Page 3 of 4 FirstFirst 1234 LastLast
Results 31 to 45 of 48

Thread: Air compressor blowing circuit breaker

  1. #31
    Join Date
    May 2018
    Location
    Lancaster, Ohio
    Posts
    85
    Is the circuit breaker rated HVACR?
    Highly doubt that it is as you stated it is a tandem breaker
    HVACR breakers are rated for high starting loads such as the air compressor, air conditioning compressor, etc
    The tandem breaker typically is designed to trip faster to protect normal not motor loads in residential use
    GOOD LUCK

  2. #32
    Join Date
    Apr 2010
    Location
    Houston, Texas area
    Posts
    1,022
    For future reference, here are the proposed potential problems so far:

    Compressor


    1. Failing unloader valve
      1. i.e. compressor pump head pressure release valve
      2. several recommendations to look at this one

    2. Dirty contractors in pressure release switch
    3. check the (motor's) start up capacitor
    4. Lube the bearings/bushings on the motor, whether they are designed to be lubed, or not


    Power


    1. Put compressor on dedicated circuit - already is
    2. Inadequate voltage at outlet - currently 123V. The shop has a dedicated 200AMP service and the trips are happening when the shop is not in use.
      1. can fluctuate during day - based on previous monitoring there is a pretty stable voltage at my location
      2. voltage drop due to wire run distance - 18' max run

    3. Inappropriate (for motor) or failing breaker
      1. Plug compressor into a different circuit - will test next
      2. Replace current 20A tandem breaker, possibly with an HVACR style breaker which is rated for high starting loads

    4. Inadequate AMPs on circuit for motor startup current inrush
      1. check startup current with clamp on ammeter
      2. current draw related to proper unloader operation
      3. increase 120V circuit amp capacity from 20A to 30A

    5. Convert compressor to 240V


    Environment


    1. Cold shop/compressor could increase startup current requirement - compressor kept between 65-70 degrees year round


    Safety Recommendation from John:

    "I hope you are turning off/disconnecting the air compressor when leaving the shop.

    Shops have burned to the ground when a break in an air line caused a compressor to run continuously."
    Last edited by mark mcfarlane; 11-15-2019 at 12:42 PM.
    Mark McFarlane

  3. #33
    Join Date
    Apr 2010
    Location
    Houston, Texas area
    Posts
    1,022

    Unloader tests

    In trying to diagnose the unloader valve I did the following tests:

    Test 1:


    • Cycle compressor: unloader valve opens at end of cycle as expected
    • Unplug compressor from wall
    • Check compressor 2 hours later, unloader valve is now closed. Breaker is fine because compressor was unplugged.


    The question becomes, did the unloader valve close because the actuator arm requires power to keep the valve open, or was this a failure of the pressure switch that operates the unloader valve and it should keep the valve open even if there is no power to the pressure switch.

    Test 2:


    • Cycle compressor: unloader valve opens at end of cycle as expected
    • leave compressor plugged in
    • Check compressor the next day, breaker is thrown and unloader valve is closed.


    Did unloader valve close due to a lack of available power, or did it close as expected when the compressor started up, and then a few ms or seconds later the breaker threw? Nothing to learn from this test.

    Test 3


    • Cycle compressor: unloader valve opens at end of cycle as expected
    • Cycle compressor: unloader valve closes at the same time the compressor starts.


    Nothing to learn from this test. I can't visually discern if the unloader valve closes before or after the compressor starts, it appears to my eye to be simultaneous. A high speed camera might resolve the exact timing.

    If I continue to manually cycle the compressor in rapid consecutive tests the unloader valve operates exactly as expected and the breaker does not blow.

    The breaker only seems to blow if the compressor has completed a several hour long rest state.
    Mark McFarlane

  4. #34
    Join Date
    Feb 2013
    Location
    Tippecanoe County, IN
    Posts
    506
    I don't want to interrupt the troubleshooting flow here but there are a couple of minor points I want to bring up.

    Quote Originally Posted by mark mcfarlane View Post
    ...check startup current with clamp on ammeter...
    Not many clamp meters are capable of capturing inrush current. If yours is not (and it should be in the manual if it is) and you motor has a proper nameplate you'll find it there. There will be a code letter for the Locked Rotor Current (LRC). It's usually labelled "CODE". Look up the code letter in the table:
    LR Codes.JPG
    Then make the appropriate calculation. For example, if your motor has a code G and a rated voltage of 115V then you start current is 2HP x 5.9kVA/HP x 1000VA/kVA / 115V = 103A.

    Quote Originally Posted by mark mcfarlane View Post
    ...This compressor is also rated at 1500 Watts, it's in the model name P1.5IU-A9, so thats 12.5 Amps. Perhaps the 2HP figure is from unscrupulous marketing.
    Both HP and Watts are units of power. Watt is metric and HP is Imperial. Motor ratings generally use a rounded number of 750 Watt per Horsepower. So 2HP x 750W/HP = 1500W. That is the rated LOAD not the input.

