Conductor ampacity

Wow! said:

If you have a nameplate full load current of a motor, when do you use the nameplate value vs looking up from hp in table 430.250 to calculate ampacity for choosing the proper conductor size?  

The solution for proguide 78 test says use the table to get 26 amps, but I thought since 30 amps was given, to take 125% of that?

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Zach Stone said:

Hi @Wow! The NEC® is pretty clear on when to use the name plate amps, and when to use the 430.250 table values.

NEC® 430.6(A)(1) instructs the use of table values instead of "the actual current rating marked on the motor nameplate" for the ampacity of conductors, ratings of switches (any device that makes or breaks a circuit), branch circuit short circuit and ground fault protection. This applies to all motors except those "built for low speeds, high torque, or multi speed motors".  

NEC® 430.6(A)(2) instructs the use of "motor nameplate current rating" for separate overload protection. 

PM me your email address if you'd like a copy of our four page PDF motor cheat sheet that we give out to our students after our live class on rotating machines:

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