Input cables for VFDs - sizing the EGC
Input cables for VFDs - sizing the EGC
(OP)
Hello,
I am working with an Eaton SPX 300 Hp drive. The drive manual recommends that for incoming power cables, phase conductors should be 2 @ 300 kcmil, and the ground conductor should be 1 @ 300 kcmil. The question I have is about the ground. The upstream breaker is 500A. According to NEC, for this size breaker I would need a #2 ground. The Eaton manual recommends a 300 kcmil, which has an ampacity of 250% more than what is required. I've asked Eaton tech support why they recommend such an over-sized ground, and they did not know.
Can anyone here explain why I should use the 300 ground?
Thanks
EE
I am working with an Eaton SPX 300 Hp drive. The drive manual recommends that for incoming power cables, phase conductors should be 2 @ 300 kcmil, and the ground conductor should be 1 @ 300 kcmil. The question I have is about the ground. The upstream breaker is 500A. According to NEC, for this size breaker I would need a #2 ground. The Eaton manual recommends a 300 kcmil, which has an ampacity of 250% more than what is required. I've asked Eaton tech support why they recommend such an over-sized ground, and they did not know.
Can anyone here explain why I should use the 300 ground?
Thanks
EE





RE: Input cables for VFDs - sizing the EGC
Read chapter 3 in this document.
http://literature.rockwellautomation.com/idc/group...
Actually, read the hole thing...
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Input cables for VFDs - sizing the EGC
RE: Input cables for VFDs - sizing the EGC
RE: Input cables for VFDs - sizing the EGC
RE: Input cables for VFDs - sizing the EGC
Ideally, you would have both a properly terminated full braided shield on the cable between the VFD and the motor, and the VFD would have internal capacitors from the positive and negative bus to ground. That way, these high frequency currents get returned directly to the VFD bus where they came from. Otherwise, they go back to the power source transformer and get back onto the phase conductors via the bonded neutral before finally getting back to the DC bus via the VFD input rectifier.
RE: Input cables for VFDs - sizing the EGC
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Input cables for VFDs - sizing the EGC