Helping a student with a problem.....I need help.

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GoldDigger said:
Are we supposed to interpret "running overcurrent protection" as meaning overload protection?
If so there is no additional allowance for motor starting. To that extent the question is poorly written, using terms that the NEC does not use or define.

Overcurrent protection (short circuit and ground fault protection) is where you can definitely increase the nominal value to allow starting.
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I was referring to 430.32(C).
 
I think i catching on. Just reading "ambient temperature" and "temperature rise", I can tell you there is a difference. I just assumed when they were referring to temperature when dealing with a motor, that they were referring to the rise. So, if it states ambient temperature, its pointless since the temperature around the motor is useless.
 
kc_hubbs said:
I think i catching on. Just reading "ambient temperature" and "temperature rise", I can tell you there is a difference. I just assumed when they were referring to temperature when dealing with a motor, that they were referring to the rise. So, if it states ambient temperature, its pointless since the temperature around the motor is useless.
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No, it's not useless. A motor rated for a certain ambient temperature will have a shortened life if operated in an environment with a higher ambient temperature. That was covered in the link Jumper provided.
 
Helping a student with a problem.....I need help.

The allowable rise over ambient is determined by the insulation class. Class B is rated for 130C and class F for 155C. So if a motor is nameplated 40C ambient and has class B insulation, the the temperature rise at SF HP cannot exceed 130 - 40 or 90C, for example.
 
I shouldnt have used the word useless. I was meaning that the ambient temperature is useless in determining overloads.

Unless the motor specifies "temperature rise", you cant use it in overload calculations.
 
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