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Hi there,
I am running a wire from my 1HP VFD to my 1/2 HP motor. I have decided to just run 12/3 BX instead of the braided cable because there are no other sensitive loads around. It's a short run. 10ft so I am not worried about noise. But my question is, the peckerhead on the motor has a KO about 1/2 in size. That there is casing around that hole which would prevent me from putting a BX connector in it, since the 1/2" hole is "sunken in" a bit from the casing. I figure I can just use some reducing bushings with lock nuts to get the distance out that I need for the BX connector. But is there another way? I notice that the hole in the peckerhead has a grommet around it. Is this meant to not have a connector if using the shielded VFD cable? And you just slip the wire in through the open hole? Thank you.
 

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Discussion Starter · #4 ·
Those are both great ideas. I have never seen those Arlington connectors. And I had not thought about nipples for some reason. Thanks.
 

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Hi there,
I am running a wire from my 1HP VFD to my 1/2 HP motor. I have decided to just run 12/3 BX instead of the braided cable because there are no other sensitive loads around. It's a short run. 10ft so I am not worried about noise. But my question is, the peckerhead on the motor has a KO about 1/2 in size. That there is casing around that hole which would prevent me from putting a BX connector in it, since the 1/2" hole is "sunken in" a bit from the casing. I figure I can just use some reducing bushings with lock nuts to get the distance out that I need for the BX connector. But is there another way? I notice that the hole in the peckerhead has a grommet around it. Is this meant to not have a connector if using the shielded VFD cable? And you just slip the wire in through the open hole? Thank you.
Mate

You should really use VFD shielded cable esp if the manufacturer states so.. You may not have issue,s now but down the track could be a different story.....

Frank
 

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Mate

You should really use VFD shielded cable esp if the manufacturer states so.. You may not have issue,s now but down the track could be a different story.....

Frank


Standard conductors in ferrous raceway is perfectly fine. VFD cable is a scam as far as I'm concerned. Bonus scam points for drive manufactures recommending their own brand of cable as well. Another point, it's usually "recommended" but never actually "required"


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Mate

You should really use VFD shielded cable esp if the manufacturer states so.. You may not have issue,s now but down the track could be a different story.....

Frank
I have installed lots of VFDs over the years and have never used VFD cable. Never had an issue- not one.
I'm sure VFD cable is great, but I just don't see the added expense as necessary- unless spec'd.
 

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I'd say 95% of the VFDs I see are wired in THHN. 4% are probably XHHW. And maybe that last percent is VFD cable.

I think for the most part the importance is overrated. Does not using it increase the risk of failure? Yes. But on reasonably short run of cable with load reactors installed, I think the risk is very minimal.
 

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I'd say 95% of the VFDs I see are wired in THHN. 4% are probably XHHW. And maybe that last percent is VFD cable.

I think for the most part the importance is overrated. Does not using it increase the risk of failure? Yes. But on reasonably short run of cable with load reactors installed, I think the risk is very minimal.
I would not use a load reactor for this very short distance.
I would also use THHN.
But I would use a line reactor.
 

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Hi Guys

We work in the Pharma industry and every motor on a VFD is wired with VFD cable....Lots of motors on long runs ...Most engineers here install as per recommened by manufacturer ....

I can recall the first time using a vfd on a transfer table on a laser cutting m/c ,everytime the table transfered the cnc display screen would blank out.....Fitting a line filter fixed it.....

Frank
 

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Standard conductors in ferrous raceway is perfectly fine. VFD cable is a scam as far as I'm concerned. Bonus scam points for drive manufactures recommending their own brand of cable as well. Another point, it's usually "recommended" but never actually "required"


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It's not a "scam", but it is a bit over sold. You are absolutely right, if using a FERROUS raceway with ONLY ONE set of VFD output conductors, the VFD shielded cable is redundant. But unfortunately that is NOT true in a lot of cases, and that's where people get themselves in trouble. Recommending the use of shielded VFD is a way of the VFD mfr trying to get users to pay attention to the details, OR spend the extra money to make those details irrelevant. I wasn'rt aware of any VFD mfr selling their own brand of cable. That does seem a bit over the top, I agree.

I have installed lots of VFDs over the years and have never used VFD cable. Never had an issue- not one.
I'm sure VFD cable is great, but I just don't see the added expense as necessary- unless spec'd.
How do you ABSOLUTELY know you NEVER had one issue? Do you personally monitor EVERY one you have EVER installed to see of the motor dies prematurely, the VFD blows up after 3 years, the local PLC memory gets corrupted or instrumentation signals go haywire and nobody can figure out why? If you ALWAYS, 100% of the time, use steel conduit with one set of output conductors on every VFD you have ever installed, OK I'll buy that.

I'm only picking on the way you said it because the issues are REAL, but not COMMON. Anecdotal absolute statements like that however, even if true in your experience because of other extenuating circumstances, give license to the less informed and less skilled to ignore the issue completely and end up causing problems down the road.

I work for a VFD mfr, so from my perspective, I get plenty of calls from people who's drives, motors or controls fail prematurely. When I go out to investigate, I see the installation mistakes and point them out. The end users get angry at the original installer, but rarely ever get them involved in correcting the errors, they just never talk to them again. So I can easily imagine that those contractors ASSUME everything was fine, but might wonder why those customers never use them again.

