Trouble with Compressor blowing Breaker

[jedens]

I have moved to a new garage and my compressor keeps (about half the time) throwing the breaker in the garage when it starts. There is nothing else plugged into the circuit. It is plugged into a 20 amp circuit with an 20 amp breaker. The motor is a 15 amp motor. I didn't have any trouble in my previous garage on a 20 amp circuit. Is there such a thing as a "slow-blow" breaker that will accomodate motor startup current, that can be put in a standard Square D residential breaker panel? The plug was a GFCI plug and I thought that might be the problem so I replaced it with a standard plug but that didn't help. Any help is appreciated.

 

[gerard]

I've heard that after a breaker trips a few times you should replace it as the bi metal contacts weaken and will trip easier next time. ie What you think is a 20 amp breaker may not be anymore. I'd also make sure the circuit is wired with 12 guage, not 14. I've seen 20 amp circuits wired with 14 which will excacerbate the situation on a cold start like when the compressor kicks on. But replace the breaker first, cheap fix and that may solve your problem.

 

[dieselsmoke1]

If it's only when it restarts under pressure (not when starting after a bleed down) perhaps the valve which unloads the pressure from the pump cylinder is not working. My compressor would trip it's breaker every time when trying to restart at 100 lbs when this valve failed. Replaced it, problem went away.

 

[Mark_in_NH]

I would double check all your specs., wire sizes etc.
you may have weekend the breaker, but doubtful. As has been said, it may only be occuring when the compressor starts up under pressure. I find this most likely when you realize and consider that the "start up load" in amps, on an electic motor is usually considered to be 3 times the running amps.
When your compressor tries to start under pressure it is harder for the motor to spin upto speed. This excessive draw of amps, will put undue strain on the breaker, thereby tripping it.
You may need to increase the size of both the circut breaker and the wire feeding your compresor outlet.

 

[DavidJ]

If it was working before on a 20 amp, it should work now. I suspect the breaker is weakened and that's where I'd start. I'd replace the breaker and see if that works. Or swap the compressor to another 20 amp one. We replace weakened breakers regularly because of nuisance trips. It happens more often than you might think.

If that doesn't work check to see if the pressure cutoff switch is still set where it was before the move. If it got jiggled to a higher
cut-on setting the motor would draw more amperage upon a loaded start.

 

[PineRidge]

If it is a moveable compressor before I spend a dime I would plug it into a different 20-amp circuit within the house itself. If a different 20-amp circuit blows then it’s in the compressor. Could be a starting switch or unloader valve.

If the new circuit holds then I would be reexamining the breaker and wire to the garage itself. Just because it's a 20-amp breaker doesn't mean they used the proper gauge wire. Which is normally 12 gauge unless it’s a real long run then it get heavier like 10 gauge.

 

[AndyMA]

</font><font color="blue" class="small">( If it was working before on a 20 amp, it should work now. )</font>
Not necessarily. The motoe is rated at 15 Amps run current. Like others have said, the starting current is much higher and will vary depending on the pressure load that the compressor tries to start with. It will even vary depending on where in the cycle the piston is. I suspect the problem is the length and guage of wire that runs to your garage. If after checking the compressor starting on a 20 Amp circuit local to your main breaker box. I would run a dedicated 20 Amp circuit with 10 guage wire to your garage so that the voltage drop would be minimized. The starting current will be much higher at a lower voltage and this is probably what is happening because of either the length or wire guage running to the garage.

Andy

 

[Junkman]

spoken like a true electrical engineer..... /forums/images/graemlins/blush.gif

 

[BIGUN]

I would first try the suggestion of swapping the compressor circuit to another breaker in the power panel in case that breaker is weak.

Then as suggested check out the unloader valve to be sure it is actually unloading the compressor every time before it tries to start. Since your problem is intermittent, the operation of this valve me be also.

It is probably already starting to get fairly cold where you live. I have heard of an instance where a compressor operating on a marginal circuit would not start when it was cold but would in warmer weather. I guess like an engine it takes more current to turn the compressor over when the oil is cold.

Before running a new dedicated circuit to the compressor I would see if the motor could be run on 220 volts. Some motors are easily converted by moving a couple of wires on terminals inside a cover at the end of the motor. Doing this would drop your 15-amp motor current to about 8 amps making a 220 volt, 12 gauge, 20-amp circuit more than adequate.

 

[MossRoad]

I have a compressor that will start just fine when it is at zero PSI. It pumps itself up then shuts off like it is supposed to. As I use air out of it, when it gets down to 80 PSI the pressure switch kicks on and it tries to start. It hums for a few seconds, then trips the breaker. The problem is the unloader is broken. The unloader takes the pressure off the compressor after the compresser shuts itself off so that the motor does not have to start the compressor under load. If this is not working properly, and does not unload every time the compressor shuts off, this could cause your problem.

To test, drain all the air out of the compressor, then attempt to start it a few times. If it starts every time with no PSI load, then let it build up pressure until it shuts itself off. Then drain some of the air until it attempts to restart. Try this several times to see if it is only popping the breaker while attempting to start with a PSI load. If it pops with a PSI load, I'd suspect the unloader. If it pops under no PSI load, I'd suspect the wiring.

Good luck. Please let us know what it turns out to be.

EDIT: "wiring" in the above comment means anything electrical, as in the motor, capacitor, outlet, wires and breaker.