Air compressor blowing circuit breaker

[mark mcfarlane]

I have a slow leak somewhere in my air line plumbing (which I possibly should not have installed in the walls...), This causes my air compressor to cycle maybe once or twice a day to refill the circular network of air lines.

Every few days the compressor throws the 20 amp dedicated 120V circuit breaker. Compressor is an IR Garage Mate, 2HP, 20 gallon, about 2 years old. Air filters are clean, pump oil is maybe 2mm above the 'fill bubble', i.e. a tad overfilled.

Any ideas why the breaker is getting thrown?

Thanks,

[mark mcfarlane]

IR offers these possibilities for "Motor overload trips or draws excessive current", I guess I should start by checking the belt tension:


1. Lubricant viscosity too high.
2. Improper line voltage.
3. Wiring or electric service panel too small.
4. Poor contact on motor terminals or starter connections.
5. Improper starter overload heaters.
6. Poor power regulation (unbalanced line).
7. Drive belts too tight or misaligned.
8. Compressor valves leaky, broken, carbonized or loose.
9. Cylinder(s) or piston(s) scratched, worn or scored.
10.Connecting rod, piston pin or crankpin bearings worn or
scored.
11.Defective ball bearings on crankshaft or motor shaft.
12.Leaking check valve or check valve seat blown out.
13.Ambient temperature too low.
14.Bad motor.

[Rob Charles]

From the outside looking in & understanding it is the panel/sub-panel feed circuit breaker that is tripping and not the motor mounter protection:
- The first place I would start looking is at the compressor pump head's pressure release valve (unloader) (between the pump head & tank check valve that is connected to the pressure switch) adjustment. It reads as if the pump's head pressure is not always releasing and the motor is trying to start the pump with pressure on the head.
- Next I would try cleaning the contractors in the pressure switch.
- If not either of those do the trick, then I would check to insure that all the wiring connections are clean & tight.

[Tom Bender]

A 2hp compressor may be drawing 20 amps, and more on startup. Available voltage will have a normal variation from the grid and more in your building due to other loads. You might need to increase the available amperage or get a breaker that blows slower. First try replacing it with a new one of the same capacity just in case it is defective.

[Pat Barry]

What other loads are on the same circuit? Maybe a bunch of lights, a heater, maybe the table saw is on the same circuit and running, etc. The startup current might be just enough on top of other loads. If it is a dedicated circuit just for the compressor then many other potential issues.

[Curt Harms]

When I had that problem it was an unloader valve sticking shut. Unloader valves release air in the cylinders so the motor isn't starting against pressure. Does the compressor, when stopping release a small amount of air? Had it previously? Otherwise a marginal circuit or circuit breaker would be a likely candidate. Could you run a heavy duty extension cord to the compressor from another circuit?

[Rollie Meyers]

A 2 HP motor will do poorly on a 20A 120 volt circuit, a 30A or larger circuit is required which is doable but it is much simpler to run it at 240V, 1 1/2 HP is the limit for common 120 volt circuits.

[Jim Becker]

I doubt that the apparent leak in the network is related to the breaker thing. The circuit itself is the first place to look. Even though this machine will run on 120v, it's still wanting it's own circuit so if it shares, it could merely be a coincidence of timing. It could also be a bad breaker. It could also be something like Curt describes.

[Lisa Starr]

The unloader is your 1st place to look. They get "sticky" (and a bit later just stop working altogether). They are not difficult to replace.

[mark mcfarlane]

What other loads are on the same circuit? Maybe a bunch of lights, a heater, maybe the table saw is on the same circuit and running, etc. The startup current might be just enough on top of other loads. If it is a dedicated circuit just for the compressor then many other potential issues.

Thank Pat for the idea. The compressor is on a dedicated circuit to a single 20 amp outlet. Nothing else plugged in.

[mark mcfarlane]

A 2hp compressor may be drawing 20 amps, and more on startup. Available voltage will have a normal variation from the grid and more in your building due to other loads. You might need to increase the available amperage or get a breaker that blows slower. First try replacing it with a new one of the same capacity just in case it is defective.

Thanks Tom. It's actually on a tandom (half-height) breaker, but I can try another one after investigating the compressor related suggestions. My new 30 slot shop panel got filled quickly :).

[mark mcfarlane]

From the outside looking in & understanding it is the panel/sub-panel feed circuit breaker that is tripping and not the motor mounter protection:
- The first place I would start looking is at the compressor pump head's pressure release valve (unloader) (between the pump head & tank check valve that is connected to the pressure switch) adjustment. It reads as if the pump's head pressure is not always releasing and the motor is trying to start the pump with pressure on the head.
- Next I would try cleaning the contractors in the pressure switch.
- If not either of those do the trick, then I would check to insure that all the wiring connections are clean & tight.

