Trouble with Compressor blowing Breaker

jedens · Nov 30, 2003

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 · Nov 30, 2003

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 · Nov 30, 2003

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 · Nov 30, 2003

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 · Nov 30, 2003

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 · Nov 30, 2003

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 · Nov 30, 2003

( If it was working before on a 20 amp, it should work now. )
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 · Nov 30, 2003

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

BIGUN · Dec 1, 2003

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 · Dec 1, 2003

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.

Junkman · Dec 1, 2003

( 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. He could use the white wire for the other hot conductor and not change the wiring, but that would violate the National Electric Code and possibly cause insurance problems for him if there was an electrical fire. )

I am quite certain that the motor could be wired for 220 use easilly by changing a few wires inside of the motor case, but the outlet can't be changed easilly because there are only a HOT, NEUTRAL, & GROUND in a 110 circuit. He would have to have 2 HOTS, a NEUTRAL & a GROUND to convert it to 220 outlet and is missing one wire. Hence he would have to run new wire to make the change and that would still make it a dedicated circuit.

Inspector507 · Dec 1, 2003

No need for a neutral on a 220V motor. 3 wires is adequate.

Soundguy · Dec 1, 2003

I went thru something similar with our upright 15 year old 60 gallon 5hp air compressor in our shop. Started poping the breaker.. so I replaced the breaker.. that got us another few months.. then it popped a starting capacitor.. got another.. then it popped them again... carted the motor down to the rebuild shop and it had some shorted windings. New 5hp motor was 20 dollars cheaper than a campbel hausfield 60 gallon upright.. so we went that route... Has been working fine for months.

As a side note.. we plumbed the tank from the old compressor ( 120 gallons ) into the line, and once it gets pumped up in the morning.. they have air all day with less cycle time on the compressor.

Look at those caps.. see if they have been leaking...

good luck

Soundguy

TheKid · Dec 1, 2003

Since the wiring to the compressor has been pretty well covered here are a couple of other things that have caused me problems. A weak motor start capacitor will cause a motor to pull more current on start up. Is the new garage colder than the old one? Colder temps equal thicker compresser oil and harder starting. I had to move mine to the basement because it didn't like my unheated garage in the winter.

Junkman · Dec 1, 2003

( No need for a neutral on a 220V motor. 3 wires is adequate. )

How do you get 3 wires out of a 110 circuit. When I upgraded my service last year, I had to separate the neutrals from the grounds to meet the new codes that CT is using. I also had to use a special meter socket that had a bypass switch inside of it. Isn't all this part of the National Electric Code that every state follows???? Is it now proper to use the white wire as a HOT wire???? I know that it is in certain instances such as an air conditioner, but a air compressor?????? Does it matter if it is plugged into a receptacle or hard wired???
/forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif

Inspector507 · Dec 1, 2003

Junkman,
The white wire, in a multi-conductor cable, can be used as a hot as long as it's re-identified by tape, paint or other approved means. It makes no difference whether it's hard wired or plugged in.

Black=HOT
White (re-identified)=HOT
Green/Bare=Ground

Voila........220V /forums/images/graemlins/grin.gif

The meter socket you had to use in your case was not a rquirement of the NEC®, but possibly necessary because of your local power company's rules.

BillyP · Dec 1, 2003

On a 110 receptacle, you have a neutral, hot and ground wire. On a 220 you have 2 hot wires and a ground. You can use 10/2 w/G for either one.

Is that what you were asking?

BIGUN · Dec 1, 2003

Junkman,

I was talking about running new wire and using a 220-volt, 20amp receptacle, which is different than a 110-volt, 20amp receptacle. You wouldn’t want 220-volts wired to a 110-volt receptacle for obvious reasons. You wouldn’t want to just wire the original circuit for 220 volts because then every receptacle on that circuit would be at 220 volts.

As Inspector507 has explained, 12/2 w/ground is all you need on this circuit, 2 hots and a ground. A neutral is only needed when you are going to tap 110-volts off the circuit as you do in your breaker panel. If it were a 3-phase motor, then you would need 4 wires, 3 hots and one ground.

The beauty of 220-volts is that the voltage drop percentage is less than on a 110-volt circuit. The actual voltage drop is the same on both, but it is a smaller percentage on the 220-volt circuit. A 5-volt drop on the 110 volt circuit is approximately 5% while it is only a little over 2% drop on the 220-volt circuit. This would be the case if the current draw were the same on both. Since the current will actually be half as much on the 220-volt circuit the voltage drop percentage will be even less.

CTyler · Dec 1, 2003

Don't know Just guessing here but Junkman may have been thinking of a 220v dryer circuit. This has two hots, neutral and ground. The neutral is used to supply 110v to the timer etc... A straight 220v on needs the two hots as stated previously.

BIGUN · Dec 1, 2003

As I discovered since moving to Oklahoma from Texas that there are two types of dryer plugs. My dryer has a 220-volt, three-prong plug. When I moved in here and got ready to plug it in, the receptacle was a four-prong type with 4 wires as you stated. Well since a new receptacle was cheaper than a new plug, I changed it out to the 3-prong type, abandoning the 4th wire. I am keeping the old receptacle, you never know when it may be needed. /forums/images/graemlins/wink.gif