Compressor motor thermal overload

[Tscott]

OK, I got the compressor wired. #6 wire 50 amp breaker. It runs fine, but for some reason the thermal overload wired in series with the magnetic contactor is tripping. This is a 7.5 hp compressor motor rated for 208 to 230 volts. The motor feels warm to the touch, but not hot. There is plenty of airflow through the motor and all the factory connection feel tight. I have 248 volts at the contactor terminals. Is it possible this higher voltage is the reason why the motor thermal overload is tripping?

Tom

 

[Greatbear]

What is the rating of the overload heater in your contactor? If it is undersized it will cause tripping. Also, check the overload current trim adjustment. If it is set too low, even if your element is properly sized, it can trip. Increase the setting and see if this helps. 248 volts at the motor is not excessive.

 

[Aceman]

Verify heater size is correct.

Put an amp clamp on it and verify it's not pulling too much current.

I've had to turn the cutoff pressure down on a new compressor before because it worked the motor too hard at the end of the cycle.

 

[Tscott]

Aceman

I did not see an adjustment for the overload today when I was trouble shooting, but I will give it a check tomorrow. The pressure switch is set to 150 PSI right now, and with this being a new compressor, I will be calling the manufacturer before
i turn down the pressure switch. They claim it is rated for 175 PSI, thats what I paid for and thats what i am going to get.

Great Bear

I was looking at this today as well. There is a universal listing of the different types of thermal cutouts on the inside cover. If I remember correctly, my model number on the list had a max of around 30 Amps which sounds too low for a 7.5 hp motor (but not by much). However, this is a brand new set up from Eaton Compressor and I have a hard time believing they would install the wrong size thermal cutout, but stranger things have happened.

I'll do some more checking in the morning.

Thanks guys,
Tom

 

[Norcal]

If this is a brand new unit, a call to the dealer for warranty service is in order.

 

[compresdcaddy]

How long is the wire run from the breaker to the overload? Sounds like you may have the wrong size wire depending on the length.

 

[hidollartoys]

Per NEC you can increase the overload current trip point up to 140% of the "nameplate amps" (depending on application) to prevent nuisance trips. This is provided that you have wired the motor circuit in accordance with Article 430.

 

[Torque1st]

Full load current for a real 7.5HP 230V single phase motor is 40A. Actual nameplate currents are usually slightly less. A "special" duty motor may have a much lower full load current.

 

[hillbilly1]

Manufactures play games with the HP ratings, it is probably 7.5 peak HP. Check your voltage with the compressor running, you will probably find that is the problem, when the compressor is reaching it's peak load, the amperage goes up, causing the voltage to go down if it is a long ways from the power company transformer. If you live up north, the utility companys load up several houses on one small transformer, this was fine many years ago when people had very small loads in a house, but the utilites failed to upgrade until they got enough complaints. My cousin had a 7.5 Hp compressor that would make all of his neighbors lights flicker.

 

[hillbilly1]

Just seen that your in Florida, it's not as much of a problem there as it is up north.

 

[Tscott]

Manufactures play games with the HP ratings, it is probably 7.5 peak HP. Check your voltage with the compressor running, you will probably find that is the problem, when the compressor is reaching it's peak load, the amperage goes up, causing the voltage to go down if it is a long ways from the power company transformer. If you live up north, the utility companys load up several houses on one small transformer, this was fine many years ago when people had very small loads in a house, but the utilites failed to upgrade until they got enough complaints. My cousin had a 7.5 Hp compressor that would make all of his neighbors lights flicker.

Nope, that is not the issue. I am the only house on my transformer and The service size is 350 with a reduced neutral. The motor is a true 7.5hp and the circuit feeding it is #6 wire with a 50 amp breaker. There is 60' of wire between the breaker and the magnetic starter. There is no noticeable voltage drop when the compressor cranks. I have not been able to get out there today, but I am almost certain the heater is under rated for this application. I am thinking Eaton installed the wrong size at the factory, probably the one for their 5hp units. Thats the current theory at least until I call on Monday.

Tom

 

[sberry]

I would tend to agree, that sounds about right for 5 hp units, as Torque said, closer to 40.

 

[hillbilly1]

Nope, that is not the issue. I am the only house on my transformer and The service size is 350 with a reduced neutral. The motor is a true 7.5hp and the circuit feeding it is #6 wire with a 50 amp breaker. There is 60' of wire between the breaker and the magnetic starter. There is no noticeable voltage drop when the compressor cranks. I have not been able to get out there today, but I am almost certain the heater is under rated for this application. I am thinking Eaton installed the wrong size at the factory, probably the one for their 5hp units. Thatsnthe currentntheory atmleast until I call on Monday.

Tom

If thats the case, then you can check the overload size by the number stamped or printed on it. There will be a sticker on the inside of the starter cover that will give the amps it is rated for. If there is no sticker, you should be able to search Eaton's web site. I know you already checked the oil level (a lot of commercial duty compressors are shipped without oil) The OL heater is mounted below the starter, and is usually held in by two screws.

 

[Tscott]

Ok, did some more trouble shooting today and I am even more convinced the heater is for a smaller compressor. The motor is rated for 35 FLA and that is what I am getting for amp flow, so the motor is not being over taxed. The listed rating of the Square D heater is a max of 25 amps which is obviously too low. The only strange thing is that the contactor is rated for 7.5HP according to its name plate, and the heater that is installed is the largest that contactor should be paired with.

Eaton is open tomorrow, so they will be getting a call first thing. When you pay $1800 dollars for something you kind of expect it to work right out of the box. I am optimistic they will resolve the problem without much hassle.

