Sparky Bill PE
Senior, Master, Professional, Licensed Electrical
I'm assuming the "gotcha" here is you don't multiple this current by 1.25% even tho its a continuous motor to size your cable?
NEC Question about getting amps for conductor sizing
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I actually think this question's solution is a mistake. I noticed and remember this question from the Complex Imaginary set.
Per NEC 430.22, you always must multiply the motor table FLC by 125% for a single continuous-duty motor.
There are a few questions I've seen whose solutions are questionable and sometimes even wrong. This is one of them.
Per NEC 430.22, you always must multiply the motor table FLC by 125% for a single continuous-duty motor.
There are a few questions I've seen whose solutions are questionable and sometimes even wrong. This is one of them.
Sparky Bill PE
Senior, Master, Professional, Licensed Electrical
The FLC for a 460V, 150HP, 3-phase AC motor is 180A per Table 430.250 as discussed.
Per 430.22, you multiply by 125% to get 225A.
Per "Equipment Provisions", 110.14(C)(1)(b)(1), since the circuit is rated over 100A, conductor ampacities are based on conductors rated 75 degrees C.
Per Table 310.15(B)(16), 4/0 conductors can be used up to 230A, so the answer is 4/0 AWG.
The question is asking for the "minimum required size", so per 110.14(C) "Temperature Limitations", "Conductors with temperature ratings higher than specified for termination shall be permitted to be used for ampacity adjustment, correction or both."
If you use the 60 degree rating, you will get, 300kcmil as your answer, but since the question asks for the minimum size required, 4/0 AWG is the correct answer.
That's how I see it anyway. Please correct me if I'm wrong!
Per 430.22, you multiply by 125% to get 225A.
Per "Equipment Provisions", 110.14(C)(1)(b)(1), since the circuit is rated over 100A, conductor ampacities are based on conductors rated 75 degrees C.
Per Table 310.15(B)(16), 4/0 conductors can be used up to 230A, so the answer is 4/0 AWG.
The question is asking for the "minimum required size", so per 110.14(C) "Temperature Limitations", "Conductors with temperature ratings higher than specified for termination shall be permitted to be used for ampacity adjustment, correction or both."
If you use the 60 degree rating, you will get, 300kcmil as your answer, but since the question asks for the minimum size required, 4/0 AWG is the correct answer.
That's how I see it anyway. Please correct me if I'm wrong!
Sparky Bill PE
Senior, Master, Professional, Licensed Electrical
If you're right, this is another example, of extreme lazy ass garbage literature. Blows my mind people have the audacity to publish work and that be the solution (if yours is right). Don't care for anyone to defend "all people make mistakes" etc.
If my work was as sloppy as this damn book I wouldn't have a job anymore doing engineering. I am so glad I finished the last exam because I have found so many mistakes, typos, and garbage solutions I won't use it again, recommend it, and take the time to write a negative Amazon review (which I've never done).
Dothracki PE
Where is my mind?
I have been doing the practice problems of the electricians exam book that Zach recommends. Unit 4 is entirely practice using the 310 tables on conductor sizing and debating.
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Sparky Bill PE
Senior, Master, Professional, Licensed Electrical
Can you post a picture or a link of what book you're referring to? I have every reference book (I thought) that Zach recommends, but I don't have that one in my library.
