However we’re not simply coping with radiated EMI due to the VFD’s excessive frequencies. To regulate the trail of a performed present, it must be terminated on each ends or it is not going to undergo appropriately. That, I might say, is the largest challenge I see with VFD cable set up issues.
AW: Within the analysis for this IEEE paper, you examined eight totally different cable varieties. For a typical manufacturing plant, are there two or three varieties you’d advocate from amongst these and why?
SW: First, I might advocate a repeatedly corrugated and welded aluminum armor, which usually has a PVC jacket excessive of it. That is actually a requirement for any Class 1, Division 1 hazardous location. Typically, it is a excellent VFD cable development as a result of that armor acts as the general electrical protect along with offering mechanical safety.
The opposite two cable varieties I might advocate are a free conductor with three grounds and a copper tape protect. The sort of cable just isn’t actually versatile, but it surely’s nice for industrial installations. And the third kind I’d advocate could be a extra versatile cable with a copper braid protect.
AW: Talking of cable shields, you’ve emphasised the necessity to terminate the cable protect at each ends. This led me to marvel, is that this one thing installers typically skip? And is there a easy means to make sure that it is completed appropriately?
SW: That is one space I might emphasize that folks take note of as a result of, for some motive, there hasn’t been numerous coaching completed round this. Drive producers all just about agree it must be terminated at each the drive and the motor, however the phrase simply hasn’t gotten out about this.
I’ve completed casual surveys of electricians and numerous them assume you need to terminate at one finish — on the drive — and float the motor. I’ve additionally seen the place individuals minimize the protect off at each ends and use a drain wire to terminate as a result of that is the way you do a communications cable. The issue is, with a VFD, you need low impedance at excessive frequency to be sure that excessive frequency flows freely. A drain wire doesn’t permit that to occur.