    Input power is output load divided by efficiency and is also measured in Watts. Apparent input power is input power divided by power factor and is measured in Volt-Amps. Input current is then apparent input power divided by input voltage. For example, a 2HP (1.5kW) motor with 85% efficiency and 90% power factor would have an input current at rated load of 1500/.85/.9/120 = 16.3A.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

  5. #35
    Join Date
    Oct 2008
    Location
    Kapolei Hawaii
    Posts
    2,956
    Quote Originally Posted by Ron Selzer View Post
    Is the circuit breaker rated HVACR?
    Highly doubt that it is as you stated it is a tandem breaker
    HVACR breakers are rated for high starting loads such as the air compressor, air conditioning compressor, etc
    The tandem breaker typically is designed to trip faster to protect normal not motor loads in residential use
    GOOD LUCK
    +1. This is it I think. I trip my tandem breaker on my 3/4 hp Delta bandsaw if I load it down on a cut.
    Move the wiring to a regular breaker slot and move the other wiring to the tandem. Should not be too difficult. Remember to swap the breakers to the proper rating.

  6. #36
    Join Date
    Apr 2010
    Location
    Houston, Texas area
    Posts
    1,022
    Quote Originally Posted by David L Morse View Post
    I don't want to interrupt the troubleshooting flow here but there are a couple of minor points I want to bring up.



    Not many clamp meters are capable of capturing inrush current. If yours is not (and it should be in the manual if it is) and you motor has a proper nameplate you'll find it there. There will be a code letter for the Locked Rotor Current (LRC). It's usually labelled "CODE". Look up the code letter in the table:
    LR Codes.JPG
    Then make the appropriate calculation....
    Thanks David, I can't see the language you have referenced on my compressor motor.

    IMG_4493.jpg
    Mark McFarlane

  7. #37
    Join Date
    Feb 2019
    Location
    Annapolis
    Posts
    51
    +2. Good call

    Quote Originally Posted by Ron Selzer View Post
    Is the circuit breaker rated HVACR?
    Highly doubt that it is as you stated it is a tandem breaker
    HVACR breakers are rated for high starting loads such as the air compressor, air conditioning compressor, etc
    The tandem breaker typically is designed to trip faster to protect normal not motor loads in residential use
    GOOD LUCK

  8. #38
    Join Date
    Feb 2013
    Location
    Tippecanoe County, IN
    Posts
    506
    Quote Originally Posted by mark mcfarlane View Post
    Thanks David, I can't see the language you have referenced on my compressor motor.

    IMG_4493.jpg
    No, I don't see it either. Those are IEC specs not NEMA on that nameplate, but it's not complete.

    The laboratory method for measuring locked rotor current is to literally lock the rotor and then measure the current. You usually don't have a lot of time before the breaker opens but most ammeters are fast enough to get a measurement. It's not difficult, you just need a good way to keep the rotor from spinning.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

  9. #39
    Quote Originally Posted by Bill Dufour View Post
    Location? I am guessing you are talking fahrenheiht?
    It's fahrenheit for me. I'm near Dallas TX so it doesn't get that cold very often.

  10. #40
    Join Date
    Apr 2010
    Location
    Houston, Texas area
    Posts
    1,022
    The compressor has run for 48 hours (cycled a few times) without throwing a breaker on a different 20AMP circuit using an extension cord . So far so good.

    I'll report back in another week, but it looks like my root electrical problem may be the tandem breaker.

    Thanks again to everyone for your thoughtful responses and assistance.
    Mark McFarlane

  11. #41
    Join Date
    Mar 2003
    Location
    SE PA - Central Bucks County
    Posts
    50,241
    Mark, even a "new" breaker can go bad, although it's certainly unusual...so at this point, I'd replace it sooner rather than later since they are not hugely expensive.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  12. #42
    Join Date
    Apr 2010
    Location
    Houston, Texas area
    Posts
    1,022
    Quote Originally Posted by Jim Becker View Post
    Mark, even a "new" breaker can go bad, although it's certainly unusual...so at this point, I'd replace it sooner rather than later since they are not hugely expensive.
    Good idea, thanks Jim.
    Mark McFarlane

  13. #43
    Join Date
    Oct 2006
    Location
    Manistique, Michigan
    Posts
    1,206
    Those tandem breakers can be a problem. Manufacturers try to squeeze everything in a half the space of a normal size breaker. There are bound to be issues. Itís interesting to listen to electricians and electrical engineers tell troubleshooting stories involving these breakers. I use them, but in lightly loaded applications.

    Most have found issues when it comes to starting current required and these tandem breakers donít have enough capacity for the in rush current.

  14. #44
    Join Date
    Feb 2011
    Location
    Central WI
    Posts
    5,322
    What Rich said. Tandems are best for lights and low load, and should be avoided for motor circuits. Dave

  15. #45
    Join Date
    Apr 2010
    Location
    Houston, Texas area
    Posts
    1,022
    Thanks everyone for your assistance with my air compressor / breaker dilemma. The compressor has run for 6 days without throwing a breaker using an extension cord from a circuit with a full size 20amp breaker. The previously used tandem breaker appears to be the root cause.

    I may try to replace the tandem breaker, since it did work fine for a year or so, before attempting some circuit rerouting which will require jumper wires in the breaker box.

    Thanks again to everyone who pitched in. I learned a lot more about how a compressor works and the various points of potential failure.

    In particular, John's post about unplugging the compressor every day to avoid a runaway compressor-caused fire due an air line leak has opened my eyes. I shall try to get in the habit of shutting off the compressor every day, and also add a new valve at the tank to slow down the effect off my slow leak in the in-wall rapid-air tubing network.

    Cheers,
    Mark McFarlane

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •