Conductor sizing

[Dave Dungan]

I have a 400 amp Meter section that is going to feed a 150 HP VFD cabinet. The motor draws 171 amps. The VFD has 350 amp, 500 volt semiconductor fuses and the VFD is about 10 feet away from the Meter section. Do I need a separate Disconnect other than the one in the VFD, and can I run wire big enough for the Motor load or do I have to run wire sized for the 350 amp fuses?

 

[justdavemamm]

AFAIK, you have to run wire big enough for the maximum amps that the VFD can (is able to) draw. The mfg. should show this in their specs.

Semiconductor fuses typically are not primary OCPD as the amps/time curve would show. See http://www.crouzet-usa.com/techtalk/index.php?showtopic=457

The motor draws 171 amps.

Is that nominal running amps or Full Load Amps ?

 

[IMM_Doctor]

Fusing Options

Fusing Options

You may be able to have your cake, and eat it too.

Bussman now has a fuse that has low (I sq t) let-through ratings to protect drives and semiconductor switching componets, yet is also rated as branch-circuit protection.

http://www.bussmann.com/pdf/752277d8-5806-4a56-b68e-d478eab18621.pdf

If link does not work, look for Bussman DFJ fuses.

 

[Dave Dungan]

Conductor sizing

171 amps is the FLA

 

[don_resqcapt19]

171 amps is the FLA

The conductors to the VFD must have an ampacity of at least 125% of the drive input amps.

430.122 Conductors ? Minimum Size and Ampacity.
(A) Branch/Feeder Circuit Conductors. Circuit conductors supplying power conversion equipment included as part of an adjustable-speed drive system shall have an ampacity not less than 125 percent of the rated input to the power conversion equipment.