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Current through Mains Cable

Discussion in 'Electrical Engineering' started by David Skinner, Sep 30, 2006.

  1. Hi, quick question if you guys don't mind...

    If a piece of mains cable can carry 240VAC at 13A safely, could the same
    cable carry 12VDC at 25A safely?

    Just looking to muck around with a couple of bits of kit out of a car -
    it's not for a permanent installation anywhere. I just don't want it to
    catch fire.
     
  2. woodglass

    woodglass Guest

    No, the quoted voltage rating of a cable is the maximum voltage that can be
    applied between it's cores (AC or DC).

    The quoted current rating is the maximum current that each core can carry.

    So, your 240V, 13A cable would be safe to use at 24V, but only up to a
    maximum current of 13A


    woodglass...
     
  3. Cable may not be up to the degree of vibration, chaffing, heat,
    and oil/fuel contamination that might be expected of cable
    used in cars.
     
  4. ehsjr

    ehsjr Guest

    Power dissipated in the wire: P = I^2R
    where I is the current and R is the resistance
    of the wire. Notice how you don't need voltage
    to arrive at the answer, when you know I.

    Therefore, a wire rated at no more than 13 amps
    cannot carry 25 amps, regardless of voltage.

    Ed
     
  5. Thanks for the replies everyone - It's nice to drop-in on a newsgroup
    which still values helpfulness and facts. Looks like I either need to
    double-up the conductors or go out and buy fatter cable.
     
  6. Guest

    | David Skinner wrote:
    |> Hi, quick question if you guys don't mind...
    |>
    |> If a piece of mains cable can carry 240VAC at 13A safely, could the same
    |> cable carry 12VDC at 25A safely?
    |>
    |> Just looking to muck around with a couple of bits of kit out of a car -
    |> it's not for a permanent installation anywhere. I just don't want it to
    |> catch fire.
    |
    | Power dissipated in the wire: P = I^2R
    | where I is the current and R is the resistance
    | of the wire. Notice how you don't need voltage
    | to arrive at the answer, when you know I.

    Indeed. The conditions of resistance and current _define_ the voltage
    that is across the wire over that distance.
     
  7. Guest

    | In article <[email protected]>, says...
    |
    |> Power dissipated in the wire: P = I^2R
    |> where I is the current and R is the resistance
    |> of the wire. Notice how you don't need voltage
    |> to arrive at the answer, when you know I.
    |>
    |> Therefore, a wire rated at no more than 13 amps
    |> cannot carry 25 amps, regardless of voltage.
    |
    | Thanks for the replies everyone - It's nice to drop-in on a newsgroup
    | which still values helpfulness and facts. Looks like I either need to
    | double-up the conductors or go out and buy fatter cable.

    I don't know about UK, but in the US, doubling up the conductors is not
    permitted unless the conductor size is already rather large (well beyond
    the 13 amps level).

    If ring circuits are still permitted in the UK, maybe you can set that
    up if it's not aready so.
     
  8. Not very relevant to OP's situation, but since you asked...
    It is permitted in the UK, but the extra protection required to
    ensure each conductor isn't overloaded (generally a multi-pole
    ganged breaker at both ends of the cable) means it's rarely
    economic to use it just because you have lots of undersized
    cable around.
    A ring circuit doesn't count under our Conductors in Parallel
    regs, as the cable size used is significantly larger than
    that required just to share the max load in a parallel cable
    run.
     
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