# Vfd load wires in conduit



## bill39 (Sep 4, 2009)

petek57 said:


> I've read and heard somewhere that it is best practice to only put 3 sets of VFD load wires in a raceway. Have not been able to find documentation on this. Any help?


Yes, I know I've seen that spec before too.

If you can't find it in the VFD manual then I would contact their tech support and get it in writing or email. If you don't follow their recommendations then you will get limited support IF their is a problem.


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## Cl906um (Jul 21, 2012)

Vfd install manual perhaps? Usually put one isolated load circuit per conduit. That's why you use shielded drive wire in cable tray. I heard of it done the other way, but synchronizing problems are a beach.


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## JRaef (Mar 23, 2009)

If you are using separate conductors in steel conduit, one circuit (3 motor leads plus full sized ground) per conduit. 

If you are using shielded VFD cables with the shields grounded at both ends, 3-4 circuits per conduit is the recommended maximum. The shielding helps contain EMI/RFI, but does little for induced voltages (cross talk) between circuits. In a regular motor running across the line, motor lead circuits are always from the same sources, so are in phase with each other and mutually cancelling each other's induced voltages. But with VFDs each set of output conductors are like a separate source with regard to the other circuits, plus they are not going to be at the same frequencies, so there is no mutual cancellation. The cables will magnetically couple with each other and add to the voltage stress problems you already have.


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