Complex Imaginary Volume 4 Problem 67

[carlospe]

In this problem the full load amps of the 150hp, 460V, 3 phase motor is 180A per NEC.  But in the book they didn't multiply the 180x1.25 as required by NEC 430.22 to size branch circuit conductors so they selected the 4/0 AWG instead of the 300KCM that will require with the 1.25 multiplier.  Any ideas?

 

[carlospe]

To expand more in my question, for a 180A load using NEC Table 310.15(B)(16) in the 60 degree column the required wire size is 4/0.  But for a motor of 180A load, 180x1.25 = 225A and using the same table and 60 degree column this will result in 300KCM wire size that has an ampacity of 240A.  I think complex imaginary has an error on this one. Anyone agrees? Thanks for any replies!

 

[cupojoe PE PMP]

 Could you post the full question? Typically you would use the 75 deg C column unless there is a reason to use to use 60 deg C.

 

[carlospe]

Problem (67) Acording to NEC2014. What is the minimum required size for the single insulated 60 degree, TW copper conductors feeding a 460V, 3-phase, AC motor rated 150-hp operating on continous duty?

-yes, typically the 75 degree ampacity can be used but in this problem the conductor is TW and the problem calls for the 60 degreee conductor.

 

[TWJ PE]

I agree; if it wasn't continuous then 4/0 would work.

How old is your CI?

I don't remember seeing this problem in my book (I don't have it anymore) - perhaps they corrected it.

 

[carlospe]

My book is from 2015. Thanks!

 

[cupojoe PE PMP]

Sure seems like this is an error in the CI solution.

 

[carlospe]

Yes, I already sent an email to complex imaginary for their review. Thanks!

 

[hebertjl5]

carlospe: 

I can also verify that I believe CI got this one wrong. I came to the same answer you did, and scratched my head as to why CI listed it differently.

 

[Dodgeviper1017]

This says single insulated conductor would that be 310.15 (B)(17)? If so wouldnt that be 2/0 either way I agree the problem is wrong.

 

[Phatso86]

definitely an error because I checked mine and the answer multiplied by 1.25

 

[carlospe]

Thanks you all for letting me know!

 

[Dodgeviper1017]

Question based on what I posted earlier. Would this not be using the single insulated table? If so wouldnt it be 2/0 at 60 degrees.