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Help/air compressor tripping 20 amp breaker

Discussion in 'Electrical Engineering' started by Bruce, Dec 1, 2003.

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  1. Bruce

    Bruce Guest

    I have a 58' run of 12/3 wire running to the shed that operated some
    lights and a small 110v sears 30 gallon air compressor nearly new.
    The first time or two of turning it on to build air the breaker blows.
    After that it seems to be fine the rest of the day, cycling on/off.
    Is my wire run to long and making to much of a current drop???
    What can I do to stop this. Anyone? Thanks in advance.
    please remove SPAMNOT to reply off list if you want
  2. SQLit

    SQLit Guest

    Not knowing the FLA and LR for the motor try this site for the voltage drop

    I have a 15 gallon Sears compressor and it says it draws 15 amps.(FLA)
    According to the site
    15 amps and 58 feet results in a 3 volt drop or 2.8% well with in
    tolerances. Max is 5%. The extra for the lights might be the problem
    Have you tried another breaker? Residential breakers do get tired and trip
    early after a long time. My home is 30 years old with SQ NQO breakers, I
    have replaced the exterior breakers and the pool circuit they just trip to
  3. 15Amp FL this might also be a breaker rating issue is it a type C breaker
    for motors?
    Darren Fletcher
  4. Bruce

    Bruce Guest

    The breaker has on it QD SWD. Does this small motor have a start cap
    that can lose stored energy over a short period of time?
    I just switched with another breaker and will see.
    Still looking for a fix in case the lights dim way down.
    Thanks again,
  5. Rusty

    Rusty Guest

    Start caps are AC devices so they don't store energy between starts.

    The problem is quite common starting a small compressor. The inrush
    current for an electric motor is about six times the FLA, or 90 odd
    amps for a fraction of a second. An ordinary domestic breaker will
    not handle this with a cold motor where the duration of the inrush
    is longer than when it is warm. You are right on the edge.
    Consider getting a breaker rated for a motor start. Fit it in a
    separate breaker box if necessary, alongside the main panel.
  6. Zzzap

    Zzzap Guest

    Circiuit breakers used as switches in 120-volt and 277-volt
    fluorescent lighting circuits shall be listed and shall be
    marked SWD or HID. [marked HID for high-intensity discharge

    Use another breaker. It's doubtful that a company would build a
    home and leave enough amperage left over on a lighting circuit
    to run your compresser.

    Keep your compresser separate from the lighting circuit.
    Otherwise no matter what you do you'll probably have the same
    problem. That might mean running a new circuit for it. It should
    be on its own circuit anyway.
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