VFD Communication Cabling

[marshatl]

I am looking for opinions on a problem we routinely have as Building Automation contractors when controlling 460V VFDs. By code all the wire that we have running into that VFD enclosure needs to match the insulation rating of the highest voltage conductor which to make life simple is 600V rated wire. It is not a big deal when it comes to signal wire since we can just have them run 600V or 1000V THHN. But the communication bus wiring whether BACNet or Modbus is a challenge. 600V rated wire for that application is available, but it is expensive with a very long lead time. And usually our electrical subs don't realize this until they are supposed to be starting up the drives.

Has anyone utilized a product like this...
https://www.techflex.com/prod_ag.asp
that could be used to sleeve normal 300V rated wire inside that enclosure and had it pass through electrical inspection? I don't see any huge issue as long as it is from the entrance to the drive up to where the comm bus wires terminate on the strip. I am sure many times the sub has just run 300V wire and never told us and has gone through inspection with no problem, but would like to have a solution that we can pull out and use to make sure we are meeting code on all jobs.

Thanks.

 

[Jraef]

A) Properly rated shielded signal conductors are available. Chances are that cheap comm cables will not have the level of shielding you will need to protect those comm wires anyway. Most VFDs will give you a minimum shielding value that you must use, often called a "M.I.C.E." rating. Mechanical, Ingess, Climatic, and Electromagnetic. Light commercial comm cable will be M.1 I.1 C.1 E.1, Indudtrial, meaning in or near equipment, must be M.3 I.3 C.3 E.3 rated or you run the risk of the EMI of the VFD bleeding over into your cables. So it's not just about the voltage level.

B) Then there is this. "Expensive" is relative to what? Something that violates code? That same argument could be made for almost anything; there is ALWAYS a cheaper option, that's what the NEC is trying to deal with. Do things slip past the inspectors? Sure, every day. But luck is not a valid strategy. The first time an inspector DOES catch it, the money "saved" all goes out the window, and then some.

C) That sleeving does not change the insulation rating of the wire. The same argument has been raised, and lost, regarding 1000V rated heat shrink tubing put over 300V wire, it didn't fly either.

 

[marshatl]

A) Properly rated shielded signal conductors are available. Chances are that cheap comm cables will not have the level of shielding you will need to protect those comm wires anyway. Most VFDs will give you a minimum shielding value that you must use, often called a "M.I.C.E." rating. Mechanical, Ingess, Climatic, and Electromagnetic. Light commercial comm cable will be M.1 I.1 C.1 E.1, Indudtrial, meaning in or near equipment, must be M.3 I.3 C.3 E.3 rated or you run the risk of the EMI of the VFD bleeding over into your cables. So it's not just about the voltage level.

B) Then there is this. "Expensive" is relative to what? Something that violates code? That same argument could be made for almost anything; there is ALWAYS a cheaper option, that's what the NEC is trying to deal with. Do things slip past the inspectors? Sure, every day. But luck is not a valid strategy. The first time an inspector DOES catch it, the money "saved" all goes out the window, and then some.

C) That sleeving does not change the insulation rating of the wire. The same argument has been raised, and lost, regarding 1000V rated heat shrink tubing put over 300V wire, it didn't fly either.

Thanks for the input. It is not about the cost of the cabling, just more frustrating when the device is 200' away and the only chunk of cable that needs 600V rated is 3' long. It is more the on the shelf availability of the product and if there is a reasonable secondary option if we come into the situation where a two week lead for some cable is difficult. Typically I keep a 1000' box on our shelf for things like this when needed, but it isn't always there.