conductor sizing for electric motor

[JIMGEN]

We have a 400hp, 60hz, 575volt, fla 360, electric motor on a portable machine. We want to use a portable power cable such as 3/c type W. We would also consider single conductor type W, DLO or G.
Cut sheets for Type W show that 3/C is rated 350amps for 350mcm, 430 amps for 400mcm, 460amps for 450mcm, and 487amps for 500mcm.

Are NEC Tables 430-150 and 400.5(B) the proper reference source? What would be the proper cable conductor size?

 

[waross]

I don't have my NEC to hand, but as I remember, the conductors must be rated for 125% of motor full load current. That would be 360 amps x 1.25 = 450 amps.
Your rated at 460 amps and 450 MCM would be the appropriate cable.
Single conductor cables does not sound like a good idea at all.
yours

 

[VxA]

If the FLA you are stating of 360A comes from the nameplate, then you can use that, otherwise you need to consult 430-150 which says to use 382A. You must size the conductors to have a rated ampacity of at least 125% of the motors FLA. Thus, if we assume your FLA is 360, the conductors must be rated to carry 450A.

I think you are correct in consulting table 400.5(B), but you must check the cable temperature rating, and the terminal temperature ratings of the motor and the source you intend to feed this motor from. Whichever temperature rating is lowest will determine which temperature rating you can size your cable to. If we assume 75C, then I would think you would be looking at needing a cable size of 500kcmil (you would be looking unde the "F" column, as you have 3 current carrying conductors).

Also, the values in table 400.5(B) only apply if you are not routing this cable in with other power cables. If you are, you will need to adjust the table values. Also, be aware of the ambient temperature, and adjust accordingly if you have reason to believe you will be subject to a different ambient temperature.