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can I supply a multiple switches with 1 conductor

Discussion in 'Electrics UK' started by buxxbuzz, 16 Aug 2014.

  1. buxxbuzz

    buxxbuzz

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    Hello all,


    quick question. with triple switches can I supply the live to one switch and feed on to the other 2. Then return the switched lives back on a 3 core +1 cable. This would save a cable and leads me onto, if I had several switches in the same location could I distribute the live from the first unit to a couple more then return these switched lives on 3 core. Saving 2 cables per unit.

    I hope this makes sense.
     
  2. davelx

    davelx

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    You can't use 3-core +1 for that if the "1" is an uninsulated core intended for use as a CPC (Earth) running directly inside the overall sheath without its own insulation layer.

    You will need 4-core+earth cable for this - I don't know if it exists. So you may have to run two cables - ether a 3C+E and a 1C+E, or more conveniently, 2 Twin+E cables.
     
  3. bernardgreen

    bernardgreen

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  4. ericmark

    ericmark

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    Commercially with conduit and grid switches it is common to have one feed to many switches but in domestic there are a few draw backs.

    First we don't use conduit any more so it needs either multi cables or special cable which can work out expensive.

    Also as not in metal conduit one has to be careful about transmitting interference early two way switching used just two wires plus earth between switches but this caused mains hum on speaker systems and telephone lines what it would do to modern broad band is anyone's guess.

    With two way switching there is also the problem of creating a borrowed neutral in the process.

    The other problem is of course a very detailed as built plan needs making one can't expect people in the future to work out what you have done unless it is written down.

    Transmission lines is quite a complex subject the distance two wires are separated by and the twists of the two wires results in either a match or miss match but with mains power at just 50 Hz this is not normally a problem. With high frequency one hears the CB boys talk of SWR and reflected power but this is not really a problem as I have said with 50 Hz. However where the feed and return are separated even with 50 Hz one can get problems especially if they don't go through the same hole in any ferrous material.

    Also the lives both line and neutral are kept within the same sleeve as the earth for safety reasons any cable crushed is likely to have a fault with will cause automatic disconnection (the fuse blows).

    So much depends on what the switches feed. Having two sets of lights in a room with a 1/3 and 2/3 split running all wires in same cable makes sense. But having multi-rooms fed from single feed likely does not as the line feed would need to follow same route as switch wires in the same way as when using conduit so it would be snaking through the house and likely would need more not less cable if mains hum on audio systems is to be avoided.
     
  5. davelx

    davelx

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    Ah yes - I was thinking flat grey sheathed stylie - using flex didn't cross my mind. Also NYY-J cables available in 3,4 & 5 core from the same source.
     
  6. buxxbuzz

    buxxbuzz

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    Thanks to everyone who replied.


    I read my own post and of course I didnt get a full enough description in. The circuit is for domestic lighting and I have rooms with 3 different light outputs in each. A main, alcove and window area light. My plan being to save some wires and not drill too many holes in the joists I would use a twin and earth to the first switch in 3 supplying the power and providing a switched live back to the junction box. Then having power to the common on each switch from this line use another cable, 3 core to return the other switched lives back to the junction box. Even onward inking this to the other 2 units. Distance being short. All mains so balanced lines dont come into it and I dont think hum is any problem as Im not creating earth loops.

    I just couldnt find, any regs, i didnt really look that hard, as to the legality of this method instead of a separate live and return for each switch.

    In the same vain I have spot lights and feed one to another but would like to feed one to two at a couple of spots, again is there any reguational objections to this?

    Thanks again for all the replies, lots of good stuff.

    SImon.
     
  7. DIYnot Local

    DIYnot Local

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