How can I terminate (3) parallel VFD cables on a motor's peckerhead?

[ibarrola]

Hi guys,
Like the above question on the subject, I am wondering how would we wire (3) VFD cables to a motor with a 4"NPT? This is a 350HP motor fed from a VFD in which I am running (3) parallel #2/0 VFD cables. Any products that I can use? This is a C1D2 area.

Looking at Belden VFD cables and this is there solution for a 350HP motor due to ease of installation and ampacity.
Thanks!
yogi

 

[petersonra]

I suggest asking Belden. They might have an answer. It seems to me it is not a trivial problem, but maybe you could use some polaris style connecters.

You could always use compression lugs and stack them.

 

[ibarrola]

Hi,
I did ask Belden but did't get an answer, I might try the motor mfg.
My problem is how to get (3) cables inside. I can't use a cable gland for each cable, I only have one 4" entry point.
I'll check with motor mfg, maybe pecker head can be requested with more entry points although this is part of a vendor's scope.
Thanks,

 

[petersonra]

Hi,
I did ask Belden but did't get an answer, I might try the motor mfg.
My problem is how to get (3) cables inside. I can't use a cable gland for each cable, I only have one 4" entry point.
I'll check with motor mfg, maybe pecker head can be requested with more entry points although this is part of a vendor's scope.
Thanks,

something like this perhaps.

 

[petersonra]

IMO, the junction box supplied by the motor manufacturer is not part of the motor. Why not just replace it?

 

[ibarrola]

Talked to Baldor and Belden, no solution lol.

Going to email vendor so they can talk to their contact to see if the peckerhead of the motor could be replaced for one with x3 2" holes.
If not then I am thinking of installing an enclosure next to the motor, so to peel cables from outer sheath and then run the wires thru a liquid tight conduit and into the peckerhead.

Which junction box?
Also, thanks for the cable gland, I'll take a look at the product, although I don't think I can install this on the peckerhead.
Thanks,
yogi

 

[paulengr]

First off VFD cable is an outright scam. Belsen should be utterly ashamed of themselves. At #14 with THHN (not THHN-2) if it gets wet it has a lower resistance to surges than the motor. XHHW never has this issue and THHN is fine at 20 mils insulation thickness or greater. Both vastly exceed the rating of even inverter duty motors. So selling 2 kV cable in a 600!V market is baloney.

As to the idea of “balanced” and somehow magically lower cable impedance it does make a difference if your feeders are significantly different in length or capacitance. This is also true in ordinary power distribution. So basically I plead baloney on the VFD cable. If there is an imbalance causing bearing failures it’s not the cable, it’s natural from any six pulse drive and only a common mode filter or a grounding brush and an insulated bearing is going to cure it. I’ve seen tons of installs where Belden scammed them with overpriced VFD cable but did not fix the issue. It doesn’t fix common mode voltages. Those are inherent in VFDs. If you can only output +VDC or -VDC, how do you get V1+V2+V3=0? You can’t. Hence....common mode voltage, wonder cable or not.

So we need 516.5 A ampacity? You did not specify 469 or 575 V motor. You could run 750 MCM fine strand like DLO but that’s crazy. Two 4/0 XHHW-2 TC-ER gets you there. Based on Service Wire that’s 1.51” diameter. I believe a Roxtec gland might make it but better check the specs closely. Otherwise remove the original peckerhead and attach a larger enclosure of your choice. A third option often practiced is just mount the box next to the motor and switch to THHN jumpers feeding through a 4” section of LFMC. Crimp lugs on the ends, stack and bolt everything together, and tape it all up. This takes up the least amount of peckerhead space.

It is quite common to have this issue with motors at 200 HP or larger. It seems like they should be using larger peckerheads but the motor manufacturers don’t. They just follow a standard. We often “upgrade” them for customers.

 

[Cow]

Hi guys,
Like the above question on the subject, I am wondering how would we wire (3) VFD cables to a motor with a 4"NPT? This is a 350HP motor fed from a VFD in which I am running (3) parallel #2/0 VFD cables. Any products that I can use? This is a C1D2 area.

Looking at Belden VFD cables and this is there solution for a 350HP motor due to ease of installation and ampacity.
Thanks!
yogi

We would run (2) sets of 350 XHHW CU in the 4" conduit. No vfd cable. Since you're class 1, div 2, I would be expecting rigid conduit and ex prf flex.

 

[ElectricMatt]

I recently had the same issue on a 480v 700hp compressor motor. The size of the peckerhead and the 2 4” holes would have made it really hard to use thhn. So I chose to go with DLO because of the increased ampacity and flexibility. Huge time saver. I ordered the DLO lugs with spacers and it worked great.

Sent from my iPhone using Tapatalk

 

[Besoeker3]

I recently had the same issue on a 480v 700hp compressor motor. The size of the peckerhead and the 2 4” holes would have made it really hard to use thhn. So I chose to go with DLO because of the increased ampacity and flexibility. Huge time saver. I ordered the DLO lugs with spacers and it worked great.

Sent from my iPhone using Tapatalk

Neat!

 

[Cow]

That install above concerns me.

The spacers you are using are intended for CT cabinets and the like, using the standard 2 hole lug spacing with those spacers intended to be sandwiched between lugs utilizing their full surface area to make contact between the lugs and busing, etc. The way you are using them, you are passing 800+ amps through them from one end of the spacer to the other, like a bus link, rather than through the entirety of the spacer if they had been sandwiched between lugs/busing as intended.

That also leads to the second problem I see. Since you are using a spacer in a way that wasn't intended, your crimp on lugs are not making full surface-surface contact with your underlying spacer. That looks like it will loosen up over time from motor vibration.

