I have a client who is relocating a 150HP VFD further away from the pump that it serves. The existing VFD cable is 3/C #4/0 with three symmetrical grounds, 2000V shieleded tray cable. I'm wondering whether we should splice the VFD cable or pull new. I've spoken to the VFD cable manufacturers and their recommendation, of course, is to provide new cable. Do any of you have experience splicing VFD cable and any input?
VFD cable splicing
- Thread starter cpiper
- Start date
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Rewire
Senior Member
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- Lake of the Ozarks
Follow the manufactures recomendation and pull new cable. Unless you are trying to save a few bucks to offset a lowball bid.
drbond24
Senior Member
- Location
- Barboursville, West Virginia
There is no way you could splice the cable and maintain the symmetry and shield congruity of the original cable. There would be two inconsistencies in the cable, and that pretty much defeats the purpose of having the VFD cable to begin with.
Just pull new cable.
Just pull new cable.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I would be inclined to contact the cable manufacturer, rather than the VFD manufacturer.
Its quite possible that the VFD guys might not be in a position to make a recommendation, so took the "safe" course.
Its quite possible that the VFD guys might not be in a position to make a recommendation, so took the "safe" course.
electricalperson
Senior Member
- Location
- massachusetts
i dont mean to be a jerk or anything but what is VFD cable? i didnt know you had to run a special cable when coming off of a drive. i know that wirenuts might fail if you use them in peckerheads on a VFD control motor but thats it
drbond24
Senior Member
- Location
- Barboursville, West Virginia
You don't have to use VFD cable, but if the cable is constructed properly there are benefits to using it. There are also speical connectors and termination kits available that can help even further.
The idea is to reduce or eliminate some of the problems inherent in a variable frequency system, such as crosstalk and common mode noise.
weressl
Esteemed Member
Splice it, splice it, splice it.
Compression barrel lug splies on both phase and ground comnductors. Make sure you double up - at least - on the heatshrink on the individual phase conductors. The overall shield continuity maintenence will be a little bit trickier, but use a copper mesh sheet to overlap about 2" on each side and overall. This is the perfect place to use NoLox(sp?). The overall jacket heatshrink should maintain sufficient pressure to maintain the contact between the two original and splicing shield materials.
drbond24
Senior Member
- Location
- Barboursville, West Virginia
weressl
Esteemed Member
Just because it works doesn't mean it is right.
:grin:
In this case it works and it IS right. I would like to see a substantiated argument why it would not be the proper course to take.
mkgrady
Senior Member
- Location
- Massachusetts
I don't know what vfd cable is but it sounds like you are describing a medium voltage , shielded cable. If you can confirm that it is the same, you could splice it with a MV splice kit that would contain all the parts you need. It could be done with hand tape, cold shrink or heat shrink. The key is to carry over all the layers of the cable through the splice. If you have never done one, you may want to sub it out to a splicer.
drbond24
Senior Member
- Location
- Barboursville, West Virginia
In this case it works and it IS right. I would like to see a substantiated argument why it would not be the proper course to take.
I don't think there is a right and wrong in this case, just personal preference. Splicing the VFD cable will almost certainly screw the benefits that cable was supposed to provide, but it will still work. If they want to maintain the benefits of the VFD cable then they need to just pull new cable.
Since no one seems to know what VFD cable is, it'll probably get spliced and work just fine anyway.
mkgrady said:
VFD cable and MV cable are not the same thing, although their basic construction is relatively the same. Symmetry is very, very important with VFD cable and splicing will kill the symmetry.
mkgrady
Senior Member
- Location
- Massachusetts
On a medium voltage cable symetry is also critical. If the shield is not symetrical throughout the cable and its terminations and splices it will stress the insulation and eventual failure of the cable.
If you look at the profile of a MV cable splice it is as symetrical as the shielded cable itself. Sounds like it would be just right to splice a VFD cable.
Splice
Splice
There is nothing wrong with splicing this cable. You do not even need a special kit or a trained "splicer" to do it for you. "VFD" cable is a waste of money. 600volt THHN will do the same job just as well. They try to sell "VFD rated" cable to get more money. Think about it: why would you want to sheild your motor leads? The purpose of a sheild on a cable is to absorb outside EMF's and funnel them to ground, preventing interference on the conductors. If this was for example a 480v 3phase motor and you had (3) phase condustors in this cable wound together and encased in a sheild, what benefit would that be? This symmetry mess everyone is talking about is not applicable here. It is just a motor lead, nothing more. The protection offered by a sheilded cable would be needed for the low-voltage control side of the drive if there was a danger of transient voltage in the proximity, or of this was a critical application; but it looks like its a motor driving a pump(not very critical). Just a common splice will suffice! (Hey, I rhymed!)
