Question, I understand that when using regular THHN it is highly advisable not to install output wiring from different VFDs in the same conduit. But what if you use Belden cable specifically for VFDs? (Belden #29502 and above). I see on this forum that having multiple VFD output wires in the same conduit can cause voltage spikes, but isn't VFD cable supposed to alleviate this? We use RMC here at my plant (mostly aluminum but some galvanized). Thanks
multiple VFD output cables in same conduit, using VFD cable?
- Thread starter adamscb
- Start date
I looked this cable up.It appears to be a 3 conductor shielded cable ( looks like a cord ) . One internet site charges over $14 a foot for the 12/3. Ouch. The large 5 million square foot hospital/research center /Ambutory care building that I retired from had over 500 VFD'S from 2 to 1,750 HP. All were feed by THHN /THWN & a copper ground wire thru steel EMT. They had some old plain and Nema frame motors from the 1970's that had drives replace motor starters. I would never pull any jacketed cable thru conduit.(except very thin say 18/6 shielded control cables ). I have asked what at least 6 drive techs from ABB, Danfoss & two independent service companies what they thought of ever using expensive shielded cable for drives and all said that it was a waste of money in 99% of applications. We always had a line reactor on the input of drives. Last few years they started installing thought they were called active reactors on load side of all but the 18 pulse drives. Load side reactors had 1 or 2 contactors & capacitors. I cannot remember what NEC limits a single conductor thru conduit but thought it might only be 40% so such a cable might require a conduit twice the diameter then if you just pulled 4 THHN/THWN wires. Even with a much larger diameter conduit you might run in a code issue on the minimum allowed 90 turn if pulled thru a LB condulet.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I believe that the reason you buy that very expensive cable is so that you can put multiple outputs in a single raceway without any issues.
We are installing multiple VFD cable in the wireway all the time. It should not be a problem to install multiple cables in the same conduit. Be aware that number of conductors in conduit de-rating rules are more strict than de-rating rules for wireway, and required conduit size may become too large.