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Thread: Air compressor blowing circuit breaker

  1. #1
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    Air compressor blowing circuit breaker

    I have a slow leak somewhere in my air line plumbing (which I possibly should not have installed in the walls...), This causes my air compressor to cycle maybe once or twice a day to refill the circular network of air lines.

    Every few days the compressor throws the 20 amp dedicated 120V circuit breaker. Compressor is an IR Garage Mate, 2HP, 20 gallon, about 2 years old. Air filters are clean, pump oil is maybe 2mm above the 'fill bubble', i.e. a tad overfilled.

    Any ideas why the breaker is getting thrown?

    Thanks,
    Mark McFarlane

  2. #2
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    IR offers these possibilities for "Motor overload trips or draws excessive current", I guess I should start by checking the belt tension:

    1. Lubricant viscosity too high.
    2. Improper line voltage.
    3. Wiring or electric service panel too small.
    4. Poor contact on motor terminals or starter connections.
    5. Improper starter overload heaters.
    6. Poor power regulation (unbalanced line).
    7. Drive belts too tight or misaligned.
    8. Compressor valves leaky, broken, carbonized or loose.
    9. Cylinder(s) or piston(s) scratched, worn or scored.
    10.Connecting rod, piston pin or crankpin bearings worn or
    scored.
    11.Defective ball bearings on crankshaft or motor shaft.
    12.Leaking check valve or check valve seat blown out.
    13.Ambient temperature too low.
    14.Bad motor.
    Mark McFarlane

  3. #3
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    From the outside looking in & understanding it is the panel/sub-panel feed circuit breaker that is tripping and not the motor mounter protection:
    - The first place I would start looking is at the compressor pump head's pressure release valve (unloader) (between the pump head & tank check valve that is connected to the pressure switch) adjustment. It reads as if the pump's head pressure is not always releasing and the motor is trying to start the pump with pressure on the head.
    - Next I would try cleaning the contractors in the pressure switch.
    - If not either of those do the trick, then I would check to insure that all the wiring connections are clean & tight.
    Last edited by Rob Charles; 11-14-2019 at 11:57 AM.

  4. #4
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    A 2hp compressor may be drawing 20 amps, and more on startup. Available voltage will have a normal variation from the grid and more in your building due to other loads. You might need to increase the available amperage or get a breaker that blows slower. First try replacing it with a new one of the same capacity just in case it is defective.

  5. #5
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    What other loads are on the same circuit? Maybe a bunch of lights, a heater, maybe the table saw is on the same circuit and running, etc. The startup current might be just enough on top of other loads. If it is a dedicated circuit just for the compressor then many other potential issues.
    Last edited by Pat Barry; 11-14-2019 at 9:15 AM.

  6. #6
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    When I had that problem it was an unloader valve sticking shut. Unloader valves release air in the cylinders so the motor isn't starting against pressure. Does the compressor, when stopping release a small amount of air? Had it previously? Otherwise a marginal circuit or circuit breaker would be a likely candidate. Could you run a heavy duty extension cord to the compressor from another circuit?

  7. #7
    A 2 HP motor will do poorly on a 20A 120 volt circuit, a 30A or larger circuit is required which is doable but it is much simpler to run it at 240V, 1 1/2 HP is the limit for common 120 volt circuits.

  8. #8
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    I doubt that the apparent leak in the network is related to the breaker thing. The circuit itself is the first place to look. Even though this machine will run on 120v, it's still wanting it's own circuit so if it shares, it could merely be a coincidence of timing. It could also be a bad breaker. It could also be something like Curt describes.
    --

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

  9. #9
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    The unloader is your 1st place to look. They get "sticky" (and a bit later just stop working altogether). They are not difficult to replace.

  10. #10
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    Quote Originally Posted by Pat Barry View Post
    What other loads are on the same circuit? Maybe a bunch of lights, a heater, maybe the table saw is on the same circuit and running, etc. The startup current might be just enough on top of other loads. If it is a dedicated circuit just for the compressor then many other potential issues.
    Thank Pat for the idea. The compressor is on a dedicated circuit to a single 20 amp outlet. Nothing else plugged in.
    Mark McFarlane

  11. #11
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    Quote Originally Posted by Tom Bender View Post
    A 2hp compressor may be drawing 20 amps, and more on startup. Available voltage will have a normal variation from the grid and more in your building due to other loads. You might need to increase the available amperage or get a breaker that blows slower. First try replacing it with a new one of the same capacity just in case it is defective.
    Thanks Tom. It's actually on a tandom (half-height) breaker, but I can try another one after investigating the compressor related suggestions. My new 30 slot shop panel got filled quickly .
    Mark McFarlane

  12. #12
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    Quote Originally Posted by Rob Charles View Post
    From the outside looking in & understanding it is the panel/sub-panel feed circuit breaker that is tripping and not the motor mounter protection:
    - The first place I would start looking is at the compressor pump head's pressure release valve (unloader) (between the pump head & tank check valve that is connected to the pressure switch) adjustment. It reads as if the pump's head pressure is not always releasing and the motor is trying to start the pump with pressure on the head.
    - Next I would try cleaning the contractors in the pressure switch.
    - If not either of those do the trick, then I would check to insure that all the wiring connections are clean & tight.
    Thanks Rob.

    There is a pressure relief valve between the two cylinders in the exhaust tube. Is this is the one to release the head pressure?

    There is as second pressure release valve mounted to the pressure switch on the front of the compressor.

    How do I 'check' these valves for proper operation, other than just exercising them?

    I opened up the pressure switch but I'm not sure exactly where the contractors are or how to clean them.

    IMG_4488.jpgIMG_4489.jpg
    Mark McFarlane

  13. #13
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    Quote Originally Posted by Curt Harms View Post
    When I had that problem it was an unloader valve sticking shut. Unloader valves release air in the cylinders so the motor isn't starting against pressure. Does the compressor, when stopping release a small amount of air? Had it previously? Otherwise a marginal circuit or circuit breaker would be a likely candidate. Could you run a heavy duty extension cord to the compressor from another circuit?
    Thanks Curt. I do have some 20 amp extension cords and a 20 amp 120V outlet about every 6 feet around the room. Thats a great idea to test the circuit.

    I just cycled the compressor and I did hear air escaping as the pumps shut down. Unfortunately I have no idea if this happens all the time, or ever happened in the past. I never listened for it before and the compressor is in a machine room.

    The breaker doesn't throw every time the compressor operates, maybe every 5th-10th time.
    Mark McFarlane

  14. #14
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    Quote Originally Posted by Rollie Meyers View Post
    A 2 HP motor will do poorly on a 20A 120 volt circuit, a 30A or larger circuit is required which is doable but it is much simpler to run it at 240V, 1 1/2 HP is the limit for common 120 volt circuits.
    Thanks Rollie. FWIW, the compressor has a NEMA 5-15 plug on it.

    Edit: 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.
    Last edited by mark mcfarlane; 11-14-2019 at 2:29 PM.
    Mark McFarlane

  15. #15
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    Quote Originally Posted by Jim Becker View Post
    I doubt that the apparent leak in the network is related to the breaker thing. The circuit itself is the first place to look. Even though this machine will run on 120v, it's still wanting it's own circuit so if it shares, it could merely be a coincidence of timing. It could also be a bad breaker. It could also be something like Curt describes.
    Yea, the leak is somewhere in the many joints of RapidAir tubing.

    It is a dedicated circuit. I just exercised the two relief valves and will watch it for a week. If the breakers blow again I'll try an extension cord to another circuit, I have an unused dedicated circuit under my workbench and a 20 amp extension.
    Mark McFarlane

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