Code question

[yaoyaodes]

I have a question regarding this one in NEC.

430.24 Several Motors or a Motor(s) and Other Load(s). Conductors supplying several motors, or a motor(s) and other load(s), shall have an ampacity not less than the sum of each of the following: (1) 125 percent of the full-load current rating of the highest rated motor, as determined by 430.6(A) (2) Sum of the full-load current ratings of all the other motors in the group, as determined by 430.6(A) (3) 100 percent of the noncontinuous non-motor load (4) 125 percent of the continuous non-motor load.

I have a question ask me that minimum size of copper conductor required for a group of three 3-phase, 460V wound rotor induction motors with nameplate ratings of 10hp, 7.5hp and 5hp. assume that each motor has 75C rated terminal.

according to table 430.250
I have 10hp-14 , 7.5hp-11, 5hp-7.6

if I add three together is 14+11+7.6=32.6 which is already higher than the 125% of the highest FLC

but the solution is 1.25*14+11+7.6=36.1 I don't understand why.

Can anyone explain to me?

 

[main197]

There are three motors, and the highest is 10 hp. The code says to sum 125% of FLC of the highest rated motor (10 hp) with FLC of other motors. So, 125% of FLC of 10 hp motor is 1.25*14=17.5A. Add this to the FLC of other motors. 17.5+11+7.6=36.1A.

On a side note, I think you should enroll in Zach Stone's class. It will help you a lot.

 

[yaoyaodes]

There are three motors, and the highest is 10 hp. The code says to sum 125% of FLC of the highest rated motor (10 hp) with FLC of other motors. So, 125% of FLC of 10 hp motor is 1.25*14=17.5A. Add this to the FLC of other motors. 17.5+11+7.6=36.1A.

On a side note, I think you should enroll in Zach Stone's class. It will help you a lot.

Thanks. taking the exam in two weeks. if I fail, I will consider taking the class.

 

[Zach Stone P.E.]

There are three motors, and the highest is 10 hp. The code says to sum 125% of FLC of the highest rated motor (10 hp) with FLC of other motors. So, 125% of FLC of 10 hp motor is 1.25*14=17.5A. Add this to the FLC of other motors. 17.5+11+7.6=36.1A.

On a side note, I think you should enroll in Zach Stone's class. It will help you a lot.

Thanks for the mention, @main197 !