Splice
There is nothing wrong with splicing this cable. You do not even need a special kit or a trained "splicer" to do it for you. "VFD" cable is a waste of money. 600volt THHN will do the same job just as well. They try to sell "VFD rated" cable to get more money. Think about it: why would you want to sheild your motor leads? The purpose of a sheild on a cable is to absorb outside EMF's and funnel them to ground, preventing interference on the conductors. If this was for example a 480v 3phase motor and you had (3) phase condustors in this cable wound together and encased in a sheild, what benefit would that be? This symmetry mess everyone is talking about is not applicable here. It is just a motor lead, nothing more. The protection offered by a sheilded cable would be needed for the low-voltage control side of the drive if there was a danger of transient voltage in the proximity, or of this was a critical application; but it looks like its a motor driving a pump(not very critical). Just a common splice will suffice! (Hey, I rhymed!)
charlietuna
Senior Member
The only times i have found this "manufacturered supplied sheilded cable" was on old original VFD units. The newer units operate fine without it with the main concern being limiting the distance between the controller and the motor. I agree with above poster - i would not be afraid to splice the manufacturered cable..
weressl
Esteemed Member
There is nothing wrong with splicing this cable. You do not even need a special kit or a trained "splicer" to do it for you. "VFD" cable is a waste of money. 600volt THHN will do the same job just as well. They try to sell "VFD rated" cable to get more money. Think about it: why would you want to sheild your motor leads? The purpose of a sheild on a cable is to absorb outside EMF's and funnel them to ground, preventing interference on the conductors. If this was for example a 480v 3phase motor and you had (3) phase condustors in this cable wound together and encased in a sheild, what benefit would that be? This symmetry mess everyone is talking about is not applicable here. It is just a motor lead, nothing more. The protection offered by a sheilded cable would be needed for the low-voltage control side of the drive if there was a danger of transient voltage in the proximity, or of this was a critical application; but it looks like its a motor driving a pump(not very critical). Just a common splice will suffice! (Hey, I rhymed!)
It would be helpful if you research the subject before you offer an opinion.
Helpful for you, so you will appear to know what you talking about and helpful to others so they not be mislead.:smile:
Just a bit on the subject.
The fast switching speeds of the solid-state (semiconductor) devices used in VFDs increase the potential for EMI and RFI. The drive?s solid-state electronics generate RF energy, which can be radiated by the drive?s inverter-to-motor power cable and can be picked up by nearby circuits. Adjacent VDF cables also can affect each other that result in faulty performance.
drbond24
Senior Member
- Location
- Barboursville, West Virginia
I was trying to find a polite way to say the same thing.
I'm not sure this is polite, but I agree. :grin:I will also add that as far as high frequency signals are concerned, 'stuff' has a differenct resistance. Therefore, those signals may not necessarily travel the way you'd expect them to. They can end up going through the motor and damaging the bearings while they're at it. Properly terminated VFD cable will provide these signals with a low resistance path to follow so they will go where you want them to go.
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
well, it's 600volt cable, so if you can get the same cable, it should be fairly
straightforward.... hipress butt splices for the power leads, stagger them so
they are not all at the same point, cold shrink with 3m cold shrink, do the same
with the grounds, and then wrap half lap the whole thing with copper shielding
foil, making sure the shield is maintained. i'm assuming the existing shield is a
copper foil product, not metallized mylar or something like that. after i got it
all wrapped, get someone who knows how to solder well to solder the patch
foil to the existing foil, without harming the material underneath.
then cover the whole thing with 3m cold shrink. i'm partial to 3m cold shrink
'cause it's a proven product, used in MV cable splicing kits. it's thick, it's
moisture tight, it pulls down tight, and seals.
megger and check everything for continuity with a good ohmmeter. smile,
and light it up.
how much cable is involved here? if this is a short run, it may not be worth it,
but if it's running over the river and thru the woods in a cable tray, it'd be
worth doing it.
pick someone you've got with good hand skills to do it... if anyone near you
is a cable splicer, that'll do nicely.
weressl
Esteemed Member
I was trying to find a polite way to say the same thing.
You have NO IDEA what it took to tone it down.......
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
well, the purpose can also be to take those nasty harmonics coming off the
vfd, and keep them from wreaking havoc with every piece of sensitive
electronic equipment in the neighborhood.... a vfd ramping up to speed,
hooked to unshielded conductors, is a lot like a piece of military jamming
equipment, looking for frequencies to jam.
most of the VFD motor controls i've done in the last 5 years specify motor leads
to be ran in their own conduit, without any other motor leads or control wires
present in that conduit. there's a good reason.
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