ECN Forum Forums General Topics of the Trade General Discussion Area please advise: compressor keeps tripping breaker

I advise you to call a licensed electrician. Good luck!

The random trips on this compressor - not being the initial startup, but when tank pressure needs to be topped off [restarting motor] really sound like:

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[*] Faulty Unloader Valve (not allowing pressure out of pump prior to restart),

if not, next could be:


[*] Start Capacitor with random short / open problem, or some other heat related problem with the Aux. (Start) circuitry,

and the last possible cause:


[*] Bearings on either the pump or the motor (or both).
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Sounds like an unloader problem. The random start or trip situations would be from where the piston stops. If it passed Top [is Top Dead Center correct for pumps???] after motor stopped, the cylinder would be heading into a vacuum state with the piston falling to the intake stroke, so no high pressure on piston in this position.
If the piston was heading up on compression stroke, then the cylinder has pressure against the piston, making it a hard start situation for the motor.

Just rambling on with my $0.02!

Scott s.e.t.

Wow, lots of things to consider... Thanks to all for the feedback.

I'm really leaning toward somethign being wrong with the compressor, as suggested by several here. I didn't realize that there was an unloader valve that could be a factor here, but the scenario described by resqcapt19 is the same as what is happening. I don't recall the breaker tripping when the tank starts up from being empty. Also, I was aware of the startup capacitors on A/C compressors, but didn't know whether this was common on an air compressor.

My next step will be to get an ammeter and try to see what the thing is pulling. It is possible, I believe, but I will have to add the meter to my christmas wish list.

It is corded, FWIW, with a very robust looking (i.e. thick) 6 foot cord. It is made to be portable (has wheels), and I'd rather not hard-wire it if I don't have to.

Also, the receptacle is GFCI, but the GFCI has never tripped, just the breaker at the panel.

I'm going to call Sears tomorrow.

Thanks to all.

INTP, you can hear the unloader hiss when the motor shuts off, either at set pressure or if you manually turn off the compressor at the pressure switch.

stamcon: yes, I do hear it. I didn't really notice it before people here pointed it out. I bled the air to try to reproduce the problem, but after about 10 tries, it never tripped. I heard the unloader each time, and it started every time. I was hoping to not hear it and also have the breaker trip on the next try. Dang.

Here are some numbers from the panel.

Peak Start Amps:
try #1 55.6
try #2 45.3
try #3 44.8
try #4 42.7
try #5 43.1
try #6 49.6

Running amps were around 12.5-13.5A (fluctuated) while the tank was mostly empty, to 15-16A as the tank got fuller.

This is a new Craftsman clamp-type ammeter, with peak hold. As a control, I tested a general purpose circuit that was running only lights. I added up 54W fluorescent (27 + 27) + 350W incandescent (150 + 100 + 100). The meter read 3.2A. Actual voltage was 126 (this meter and another meter). 404/126 = 3.206. I know this isn't exact, but I thought it would be a sanity check.