If it's a VFD by a certain large company (that starts with A) they have MOVs across the lines and to ground that will fail short circuit (usually if installed on an ungrounded system) and at least take out the fuses, if not the whole drive. (been there, done that) Check the instruction manual on how to disconnect them.
Conductors for VFDs
- Thread starter charlie b
- Start date
- Status
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
kameele said:
yep. can be a big problem if the guy doing the install fails to follow the instructions. there is certainly no excuse for it in this case. "A" has clearly indicated this situation in the manual and made it easy to solve.
John Valdes
Senior Member
- Location
- SC.
- Occupation
- Retired Electrician
iwire said:
Bob,
I meant three CCC and one EGC in one conduit. Not to separate the ECG from the other three.....John
megloff11x
Senior Member
don_resqcapt19 said:
Haven't been on this one in a while. These were ultra sensitive capacitive sensors. If you looked at them they got noisy. Their cables were shielded and the shields grounded, but they were still having issues.
I've done VFD motor systems with just wires or just wires in conduit with no persnickety sensors before and they ran, and we never looked at the noise. After this particular headache, I tried the fancy VFD optimized cable, in this case it was more or less a flexible layered shielding conduit with outer plastic coating, and it just killed the noise. I think it was under $8 a foot for 4-conductor 6AWG.
I do agree on separate shielded runs for power and signals. Another trick is getting them at right angles. Fields couple more readily parallel. I always say picture trying to pass a baton in one of those track and field things. They do it running alongside. If they met at an intersection, the handoff would get really tricky.
If it costs about the same, why not the fancy stuff.
Matt
- Status