Thanks Rob.

There is a pressure relief valve between the two cylinders in the exhaust tube. Is this is the one to release the head pressure?

There is as second pressure release valve mounted to the pressure switch on the front of the compressor.

How do I 'check' these valves for proper operation, other than just exercising them?

I opened up the pressure switch but I'm not sure exactly where the contractors are or how to clean them.

419528419527

[mark mcfarlane]

When I had that problem it was an unloader valve sticking shut. Unloader valves release air in the cylinders so the motor isn't starting against pressure. Does the compressor, when stopping release a small amount of air? Had it previously? Otherwise a marginal circuit or circuit breaker would be a likely candidate. Could you run a heavy duty extension cord to the compressor from another circuit?

Thanks Curt. I do have some 20 amp extension cords and a 20 amp 120V outlet about every 6 feet around the room. Thats a great idea to test the circuit.

I just cycled the compressor and I did hear air escaping as the pumps shut down. Unfortunately I have no idea if this happens all the time, or ever happened in the past. I never listened for it before and the compressor is in a machine room.

The breaker doesn't throw every time the compressor operates, maybe every 5th-10th time.

[mark mcfarlane]

A 2 HP motor will do poorly on a 20A 120 volt circuit, a 30A or larger circuit is required which is doable but it is much simpler to run it at 240V, 1 1/2 HP is the limit for common 120 volt circuits.

Thanks Rollie. FWIW, the compressor has a NEMA 5-15 plug on it.

Edit: This compressor is also rated at 1500 Watts, it's in the model name P1.5IU-A9, so thats 12.5 Amps. Perhaps the 2HP figure is from unscrupulous marketing.

[mark mcfarlane]

I doubt that the apparent leak in the network is related to the breaker thing. The circuit itself is the first place to look. Even though this machine will run on 120v, it's still wanting it's own circuit so if it shares, it could merely be a coincidence of timing. It could also be a bad breaker. It could also be something like Curt describes.

Yea, the leak is somewhere in the many joints of RapidAir tubing.

It is a dedicated circuit. I just exercised the two relief valves and will watch it for a week. If the breakers blow again I'll try an extension cord to another circuit, I have an unused dedicated circuit under my workbench and a 20 amp extension.

[Mikail Khan]

Clip on ampmeters are cheap and help with troubleshooting. Will tell you actual current draw.

MK

[mark mcfarlane]

The unloader is your 1st place to look. They get "sticky" (and a bit later just stop working altogether). They are not difficult to replace.

Thanks Lisa Is this the unloader? It does actuate when the compressor shuts off.

419535

Does one typically just replace the little brass fitting with the valve, or the actuating arm assembly which is part of the pressure switch? Unfortunately my manual and IR's web site don't even show this valve as one of the parts.

[Tom M King]

The first thing I would try is to lube the bearings/bushings on the motor, whether they are designed to be lubed, or not. I have a motor on a wet tile saw, that was doing the same thing, that has kept working for several years, so far.

[Rob Charles]

Mark; What I was referring to is the part that you have correctly identified as the Unloader in the photo responding to Lisa's post. Typically, they work so that, when the pressure switch turn off, the lever moves and pushes in a one way check valve releasing the pressure in the tubing between the compressor pump head and the tank check valve. A small amount of air is released. When the pump turns on, the lever moves closing the valve (unloader) until the switch turns is back off again. Probably the easiest way to check it is, the next time you find the breaker tripped, check to unloader to verify the pressure was released.

Depending upon your switch configuration, the contacts may not be visible or accessible. I was unable to tell from your photos.

[Bill Dufour]

You need to convert to 240 volts or pull new 120 volt wire to carry 30 amps at 120 V. The breaker and wire is fine you are just at the limits.
How far from the service entrance does the wire run? Over fifty feet can cause a noticeable volt drop under load and a corresponding amp increase.
Bill D

[mark mcfarlane]

Thanks Rob I’ll check this valve the next time I throw a breaker. That’s a great idea.

[mark mcfarlane]

Thanks Bill. The service panel is about 7 feet away from the outlet where the compressor is plugged in. Add 5 foot to the ceiling and 5 foot back down to the outlet you’re looking at about 18’ for the wire.

[Mike Henderson]

I had that same problem when I had my compressor on 120 volts. I changed it to 240 volts and never had another problem.

Mike

[John K Jordan]

Thanks Rob I’ll check this valve the next time I throw a breaker. That’s a great idea.

