Multiply drives an motor burnt up

[Sparky_1]

I had a service call to troubleshoot a commercial kitchen exhaust system, this system was two years old.
I found 3- 3/4 hp exhaust fans and 1 - 3hp make up air for the hood system.
They were all on VFD's. The makeup air was feed from across the store 300 foot away with a 15 amp three phase 480 volt breaker,
the three 3/4" hp motors were feed from a different location, 50 foot away with a 20 amp three phase 480 volt breaker.
They both meet in a common control panel, where all of the drives were located.

What I found was that the 3Hp motor was burnt out and three out of the four drives were burnt out, the 3 hp drive
and two of the 3/4 hp drives.

The colors on the conductors where brown orange and yellow, I found that a brown from one breaker wire bundle
was not spliced correctly all the way through to the appropriate drives. The browns were interchanged, causing a very
dangerous configuration, with one breaker off the conductors were being back feed from the other location.

The 3hp motor burnt out, causing one breaker to trip and then causing single phasing to the 3/4 hp drives

My question is, could this wiring configuration cause the premature death of the motor and drives???

We contacted the original electrical contractor that installed this unit, and his reply was that it passed inspections and the year warranty was up.

Thanks for your help

 

[petersonra]

I don't see how the swapped brown wire could cause damage to the motor or drives.

My guesses would be:

The VFD minimum speed was set too low and the motor overheated because the internal fan was not going fast enough to cool the motor.

The motor was not rated for use with VFDs.

I don't know what you mean by "burnt up" WRT to the failed drives.

 

[growler]

I don't see how the swapped brown wire could cause damage to the motor or drives.

It sounds like ( if I understand what he saying) that there would need to be two breakers trip to disconnect power from a motor or drive.

When the first breaker tripped it acually disconnected one phase to the other motors and drives (single phasing ).


I would draw out the circuit as to what you find and leave any problems between the owner and the original EC. If the owner wishes to try and take the original EC to court that's his business. MY guess is that's the only way he would ever get any money.

 

[Jraef]

I agree that the death of the 3HP motor was not likely the result of the miswiring of the supply conductors, there is no direct relation to supply and load through a VFD, other than the supply being the "raw material" from which the VFDs derive power.

But assuming that the drives were sized ONLY for the expected 3 phase input, as 480V drives would be, then what happens to the drives that lose an incoming phase is the the current through the diode bridge rectifiers will increase by the sq. rt. of 3, or 1.732x on the line side, while remaining normal on the load side. If the drives do not have phase loss protection, or it is disabled, the rectifier sections of the drives will over heat and the diodes short, which kills the drive. So either your drives were very cheap and did not have phase loss protection, which is the fault of the design, or someone saw the trouble, but could not figure out the cause, so they cured the symptom (as many people do) by turning off the phase loss trip. That would make THAT person the culpable party.

With only your info to go on, but a lot of experience with the mistakes people make with drives, here's my conjecture of how this went down:

The initial install had a problem because of the miswire; one leg off of one breaker was feeding all 4 drives, which kept causing it to trip. When it did, all of the drives tripped on phase loss. The installer checked voltages only, always reading the correct voltages, so was convinced there was a "phantom" problem and blamed it on the drives, because that is easier than the more thorough troubleshooting you just did (where you found the root cause). Then in describing the phantom problems to someone like a vendor, be mentions that the motors are 3/4 HP and 3HP. The person hearing this says "Oh, at that size, the drives can take single phase or 3 phase, so just disable the phase loss and it won't matter!" The problem is he likely did not know it was 480V, a detail left out of the conversation, and while that statement is true for most 230V drives it is NEVER true for 480V drives. So in order to get paid, the installer turns off the phase loss trip, everything passes inspection (because that is not part of it) and he gets paid. Meanwhile that breaker only trips under heavy loads again, which may not be often, but it only now affects the one drive it is feeding (likely the one that survived). But still nobody finds that root cause, so they just keep calling it a weird drive problem and reset the breaker and/or they ignore it. Or worse, they just learn to leave it off because the other motors run to make up for it anyway so they just don't use that one. Over time however, they are single phasing the remaining drives and they eventually cook themselves.

 

[petersonra]

This is another one of those posts where the OP has provided us almost no useful information upon which one might base any help we could otherwise offer, forcing us to speculate on what might have happened.

