motor calculation

[mark4160]

Please I need to understand this. I`m studing for a examine and maybe I am getting old but i can`t figure out the difference with art 430.24 and my test question.Here`s the problem.Art 430.24 states when conductors suppling several motors to add them up then 125% of the largest motor.I get that but here is what the book says.question What is the minimum size feeder conductor for the following 3 phase 460volt motors 40hp, 150hp, 10hp the the way they proceed to the answer is add all the motors then 25% of the largest. why 25% and not 125% I know there is`a big difference in the answer Please help Thanks Maybe I had to much wine

 

[roger]

Re: motor calculation

Notice the wording, "shall have an ampacity not less than 125 percent of the full-load current of the highest rated motor.

The 150 hp would be 180 x 125% = 225 or 180 x 25% = 45 180 + 45 = 225

The answer will be the same either way.


14 + 52 + 180 + 45 = 291

Roger

[ October 09, 2005, 11:54 AM: Message edited by: roger ]

 

[magoo66]

Re: motor calculation

430.24 says 125% of the largest motor plus the full load current of the REST of the motors. By adding the full load currents of all the motors and adding 25% of the largest you are doing the same thing.

 

[magoo66]

Re: motor calculation

Dang it.....too slow again!

 

[iwire]

Re: motor calculation

Yeah that Roger is fast.

Welcome back Roger, did you get any keepers?

 

[roger]

Re: motor calculation

Magoo66, I appologize.

I did edit to add the last line while you were posting though.

Roger

 

[mark4160]

Re: motor calculation

Thanks Alot maybe I did drink to much wine

 

[roger]

Re: motor calculation

Hello Bob, thanks for the welcome back.

We had good luck and actually limited out everyday we went out except one.

Roger