electrical cable sizing for 3 phase

[titan11]

anyone have the formula to select the cable size for a 3 phase line.

info i have

3 phase 460v
3 - motors... 8.9A, 8.9A, 13.2A
1 way distance of 2480'

 

[rbulsara]

Google search for voltage drop calculators.

Also half a mile long 480V circuit is a bad idea, but that was not your question.

 

[titan11]

why is it a bad idea.. most sites dont give me a formula so thats why im asking here

 

[Eleceng01]

Using the simple calculator that I have, I came up with a ~5% voltage drop along for a 4/0-cable with (31A load). This is right at the critical voltage drop according to IEEE Std. 141 so any other loads will only make it worse.

Also, motor starting might become an issue. I would recommend modeling your circuit in either ETAP, SKM, or EasyPower to determine the best design.

 

[rbulsara]

Take a deep breath. I am in worse mood than you are today.

It is just too long a circuit at that voltage. You will see when you do the calc. I am not saying it won't work.

If you are really designing something you need to make an effort to learn some basics. This site is not here to teach basics to novices. There are schools for that purpose. This is a forum for "professionals" to bounce off ideas and benefit from each other's experience. Not to learn basics.

Search a little harder or buy/borrow basic electrical engineering book/hand book. Even try Ugly's handbook.

If you keep this attitude, it will not be long before your post disappears from this site!

 

[waross]

We usually don't use a formula for this type of issue. We look it up in tables and extrapolate if we have to.
Why is it a bad idea? High cost and poor performance. Consider transformers and a higher voltage.

Bill
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"Why not the best?"
Jimmy Carter