Jraef has a plausible scenario, especially with a very low end type of drive, but I still don't know what "burnt up" means.

 

[growler]

This is another one of those posts where the OP has provided us almost no useful information upon which one might base any help we could otherwise offer, forcing us to speculate on what might have happened.

Jraef has a plausible scenario, especially with a very low end type of drive, but I still don't know what "burnt up" means.

I agree that there is not much imformation.

It is common practice to mark circuit conductors with corresponding breaker numbers so that mix ups will not happen. Wire numbers of say 1,3,5 and next circuit 7,9,11. If the conductors were properly marked there would not be a problem for anyone trouble-shooting to find.

Anytime you don't perform an install corectly you leave yourself open to being blamed for problems. If the original EC had done a proper install there wouldn't even be a question of if he is at fault.

 

[Sparky_1]

Jraef,

Thanks for your reply to my question, it was an excellent answer. The original contractor called the store and they said that they have a reputation to live up to, so
they are driving over on Monday to rectify there screw up.

Bob, I could have gone all morning without reading your reply, you never heard the term burnt up??
Be very hot: to be very hot or overheated / winding failed and caused motor to "burn up"

There is certainly enough information that I provided to come up with a scenario on what has happened.
Have a nice day Bob.

 

[Jraef]

Jraef,

Thanks for your reply to my question, it was an excellent answer. The original contractor called the store and they said that they have a reputation to live up to, so
they are driving over on Monday to rectify there screw up.

Bob, I could have gone all morning without reading your reply, you never heard the term burnt up??
Be very hot: to be very hot or overheated / winding failed and caused motor to "burn up"

There is certainly enough information that I provided to come up with a scenario on what has happened.
Have a nice day Bob.

I think (because he said) that Bob was referring to the vagueness of "burnt up" with regard to the VFDs, not the motor, and his point has validity. If the INPUT section of the drives were damaged (and the outputs might be too), my scenario fits. But if only the OUTPUT sections of the drives are damaged, then it might not. The only problem is that to an untrained eye and barring obvious visual indicators such as char, it's difficult to tell. Just like people, once a drive is dead it loses it's ability to tell you what's wrong with it. That's what makes forensic analysis so challenging.

 

[kwired]

If I were the original installer and if it went down as Jraef described, I would be asking the owner why they did not inform me of the tripping problems earlier on, I very well have made mistakes like mentioned and maybe could have fixed the problem long before something failed. I would sure hope that if owner tried to make me pay for this that mentioning that he never contacted me about any problems would help my side of the case.

 

[Jraef]

If I were the original installer and if it went down as Jraef described, I would be asking the owner why they did not inform me of the tripping problems earlier on, I very well have made mistakes like mentioned and maybe could have fixed the problem long before something failed. I would sure hope that if owner tried to make me pay for this that mentioning that he never contacted me about any problems would help my side of the case.

I agree, but my thinking was that this was something installed by an equipment vendor, not a separate EC. Any responsible EC would, I hope, act in the manner you described because he would not want to take on responsibility for damaging equipment, especially that which he did not supply. An equipment vendor however, hungry to get paid and/or facing LD issues, will often settle on "good enough" to get it signed off so he can out of there with a check. Seen that waaaaay too often unfortunately. So those first trips may have only been seen by the vendor's technicians, they solved the initial symptom, maybe a couple of subsequent ones under warranty, got it signed off on, and left without anyone else having witnessed the problems.

 

[kwired]

I agree, but my thinking was that this was something installed by an equipment vendor, not a separate EC. Any responsible EC would, I hope, act in the manner you described because he would not want to take on responsibility for damaging equipment, especially that which he did not supply. An equipment vendor however, hungry to get paid and/or facing LD issues, will often settle on "good enough" to get it signed off so he can out of there with a check. Seen that waaaaay too often unfortunately. So those first trips may have only been seen by the vendor's technicians, they solved the initial symptom, maybe a couple of subsequent ones under warranty, got it signed off on, and left without anyone else having witnessed the problems.

Good point, and if the drives are fried we may never know if any settings contributed to the problem though it may be possible to power up the control section and at least see parameters in many cases, otherwise those small drives are often throwaways and not worth the cost of trying to repair them.