experience pulling type MC pvc jacketed vfd cable thru sch 40 pvc conduit

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Joe Corbin

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Key West Florida
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Master Electrician
Does anyone have experience pulling aluminum pvc coated MC thru sch 40 pvc conduit. We are to install this cable in /thru pvc sch 40 conduit from the vfds to the motors. The conduit fill ratio is good. However the maximum bend radius for two sizes of the cables is very tight. On 4" conduit the standard radius of a 90 is 16". The 500mcm cable to be installed has a OD of 2.290 x 7 = 16.03" maximum radius bend. For the 3" conduit the standard radius of a 90 is 13". The 250mcm cable OD is 1.845 x 7 = 12.915 maximum radius bend. The ODs listed are for just the metalic sheath only, with the pvc jacket coating the OD is slightly larger for both cables. The pvc conduit is already installed. I am wondering how hard this will pull or if the 90s/fittings should be changed out to larger special radius 90s. Has anyone had experience with this type of installation? I may have to just try one pull to find out.
 
Why are you pulling MC through conduit in the first place? If you need "shielded" cable for VFD use, use VFD cable instead.


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Not my design. This was prescribed by the engineer. Spec. for vfd cables this job: Type MC XHHW pvc jacketed aluminum Armor X vfd cable. Spec, conduit for vfds this job: Pvc sch 40 will be installed between the vfd and motor terminals where ever armored cable is used. Inside and outside. ? Anybody that has pulled this type of cable thru conduit please advise. Joe
 
I don't see how you're going to make a compliant termination of the MC at the peckerhead if the MC is in PVC conduit and the conduit terminates at the peckerhead. That said, long radius bends seem like a good idea. And lots of wire lube. That PVC jacket may "stick" in the PVC. Also, ensure all cut pipe ends are properly and reamed - you don't want sharp edges tearing the PVC jacket.


SceneryDriver
 
Joe Corbin said:
Not my design. This was prescribed by the engineer. Spec. for vfd cables this job: Type MC XHHW pvc jacketed aluminum Armor X vfd cable. Spec, conduit for vfds this job: Pvc sch 40 will be installed between the vfd and motor terminals where ever armored cable is used. Inside and outside. ? Anybody that has pulled this type of cable thru conduit please advise. Joe
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Does the engineer understand that in this case the PVC is just a sleeve and can't connect to the enclosure at each end? There would be know no way connecting both the PVC and the coated MC.
 
Side note: large place that I retired from had over 500 VFD'S from 2 to 1,750 HP and not one was on overated shielded cable. Used THHN/THWN wire in metal conduit and never had a problem. Some were MCC change outs from starters to drives on 1970 plain Jane NEMA frame 2 & 4 pole motors that ran 24/7 and had very few motors burnt out. They had 18 pulse drives for motors 40 HP & higher in their newest building again all on THHN/THWN wire with no problems. Several times I asked techs from Danfoss & ABB drives about what they thought of using shielded cable to supply drive motors and thought that it was not necessary in almost most applications.
 
Guys, I appreciate and agree with your comments. I was brought onto this job late and now I am trying to deal with the existing conditions. The radius bends are very tight for pulling the MC cable. As mentioned, other than using pvc conduit for a protective sleeve or support in a straight run I have never pulled MC thru 90s or 45 ells. This looks like it will be a learning experience. I will have to try one pull to see how it goes. If the pull is hard, I will have to go back and have all the standard radius fittings changed out. Going to use lots of soap.
 
Guys, just to bring you up to date, we have pulled all of the pvc coated MC cables. We used a lot of soap/lube and a tugger.
My advice, if you run into this requirement use larger radius 90s, 45s, and make any hot box offsets with as much radius as possible. Joe
 
Joe Corbin said:
Guys, just to bring you up to date, we have pulled all of the pvc coated MC cables. We used a lot of soap/lube and a tugger.
My advice, if you run into this requirement use larger radius 90s, 45s, and make any hot box offsets with as much radius as possible. Joe
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I think I would simply tell the engineer he's clueless.
 
roger said:
I think I would simply tell the engineer he's clueless.
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I don't understand what the point of putting mc inside of pvc is either but I see a lot of boiler plate specs that contractors just accept and then they are kind of trapped into doing it that way. Better to get stuff like this removed up front if possible. But once you are trapped into it, you just kind of have to get it done as best you can.

I have had specs where they want VFD cable on the line side of the vfds in an industrial control panel. Usually they go along with taking it out on the grounds that it is kind of pointless to run VFD cable from the ocpds to the vfds. But it is hard to get them to update the specs.
 
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