What size cable to feed consumer unit??

Discussion in 'Electricians' Talk' started by BrainBox, May 22, 2008.

  1. BrainBox

    BrainBox New Member

    Hi,

    In a conversion of a property to flats, the 3 phase head is to be located in the communal entrance together with isolator switches. The consumer units will be located some distance away within each flat on each floor.

    Which cable should be used to connect the consumer unit to the isolator switch?

    If the unit was in clos proximity, I'd of used 25mm tails, but that's not practical here. My electrical wholesaler suggests I'd be ok with 16mm T&E as flats are only 1/2 bedroom unit.

    Or should I use 25mm armoured?

    Any advice appreciated.

    Thanks.
  2. Omniscient Polymath

    Omniscient Polymath New Member

    25mm tails sound tad to much for 1-2 bed flats.
    Your whoesaler is probably talking about about 16mm tails and posibbly a 10mm main earth cable? but what do they know.

    Run 3 core 16mm SWA and you'll be fine. After all how and where is the cable going to be run.

    Get a timeserved sparks in and not a 5 day part-p I was ex forces or a milkman cowboy.
  3. Lokkars Daisy

    Lokkars Daisy New Member

  4. madmaz

    madmaz New Member

    what size is main fuse ??
  5. BrainBox

    BrainBox New Member

    Cable with be burried in wall/ceiling void.

    Main fuse will be installed by electricity board. Previously on similar projects it's been 100A. Mayb if they instally 68A fuse, I'd be ok with the 16mm SWA??

    Thanks for helping people, much appreciated!!! :)
  6. sinewave

    sinewave Screwfix Select

    Central Heating is?
  7. M107

    M107 New Member

    Get a timeserved sparks in and not a 5 day part-p I
    was ex forces or a milkman cowboy.

    Now Now P&E I take exception to your comments, you cant tar all milkmen with the same brush :^O
    On the serious side not all Ex forces are cowboy sparks you know;)
  8. mbat666

    mbat666 New Member

    personally i would install 16mm T&E with a 10mm earth cable to each. You'll need to terminate into a 60a switch fuse at meter end, cuz run over 3m, (click make the same one as mem but 20 quid cheaper) and then you can run straight into plastic fuse box's within each flat. I you use swa you'll have to either use a metal clad fuse board or terminate into a box before. Also i wouldn't chase this size cable into wall but run up with some large trunking
  9. madmaz

    madmaz New Member

    personally i'd install 16mm 3core armoured terminated in metal clad 60A switch fuse in meter cupboard and then terminated in standard consumer unit complies with 17th too ;)
  10. madmaz

    madmaz New Member

    oh yeah and put it in the wall dot'n'dabbed of course we dont want to chase too deep !!
  11. pcelectrics

    pcelectrics New Member

    I would say we don't have enough info to give a considered reply about the size of the cable required. In particular: 1) are the flats all electric or part leccy part gas - affects overall loading and switch fuse rating and 2) distance of the CUs from the meter point - is this a Victorian semi in the middle of town or an old cotton mill (ie huge)?

    Choice of cable type will be mostly down to sparky preference and installation method employed.

    Question though (I'm doing my 17th in a couple of weeks): do these submains need 30mA RCD protection if they are buried (less than 50mm deep)? If so, isn't this a problem with each flat entirely on one RCD?
  12. The Electrical Yoda

    The Electrical Yoda New Member

    I have seen a similar installation using 25mm2 split concentric cables.

    ie. the line conductor 25mm2 in the centre and neutrals adding up to 25mm2 and cpcs adding up to 16 mm2 around the outside.

    As these cables don't really need to be armoured they are small and do a great neat job.

    Yoda
  13. madmaz

    madmaz New Member

    I would say we don't have enough info to give a
    considered reply about the size of the cable
    required. In particular: 1) are the flats all
    electric or part leccy part gas - affects overall
    loading and switch fuse rating and 2) distance of the
    CUs from the meter point - is this a Victorian semi
    in the middle of town or an old cotton mill (ie
    huge)?

    Choice of cable type will be mostly down to sparky
    preference and installation method employed.

    Question though (I'm doing my 17th in a couple of
    weeks): do these submains need 30mA RCD protection if
    they are buried (less than 50mm deep)? If so, isn't
    this a problem with each flat entirely on one RCD?


    using armoured cable means no rcd needed thats why i say run 16mm swa
  14. madmaz

    madmaz New Member

    or as yoda says use split concen
  15. ictmtb

    ictmtb New Member

    split con is far too expensive. Yeah it's easier to handle, but what a waste of dough. As others have said, 16mm swa is fine in most cases. If in doubt, run it in 25mm.
  16. edward current

    edward current New Member

    what size is main fuse ??

    finally someone asks a relivant question
  17. firstline37

    firstline37 New Member

    Brain box , the only way to do this is carry out proper calculations . without knowing what your design current is , the length of run or any correction factors it is impossible to say for definite.
    Once you know the above you can calculate the size of cable required.
    It will also be worth knowing what capacity the electricity provider has and if the fuse can be uprated.
    If it was my flat to keep for a few years id probably go for the 25mm swa.
  18. stoneroses

    stoneroses New Member

    in this situation how will you go about metering each flat so the leccy bill will be charged to each flat?
  19. JP.

    JP. Screwfix Select

    Hi,

    In a conversion of a property to flats, the 3 phase
    head is to be located in the communal entrance
    together with isolator switches. The consumer units
    will be located some distance away within each flat
    on each floor.

    Which cable should be used to connect the consumer
    unit to the isolator switch?

    If the unit was in clos proximity, I'd of used 25mm
    tails, but that's not practical here. My electrical
    wholesaler suggests I'd be ok with 16mm T&E as flats
    are only 1/2 bedroom unit.

    Or should I use 25mm armoured?

    Any advice appreciated.

    Hi M8..done the same thing you are doing some time back..

    16mm SWA is quiet sufficient..

    1 x switchfuse per flat in corridor meter cab etc etc..

    25mm SWA is not indicated.

    Thanks.
  20. BIG LEROY

    BIG LEROY New Member

    Jeezus feckin wept.

    Is it any wonder real electricians sometimes find it quiet when you have wannabes offering their services for stupid prices.

    I mean how the fek can someone price and get a job without knowing what they will be installing?

    Do the people who reply to these questions not realize what they are doing?

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