# Complex Imaginary Volume 4 Problem 67



## carlospe (Oct 23, 2016)

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?


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## carlospe (Oct 23, 2016)

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!


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## cupojoe PE PMP (Oct 23, 2016)

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.


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## carlospe (Oct 23, 2016)

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.


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## TWJ PE (Oct 23, 2016)

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.


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## carlospe (Oct 23, 2016)

My book is from 2015. Thanks!


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## cupojoe PE PMP (Oct 23, 2016)

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


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## carlospe (Oct 23, 2016)

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


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## hebertjl5 (Oct 24, 2016)

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.


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## Dodgeviper1017 (Oct 25, 2016)

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.


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## Phatso86 (Oct 26, 2016)

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


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## carlospe (Oct 26, 2016)

Thanks you all for letting me know!


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## Dodgeviper1017 (Oct 26, 2016)

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.


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