ABB Drives and Conduit Routing

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infinity

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I have five ABB VFD's that will be feeding five fans (5 and 10 HP). I've been getting varying information regarding the conductors between the fans and the drives. One opinion is that all five feeds must be run in separate conduits from each individual drive to the fans. The other opinion is that the drives can be linked together via a wireway and that the feeds can be all run in one conduit from the drive location to the fans. I've glanced at some ABB literature but couldn't find a definitive answer either way. Anyone have experience with these setups?
 
From what I've read, drive companies want vfd cable or THHN in metal conduit the whole way. I've always heard it's bad practice to run more than one drives motor leads next to each other, so if your wireway was very long, I'd be looking at individual conduits instead.
 
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Cow said:
From what I've read, drive companies want vfd cable or THHN in metal conduit the whole way. I've always heard it's bad practice to run more than one drives motor leads next to each other, so if your wireway was very long, I'd be looking at individual conduits instead.
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The wireway will just be long enough, about 5' with short nipples, to link the drives together with a single conduit running out to the fans for a distance of about 50'.
 
When you run any 3 phase circuit, there is the possibility of mutual inductance on adjacent cables in an enclosed raceway such as conduit. But, if the 3 phases are all at the same frequency, the effect is canceled out because the net voltage sum will (should) always end up as zero. Now add VFDs into the situation. The three output wires for VFD 1 are running at 30Hz, the 3 for VFD 2 are running at 40Hz, the 3 for VFD3 are running at 50hz. etc. etc. and if they are all in the same conduit, the cancellation effect is no longer in play because the frequencies are different. You end up exacerbating the known effects of "standing waves" on the motor insulation and can cause self-commutation (uncommanded firing) of the VFD transistors, which will damage them.

You can get around this by using VFD cable, which is triplexed shielded cable designed for this purpose. It is expensive compared to THHN, but less expensive than separate conduits installed for each drive.
 
Jraef said:
When you run any 3 phase circuit, there is the possibility of mutual inductance on adjacent cables in an enclosed raceway such as conduit. But, if the 3 phases are all at the same frequency, the effect is canceled out because the net voltage sum will (should) always end up as zero. Now add VFDs into the situation. The three output wires for VFD 1 are running at 30Hz, the 3 for VFD 2 are running at 40Hz, the 3 for VFD3 are running at 50hz. etc. etc. and if they are all in the same conduit, the cancellation effect is no longer in play because the frequencies are different. .
Click to expand...
I think the bigger concern might be the switching edges rather than the fundamental frequency.
 
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