photo of the wires in the wall...

    [​IMG]


    I've promised I will go around there Monday night to sort it out so I will be mega super grateful for the answer as I was only trying to be supportive of my mate through this hard time he's having.
     
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  3. EFLImpudence

    EFLImpudence

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    Well, for a start the picture shows two pairs of wires - one pair of cables.

    You have four wires so presumably three of them go to the three lights and the other is the supply live.
    You will have to determine which is this live (presumably one of the reds) and connect it to the new L with a link to the other Ls.
    The remaining three will each be connected to the L1s (if that's how the switch is marked).

    Do you have a multimeter?
     
  4. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    As above you have two sets of twin and earth (ideally the earth/bare copper require sleeving with green/yellow PVC sleeve).

    The core colours are red and black, and you have link wires connecting the coms/Ls.

    After that it is guesswork without the means to test for continuity and voltage.

    We can only make an educated assumption that one core is a permanent live, and this would normally be red core (but we do no know what was in the installers head at the time, so again an assumption).
    If that assumption is correct then the remaining cores operate the three lighting points.

    You would then connect the permanent live in to the Com/L of the new switch and link all the Coms/Ls with the link wire.
    Then each remaining conductor would be connected separately to L1 of each of the three gangs.

    It maybe that your first attempts without testing, you get the conductors incorrectly terminated. It maybe as simple as swapping the red cores over from Com/L to L.

    The earth conductors will require to be terminated at the backbox and if metallic switch plates are being used then an earth link to the switch plate advised and continuity of the the earth path proved.
     
  5. bernardgreen

    bernardgreen

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    A voltmeter ( NOT a neon screwdriver ) would enable you to quickly identify the permanent Live suppy

    However provided there are three lamps switched then this will work.

    POWER OFF

    Using a terminal blocks link one red [1] to the black [2] in the same cable and protect the ends of the other two wires with two more terminal blocks

    POWER ON

    If a lamp lights then the red [1] is probably the permanent Live, confirm this by

    POWER OFF

    Link red [1] to the black in the other cable [4]

    Black [2] not connected

    POWER ON

    if a different lamp lights then red [1] is the permanent Live.

    POWER OFF

    If Red [1] is not the permanent Live then repeat using the other cable.

    Connect Permanent Live to all the commons and the other wires to the three L1 terminals.
     
  6. lateintheday

    lateintheday

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    Thanks for the replies, this makes total sense now! I got myself in a right muddle over it. I'm popping round there at 6pm on the way home from work and I'm certain what your all saying is right.

    I have a multimeter at work as I work in IT and use it for testing laptop chargers etc but I Google it every time as I don't really know what I'm doing with it to be honest, what setting do I put it on to find the live?

    [​IMG]

    I know I shouldn't have touched this wiring by the way before anyone says only electricians should touch it lol.

    We've bought all new plug sockets too but I think I'm just gonna tell him we're better off leaving it cos it's too complicated. But they are so orange with smoke they are nearly brown. We bought them from screwfix so can just get a refund.
     
  7. Taylortwocities

    Taylortwocities

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    Put the bare ends of the wires into separate terminal blocks first, as you will have to do the test with the power on!!

    Put the select switch on to the AC range (750V~) located at about 2 o'clock.

    Test leads in COM and V

    Test between the earth wires and each one of the reds. When you get a 230v(ish) reading, that's your live. This wires goes to all of the COMs on the switch.


    PS. The earth wires should be sleeved with green/yellow earth sleeving.
    I assume you are fitting plastic switches etc?
     
  8. bernardgreen

    bernardgreen

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    Set the meter to an AC voltage range 250 volts or higher. On the meter shown that would be 750 volts

    Ensure the probes are put into the COM and VΩHzF sockets

    POWER OFF

    put terminal blocks onto the four wires

    POWER ON

    With one probe on the metal back box ( assuming earth wires are still connected to it ) touch the other wires in turn with the other probe. One of them will give a voltage around 230 to 250 volts.

    The HOLD button must be avoided. With the probe NOT touching a wire the display should drop to zero. If it stays at 230 then the HOLD function needs to be switched off.

    Have a practise at work with a colleague who is used to the meter.

    The others should give low voltages, around 0 to about 10 volts provided there are lamps in the holders. Without a lamp some voltage will be induced in the switched Live and this could give a reading close to Live potential. The lamp absorbs much of the induced voltage,
     
  9. Taylortwocities

    Taylortwocities

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    Haha me first!!! :LOL: :LOL: :LOL:
     
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  11. lateintheday

    lateintheday

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    Lol I'm really chuffed with these quick replies cheers.

    Why do I need terminal blocks, what would happen if I touched the wires direct with the multimeter probes?
     
  12. bernardgreen

    bernardgreen

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    OK Tailor made instructions are fine but why only at two o'clock. The OP wants to do this in the evening after work.
    :mrgreen:
     
  13. Taylortwocities

    Taylortwocities

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    To stop you putting your fingers on the wires. At least one of those will be LIVE and can kill you.
     
  14. bernardgreen

    bernardgreen

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    Using terminal blocks reduces the risk of you touching a live wire by accident or one of the wires touching the metal back box.

    It is an added layer of safety while you do the testing.
     
  15. lateintheday

    lateintheday

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    OK I understand, I thought that would be the case.

    The switch I'm putting in is plastic like the original switch.


    Do you think I'm doing the right thing bailing out of doing the wall sockets? Going by how confused I've got over doing 1 light switch haha!
     
  16. Taylortwocities

    Taylortwocities

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    Depends on your level of competence. Sockets are easier than light switches as you only have L N and E.

    As with any job, there are some gotchas.
    Why not try doing one and see how you get on.

    Always test the continuity of the ring final (or radial) circuit before and after doing the work. You'll need your multimeter for that too.
     
  17. lateintheday

    lateintheday

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    Well I just really feel like I'm in over my head here and I feel really bad for it because both of my mates parent's have died over the past year and he's got this big old house that he now needs to clean up and sell and I offered to help and I've just bloody made a right pigs ear of it.

    Wish I'd not even mentioned it and just helped with the cleaning part instead. But the switches looked so skanky!


    We've even bought replacement aerial ports. Think I'm gonna bail once I've finished the last few lights.

    Also, why do they make these plastic surface boxes out of such brittle plastic?? They seem to crack and split at the slightest tension so you can't do them up too tight.
     
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