Temperature Motor T-Rating.

[Dale001289]

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.

 

[just the cowboy]

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.

 

[don_resqcapt19]

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.

 

[Dale001289]

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?

 

[don_resqcapt19]

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.

 

[Dale001289]

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.