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What gauge do I need?

Discussion in 'General Electronics Discussion' started by icor1031, Dec 3, 2013.

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  1. icor1031

    icor1031

    65
    0
    Apr 27, 2010
    I want to run a wire 150ft away from the breaker box, and have it supply 15 amps.

    It's 220v, but that doesn't matter because it's using 4 wires.. Is that right?

    It will power a 220v, 15amp air compressor.


    What gauge do I need, to be safe?
    And no, I'm not adding a breaker. I'm running an extension cord from the 220v that already exists.

    Thanks.
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Since the start current of a SPH motor can be 3 times the run current the AWG should be 10 gauge minimum. 8 gauge would be better.

    Chris
     
  3. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    The 15A rating is a maximum continuous current rating so the charts show 8 gauge for 100' and 6 gauge for 200'. You could probably get away with 8 or even 10 gauge if the compressor isn't run hard and the ambient temperature isn't too high. The chart below is for 115V but will apply equally to two phases.

    [​IMG]
    http://www.engineeringtoolbox.com/extension-cords-full-load-rating-d_1740.html

    You may see charts for single wires that allow for higher amperage on smaller conductors but those don't take into account the mutual heating and thermal insulating properties of service cord construction present in extension cords.
     
    Last edited: Dec 3, 2013
  4. duke37

    duke37

    5,361
    767
    Jan 9, 2011
    There will not be any problem with cable heating, the problem will be with voltage drop on starting as Chris says..This can be calculated using the wire resistance.

    Compressors can be difficult to start since they may be pumping the air during start and they often have a heavy flywheel.
     
  5. icor1031

    icor1031

    65
    0
    Apr 27, 2010
    Thank you.
     
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    There's another factor that's worth mentioning... That would be temperature. An ice cold compressor puts an heavier load on the motor and therefore the mains feeding it. Is this compressor exposed to winter temperatures?

    Chris
     
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