winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
weressl said:155C is the rise over maximum ambient, so the actual temperature could be 195C. If you have a 20C ambient you are still OK with a higher rise of 175C as long as the actual temperature does not rise above 190C.
I stand partially corrected and partially in disagreement.
When I buy magnet wire for motor windings, it always has a temperature rating, not a temperature rise rating. The motor suppliers that I've worked with always rated in terms of maximum temperature.
However it appears that 'Class x' temperature rating can be used to describe both a maximum temperature and a temperature rise. See
http://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html
'Class F' means either a maximum temperature of 155C _or_ a 105C rise in a 40C ambient.
Note that while the winding hotspot rating might be 311F, and the outer frame is at 200F, I'm still uncomfortable with the temperature level. The 'temperature rating' is the temperature at which the expected insulation life is 20000 hours, or about 2.5 years. If the outer frame is 200F, then the 'hot spot' will be close to or possibly exceed 311F.
-Jon