# vfd fault issues



## ponyboy (Nov 18, 2012)

You need the fault codes. Is there anyone that can handle opening the cabinet and reading the screens to you


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## LuckyLuke (Jun 1, 2015)

When this happens to us and we don't have all the info we load up our fuse collection and ipad or laptop to check the fault code when we get there so we are not scrolling through on a phone. Without a code there isn't too much I could help you with sadly. Maybe sell him on a spare drive for future calls like this or ask if he wants you to pick one up before heading out there.


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## Flyingsod (Jul 11, 2013)

LuckyLuke said:


> When this happens to us and we don't have all the info we load up our fuse collection and ipad or laptop to check the fault code when we get there so we are not scrolling through on a phone. Without a code there isn't too much I could help you with sadly. Maybe sell him on a spare drive for future calls like this or ask if he wants you to pick one up before heading out there.


Yea, sounds like a small drive. Should be a fraction of the cost of the trip if you are charging standard tech fees.

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## JRaef (Mar 23, 2009)

garfield said:


> I have a 3 hp vfd that's giving faults. I don't know what the faults are. The customer is telling me this and doesn't have the info. We did run the line and load vfd conductors together for about 7 feet. It was run with 14 gauge thhn. It's about 140 feet up to the motor. There is also a lighting circuit in the same conduit that feeds 2 400 watt metal halide lights. Their voltage is 496 with no loads on. 480y277 1000 kva transformer about 10 feet from the electrical room. It's about a 5 hour drive to this job so I was hoping to get some clues before I go. Drive is a Schneider.


For the future, take note of the following:


_"We did run the line and load vfd conductors together for about 7 feet."_

Bad idea, you can cause severe stress to the motor winding insulation. I had a project last year with a Mitsibishi VFD running a 50HP _Inverter Duty_ motor, and they ran the input and output conductors in the same conduit for about 12ft., took out the motor in 6 months. We recorded voltage spikes of 2200V at the motor terminals, less than 1000V at the drive terminals (they had a load reactor). That short distance of the conductors being next to each other at DIFFERENT FREQUENCIES resulted in a multiplication effect of the standing waves, which the motor would have otherwise survived. Another member of this forum had me take a look at a similar one a couple of years ago, same issue; 12-15ft of the input and output conductors mixed in open cable tray, took out a 250HP Reliance Inverter Duty motor in under a year.
_"It was run with 14 gauge thhn."_

I've been strongly recommending NOT using THHN on the _OUTPUT_ of VFDs. Those standing wave issues can much more easily punch through the insulation material used on THHN (PVC). This is because it is extruded as a liquid, then "thermoset", so it has microscopic bubbles in it. Those bubbles reduce the dielectric strength of the insulation, making it more susceptible to what's called "corona discharge effects" of the high voltage spikes in the output. Use RHH/RHW or XHHW insulation for output cables, it uses Cross-Linked Polyethelene (XLPE) for the insulation that is essentially heat shrink tubing, so no voids and bubbles in it.
_ "There is also a lighting circuit in the same conduit that feeds 2 400 watt metal halide lights." _ 

Another very bad idea, similar to #1.
One way to avoid problems if you are forced to mix circuits in the same conduit, is to run the VFD output using the new shielded VFD cable. Tt protects the VFD circuit from influences of the other cables, and protects the other cables from the EMI/RFI coming out of the VFD. With this kind of cable, you *ground the shields at BOTH ends*, unlike shielded SIGNAL cables. You are creating a "Faraday cage" around the VFD output conductors.


I'm going to guess that you will find one or more of the following faults (although, Heaven help you, the French will call them something totally different and bizarre...)


Over Current faults: the conductors are acting like a set of capacitors and the capacitive charging current is exceeding what the VFD can put out under some circumstances.
Over Voltage Faults: the standing wave spikes are making it back into the VFD and charging up the DC bus.
Motor Short Circuit: the motor insulation is already failing from the standing wave spikes. Could also be the result of the THHN already breaking down and leaking to ground.


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## garfield (Jul 30, 2009)

If I pull the vfd shielded cable through the 8 feet of conduit where the line and load are together will this be ok or do i need to run a new conduit? I have never used the drive cable. Is there any merit to line and load reactors?


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## Cow (Jan 16, 2008)

That's interesting Jraef. I've seen you preach about the drive cable but never would of guessed something as short as 12' would of given you problems. 



garfield said:


> If I pull the vfd shielded cable through the 8 feet of conduit where the line and load are together will this be ok or do i need to run a new conduit? I have never used the drive cable. Is there any merit to line and load reactors?


