# Motor case temps



## Rockyd (Apr 22, 2007)

MDShunk said:


> Does anyone have any charts, or even rules of thumb, that would relate measured motor case temperature to the winding temps for various motor types? For instance, here's some real numbers... I have a 7.5hp TEFC footless c-face motor, working at its rated horsepower for 4 hours, and I measure the case temperature in the middle at 190 degrees F. Type F winding insulation. I don't personally worry about that, even though it's warm to the touch, but how can I prove to someone else that the windings are okay with no way to measure winding temps?


Maybe a copy of NEMA MG1 spec's? My best guess if you have access to NEMA library.


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## Wirenuting (Sep 12, 2010)

MDShunk said:


> Does anyone have any charts, or even rules of thumb, that would relate measured motor case temperature to the winding temps for various motor types? For instance, here's some real numbers... I have a 7.5hp TEFC footless c-face motor, working at its rated horsepower for 4 hours, and I measure the case temperature in the middle at 190 degrees F. Type F winding insulation. I don't personally worry about that, even though it's warm to the touch, but how can I prove to someone else that the windings are okay with no way to measure winding temps?


Is this what your looking for?
I asked a similar question 6 months ago. I think Zog or Harry gave me a better link. 

http://www.toshont.com/ag/mtrldesign/AG05 (Temperature Rise).pdf

Sorry for the sideways pic.


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## MDShunk (Jan 7, 2007)

Sorta. Those are winding temps. Maybe it doesn't exist, but I guessed that maybe someone has a rule of thumb that relates case temperature to estimated winding temperature. In retrospect, that might be kinda hard. Take the same horsepower Leeson motor with a cast iron case, a Baldor with a sheet metal case, and an SEW with a "ribbed" radiator type case, all three would likely have dramatically different case temperatures when put to the same duty .


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## JRaef (Mar 23, 2009)

MDShunk said:


> Sorta. Those are winding temps. Maybe it doesn't exist, but I guessed that maybe someone has a rule of thumb that relates case temperature to estimated winding temperature. In retrospect, that might be kinda hard. Take the same horsepower Leeson motor with a cast iron case, a Baldor with a sheet metal case, and an SEW with a "ribbed" radiator type case, all three would likely have dramatically different case temperatures when put to the same duty .


Way too variable. It depends not only on the winding insulation temperature rating, but also on the cooling design, frame design and material, rated efficiency, bearing types, allowable hot spots etc. etc. External case temperature is not even as good as an "idiot light" on the dash board of your car as far as telling you anything useful. By the time you notice something dangerously hot on the outside, it's already WAY too late on the inside.

PS: But that said, one valuable bit of information you can glean from thermal scans is that OVER TIME, if you see it trending up (with relation to load and ambient temperature rise), then you can predict a scheduled maintenance shutdown to find out why.


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## eric7379 (Jan 5, 2010)

MDShunk said:


> Does anyone have any charts, or even rules of thumb, that would relate measured motor case temperature to the winding temps for various motor types? For instance, here's some real numbers... I have a 7.5hp TEFC footless c-face motor, working at its rated horsepower for 4 hours, and I measure the case temperature in the middle at 190 degrees F. Type F winding insulation. I don't personally worry about that, even though it's warm to the touch, but how can I prove to someone else that the windings are okay with no way to measure winding temps?


I ran into a very similar situation in the past on a chilled water system. The pump motor had a case temp of right around 190 degrees F and the customer screamed and howled about it "being too hot, the motor is going to burn up". In the end, we had to have a spec sheet for the motor and something in writing from the motor manufacturer stating that the case temperature was normal before the customer would shut up about it. To my knowledge, the motor is still running today and this was over ten years ago. 

Maybe contact the motor manufacturer/distributor and see if they have anything on it that would appease somebody if they started asking questions?


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## zwodubber (Feb 24, 2011)

MDShunk said:


> Does anyone have any charts, or even rules of thumb, that would relate measured motor case temperature to the winding temps for various motor types? For instance, here's some real numbers... I have a 7.5hp TEFC footless c-face motor, working at its rated horsepower for 4 hours, and I measure the case temperature in the middle at 190 degrees F. Type F winding insulation. I don't personally worry about that, even though it's warm to the touch, but how can I prove to someone else that the windings are okay with no way to measure winding temps?


You're about an hour from me, if you need a thermal imager I might have 1 or 2 days off next week and could scan it if that would help you prove it to them.


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## MDShunk (Jan 7, 2007)

zwodubber said:


> You're about an hour from me, if you need a thermal imager I might have 1 or 2 days off next week and could scan it if that would help you prove it to them.


I actually have a thermal imaging camera, but even that won't take core temp measurements. It will still tell us case temps. 

This is actually solved anyhow. I got a white paper from Baldor.


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## zwodubber (Feb 24, 2011)

MDShunk said:


> I actually have a thermal imaging camera, but even that won't take core temp measurements. It will still tell us case temps.
> 
> This is actually solved anyhow. I got a white paper from Baldor.


OK, good to hear it's resolved


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## Zog (Apr 15, 2009)

MDShunk said:


> This is actually solved anyhow. I got a white paper from Baldor.


Please share


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## John Valdes (May 17, 2007)

Just FYI. Hot motors are not always a bad thing. Heat must go somewhere. On rolled steel frames, the skin temp can get hot enough you cannot keep your hand on it and still be fine.
Cast frames tend to feel cooler as they have more surface area to dissipate heat. Generally speaking. If a motor is in its FLA range, chances are the motor is doing what it is supposed to do. Let heat out, not keep it in.


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## CheapCharlie (Feb 4, 2011)

John Valdes said:


> Just FYI. Hot motors are not always a bad thing. Heat must go somewhere. On rolled steel frames, the skin temp can get hot enough you cannot keep your hand on it and still be fine.
> Cast frames tend to feel cooler as they have more surface area to dissipate heat. Generally speaking. If a motor is in its FLA range, chances are the motor is doing what it is supposed to do. Let heat out, not keep it in.


If I'm doing a thermal scan report for a motor at our station here, I always check the deg rise on the nameplate. If I'm looking at a 55 deg rise over ambient motor and I'm reading 60 deg rise on the case of the motor I can say for certain that it's AT LEAST 60 deg rise in the winding. That you know for certain. Heat inside will ALWAYS be hotter than the case temp. As thermographers, we don't have a heat x-ray camera which alot of people don't seem to grasp. I don't know how many times I've been asked what the temperature is inside a motor or inside that 230kV splice.


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