Output VFD Cables in a Single Conduit

[emartinez]

Due to project constraints, I am proposing to use a single existing conduit to run 4 separate VFD shielded cables to 4 separate motors ~450 ft. Is this possible? I understand it’s not advisable, but I just wanted to run it by here first for other input.

We are planning on using the X-Olene - Okoseal Shielded VFD cables.

 

[Boingo1972]

As you mentioned it's not advisable but the sheilding on the cable is really important to minimize the "cross talk". That cable you're planning on using has a 5 mil copper tape shield which is standard. But it has an overlap of only 25%, meaning half of that shield will be 10 mils thick but the other half will only be 5 mils thick. It would be better to find one with a 50% overlap wherein the shield will be 10 mils thick the entire lenght. A lot will depend on the voltage and voltage spikes the motors will generate. Even better would be to use a CCW VFD cable and forego the conduit alltogether and properly space each one.

 

[jtinge]

Aside from possible noise and EMI concerns, which may be addressed with the correct type of VFD shielded cable, do you have to oversize the cable conductors oversized to account for derating when more than 3 current carrying conductors are in a conduit? You don't mention size of the motors, conductor size or conduit size? Is there a conduit fill concern?

 

[emartinez]

As you mentioned it's not advisable but the sheilding on the cable is really important to minimize the "cross talk". That cable you're planning on using has a 5 mil copper tape shield which is standard. But it has an overlap of only 25%, meaning half of that shield will be 10 mils thick but the other half will only be 5 mils thick. It would be better to find one with a 50% overlap wherein the shield will be 10 mils thick the entire lenght. A lot will depend on the voltage and voltage spikes the motors will generate. Even better would be to use a CCW VFD cable and forego the conduit alltogether and properly space each one.

Thanks for the reply! I didn't know they made VFD shielded cables with 50% overlap. I'll look into that.

 

[emartinez]

Aside from possible noise and EMI concerns, which may be addressed with the correct type of VFD shielded cable, do you have to oversize the cable conductors oversized to account for derating when more than 3 current carrying conductors are in a conduit? You don't mention size of the motors, conductor size or conduit size? Is there a conduit fill concern?

I'm not too concerned about the conduit fill. The motors are 1.5 hp. The existing spare conduit is 4". Accounting for derating and voltage drop, the conductors would be able to fit. My main concern was whether this was possible with VFD cables :/

 

[Boingo1972]

VFD cables are actually not a thing. There is no standard for making them. Most list things like UL-44 which is thermoset insulated wire or UL-1277 which is power and control cables. There is no standard for VFD cables. They are essentially a sheilded cable that has symetrical grounds in contact with the shield. So if what you are doing is allowed for a shielded cable, it's allowed for this cable as well.