# 480, 3 phase motor running hot.



## Dennis Alwon (May 9, 2009)

What is the current under load. I would expect most motors to be hot after running for some time. Is it hotter than before you did work on it?


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## Zog (Apr 15, 2009)

fpmaintenance said:


> Still runs smooth but a lil hot. Do you think the wibndings are slowly going?


Well, what were you insulation resistance readings and DAR/PI ratios before and after you "refreshed" it?


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## Meadow (Jan 14, 2011)

In all honesty it sounds normal. Ive seen motors run for years at uncomfortably hot tempratures with out problems. Take a few temp readings along with current readings after several hours of operation, that would be your best gide.


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## Bbsound (Dec 16, 2011)

Is it driving a centrifugal pump? If so your load is heavier on the motor the more product is flowing. If the flow is reduced (ie: restricted by a valve) the motor load will go down.


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## Mshea (Jan 17, 2011)

It has been a long time since I did regular motor work but running above nameplate current with no load is not normal. The current should be lower than under load and certainly lower than nameplate. Something is broken.
A lot of newer motors run very hot to touch.


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## BBQ (Nov 16, 2010)

fpmaintenance said:


> Name plate states 12.10 amp draw @ 480. I tested in the shop no load, it ran at 14.7.


Seeing as the no load current was higher than the FLA it would seem to me there is a problem with the motor.


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## B4T (Feb 10, 2009)

I've never come across this before so let me ask..

If a motor is rebuilt.. how close to the name plate specs can you get..

Usually I buy new and dump the old..


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## Big John (May 23, 2010)

fpmaintenance said:


> ...Name plate states 12.10 amp draw @ 480. I tested in the shop no load, it ran at 14.7....


 You sure these numbers are right? 

-John


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## varmit (Apr 19, 2009)

If this motor draws more than nameplate amps, with no load connected, something is wrong with the motor- windings, bearings, mechanical interference or something. Usually, a standard AC motor with no load attached, A BARE SHAFT spinning, will draw about 50% to 60% of nameplate.

This is assuming that the supply voltage is correct, the motor is connected correctly, and there is no "single phasing" condition.


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## wdestar (Jul 19, 2008)

You neglected to say whether or not the no load high current reading was consistent for each phase. If it is, I would say that there's a problem within the motor. No amount of cleaning and re-applying of insulation will fix this problem as some of the windings are shorted - I say this assuming that it is a 60 Hz motor, because if it's 50 Hz you have other problems.

If the high current reading varies significantly across the phases, you need to check the supply voltage - be it phase or voltage unbalance.

A healthy 3 phase motor should never draw more than FLA unloaded. As a matter of fact, I question any application that requires a motor to consistently perform at FLA - I wouldn't do it unless it had a high SF rating.


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## micromind (Aug 11, 2007)

What was the actual voltage applied to the motor while it was running unloaded? There are a lot of factors in this, but high voltage will saturate the core, thus causing the current to rise. 

Also, were all 3 lines roughly the same voltage and current? It doesn't take much of a voltage imbalance to cause a large current imbalance. 

If the insulation class is F, it's normal for the frame to run way hot. Even class B can run hotter than you think. 

And, as noted, what is the current while it's running under load?


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## Dennis Alwon (May 9, 2009)

I guess we scared him away. :laughing:


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## John Valdes (May 17, 2007)

Why he put it back on line is what I don't get?
The current was high from the start. It should have never been put back into operation.
I am of the opinion motors should be refreshed as he said, by a professional motor shop. That winding insulation in a can is a joke and really has no purpose.
I would guess he did not check bearing tolerances along with all the other checks a motor shop would do.
Like Zog asked him about the resistance testing? (I doubt we had a winding issue as it did run).
Since he is gone, I would bet his issue was mechanical and not electrical. It was his description of the steps he took and the lack of information he did not provide that leads me to this possible conclusion. My guess?


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## BBQ (Nov 16, 2010)

John Valdes said:


> Why he put it back on line is what I don't get?
> The current was high from the start. It should have never been put back into operation.