I didn't make it through all the posts so maybe already mentioned - occasionally a breakers can become "weak" and need to be replaced. But I also vote for checking the actual amperage with a meter. And check the voltage to that receptacle and to the shop itself. If the voltage is low at times for some reason the motor will draw higher current.

I hope you are turning off/disconnecting the air compressor when leaving the shop. Shops have burned to the ground when a break in an air line caused a compressor to run continuously.

JKJ

[Bill Dufour]

Thanks Bill. The service panel is about 7 feet away from the outlet where the compressor is plugged in. Add 5 foot to the ceiling and 5 foot back down to the outlet you’re looking at about 18’ for the wire.


36' is nothing to the source of unlimited amps so voltage drop is not a problem due to long wire runs.
Bill D

[Osvaldo Cristo]

IR offers these possibilities for "Motor overload trips or draws excessive current", I guess I should start by checking the belt tension:


1. Lubricant viscosity too high.
2. Improper line voltage.
3. Wiring or electric service panel too small.
4. Poor contact on motor terminals or starter connections.
5. Improper starter overload heaters.
6. Poor power regulation (unbalanced line).
7. Drive belts too tight or misaligned.
8. Compressor valves leaky, broken, carbonized or loose.
9. Cylinder(s) or piston(s) scratched, worn or scored.
10.Connecting rod, piston pin or crankpin bearings worn or
scored.
11.Defective ball bearings on crankshaft or motor shaft.
12.Leaking check valve or check valve seat blown out.
13.Ambient temperature too low.
14.Bad motor.


Good list!

I add check the start up capacitor as sometimes when it is defective it can result in an atypically high start up current and by consequence blowing your surge protection.

[Tom Bender]

The grid provides 120 volts plus or minus 10%. Normally it is much closer than 10% but you may be in a place that is up there. And in your building you have some loads that can pull it down a bit more. This includes motors starting, electric clothes dryers, electric heat, electric water heater. Since your compressor is at the limit for your circuit breaker you may be experiencing bad timing vs available voltage when it starts.

[Edward Dyas]

I have a slow leak somewhere in my air line plumbing (which I possibly should not have installed in the walls...), This causes my air compressor to cycle maybe once or twice a day to refill the circular network of air lines.

Every few days the compressor throws the 20 amp dedicated 120V circuit breaker. Compressor is an IR Garage Mate, 2HP, 20 gallon, about 2 years old. Air filters are clean, pump oil is maybe 2mm above the 'fill bubble', i.e. a tad overfilled.

Any ideas why the breaker is getting thrown?

Thanks,An air compressor draws a lot of power at startup. If you are a long distance from the breaker it draws even more. Also if your shop is cold it makes it all the harder to start. I have a large commercial compressor I just have to turn off when the temperature is in the teens or below.

[Bill Dufour]

An air compressor draws a lot of power at startup. If you are a long distance from the breaker it draws even more. Also if your shop is cold it makes it all the harder to start. I have a large commercial compressor I just have to turn off when the temperature is in the teens or below.


Location? I am guessing you are talking fahrenheiht?

[John K Jordan]

Location? I am guessing you are talking fahrenheiht?

Just an idea - if more people would put their location in their profiles lots of the conversations here would be clearer or at least simplified. Those in the witness protection program or hiding from the authorities or creditors could leave off the city name or list something like "Southwest US" :)

JKJ

[Ron Selzer]

Is the circuit breaker rated HVACR?
Highly doubt that it is as you stated it is a tandem breaker
HVACR breakers are rated for high starting loads such as the air compressor, air conditioning compressor, etc
The tandem breaker typically is designed to trip faster to protect normal not motor loads in residential use
GOOD LUCK

[mark mcfarlane]

For future reference, here are the proposed potential problems so far:

Compressor



Failing unloader valve

i.e. compressor pump head pressure release valve
several recommendations to look at this one


Dirty contractors in pressure release switch
check the (motor's) start up capacitor
Lube the bearings/bushings on the motor, whether they are designed to be lubed, or not


Power



Put compressor on dedicated circuit - already is
Inadequate voltage at outlet - currently 123V. The shop has a dedicated 200AMP service and the trips are happening when the shop is not in use.

can fluctuate during day - based on previous monitoring there is a pretty stable voltage at my location
voltage drop due to wire run distance - 18' max run


Inappropriate (for motor) or failing breaker

Plug compressor into a different circuit - will test next
Replace current 20A tandem breaker, possibly with an HVACR style breaker which is rated for high starting loads


Inadequate AMPs on circuit for motor startup current inrush

check startup current with clamp on ammeter
current draw related to proper unloader operation
increase 120V circuit amp capacity from 20A to 30A


Convert compressor to 240V


Environment



Cold shop/compressor could increase startup current requirement - compressor kept between 65-70 degrees year round


Safety Recommendation from John:



"I hope you are turning off/disconnecting the air compressor when leaving the shop.

