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Brian Hartley 11-13-2012 03:47 PM

air compressor motor
I have a 1 1/2 hp air compressor with a Dayton capacitor start motor [115/230]
wired for 115 volts. it's started tripping the circcut breaker after running for 15-20 minutes. now it trips at turn on. checked capacitor with volt meter seems good. can't find any shorted wires. help!

k_buz 11-13-2012 03:48 PM

Is anything else on the circuit?

Missouri Bound 11-13-2012 06:40 PM

Pick up a clamp on ammeter. It will help tell you if it's the compressor or the circuit which has the problem.

micromind 11-13-2012 07:10 PM

A 1-1/2HP motor is pushing a 20 amp 120 volt circuit pretty hard. I'm not surprised that the breaker is tripping.

Most likely, all the recent tripping has weakened the breaker to the point it's no longer capable of starting the compressor.

It's certainly possible that something is wrong with the motor, but I doubt it.

Also, a compressor is WAY harder to start when it's cold than when it's warm.


DexterII 11-13-2012 07:20 PM

If you happen to be running it on an extension cord, move it, so that you can plug it dirtectly into a receptacle. Is it unloading properly?

Brian Hartley 11-14-2012 10:23 AM

air compressor motor
compressor is on a dedicated 20amp circut with new breaker in a warm basement

iamrfixit 11-14-2012 11:02 AM

While it certainly could be a problem in the motor or with the circuit;
you may have some issues with the compressor itself, most likely causes would be that the check valve is not seating or the unloader valve not functioning.

Between the compressor and the storage tank there is a check valve that holds the compressed air in the tank. If this valve is leaking it causes the compressor to have to re-start under load and that would likely trip the breaker. During a run cycle pressure from the tank backing up against the compressor may cause the motor to overload before it reaches it's cut out pressure.

Sometimes the check valve can get sticky from oil vapor or get a small piece of debris lodged in it and hold it open, it takes very little to cause problems.

If the motor will run with the tank bled down or the belt removed I would look into the check valve.

ddawg16 11-14-2012 11:07 AM

Take the belt off and see if the motor runs without an issue.....if so, it pretty much confirms that your running on the ragged edge....

As an FYI....I have pretty much the same motor....I would highly suggest wiring it up for 240Vac....

J. V. 11-14-2012 11:13 AM

Does this compressor come with a cord and plug attached? If not, take the FLA x 2.50. This will give you the current breaker required.
NEMA says your compressor motor pulls 20 amps at 120 volt and 10 amps at 230 volts.
The question regarding the cord and plug is very important. Does it have a factory cord and plug? If not, you take the FLA (current on motor nameplate) and multiply it by 2.5 or 250%. This will be your breaker size.
I am fairly certain you need a larger breaker.

electures 11-14-2012 01:30 PM

2008 NEC requires #12 CU and up to a 50A breaker
2011 NEC requires #10 CU and up to a 50A breaker

WHat does the manufacturer of the compressor require in the installation instructions?

kbsparky 11-14-2012 08:35 PM


Originally Posted by electures (Post 1052073)
2008 NEC requires #12 CU and up to a 50A breaker
2011 NEC requires #10 CU and up to a 50A breaker

WHat does the manufacturer of the compressor require in the installation instructions?

Requires? How about allows?

Missouri Bound 11-14-2012 08:54 PM

Despite the NEC allowances, I have seen and operated several compressors, 5HP 240v on 20 amp circuits with 12 guage wire.....on continuous duty cycles. That being said there is an issue with either the compressor or the comprressor circuit itself. There are no quick answers here....this just needs some old fashion troubleshooting.:yes:

electures 11-15-2012 07:04 AM


Originally Posted by kbsparky

Requires? How about allows?

Ok so I missed a comma. Wire size is required. Up to 50A breaker is allowed. There I go applying "commercial thoughts" to residential applications again.

Brian Hartley 11-15-2012 08:08 AM

air compressor motor
The compressor spins over easily and no air in tank, original power supply cord.
wiring is 12 ga, 20 amp plug. i've had this compressor for 10 years with lite use.
trips new breaker immeiditely upon switching on.

micromind 11-15-2012 08:20 AM

What type of breaker?

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