Drive cable is big. Picture stuffing an SO cord into your conduit. We ran into issues with it being so much oversized that when we would do dairy remodels and switch motors over to vfd cable from the thhn that was already there, it wouldn't fit. 

Of course, on new installs I bump the conduit up a size or two now.


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## garfield (Jul 30, 2009)

Nst is the error. on an altivar 312 In the book it says
"The stop is activated when the logic state of the input is at 0. if the input falls back to state 1 and the run command is still active the motor will only restart if 2 wire level control has been configured. In other cases a new run command must be sent." Is this an error that would be generated from the line and load in the same conduit? This is a 9 position distributor with an encoder. It's run by it's own plc and touch screen.


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## just the cowboy (Sep 4, 2013)

First are any of the control wires routed next to or cross the power wires? 
If no it sounds like it is a logic problem. It sounds like the drive is set for three wire control, and the PLC sends both srart and stop commands. While the PLC is giving a start command the stop circuit is opening. You can probably simulate this fault by holding the start button in and pressing the stop. If this has been working and running in this mode I would think it is something in the stop circuit opening up, not programmed wrong.


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## garfield (Jul 30, 2009)

All of what you described is outside my scope unless the wire itself is bad or a loose connection. That's a relief.


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## JRaef (Mar 23, 2009)

garfield said:


> Nst is the error. on an altivar 312 In the book it says
> "The stop is activated when the logic state of the input is at 0. if the input falls back to state 1 and the run command is still active the motor will only restart if 2 wire level control has been configured. In other cases a new run command must be sent." Is this an error that would be generated from the line and load in the same conduit? This is a 9 position distributor with an encoder. It's run by it's own plc and touch screen.


Clear as mud eh...

I've run into this with other drives (TECO has this issue all the time, for them it's an STP2 error) It usually means that you have the drive configured to respond to the terminal block I/O as the Run / Stop command, but when the TB command input is Low (zero), there is another Stop command coming from somewhere else, usually the keypad or a Safety Input (don't know if that drive has one though). In other words, for safety reasons most drives are configured to respond to only ONE source of a Run / Start command, but will respond to ANY source of a Stop command. That way if someone hits the Stop key on the keypad instead of the Stop push button, it still stops. But that essentially creates a different safety issue in that if the Stop command came from somewhere OTHER than where it is expecting (in this case the TB Inputs), then it does not know WHY that was given, so it "faults" in order to REQUIRE that the selected control point is put back in control by resetting the sequence with that command. 

What can make this happen is that you have a PLC output controlling the VFD Run command via the TB Input of the drive, but someone in the field is using either an E-Stop button or using the Stop button on the keypad "to be sure it is stopped". It creates that conflict, but they don't understand that (or care). Happens a lot actually. It's also possible that you have a loose connection somewhere, but my experience is that it's usually a procedural problem with the operators. "Hitting the Stop button whether you need to or not is safer than not hitting it".

It's also possible that the control commands are getting corrupted if they too are in the same conduit as the otuput conductors and not shielded.


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## garfield (Jul 30, 2009)

The control wires are in a control conduit. There is rs485 communication and maybe 24 volt for a safety system in that conduit.


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## JRaef (Mar 23, 2009)

So are you using the RS485 comms to control the drive AND have a Safety input to it then? If so, hitting the Safety function AFTER the RS-485 comm port has told the drive to stop already would cause this.


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## garfield (Jul 30, 2009)

JRaef said:


> So are you using the RS485 comms to control the drive AND have a Safety input to it then? If so, hitting the Safety function AFTER the RS-485 comm port has told the drive to stop already would cause this.


The RS-485 is another system for bearing temperature etc at the facility. It is not interfaced with this at all except the wires are in the same control conduit. I don't know exactly how the encoder works or what technology is used. 3 wire shielded cable...possibly 4-20 milliamp on the encoder.


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## T-DAWG (Jun 30, 2021)

garfield said:


> I have a 3 hp vfd that's giving faults. I don't know what the faults are. The customer is telling me this and doesn't have the info. We did run the line and load vfd conductors together for about 7 feet. It was run with 14 gauge thhn. It's about 140 feet up to the motor. There is also a lighting circuit in the same conduit that feeds 2 400 watt metal halide lights. Their voltage is 496 with no loads on. 480y277 1000 kva transformer about 10 feet from the electrical room. It's about a 5 hour drive to this job so I was hoping to get some clues before I go. Drive is a Schneider.


My useless contribution. To me this sounds all bad.


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## just the cowboy (Sep 4, 2013)

T-DAWG said:


> To me this sounds all bad.


@T-DAWG watch the date in the post this one is 5 years old.


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