Shops have burned to the ground when a break in an air line caused a compressor to run continuously."

[mark mcfarlane]

In trying to diagnose the unloader valve I did the following tests:

Test 1:



Cycle compressor: unloader valve opens at end of cycle as expected
Unplug compressor from wall
Check compressor 2 hours later, unloader valve is now closed. Breaker is fine because compressor was unplugged.


The question becomes, did the unloader valve close because the actuator arm requires power to keep the valve open, or was this a failure of the pressure switch that operates the unloader valve and it should keep the valve open even if there is no power to the pressure switch.

Test 2:



Cycle compressor: unloader valve opens at end of cycle as expected
leave compressor plugged in
Check compressor the next day, breaker is thrown and unloader valve is closed.


Did unloader valve close due to a lack of available power, or did it close as expected when the compressor started up, and then a few ms or seconds later the breaker threw? Nothing to learn from this test.

Test 3



Cycle compressor: unloader valve opens at end of cycle as expected
Cycle compressor: unloader valve closes at the same time the compressor starts.


Nothing to learn from this test. I can't visually discern if the unloader valve closes before or after the compressor starts, it appears to my eye to be simultaneous. A high speed camera might resolve the exact timing.

If I continue to manually cycle the compressor in rapid consecutive tests the unloader valve operates exactly as expected and the breaker does not blow.

The breaker only seems to blow if the compressor has completed a several hour long rest state.

[David L Morse]

I don't want to interrupt the troubleshooting flow here but there are a couple of minor points I want to bring up.


...check startup current with clamp on ammeter...

Not many clamp meters are capable of capturing inrush current. If yours is not (and it should be in the manual if it is) and you motor has a proper nameplate you'll find it there. There will be a code letter for the Locked Rotor Current (LRC). It's usually labelled "CODE". Look up the code letter in the table:
419621
Then make the appropriate calculation. For example, if your motor has a code G and a rated voltage of 115V then you start current is 2HP x 5.9kVA/HP x 1000VA/kVA / 115V = 103A.


...This compressor is also rated at 1500 Watts, it's in the model name P1.5IU-A9, so thats 12.5 Amps. Perhaps the 2HP figure is from unscrupulous marketing.

Both HP and Watts are units of power. Watt is metric and HP is Imperial. Motor ratings generally use a rounded number of 750 Watt per Horsepower. So 2HP x 750W/HP = 1500W. That is the rated LOAD not the input.

Input power is output load divided by efficiency and is also measured in Watts. Apparent input power is input power divided by power factor and is measured in Volt-Amps. Input current is then apparent input power divided by input voltage. For example, a 2HP (1.5kW) motor with 85% efficiency and 90% power factor would have an input current at rated load of 1500/.85/.9/120 = 16.3A.

[Kyle Iwamoto]

Is the circuit breaker rated HVACR?
Highly doubt that it is as you stated it is a tandem breaker
HVACR breakers are rated for high starting loads such as the air compressor, air conditioning compressor, etc
The tandem breaker typically is designed to trip faster to protect normal not motor loads in residential use
GOOD LUCK

+1. This is it I think. I trip my tandem breaker on my 3/4 hp Delta bandsaw if I load it down on a cut.
Move the wiring to a regular breaker slot and move the other wiring to the tandem. Should not be too difficult. Remember to swap the breakers to the proper rating.

[mark mcfarlane]

I don't want to interrupt the troubleshooting flow here but there are a couple of minor points I want to bring up.



Not many clamp meters are capable of capturing inrush current. If yours is not (and it should be in the manual if it is) and you motor has a proper nameplate you'll find it there. There will be a code letter for the Locked Rotor Current (LRC). It's usually labelled "CODE". Look up the code letter in the table:
419621
Then make the appropriate calculation....

Thanks David, I can't see the language you have referenced on my compressor motor.

419632

[Rob Charles]

+2. Good call


Is the circuit breaker rated HVACR?
Highly doubt that it is as you stated it is a tandem breaker
HVACR breakers are rated for high starting loads such as the air compressor, air conditioning compressor, etc
The tandem breaker typically is designed to trip faster to protect normal not motor loads in residential use
GOOD LUCK

[David L Morse]

Thanks David, I can't see the language you have referenced on my compressor motor.

419632

No, I don't see it either. Those are IEC specs not NEMA on that nameplate, but it's not complete.

