Temperature Motor T-Rating.

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Dale001289

Senior Member
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Georgia
How do I determine the T-rating for a motor that has no listing on the nameplate or data sheet? Do I take the ambient temperature (95 deg F) and add it to the maximum temperature rise of the windings under motor running FLA?

Thanks in advance.
 
40 degrees C

40 degrees C

Motor manufactures use 40 degree C as the base point for temperature rise, anything above that in your plant must be derated for that temperature.
 
The only place I know of where we use the motor "T" rating is for classified areas. I would not want to calculate my own "T" rating. I would want that information from the manufacturer and on the nameplate.
 
The only place I know of where we use the motor "T" rating is for classified areas. I would not want to calculate my own "T" rating. I would want that information from the manufacturer and on the nameplate.


Agreed, but NEC 501.125(B) allows squirrel cage motors without labeling for Class I, Division 2 locations provided there are no switching, sparking and arcing mechanisms AND surface temperatures do not exceed 80% of AIT.
If I have a general purpose 460V motor, say a Baldor- Reliance VEM3558, I'd take 40 deg C ambient and maximum 65 deg C rise on the windings, (105 deg C) and compare this to the Area Classification drawings/AIT's to determine a relative 'T-rating'.

Where am I wrong?
 
I never really worried about it in a Class I, Division 2 application. The AIT is high enough for most products that no motor has an normal operating temperature anywhere near 80% of AIT. Of course there are always special cases where the product has an abnormally low AIT.
 
I never really worried about it in a Class I, Division 2 application. The AIT is high enough for most products that no motor has an normal operating temperature anywhere near 80% of AIT. Of course there are always special cases where the product has an abnormally low AIT.

Agreed. thanks for your feedback.
 
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