"VFD rated cable"

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steve66

steve66

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Illinois
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Engineer
Has anyone heard of MC cable that has a rating for VFD use? This would be for the cable feeding a VFD?

A contractor asked if they needed to use VFD rated cable. They said they had problems with the power ran to another VFD and had to use a VFD rated cable.


Steve
 
steve66 said:
Has anyone heard of MC cable that has a rating for VFD use? This would be for the cable feeding a VFD?

A contractor asked if they needed to use VFD rated cable. They said they had problems with the power ran to another VFD and had to use a VFD rated cable.


Steve
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I am not aware of any special cables used to feed the VFD. There are some made for feeding from the VFD to the motor. How necessary they are is unclear. My guess is far more VFDs are wired to their motors with regular wire then with special VFD cable.

Having said that, my drawings mostly show cables, usually what is spec'ed by the VFD manufacturer. Most of the time the electricians don't bother and just run wire. Can't say it has ever made any difference one way or the other.
 
I've used the VFD cable from Belden from the VFD to motor.
If I recall, I have to close my eyes sometimes when reviewing the submittal, as the EGC is undersized for most cable selections.
 
lakee911 said:
We use VFD rated cable on long cable runs where IIRC, harmonic issues develop. Most short runs use regular cable.
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VFD Cable helps on long runs from standing waves, because the cable I have used is 1000v rated. Although if you have standing wave concerns you should solve it with load side reactors and not bandaid it with cable that can handle it.

It is more important for containing electrical noise, which is imporant for a long or short run.
 
I do not know what he ment by "VFD Rated cable", maybe a higher voltage rating as stated earlier to allow for the standing waves issue. If he meant sheilded VFD cable, It is highly desirable in reducing common mode noise by providing a very low impeadence path back to the drive from the motor. When you use standard non sheilded wire on drives, small, high frequency currents find their way into your grounding system trying to find their way back to the drive from the motor. This can cause havoc on instrumentation and controls. The shield is design to provide the lowest impeadence path back to the drive and thus keeping those stray currents off of your ground
 
Thanks for all the replies. Doesn't sound like anyone has ever heard of needing anything special to feed the VFD's though.
 
steve66 said:
Thanks for all the replies. Doesn't sound like anyone has ever heard of needing anything special to feed the VFD's though.
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In Europe most wiring is done using cords instead of grounded metallic raceways. Shielded cable is a must in these cases, which is why most universal language instruction books include this spec even for input cabling. The CE requirements for reducing EMI/RFI are pretty stringent. In the US most wiring has been individual conductors in grounded metallic conduit, so 'noise' is not as much of an issue in maybe 90% of the VFD applications.
 
steve66 said:
Thanks for all the replies. Doesn't sound like anyone has ever heard of needing anything special to feed the VFD's though.
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The folks at Belden and Rockwell wrote a paper in 1999 and demonstrated that EMI emissions can be reduced by using shielded cable between the VFD and line reactor and from the line reactor to the feeder breaker. I can't post it to the site due to copyright restrictions. If you are a member of the IEEE IAS or have access to the PCIC paper archives, look for a paper by Gary Skibinski and two Belden engineers that was presented at the 1999 PCIC.
 
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