Temperature Motor T-Rating.

Status
Not open for further replies.

Dale001289

Senior Member
Location
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.
 

just the cowboy

Inactive, Email Never Verified
Location
newburgh,ny
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

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
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

Senior Member
Location
Georgia
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

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
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

Senior Member
Location
Georgia
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.
 
Status
Not open for further replies.
Top