NEMA design letter and conductor temperature rating

[wallypiper]

I've searched and searched but cannot find any place that links termination temperature rating to NEMA design letter. The NEMA design letter is about torque and current limits. So far as I can tell, it says nothing about a temperature rating. Why are NEMA design letters used in 110.14? And why is design A excluded? I see design A motors fairly often (on fans, mostly, where starting torque isn't much of an issue).

Motor lead wire typically has a very high temperature rating compared to general purpose wire such as THHN etc. What am I missing?

I understand what the code says but can't figure out why it says it.

 

[cadpoint]

Nema design letters

Google

First listing state "A" listing! and another a PDF gives a total break down
of the letters. Sorry I opened a few I think the fifth is complete listing...

Interesting that the torque variables change as the motor usage changes!
I've never gave it a thought that something needed variable torque based on letter
sizing!

 

[wallypiper]

Yes, there are many places on the web which describe what the design letters mean in terms of torque, locked rotor amps, starting amps etc. I can't find any reference to temperature rating of the terminals or, in the case of most motors in the US, the motor leads. If you dig around a little, you will find that most motor lead wires have very high temperature ratings, much higher than the 60-75-90 ratings listed for most conductors in the NEC.

So if the design letters don't indicate any kind of temperature rating, what are they doing in 110.14? 110.114 is about wire termination and the section with the exemption or exception or whatever you want to call it for motors with design letters B, C or D is about which conductor temperature rating you have to use when choosing a conductor for a given circuit.

I did find a pretty good article about the temperature rating in general which offers some good lay explanation of the why of it all.

http://static.schneider-electric.us/docs/Power Management/0110DB9901.pdf