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Thickness of main flex

Discussion in 'Electronic Components' started by Santa Al, Dec 20, 2006.

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  1. Santa Al

    Santa Al Guest

    For the purposes of this posting ...

    (a) ... keep the current carrying capacity of a three-core mains flex

    (b) ... ignore any specialist mains flex such flex designed for
    permanent outdoor use.

    (c) ... do not ignore the possibility that there may be a greater or
    lesser number of filaments (depending on what is permitted) in the
    multi-stranded cores.


    (Q1) Is there a defined range of dimensions which the insulation
    protecting each of the three cores must adhere to?

    (Q2) Is the size of outer protective sheath (often PVC) subject to
    some regulations which dtermine a max and a min diameter?

    I am in the UK.


    In the end, I would like to know how (in percentage terms) the
    maximum variation is final outer diameter I am likely to encounter
    when buying flex only by specifying its current carrying capacity.

  2. Tim Dunne

    Tim Dunne Guest

  3. Santa Al

    Santa Al Guest

    Hi Tim, that's the nicest thing anyone has said to me all day!


    I think you will find that the specs governing cables and similar
    items are not freely available on the Net.

    They are often chargeable documents (at hugley inflated prices)
    available from the standards' institutions concerned.

    This question is about just a portion of a standard so no one is
    going to buy one or more of the standards just because you post your
    strange goading stuff.

    I know Xmas can be a stressfull time but why do you want to show us
    all how badly you are coping?

    OTOH if you have the answer then please let me know.
  4. Ain`t no totally defined current carrying standards either, got a reel
    sitting here thats going back mainly because its the wrong colour, its
    catalogue page said 13A 3 core flex, conductor area is 1.25mm, usually
    wouldn`t pull 13A along much thinner than 1.5mm or 2.5mm at any
    distance. Current handling and length are related.
    PVC, toughened rubber, silicone etc. Best bet would guess would be
    taking an average of O.D.s of appropriate cables from somewhere like

  5. The PAT test guidelines are good for this. For a 13A extension cable:
    1.25mm² max length 12m
    1.5mm² max length 15m
    2.5mm² max length 25m (but won't fit nicely into 13A plugs).
    (spot the pattern -- these are easy to remember:)

    These max lengths are to ensure earth fault loop impedance is
    still acceptable at the far end of the cable. Other alternatives
    are to use an RCD at the start of the cable, or to reduce the
    fuse value below 13A, in inverse proportion to the excess length
    above the maximum values above.
  6. (Andrew Gabriel) wrote in
    Nice guide. I question that bit about the fuse though, mains voltage is
    usually constant enough that it can't drive extra current to overcome the
    extra resistance. Even if it did, the heat dissipated per unit length is
    the same along the whole length, so there's no danger unless the cable is
    coiled up tightly enough to allow enough heat buildup to melt the

    It makes sense to choose the fuse value to suit the appliance's maximum
    draw (which will be partly based on knowing what the cable can supply), but
    it doesn't make sense to base the fuse value on the cable directly except
    where the current can rise, unless you take into account the effect of heat
    buildup, maybe.
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