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Thread: advice - OT

  1. #1
    Join Date
    Sep 2006
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    Big Prairie Mi.
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    2,139

    Default advice - OT

    Several years ago a good friends brother in law bought an air compressor, 230v ran great, only had 115v, so re-wired motor. He never got it to run right, every time he turned it on it blew the breaker, he got fed up and gave it to my friend.
    Fast forward 5 years later, My air compressor died, Friend says 'brother in law' gave me his, if you want to fix it, it's yours.
    So, drag it home, and of course, first thing I do is plug it in, boom, breaker blows, yep something wrong.
    several days later, after installing new caps, unloader valve etc, and still blowing breakers, I -finally- take a real good look at the tag on the motor, it says '20 amp at 115' umm, I've been using a 15 amp circuit.....

    Hook it to a 20 amp circuit and it runs extremely well.

    So read the effin tags before you waste a lot of time on fixing something.

  2. #2
    Join Date
    Mar 2013
    Posts
    1,065

    Default

    That is the best kind of deal in my book. I bought a new $1100 HEPA vac fro $25 because it didn't run. Took the cover off the motor, a wire was hanging loose, that was it.

  3. #3
    Join Date
    Oct 2013
    Location
    USA MD 21030
    Posts
    3,793

    Default

    A 15 amp breaker may carry 20 amps for 10 minutes or so. If it blew instantly the surge current may be over 100 amps. Breakers generally have an inverse square time versus current curve using a thermal element that starts at about 120% to 130% of nominal. Then at something like 6x to 12x nominal current a magnetic element trips instantaneously, in 3 cycles (50 mSec) or less.

    http://electrical-engineering-portal...current-curves

    http://blog.mavtechglobal.com/blog/2...-curves-part-1



    http://www.electrical-installation.o...ircuit-breaker

  4. #4
    Join Date
    May 2017
    Location
    New Jersey
    Posts
    95

    Default

    Quote Originally Posted by kendall View Post
    Several years ago a good friends brother in law bought an air compressor, 230v ran great, only had 115v, so re-wired motor. He never got it to run right, every time he turned it on it blew the breaker, he got fed up and gave it to my friend.
    Fast forward 5 years later, My air compressor died, Friend says 'brother in law' gave me his, if you want to fix it, it's yours.
    So, drag it home, and of course, first thing I do is plug it in, boom, breaker blows, yep something wrong.
    several days later, after installing new caps, unloader valve etc, and still blowing breakers, I -finally- take a real good look at the tag on the motor, it says '20 amp at 115' umm, I've been using a 15 amp circuit.....

    Hook it to a 20 amp circuit and it runs extremely well.

    So read the effin tags before you waste a lot of time on fixing something.
    I agree, its also why my shop has twin brakers, one 20A and one 30A and both on separate lines that come into the shop. I think the service is twin 100A service.
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