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Power mains question: wire gauge

Discussion in 'Misc Electronics' started by DaveC, Dec 28, 2012.

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    The person who mentioned PVC is who fucked up. Let's go take a look at
    who that was... Oh, that's right... it was YOU, you fucking

    YOU mentioned incorrect media. To which I immediately responded is the
    WRONG choice.

    YOU can squirm all you want, but the truth will not change.
  2. Guest

    Of course you project you inadequacies on others. It's always been
    your MO.

    You're a liar.
    You're a liar. But that's nothing new.
  3. Guest

    AlwaysWrong runs away from his own position. Who wudda thunk!

    <AlwaysWrong babble snipped>
  4. Guest

    I don't need you to tell me you're stupid. Like DimBulb, you
    advertise the fact constantly.
  5. DarkMatter

    DarkMatter Guest

    The blind shall not see...

    This is why, despite the only pre-requisite being a pre-death
    repentance, most sinners will *still* not ever be saved.

    Despite being told that you were acting like an adolescent worm, you
    continued to do so, and enhanced your pathetic wormage even further.

    You illustrate for the intelligent among us, just what the flaws in the
    human race are.

    Not with your diatribes, but with your attempts at making a diatribe.
    It borders on funny, considering that you tout yourself as intelligent
    and civil.

    Your senility onset is showing again.

    Must be that curse I put on you about 8 years ago, when you started
    your baby bullshit back then, over in a.e.e. I hope the pain settles in

    Maybe you can figure out why an Easy-Bake-Oven works better with a 100W
    heating coil than it does with a 100 W light bulb.
  6. josephkk

    josephkk Guest

    No John Larkin, you are full of baloney on this one. I do the wire gauge
    for motor starts all the time. I(sc) is NOT used.
    Incorrect setup. What is of concern is the drop during motor start. Not
    motor run and not wiring fault conditions. The goal is to keep it below
    5% including all other losses to the service transformer. Generally a 2%
    to 3% drop during normal operation, and no more than 8% during motor
    start, is allowed in the building, all the way to the main service lugs.

    Thus #14 is a bit wimpy but #12 is fine. No real advantage going to #10.
  7. josephkk

    josephkk Guest

    4" really? How big it that compressor, 500 kW? Does it go over 3000'?
    Not that i am all that expert but that is the size of compressor and the
    run length i saw last time i saw one plumbed at 4". And that one was done
    by an expert.

  8. josephkk

    josephkk Guest

    Conduit is mentioned in the leadoff post by OP. The cost of putting in
    conduit almost completely swamps the wire gauge issue.

  9. josephkk

    josephkk Guest

    Small wonder you get raped on #10. You don't know where to buy stuff.

  10. Guest

    Of course not. Michael is being silly with his suggestion of running
    #6 wire for the compressor. I thought I'd join in. For anything I've
    done, 1/2" Type-L copper is fine. That's probably what I'll use again
    but it's getting rather pricey.
  11. Guest

    Agreed, sorta. PVC isn't too bad, though. This whole thing has
    gotten absurd.
  12. Guest

    Those who are always wrong, are certainly stupid, AlwaysWrong.

    <nothing more needs to be known about AlwaysWrong>
  13. Guest

    When was the last time you bought wire?
  14. John S

    John S Guest

    I'm curious about this. Doesn't a motor draw about 6-10 times FLA during
    start? If so, wouldn't that cause a 18-30% drop during start if you have
    a 3% drop normally? Or, looking at it the other way, if you size for 8%
    starting drop, your normal operating drop would be only 1.3%.
  15. Guest

  16. Guest

    You're just helpless.
  17. SoothSayer

    SoothSayer Guest

    That is right on the mark.

    It was always fun to un a 100 foot extension cord to a construction
    work area and run a device like a circular saw or such. Then try it with
    two 100 foot cords together for 200 feet. It (the difference) is very

    Most of those cords are #14 at those lengths (or they'd better be), but
    at the price difference for raw wire and a buried run, I'd say that
    dropping to #12 or eve the #10 run was not an improper suggestion,
    considering it was going to be a permanent install, and the device being
    powered may not be, and wiring a service outlet is what we are doing.

    So, yes, as you illustrate, #14 is sufficient, even good, considering
    what I have seen houses and such wired with.

    At 200 feet away, and not knowing if the device will be the only item
    being powered, I would at least examine the cost tables for the job using
    #10, #12 and #14 Thhn, no conduit.

    As far as the conduit goes though, if one gets small diameter PVC, and
    all the fittings, no 200 foot pull needs to be done. The segments and
    fittings can all be fed down the wire bundle and build the conduit in
    place right on the wires, then bury the finished run.
  18. bud--

    bud-- Guest

    The NEC gives the full load current of a 1/2 HP 230V motor as 4.9 A.
    Power factor adds to the motor current. (In most cases this will be
    high, but is used to determine wire size.)

    The NEC gives the locked rotor amps as 29.4 (which is 6x the running amps).

    The NEC gives the resistance of 200 ft of #12 as 0.62 ohms (about the
    same as you used).

    The running voltage drop is 4.9V = 3%.
    The starting (locked rotor) voltage drop is 18.2V = 7.6%.

    #14 sounds reasonable. Can't remember if the motor was actually 1/2 HP.
  19. John S

    John S Guest

    I believe the motor current given by the NEC includes efficiency and
    power factor.

    In fact, the NEC info indicates an inefficient motor with a poor power

    Motor running VA is the motor volt-amps (4.9 * 230) = 1127.

    The power output of a motor is nameplate horsepower times 746 = .5 * 746
    = 373 Watts.

    The product of motor efficiency and power factor is:
    N*Pf = P/VA where N is efficiency and Pf is power factor. That product
    is 373/1127 = .331

    I know neither the efficiency nor power factor of the NEC's motor, but
    as a quick rough "feel" for the numbers, I can take the square root of
    the .331 = .575. Roughly .6 for power factor and .6 for efficiency.

    If power factor was actually typical of larger HP motors, say .7, then
    the efficiency is .331/.7 = .47 or about 50%.

    Fractional horsepower single phase motors typically have a lower power
    factor and lower efficiency than integral horsepower three-phase motors.

    However, that is not my point.
    Yes, I was thinking somewhere between 6 and 10 times.
    ISTM that if there is a 3% drop at FLA, then the drop will be 6 times
    that at 6 times the current. That would be 18%
    I am not questioning the wire gauge chosen.
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