Message Board Thread - "Motor / Circuit Breaker Temperature"

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Motor / Circuit Breaker Temperature Rookie 4/2/2009
Is there a standard for what an ac motors temperature would be in an ambient 21C environment?

Also, If a circuit breaker is rated for an operating environment of 40C, How hot can it run when the current and connections are within tolerances?
 
Re:Motor / Circuit Breaker Temperature IRJay 4/2/2009
Outside temps on motors is not defined but the winding temps are by the MG1 moter guide for insualtion types. Then interpretation to outside skin comes from experience and training. Some motors the difference is 3 to 1 but not all.

Circuit breakers are the same. UL489 standard gives acceptable rise at the lug but nothing for the breaker. I accept rise with load but use the insulation of the wire to be my limit. A THHN wire has a max temp of 194F per NEC 310-13. This is good conservative approach.

Come to the Electrical App class, this is the stuff we discuss for 2 days.
 
Re:Motor / Circuit Breaker Temperature Rookie 4/2/2009
Thanks! That was exactly what I was looking for. I would attend the class but my company is a little tight with the bucks right now.
 
Re:Motor / Circuit Breaker Temperature Bob Berry 4/2/2009
Understanding the external temperature that a motor should run at is complicated, and to be honest you should not rely on the surface temperature alone.

Check out http://www.motorsanddrives.com/ , particularly the "Cowan papers". there is a very good paper on motor temperature ratings.
 
Re:Motor / Circuit Breaker Temperature Rookie 4/2/2009
That is a great web site. Thanks for the tip.
 
Re:Motor / Circuit Breaker Temperature bmarcum 5/6/2009
Bob Berry wrote:
anding the external temperature that a motor should run at is complicated, and to be honest you should not rely on the surface temperature alone.

Check out http://www.motorsanddrives.com/ , particularly the "Cowan papers". there is a very good paper on motor temperature ratings.
Great site , very helpful about questions I have had .
 


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