I was thinking the same things.


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## Big John (May 23, 2010)

What I can't figure is that if those numbers are accurate, he's probably pulling 150% FLA or more trying to run the thing.

Unless someone jacked with the OL setpoints, I wouldn't expect it to run for long.

-John


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## WarAdmiral (Jul 13, 2012)

No motor should be running hot or it will decrease its ability to perform and then burn out. is the overload protection correct? Is there a voltage drop? Has the ambient temp changed? Why was it repair in the first place? Is it under sized? Evaluate then determine if it should be replaced


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## John Valdes (May 17, 2007)

WarAdmiral said:


> No motor should be running hot or it will decrease its ability to perform and then burn out. is the overload protection correct? Is there a voltage drop? Has the ambient temp changed? Why was it repair in the first place? Is it under sized? Evaluate then determine if it should be replaced


What do you consider hot? Rolled steel motors run hot. Cast iron constructed motors run less hot. It is the temperature, not how hot or cold it is. Motors inherently produce heat.
I do agree with your statements after the "hot" statement.

When the OP put this motor back together, he did something wrong. Or a number of things wrong. Or the motor was not operating as it should before he touched it.
The rotor could be 1/4" out (horizontally) and this will cause high current.
The rotor could have been installed backwards. 
I wonder if he marked the end bells to the stator?
All speculation since he cut and ran.


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## Electric_Light (Apr 6, 2010)

Check voltage for each phase. Correct voltage imbalance if needed.


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## fpmaintenance (May 10, 2012)

*The 3 phase 480 motor running hot.*

It's monday morning, I came in and reset the chiller system and did the diagnostic. Both my main motor and my backup run at 8 amps loaded. Maybe I misread the amperage in the shop when I tested it but now they both run 8 amps fully loaded, they just get kind of hot. You can touch them with your hand for a few seconds but then that gets a bit much. I only became aware of the running hot thing when the boss told me the rejuved motor seemed hot. 
After running the back up motor for several hours, I found it runs just as hot as the main. But seeing that they're pulling only 75% of load amperage, I'd have to say this is normal heat temp. What do you guys think?

Thanks, I read everyones response, it helped me a lot to think about it over the weekend.


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## fpmaintenance (May 10, 2012)

By the way. All resistance test were okay and balanced in the shop when I rejuvednated the motors parts. I used to repair and rewind 3 phase motors for Westinghouse and am quite experienced in a motors d.e. or o.d.e. its winding's, bearings and stator core problems. I just never had the opportunity to see my rebuilds in action and experience them operating at such warm temps in the field. But thanks to all that gave me perspective about my motors performance. I think I'm gonna be all right.


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## JRaef (Mar 23, 2009)

fpmaintenance said:


> It's monday morning, I came in and reset the chiller system and did the diagnostic. Both my main motor and my backup run at 8 amps loaded. Maybe I misread the amperage in the shop when I tested it but now they both run 8 amps fully loaded, they just get kind of hot. You can touch them with your hand for a few seconds but then that gets a bit much. I only became aware of the running hot thing when the boss told me the rejuved motor seemed hot.
> After running the back up motor for several hours, I found it runs just as hot as the main. But seeing that they're pulling only 75% of load amperage, I'd have to say this is normal heat temp. What do you guys think?
> 
> Thanks, I read everyones response, it helped me a lot to think about it over the weekend.


What's the insulation class on the nameplate?

Touching a motor doesn't really tell you anything useful unless your hand starts smoking immediately and you leave most of your skin behind when you take it off.

If it has Class F insulation, common in older motors, that means the insulation temperature can RISE by 105C above an ambient of 40C, with a "hot spot" of up to 10C more. So technically, you could have a maximum temperature inside of the motor of up to 155C, or *311 degrees F* and that is still OK for that motor. Now you would not necessarily feel all 311 degrees on the outer surface if there is any kind of cooling fan in it, but it would still be a lot worse than "a bit much".


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