Air compressor tripping 20 amp breaker

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I have a Sears 25 gallon/4HP horizontal compressor. When I first turn it on it runs fine and shuts off at 150psi. The problem I have is when the pressure gets at the level where it automatically kicks on again it then pops the breaker off and I then have to reset the breaker before it will run again. I have a dedicated 20 amp circuit with 12/2WG using a Square D breaker and a 20 amp duplex receptacle for the compressor, and nothing else is on this circuit. Do any of you folks have any suggestions as to how I can cure this problem? Thanks for your help.
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If this was working and it stopped I would suspect a bad check valve. If it is new you will have to look at the nameplate FLA rating on the motor to see what you are dealing with. The number on the tank label is usually a fantasy.
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Check motor startup peak amp draw with tank empty and as it trips the breaker, You will be suprised. Then contact sears for maximum amp draw guidlines and remedies.
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Tom wrote:

Hi, There are breakers with different peak surge and trip delay rating, what kind of breaker do you have in there? Tony
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Tony, It says on the Square D breaker 10KA 120/240V-

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Congratulations, your electrical system is working as it should.
<< Do any of you folks have any suggestions as to how I can cure this problem? >>
Obviously, the compressor motor has a current surge problem on starting. You have several options: 1) Run it from a dedicated 30 amp circuit, new breaker, 10 ga wire, etc. 2) If it is a capacitor equipped motor, have a qualified shop check and/or replace the capacitor(s). 3) Replace the motor with one more suitable for the machine. 4) Rewire the system to run on 220 volts after ensuring that everything is OK otherwise. 5) Install a smaller motor pulley. That will reduce the starting current modestly, at the expense of slower output (no free lunch, ya know). One or more of the above ought to work. Good luck.
Joe
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are you serious ? ? ? and if it trips the 30 should he go up to . . .ohhh maybe 60? Hell just go directly to the power co. feeder. and going to 220 isn't gonna do a damn thing either. if you go 220 then your F.L.A is 1/2 of F.L.A at 110. the moter is draw as much as it can to try and start.
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What does the manual say the circuit should be rated for?
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on
run
else
can
Make sure the unloader isnt clogged and the check valve is working correctly--when it shuts down, it should hiss for a couple seconds then stop.
Otherwise it will be under too high of mechanical load on startup, not good as it will draw too much electrical current.
--

SVL



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If the machine starts OK with low tank pressure but trips a breaker with some tank pressure (its low pressure limit), then it's almost certainly the check valve, AKA the unloading valve. These don't last forever, and they're really not expensive.
If the motor is trying to turn the pump against existing tank pressure, almost any motor, even brand new, will draw excess current.
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Robert Barr wrote:

(Correction -- the unloading valve is an entirely different creature than the check valve.)
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on
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You do not mention the distance the circuit is. I assume you ran #12 copper?
Have you checked the connections on the breaker and recpt. An motor can draw 6 times FLA on start up. With an air compressor with partical pressure the high current draw could be lasting longer than the breaker likes.
Try changing breakers with another in the panel. If it still happens then check out the compressor.
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Tom, does the compressor make a loud hissing noise after it shuts down at 150 psi? This would be the "un-loader" valve. The unloader allows the compressor to start with little of no pressure in the cylinders. This allows for a low starting amps until the compressor gets up to speed. If the unloader is not working, then the full system pressure is adding resistance to the starting load and may be too much for the breaker.
john
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John When it shuts off there is no hissing noise. It's just quite.

allows
resistance
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The unloader valve should release the pressure from the output line of the compressor as the compressor turns off. If you don't hear the air release, that valve is not doing its job.
Bob

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Check to see what the unit is rated at. Does it call for a 30 amp breaker?
Also, you aren't running it with an extension cord are you? I had a neighbor that had trouble with his. Worked fine for years and it started tripping the breaker. He put a new breaker in - same thing. Bought a new capacitor and then eventually bought a new motor. I asked him what he was doing different and he said he was using it away from his shed and had it hooked to a 100 foot extension cord. Bingo. That was his problem.
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No I'm not using an extension cord. I go directly to a dedicated outlet from the compressor.

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On Thu, 28 Oct 2004 21:02:05 GMT, "Red Neckerson"

That was exactly my problem too. There is a voltage drop if your extension cord is too long. That plus the start-up load trips the breaker. The solution
1. Use an extra long air hose instead. There won't be any air pressure drop and the tools will work at full power. 2. Open the air tank valve to release the pressure so that the start-up load isn't high enough to trip the breaker. This is still a poor solution because the breaker will still trip, though less often.
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I was also thinking start up load. Sometimes the electrical switch has an adjustment, so you can set the "turn on" pressure down a bit lower.
Or you can make a pinhole leak right after the compressor, so that when the comp starts, it's under zero pressure. Needs a check valve after the pinhole leak.
Best bet is to check the volts and amps at startup, and see if that tells you something useful.
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I have a Sears 25 gallon/5HPhorizontal compressor as well and mine did the same thing after about two years. It was on a 20A 110V breaker 5 feet from the panel on a dedicated outlet. I rewired the motor to 220v (simple jumpers and the schmetic is in the motor junction box) and put it on a 20A 220V breaker and has been fine since. When I was having the problem I checked the motor with a megger and checked the amperage of the load and the motor was fine but the startup current was around 22 amps. My guess is that this was due to the fact that it is a oil less compressor and is now wearing in a bit and has become hard starting. It has been fine on 220v and is drawing 8.5 amps on startup.

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