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Question about wire table

Discussion in 'Electronic Design' started by K Wind, Oct 20, 2003.

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  1. K Wind

    K Wind Guest

    I was looking at a wire table to see how much current a particular gauge
    wire could safely handle. Unfortunately, I don't understand the table. Here
    is a web site with a table.

    http://www.pitt.edu/~gszekere/copper1.htm

    I don't know what "ampacity" means. How do you determine how much current
    for instance, can 14/2 romex for home wiring handle safely? I know that the
    limit for home wiring is 15 Amps, but want to "prove" it if I can.

    Thanks,

    Ken
     
  2. There isn't any easy answer to this.. for residential electrical
    wiring, just do it to code.

    If you use better insulation such as PTFE or polyimide or fiberglass
    or ceramic fiber and plate the copper with a material such as silver
    you may be able to "safely" let it run very hot indeed. If it's 60'C
    rated PVC in a home, then much less for the exact same gauge.

    There is one limit- the current at which the wire melts, (assuming a
    given ambient temperature, of course).

    Compare this table:

    http://pages.interlog.com/~speff/usefulinfo/fusing.htm

    ... which shows that an AWG20 copper wire will melt at around 58A,
    compared to the 10A or so in the reference you gave.

    Best regards,
    Spehro Pefhany
     
  3. John Larkin

    John Larkin Guest


    Without context, it means almost nothing.

    It's hard to prove. Romex is copper with two layers of plastic
    electrical/thermal insulation. For residential use, one has to assume
    it will be buried in a wooden wall, inside more fiberglas insulation,
    overloaded a bit, with the sun beating on the outside of the wall, and
    you don't want to start a fire or melt the insulation. This is
    complex.

    The same #14 copper wire, if bare and dunked in flowing ice water,
    would cheerfully carry hundreds of amps.

    John
     
  4. Rein Wiehler

    Rein Wiehler Guest

    google for it
     
  5. As I understand it, "Ampacity" is the maximum current permitted by the
    Electrical Code for a given wire size in a given environment.

    For normal house wiring using Loomex cable, you can use #14 wire for
    up to 15 amps, but when running several wires in a conduit, you may
    require #12 for the same current.
     
  6. The other consideration, that I haven't seen addressed in any of the
    replies here, is how much voltage drop you can "afford" for a given run of
    cable. For most normal house wiring this isn't much of an issue, but for
    some situations it becomes much more important -- look at distributing say
    12 volts DC from a windmill or solar panels for an example of such a
    situation. You can afford a *lot* less voltage drop in these contexts, and
    much heavier wire is normally used, as well as shorter runs.
     
  7. Active8

    Active8 Guest

    The other consideration, that I haven't seen addressed in any of the
    replies here, is how much voltage drop you can "afford" for a given run of
    cable. For most normal house wiring this isn't much of an issue, but for
    some situations it becomes much more important -- look at distributing say
    12 volts DC from a windmill or solar panels for an example of such a
    situation. You can afford a *lot* less voltage drop in these contexts, and
    much heavier wire is normally used, as well as shorter runs.
    [/QUOTE]
    good point - run length. A/C units generally have a spec on max run
    for aluminum wire. 110' on one spec IIRC. too much drop and the
    motor draws more current and gets hot.

    can't remember the 2 specs for motor current and the abbrevs

    i think one was FLA or full load current and another was starting
    current.

    brs,
    mike
     
  8. Active8

    Active8 Guest

    what's your friend trying to destroy now? :) haven't you had him
    commited? :) with all that oil lying around, the last thing you
    need is an electrical project.

    check the local codes. some require 12/3 which is good to 20A and
    no 14 awg is allowed. actually i think it's called 12/2 with
    copper. i wouldn't use 14/2 at all without copper - call it 14/2
    with copper.

    copper just means that there's a bare wire for safety ground. use
    the safety, luke.

    there's a couple of do it yourself electrical sites out there.

    hth,
    mike
     
  9. K Wind

    K Wind Guest

    Thanks for the information.

    Ken
     
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