# Motor branch circuit conductor calculations



## Brentwerks (Nov 6, 2020)

Question: _Two 10-horsepower, 440-volt, 3-phase, continuous-duty, induction type Design B motors are supplied by a single motor branch circuit. Calculate the minimum ampacity for the single motor branch-circuit conductors supplying both motors. *I'm confused on what to do with 2 motors of the same size. *_

using *(2020)NEC table 430.250: *10HP 3-ph 440V = 14A
*NEC 430.6(A)* 14A x 125% = 14x1.25 = 17.5A
*NEC 430.24 Several Motors* etc. 
(1) 125% of the FLC of the highest rated motor as determined by 430.6A and 
(2) Sum of all the FLC ratings of all the other motors in the group as determined by 430.6A

so should this be 17.5A + 17.5A = 35A since they are both the highest rated or...
is motor 1 x125% and motor 2 x100% 17.5A + 14A = 31.5A?

I understand that in this particular case both answers would result in most likely being #10AWG according to 
*table 310.16 *but what is correct when they don't fall in the same range of ampacity
thank you for your help


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## Viggmundir (Sep 13, 2019)

(14A * 125%) + 14A=31.5A

In this case, because both motors are the same size, it doesn't matter which one you pick to take at 125%, but you still only do one at 125%.
If we added another larger motor (say 16A FLC) then it would be (16A *125%)+14A+14A=48A
If the added a smaller motor instead (say 12A FLC) then it would be (14A *125%)+14A+12A=43.5A


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## micromind (Aug 11, 2007)

One of the motors is the largest, the other isn't, even if they're both the same size.


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## Brentwerks (Nov 6, 2020)

thank you for the clarification


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