VFD Cables?

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dicklaxt

Senior Member
A few years ago say back in the late 1990's and on into the new century,many studies were being done by cable manufacturer's,IEEE guys etc, on cables used in 600v and less VFD service.When I quit following it(retired),it looked like 3 phase conductors and 3 symmetrical grounds with an overall shield was the direction it was taking and would become the preferred cable makeup.Did this ever come to the table as a must or highly preferred method?:-?

I don't even remember the reasons behind the studies.This would have applied to only the cable from the controller to the drive itself

dick
 
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realolman

Senior Member
.....it looked like 3 phase conductors and 3 symmetrical grounds with an overall shield was the direction it was taking ....
dick


What would be the reason for an arrangement like that? :-? I'm not even sure I understand what you mean by three symmetrical grounds.
 

dicklaxt

Senior Member
Technically I can only guess on the reasons so will stay mum on that but 3 Symmetrical grounds are 3 ground conductors spaced evenly and equally around the 3 phase conductors in the interstice's of the cable.

I did find a lot of data on a Google search by different cable companies etc and it is above my head,I just plugged in VFD Cables and here comes more than I care to read.

dick
 
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big john

Senior Member
Location
Portland, ME
Wasn't the idea the same reasoning as having "inverter-duty" motors? Where there was some question about whether the insulation on 600V wire could stand the long-term repeated transients that VFDs can introduce?

I've never heard much about it. I've been involved in a fair number of mid-sized VFD installs and we always just used THHN or similar.

-John
 

TxEngr

Senior Member
Location
North Florida
Most drive manufacturers require the use of the inverter cable as part of their installation practices. Since I've always used the 'special' cable in my most recent installations, I haven't had any issues but I suspect that a manufacturer could use this as a reason to not honor a warrenty if you blew up a drive and weren't using the right cable.
 

a.bisnath

Senior Member
vfd cable usage

vfd cable usage

with the advent of electronic overload units and electronic circuit breakers it became more important to use vfd grade cables as the transient and harmonics of the modified sine wave would trip these electronic units,among other negative effects. I have seen it happen ,leading to a better practise that all new installations use the 3 symmetrical grounds with an overall shield giving protection from this undesirable interferences,if for reasons in existing installations where a vfd was added and the cable could not be changed reactors and filters were added to the line and load side to compensate for this,some vfd units come with them built in now,in older mechanical relay systems they can work well without the special vfd cable or filtering but with electronics around there can be trouble
 
with the advent of electronic overload units and electronic circuit breakers it became more important to use vfd grade cables as the transient and harmonics of the modified sine wave would trip these electronic units,among other negative effects.

VFD grade, to be more precise ASD, cables manufactured for the use with ASD's have NOTHING to do with transients and harmonics that would effect electronic overloads or 'electronic' circuit breakers. They are GALVANICALLY isolated from each others. If you want to talk about EM or RF interference, then talk about that.

Cables constructed for specific problems arising from non-sinusodial, high frequency, chopped waveforms are attempting to mitigate the problems those generate, namely:
  • Overvoltage stresses associated with fast switching resulting in transient spikes,
  • Formation of reflected or resonant standing waves of cumulative overvoltages,
  • Mitigation of additional heating effects by higher frequencies that the equipment was not designed for,
  • Radiated and common mode noises.
Cables are constructed to a higher(voltage) insulation level and with increased corona resistance, evenly spaced, split and triangulated integral grounding conductors for even stress distribution, shielding to reduce EMF and RF radiation.
 
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