THHN: it's going to work fine, until it doesn't because of some (again) extenuating circumstance. To my mind it's no big deal to just use RHW or XHHW on the output conductors and be sure of it rather than risk it out of convenience. I have, on two separate occasion, pulled THHN out of conduits and seen the evenly spaced burn marks where the standing waves caused Corona Discharge to take place between conductors. That is now known to be the result of the microscopic bubbles in the liquid thermoplastic (PVC) used in THHN. Not a problem at 600V sine wave power, but standing waves caused by inverters can reach well over 1200V, where those bubbles make it easier for CD to take place between conductors.

Unshielded flex cable: You are making a relatively powerful local FM radio transmitting antenna... If there is nothing around it to be affected, then no problem. But I have had someone triangulate on my machine testing from 20+ miles away by monitoring the RF from a 5HP motor cable on a VFD, wired with SO cord. (Government installation in the Nevada desert, scientists with sensitive instruments getting corrupted and looking for the source).
 

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It's not a "scam", but it is a bit over sold. You are absolutely right, if using a FERROUS raceway with ONLY ONE set of VFD output conductors, the VFD shielded cable is redundant. But unfortunately that is NOT true in a lot of cases, and that's where people get themselves in trouble. Recommending the use of shielded VFD is a way of the VFD mfr trying to get users to pay attention to the details, OR spend the extra money to make those details irrelevant. I wasn'rt aware of any VFD mfr selling their own brand of cable. That does seem a bit over the top, I agree.


How do you ABSOLUTELY know you NEVER had one issue? Do you personally monitor EVERY one you have EVER installed to see of the motor dies prematurely, the VFD blows up after 3 years, the local PLC memory gets corrupted or instrumentation signals go haywire and nobody can figure out why? If you ALWAYS, 100% of the time, use steel conduit with one set of output conductors on every VFD you have ever installed, OK I'll buy that.

I'm only picking on the way you said it because the issues are REAL, but not COMMON. Anecdotal absolute statements like that however, even if true in your experience because of other extenuating circumstances, give license to the less informed and less skilled to ignore the issue completely and end up causing problems down the road.

I work for a VFD mfr, so from my perspective, I get plenty of calls from people who's drives, motors or controls fail prematurely. When I go out to investigate, I see the installation mistakes and point them out. The end users get angry at the original installer, but rarely ever get them involved in correcting the errors, they just never talk to them again. So I can easily imagine that those contractors ASSUME everything was fine, but might wonder why those customers never use them again.

THHN: it's going to work fine, until it doesn't because of some (again) extenuating circumstance. To my mind it's no big deal to just use RHW or XHHW on the output conductors and be sure of it rather than risk it out of convenience. I have, on two separate occasion, pulled THHN out of conduits and seen the evenly spaced burn marks where the standing waves caused Corona Discharge to take place between conductors. That is now known to be the result of the microscopic bubbles in the liquid thermoplastic (PVC) used in THHN. Not a problem at 600V sine wave power, but standing waves caused by inverters can reach well over 1200V, where those bubbles make it easier for CD to take place between conductors.

Unshielded flex cable: You are making a relatively powerful local FM radio transmitting antenna... If there is nothing around it to be affected, then no problem. But I have had someone triangulate on my machine testing from 20+ miles away by monitoring the RF from a 5HP motor cable on a VFD, wired with SO cord. (Government installation in the Nevada desert, scientists with sensitive instruments getting corrupted and looking for the source).
On a similiar note, Many years ago i was contracted to engineering companies who built machines for the car industries.....Every AC relay had a snubber across the coil and every DC relay had a back emf diode across the coil...Panel builders these days dont bother its an extra cost to them..

Frank
 

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On a similiar note, Many years ago i was contracted to engineering companies who built machines for the car industries.....Every AC relay had a snubber across the coil and every DC relay had a back emf diode across the coil...Panel builders these days dont bother its an extra cost to them..

Frank
On a lot of the new stuff the snubbers are built in. Especially on IEC stuff. Bigger stuff that is piloted anyways doesn't have it built in.

The one instance where vfd cable comes into play is cable trays and even then most places just use teck cable.
 

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On a lot of the new stuff the snubbers are built in. Especially on IEC stuff. Bigger stuff that is piloted anyways doesn't have it built in.

The one instance where vfd cable comes into play is cable trays and even then most places just use teck cable.
Hi

The control gear with builtin snubbers still cost extra and people dont want to pay the little bit extra , cause they never have issues with the snubberless gear....

We use cable tray a lot over here in Oz....

Tech cable , the one with a metal outer sheath ???

Frank
 

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One of the jobs I'm on now will be interesting. I built the control panel and connected the instruments, about 60 of them but I arrived after the power wiring was ran.

There are about 15 VFDs, very few the same manufacturer and type. Most of the VFD to motor wiring is MC cable, some of it is EMT, a lot has more than 1 VFD and/or a mix of VFD and utility power. Most runs are less than 50'. About half of the VFDs are 208, half are 480.

Should be interesting.........
 

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Hi

The control gear with builtin snubbers still cost extra and people dont want to pay the little bit extra , cause they never have issues with the snubberless gear....

We use cable tray a lot over here in Oz....

Tech cable , the one with a metal outer sheath ???

Frank
Teck cable in Canada has a rubber coated, aluminium outer armour...
 
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