Tom

Oh, and yes the compressor has oil. and all the connections in the control box have been checked.

 

[W-Cummins]

So the contactor/starter is what a NEMA 2? I assume that this is a 2 pole single phase contactor? If it is a 3 pole, 3 phase contactor it might be rated for 7.5hp and use the lower amp heaters. I don't have a SqD book handy to look it up. Also the use of the contactor makes a difference in the rating of the heaters. Depending on the mounting, enclosure, and ambient temperature you can run different heaters. The manufacture has charts for all of that info.



William....

 

[hillbilly1]

Ok, did some more trouble shooting today and I am even more convinced the heater is for a smaller compressor. The motor is rated for 35 FLA and that is what I am getting for amp flow, so the motor is not being over taxed. The listed rating of the Square D heater is a max of 25 amps which is obviously too low. The only strange thing is that the contactor is rated for 7.5HP according to its name plate, and the heater that is installed is the largest that contactor should be paired with.

Eaton is open tomorrow, so they will be getting a call first thing. When you pay $1800 dollars for something you kind of expect it to work right out of the box. I am optimistic they will resolve the problem without much hassle.

Tom

Oh, and yes the compressor has oil. and all the connections in the control box have been checked.

I didn't catch whether this three phase or single phase, if it is single phase, and the starter is a three pole, it will be rated for 7.5 hp at three phase, but not at single phase. I was just ribbing you about the oil, you sound like you know what your doing!

 

[Tscott]

OK, guys I just got off the phone with Eaton. I gave the guy the vitals on the motor and he says they did indeed use the wrong mag starter assembly. Cummins and Hillbilly are correct, the installation is a 1 phase, but the contactor and the heater are 3 pole units rigged to run on 2 poles. He is mailing one to the house today and it should be here pretty quick.

So far, I must say that Eaton has been a dream to work with. It literally took a 2 minute phone call for the guy to tell me they used the wrong part and that they would get it in the mail to me today. If they follow through as quickly as it sound like they will, they will be getting a glowing recommendation from me from now on. I don't really mind mistakes like this as long as the problem is solved correctly. I will let you guys know how the rest of the process goes.

Tom

 

[Charles (in GA)]

Manufactures play games with the HP ratings, it is probably 7.5 peak HP.

For some reason, and I don't know why, every 7.5 hp compressor I've looked at was a true running 7-1/2 hp. Every 7 hp I've looked at was PEAK or starting hp.

Seven and a half seems to be the starting point of the real hp motors and compressors, and you will also find true running hp on many 5 hp units from the big names like Saylor-Beale, Quincy, Champion, etc.

Charles

 

[sdowney717]

So far, I must say that Eaton has been a dream to work with. It literally took a 2 minute phone call for the guy to tell me they used the wrong part and that they would get it in the mail to me today.

Ok good, BUT not so good, problem should never have happened at all. How many other customers get the wrong parts?
Most people likely would not have skills to troubleshoot and either put up with it, take it back, or call and complain.

 

[Tscott]

Ok good, BUT not so good, problem should never have happened at all. How many other customers get the wrong parts?
Most people likely would not have skills to troubleshoot and either put up with it, take it back, or call and complain.

Well, I do agree to a point and yes I am probably better equipped to trouble shoot a unit like this than the average person but how often does the average person order a 7.5 HP compressor? It's the kind of equipment only the technically minded would typically buy.

I agree, that it should not have happened, but it did and I appreciate the proper handling of the situation. I am not perfect and therefore cannot expect perfection from anyone else. I am pretty sure there have been a large number of Eaton compressors bought by the members here and I have not heard of any with any problems at all. I am forced to assume that this is just an isolated incident and that I was just the one unfortunate enough to get the one they made a mistake on.

Tom

 

[hillbilly1]

For some reason, and I don't know why, every 7.5 hp compressor I've looked at was a true running 7-1/2 hp. Every 7 hp I've looked at was PEAK or starting hp.

Seven and a half seems to be the starting point of the real hp motors and compressors, and you will also find true running hp on many 5 hp units from the big names like Saylor-Beale, Quincy, Champion, etc.

Charles

They seem to play that game with the non-commercial/industrial units, I have a 2 hp belt drive industrial unit that actually is a 2hp. They make a homeowner think their getting a bigger bang for the buck, like a 3 hp shop vac that plugs into a standard 15 amp outlet! Glad TScott got his issue resolved!

 

[Greatbear]

I figured the contactor was fitted with an undersized heater meant for a 5HP motor. An honest mistake, albeit inconvenient and troubling at first.

And, agreed, I have yet to see HP ratings shenanigans played on true industrial/commercial equipment. That is a market that will not stand for it, in fact, with the preponderance of "enthusiastic" ratings being slapped on so much consumer gear, it began to make industrial buyers wary of what they were buying. Thankfully, the HP game has been taken out of commission.

 

[Tscott]

Just wanted to make sure this thread got closed out. The new contactor and heater assembly arrived. I was hoping for a little easier install than I got. The box they sent still needed to be drilled to fit on the compressor mounting plate, and the contactor had to be wired to accept 1Ø instead of 3Ø. The new unit was a little more complicated than the old Square D unit and has a few more bells and whistles. Ideally, I would have liked it to be set up and ready to go when I got it or at least come with some instructions, but I got it all together and running after a little head scratching.

So the pros of the situation are that they responded quickly and got me what I needed to get up and running. The new parts arrived in a week.

The cons are that the parts they sent were straight from WEG and were not set up to run in the configuration I needed. No instructions were included other than the wiring diagram on the inside of the box.

All in all I am fairly happy with how this was handled by Eaton, but they could have done better.

Tom