VFD analog signal cable in conduits

[slavan]

I wonder if someone can shed a light on this matter. I was talking to an engineer about VFD analog signal and running the 18 awg belden cable in separate conduit. The engineer stated to limit 3 cable only that can be run in a conduit; if run too many, the cable can degrade due to frequency from the drive or something like that. I can not find anything about this limitation online or anywhere else.

 

[Besoeker]

I wonder if someone can shed a light on this matter. I was talking to an engineer about VFD analog signal and running the 18 awg belden cable in separate conduit. The engineer stated to limit 3 cable only that can be run in a conduit; if run too many, the cable can degrade due to frequency from the drive or something like that. I can not find anything about this limitation online or anywhere else.

Separate coiduit I can understand. The degrading bit sounds like nonsense to me.

 

[jeremy.zinkofsky]

Maybe he is talking about harmonic distortion. When there are multiple cables with different analog currents at different frequencies in the same conduit, the electromagnetic field induced can add noise to the system. Basically, it may produce a waveform that looks more like what a seismograph waveform looks like instead of a clean line. Thos little fluctuations can potentially add up and make the VFD less efficient.

 

[kwired]

Maybe he is talking about harmonic distortion. When there are multiple cables with different analog currents at different frequencies in the same conduit, the electromagnetic field induced can add noise to the system. Basically, it may produce a waveform that looks more like what a seismograph waveform looks like instead of a clean line. Thos little fluctuations can potentially add up and make the VFD less efficient.

Sounds like you are maybe talking about the drive output conductors?

OP is talking about control signal conductors/cables for the drive.

 

[slavan]

Maybe he is talking about harmonic distortion. When there are multiple cables with different analog currents at different frequencies in the same conduit, the electromagnetic field induced can add noise to the system. Basically, it may produce a waveform that looks more like what a seismograph waveform looks like instead of a clean line. Thos little fluctuations can potentially add up and make the VFD less efficient.

That sounds more in tune to what he was saying. There are instances where multiple cables are run in a dedicated wireway for several drives and the signal are fine to the drive. I don't see a difference with running 8 cables in maybe a 2" conduit, maybe smaller conduit, or in a wireway. Quicker to run one conduit than multiple conduits for the job.

 

[Jraef]

Is this a 480V drive? If so, the analog signal cables would need to not only be twisted shielded pairs, but the insulation rating would need to be 600V minimum. That's one thing that snags people because some 'signal" wire, even if shielded, is NOT rated for 600V.

But other than normal conduit fill rules it shouldn't matter.

 

[RobertKLR]

The PWM output of the drive can put microscopic pinholes in the insulation of the power conductors, that degrades the insulation. The process is very slow but it would not affect the insulation of any other wires in the conduit. A line reactor can alleviate that but no comm or control wires should be in that conduit anyway. They should be in separate conduit and that conduit, if it parallels the power conduit for more than a few feet, should be separated by 6 inches (some say 3") to avoid interference. If the two conduits need to cross ideally they should cross at right angles to each other or as close as possible to 90 degrees.

 

[Cow]

Analog signal cables are all low voltage(4-20mA, 0-10v). There is no issue with running multiple analog signal cables in a conduit or in close proximity to each other. Drive output conductors and cables is another story.