AWG Wire gauge ratings

Discussion in 'General Electronics Chat' started by alababaju, Apr 23, 2014.

  1. alababaju

    Thread Starter New Member

    Apr 17, 2013
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    I was just about to post this message, before I saw this post and a new (more realistic) table among the comments. You may wish to read it after my post. See post here: http://forum.allaboutcircuits.com/showthread.php?t=80299


    I am planning a solar power project and came across the task of selecting wires to use. I don't know if it's just me but it seems 90% of all the wire I've ever bothered to check over the years (even before I knew what it was) that have an a 22 AWG rating. As I was planning a project with potentially high current I decided to investigate the ratings and came across maximum current ratings, (enclosed and in free air, solid core/single conductor and multi stranded) for each wire gauge number. The lower the AWG number, usually the more expensive the wire, but the more current it's rated to carry. I am trying to minimise power loss and project cost so I was trying to balance between energy used in converting to a higher voltage for transmission and cost of a higher capacity wire. You could search around the internet for a few tables (I see slightly different values on different websites!), I'll use the one on Wikipedia for reference.

    http://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes

    Look at 24 AWG wire. My HP 135W charger uses that for the part between the adapter and the laptop, to send 19V 7.1A and I touched it now, it's not even hot! I believe it runs at full power sometimes because I got the laptop with a 150w charger (it's a HP 8730w) and sometimes I get a HP popup, when I once-in-a-blue-moon to visit my Windows 7 dual boot, that I am not using a powerful enough charger.

    So my point is (thank you for persevering this far :D ), what on earth is with the AWG amp ratings on Wikipedia? It's not only Wikipedia too! Scare tactics? Over conservativeness? :confused:
     
  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,908
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    Look at voltage drop tables to see if the wire will work for your solar application even if it will carry the current safely (those rating are realistic when real world construction factors are calculated in). I've no idea what power levels you wish to run but I have a 2kw 12 dc volt inverter on my solar off-grid system. To get acceptable voltage drops at 150+ amp currents I used 0000 gauge wire for direct battery load interconnects and 00 gauge wire for charging (40+ amps) connections as they are critical for keeping proper charge profiles at high currents.
    http://www.windsun.com/Hardware/Voltage_Calc.htm
     
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    You need to look at exactly the nature of the cable and application in a type of enclosed cable or raceway.
    For example, the Wiki chart does not show all the NEC ratings, for this you would need to go to something like NFPA79 etc.
    e.g. 24g is 2amps at 60° in a raceway or cable and also in a control enclosure.
    Max.
     
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  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the wire size is also related to distance. if your going farther from your solar panels, get the next sze larger wire than recomended. less resistance losses. I had 2 7 watt panels on my roof using doubled up 24 guage wire and there was a measureable voltage drop across the wires. and yes, the lower the awg number, the larger the wire.
     
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  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,770
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    NEC table 310.16 for up to 3 conductors in a raceway or 310.17 for conductors in free air.
    Then you might want to look at voltage drop calcs too to see if its sufficient for your system.

    LOTS of information out there
    http://www.freesunpower.com/wire_calc.php
     
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  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    after all, 1/2 volt drop is MUCH more important at 12 volts than 120 volts.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Work up a budget by assigning power levels to your sources and destinations. From that you can caluclate/adjust/assign power levels to your transmission paths, connectors, etc. Once you have those you can calculate resistances and select parts.

    In fighter aircraft, weight is everything. F-15s routinely run 40+ amps through #18, but the wire is silver plated and teflon insulation is good for 500degC. IOW, when looking at other applications for guidance, qualify the apps.

    ak
     
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  8. alababaju

    Thread Starter New Member

    Apr 17, 2013
    2
    0
    My first question! Thanks guys for being helpful.

    It's clear now that the wire ratings are not all black and white (must be the reason for the varying tables on different websites).

    Thanks for this bit AnalogKid :) So teflon in this case is absorbing the heat, allowing the wire to carry more current and not combust? Nice technique there. Probably my HP 24awg wire is dealing with the 7A in some similarly special way.

    Thanks again to everyone that posted! :)
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,540
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    More like teflon is withstanding the heat without melting. Teflon is not a great thermal conductor, but eventually the wire heat getw through it and radiates into the compartment atmosphere.

    Pretty much nothing is combustible in military hardware. They're picky about that, what with the bombs and jet fuel and stuff.

    ak
     
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