Motor conductor minimum size

[LBolt]

I have an existing 500hp motor drivin through a VFD. There are parallel 500MCM cables. There is also a bypass contactor around the VFD. We plan to upgrade to 600HP motor. I can limit the output of the drive to 600HP. If I use the FLA of the new motor 680 x 1.25 then I need a cable good for 850 amps. I am feeding the drive and by-pass contactor from a LVCB with an 800Amp trip unit set at 800Amps. I know that the 125% sizing is based on service factor and power factor,etc. Does the NEC allow me to use smaller than a 125% sized conductor if my overcurrent protection is set below that?

 

[dpc]

No.

David Castor

http://www.cvoes.com