The laboratory method for measuring locked rotor current is to literally lock the rotor and then measure the current. You usually don't have a lot of time before the breaker opens but most ammeters are fast enough to get a measurement. It's not difficult, you just need a good way to keep the rotor from spinning.

[Edward Dyas]

Location? I am guessing you are talking fahrenheiht?It's fahrenheit for me. I'm near Dallas TX so it doesn't get that cold very often.

[mark mcfarlane]

The compressor has run for 48 hours (cycled a few times) without throwing a breaker on a different 20AMP circuit using an extension cord . So far so good.

I'll report back in another week, but it looks like my root electrical problem may be the tandem breaker.

Thanks again to everyone for your thoughtful responses and assistance.

[Jim Becker]

Mark, even a "new" breaker can go bad, although it's certainly unusual...so at this point, I'd replace it sooner rather than later since they are not hugely expensive.

[mark mcfarlane]

Mark, even a "new" breaker can go bad, although it's certainly unusual...so at this point, I'd replace it sooner rather than later since they are not hugely expensive.

Good idea, thanks Jim.

[Rich Aldrich]

Those tandem breakers can be a problem. Manufacturers try to squeeze everything in a half the space of a normal size breaker. There are bound to be issues. It’s interesting to listen to electricians and electrical engineers tell troubleshooting stories involving these breakers. I use them, but in lightly loaded applications.

Most have found issues when it comes to starting current required and these tandem breakers don’t have enough capacity for the in rush current.

[David Kumm]

What Rich said. Tandems are best for lights and low load, and should be avoided for motor circuits. Dave

[mark mcfarlane]

Thanks everyone for your assistance with my air compressor / breaker dilemma. The compressor has run for 6 days without throwing a breaker using an extension cord from a circuit with a full size 20amp breaker. The previously used tandem breaker appears to be the root cause.

I may try to replace the tandem breaker, since it did work fine for a year or so, before attempting some circuit rerouting which will require jumper wires in the breaker box.

Thanks again to everyone who pitched in. I learned a lot more about how a compressor works and the various points of potential failure.

In particular, John's post about unplugging the compressor every day to avoid a runaway compressor-caused fire due an air line leak has opened my eyes. I shall try to get in the habit of shutting off the compressor every day, and also add a new valve at the tank to slow down the effect off my slow leak in the in-wall rapid-air tubing network.

Cheers,

[John K Jordan]

In particular, John's post about unplugging the compressor every day to avoid a runaway compressor-caused fire due an air line leak has opened my eyes. I shall try to get in the habit of shutting off the compressor every day, and also add a new valve at the tank to slow down the effect off my slow leak in the in-wall rapid-air tubing network.



I have a friend who lost his shop and all tools this way. What are the chances: many years after rebuilding he had a similar incident with his compressor when a component failed after he stepped out of the shop for a bit but caught it in time.

My compressor (5hp IR 60 gal) is in a sound-insulated closet. So the controls would not be out of sight I ran the pipe from the compressor though the wall and added a gauge and shut off valve along with my dryers, regulator, and distribution manifold. The electrical disconnect is also in plain sight in the main shop so I don't forget about it. I put a colored flag on the switch to make the switch state it more visible from across the shop but I'm planning to wire in a bright "compressor motor enabled" light.

420312

JKJ

[Mike Henderson]

In particular, John's post about unplugging the compressor every day to avoid a runaway compressor-caused fire due an air line leak has opened my eyes. I shall try to get in the habit of shutting off the compressor every day, and also add a new valve at the tank to slow down the effect off my slow leak in the in-wall rapid-air tubing network.

Cheers,

What I did to handle that problem is I put a motion sensor in the circuit. I have my compressor running on 240 volts so the motion sensor controls a contactor (a type of relay) that then controls the 240 volts. If there's no motion, the power is off to the compressor. I figured that a motion sensor was more reliable than me remembering to turn the power off to the unit.

Mike

[Mike Henderson]

Most have found issues when it comes to starting current required and these tandem breakers don’t have enough capacity for the in rush current.

I've had to use tandem breakers in my subpanel. They're the ones with the two 120V breakers on the outside and a bonded (double breaker) between the two 120 volt breakers for controlling a 240 volt circuit. It was that, or replace the subpanel with a bigger panel. I added more 240 volt tools than I expected when I put in the subpanel so I needed more bonded 240 volt breakers, while still having the same number of 120 volt breakers.

So far, I haven't had any issues at all with the setup. But even with the tandem breakers I'm completely full now. If I try to add another 240 volt tool it's either do a multidrop on an existing circuit or put in a bigger subpanel.

Mike