Third, I can see the edges and profile of the lugs through your tape job. When we tape with a combination of cambric, 130c, super 88, and maybe some insulation putty if need be, the thought is to tape in a way that the splice ends up round'ish, such that a person can't see the overall profile of the lugs/bolts/hardware underneath along with the sharp edges from those materials.

When we do larger motors, we will often times pull wire to the motor at a one-one ratio with the motor leads. It is not uncommon for us to have 6 motor splices in a motor with one of our wires spliced to just one motor lead.

 

[ElectricMatt]

That install above concerns me.

The spacers you are using are intended for CT cabinets and the like, using the standard 2 hole lug spacing with those spacers intended to be sandwiched between lugs utilizing their full surface area to make contact between the lugs and busing, etc. The way you are using them, you are passing 800+ amps through them from one end of the spacer to the other, like a bus link, rather than through the entirety of the spacer if they had been sandwiched between lugs/busing as intended.

That also leads to the second problem I see. Since you are using a spacer in a way that wasn't intended, your crimp on lugs are not making full surface-surface contact with your underlying spacer. That looks like it will loosen up over time from motor vibration.

Third, I can see the edges and profile of the lugs through your tape job. When we tape with a combination of cambric, 130c, super 88, and maybe some insulation putty if need be, the thought is to tape in a way that the splice ends up round'ish, such that a person can't see the overall profile of the lugs/bolts/hardware underneath along with the sharp edges from those materials.

When we do larger motors, we will often times pull wire to the motor at a one-one ratio with the motor leads. It is not uncommon for us to have 6 motor splices in a motor with one of our wires spliced to just one motor lead.

So we will start with the spacers. I worked with my distributor to find a combination that was meant for this application. I spoke directly with his Burndy rep explained what I needed, he said this is a combination that is suitable for the application.

Originally I wanted 2 offset lugs and 2 straight lugs then sand which the motor leads in between all of those with 2 bolts per phase. However, they do not make DLO offset lugs. I told the rep we needed to have as much surface area contact as we would with sandwiching the lugs and this was the solution. So I have emails with a rep to cover my a** if something goes wrong.

Onto the taping, I make up a lot of big motors and have not had one fail due to a bad tape job as of yet. However, so you know what your looking at here is my process on these lugs
1. Super88 backwrapped
2. 130c flat pads doubled up and placed on both end of the bolt heads
3. 1 entire roll of 130c 2” wide per phase
4. 2 half lapped wraps of friction tape
5. Top it all of with 4 half laps of Super88


While I respect everyone’s opinion, I strive to do a good, safe, and quality job. I always try to research and make sure the parts I use to make sure they are meant for the application.


Sent from my iPhone using Tapatalk

 

[petersonra]

I think I would have just made a spacer out of copper bar stock. In fact, I have a standard drawing I made years ago for just such a thing. It is just a square of copper bar with a hole in the middle to fit on the back of Camlok receptacles when I need more than two lugs.

 

[ibarrola]

First off VFD cable is an outright scam. Belsen should be utterly ashamed of themselves. At #14 with THHN (not THHN-2) if it gets wet it has a lower resistance to surges than the motor. XHHW never has this issue and THHN is fine at 20 mils insulation thickness or greater. Both vastly exceed the rating of even inverter duty motors. So selling 2 kV cable in a 600!V market is baloney.

As to the idea of “balanced” and somehow magically lower cable impedance it does make a difference if your feeders are significantly different in length or capacitance. This is also true in ordinary power distribution. So basically I plead baloney on the VFD cable. If there is an imbalance causing bearing failures it’s not the cable, it’s natural from any six pulse drive and only a common mode filter or a grounding brush and an insulated bearing is going to cure it. I’ve seen tons of installs where Belden scammed them with overpriced VFD cable but did not fix the issue. It doesn’t fix common mode voltages. Those are inherent in VFDs. If you can only output +VDC or -VDC, how do you get V1+V2+V3=0? You can’t. Hence....common mode voltage, wonder cable or not.

So we need 516.5 A ampacity? You did not specify 469 or 575 V motor. You could run 750 MCM fine strand like DLO but that’s crazy. Two 4/0 XHHW-2 TC-ER gets you there. Based on Service Wire that’s 1.51” diameter. I believe a Roxtec gland might make it but better check the specs closely. Otherwise remove the original peckerhead and attach a larger enclosure of your choice. A third option often practiced is just mount the box next to the motor and switch to THHN jumpers feeding through a 4” section of LFMC. Crimp lugs on the ends, stack and bolt everything together, and tape it all up. This takes up the least amount of peckerhead space.

It is quite common to have this issue with motors at 200 HP or larger. It seems like they should be using larger peckerheads but the motor manufacturers don’t. They just follow a standard. We often “upgrade” them for customers.

Thanks Paul... the motor is 460V
I have heard that XHHW is a good cable to use with VFD, any thoughts on that?

At the moment, I'm planning on installing the enclosure/junction box next to the motor and removing the outer sheath of the cable (within the enclosure) to then feed thru a 4" LFMC and terminate at the peckerhead. So basically the same as sure 3rd option but instead of a splice in the junction box, I would just feed the wires thru. This would avoid an extra point of failure IMO.

 

[ibarrola]

We would run (2) sets of 350 XHHW CU in the 4" conduit. No vfd cable. Since you're class 1, div 2, I would be expecting rigid conduit and ex prf flex.

Thanks Cow, I'll look into this, although we'll be running cable tray with multiconductor.

 

[Devin Hanes]

what we've done is used a larger box and then used pieces of bus bar to connect the lugs.