Input cabling from LV SWGR to VFDs

[JBUDA54]

I have a situation where the owner is trying to save cost for cabling to a VFD from a LV Switchgear (600V). The Cable was designed to be Continuously Corrugated Welded with 3 GND Conds with 3 Phase Conds. The owner's stance is that this type cable is only require from drive to motor and not from Switchgear to drive.

Can anyone please advise as to what the best recommended cable installation would be from the Switchgear to the Drive?

I have read a number of VFD Cable specifications and there wasn't any stance for the cables from LV SWGR to Drive.

Thanks for your help in advance.

Best Regards,

Jason

Jason Buda, PE
Greenville, SC
jbuda54@yahoo.com

 

[peebee]

I'm not aware of any particular VFD input feeder design criteria, nothing different from any other load. Use whatever cable you want that's sized to meet code.

The only problems upstream of VFD's are the typical problems you get with any harmonic-generating source. But, those problems would typically affect transformers, not the VFD line-side cabling.

Downstream of the VFD can be a very different story, due to the high frequency PWM used to synthesize the output wave. But you are apparently already aware of those issues.

 

[jacquesgiraud]

No specific conductor type is needed for your VFD supply side cabling.

First prize for your load side cabling is continuously welded corrugated armor jacket with three power conductors and three ground conductors as you stated.

Our experience has shown that a suitable substitiute for this on motors less than 25 Hp is ordinary shielded tray cable - PVC jacketed 600V rated with the same type of foil shield that you find in instrument cable. We have used this on installations where metal clad cable would have been completely impractical and have had no problems at all.

Additionally, insist on following the manufacturer's fusing recommendations if the unit does not have integral line side fuses. The thermal magnetic circuit breakers and time delay fuses found in most indistrial switchgear do not provide adequate protection for variable drives. You may have to modify the fuseholder system in your switchgear or install a separate fuseblock because some drive manufacturers specify European/DIN standard fuse assemblies.

 

[jraef]

I agree with peebee. No special cable issues on the input side, just the output. The probable reason why the cable sources wouldn't differentiate is that there would be no harm in using it for the input, just no benefit except that way they get to sell more of the expensive cable (so the benefit is to them).

"Venditori de oleum-vipera non vigere excordis populi"

 

[dpc]

If you're using metal-clad cable for both, there may not be any difference. Okonite CLX now has the three-ground wire configuration as a standard.

If you want to reduce costs, you can use single conductors pulled in conduit.