UL508 Questions and Concerns

Hi all my skepticism radar is in full swing and I'm hoping someone more experienced can help me out.

Short story is that I'm currently reviewing a large capital project and specifically looking at the cabinet design and feeder requirements for an enclosure housing eight servo drives, four fractional motor controls and a small control transformer. While reviewing the drawings the size of the feeder seemed very small (#4 behind 70A protection). I crunched all of the numbers and applied NEC to everything and am coming up with needing a feeder suitable for 125A. All branch circuits within seemed to be sized correctly.

I expressed my concerns to the OEM wanting clarification on their numbers and was responded to with scenario specific verbiage as to the reasoning behind their calculations, ie; two of the servos will only run one at a time and all motors were accounted for based on their full load amps. Along with this came "The panel is UL508 listed and we will not be discussing this any further".

How far can I trust this from you more seasoned guys? The system as it is specced seems grossly inadequate to me. Per the NEC, specifically looking at 430.122 in relation to drives and conductor/OCPD sizing, it's illegal as all get out. Most info I have found seems to corroborate with my findings, however I have been told that a UL listing trumps all as well. Making matters worse it looks like I need to fork over $1000 to gain the official codebook for me to verify the UL side of things.

A big thank you to anyone that helps me out on this. I do alot of in house design and have prided myself on never failing an inspection or screwing up big wire pulls. I don't want to start now.

Putting a UL sticker on something doesn't prove that the fusing or conductor sizes are accurate. In fact, it has nothing to do with that at all. It's more about components inside of a panel and following basic workmanship guidelines.

Can't comment on the exact code you're referring to but my understanding is that the supply to a panel doesn't need to be large enough for all loads if they're not goinf to be running at the same time.

The basic rule is take 125% FLA of largest motor plus sum of all the other motors & loads. If some of them are interlocked to prevent them from running at the same time then the one(s) interlocked out should not be counted.

The feeder wire has to have a 20% buffer. In other words, if the wire is rated at 100A then it can only carry 80A continuous.

I don’t have the documents in front of me so I’m going by memory. Hope this helps.

thumperbs said:

Along with this came "The panel is UL508 listed and we will not be discussing this any further".

Click to expand...

I would be telling them "You are correct that we will not be discussing this further, because we are going with another vendor."

If they cop this kind of attitude before they get your money, what do you think there response will be on other issues. It's a big red flag to me that the want to hide behind a supposed UL listing rather than showing you why you may be wrong. It sounds like they could whip up a response showing the calcs for four motors (either that or they have already done it and found you are correct).

I've been told way too many times that an installation is "code-compliant" and found upon closer examination it wasn't even close.

Have you been able to independently confirm that the cabinet is "UL Listed"?

Thanks for the replies guys. I’ve been digging through as much material as I can and I still believe I am correct.

As far as getting forceful with them, it’s somewhat complicated however I do have one portion of the bill still outstanding for leverage. I came into this project mid cycle and have battled numerous vendors including this one over the last year who obviously slipped things in on previous engineers. This is the last phase and they are still attempting what appears to be BS. Last step will be as suggested reaching out to an old colleague for some UL assistance.

If the feeder circuit protection is 70A the #4 wire is perfectly fine, but that is a different question than if the 70A protection is sized correctly. We would need much more information about the panel design.

I would like to reiterate what others have said, that there is no spec that says the feeder has to power every single device simultaneously. It all depends on the machine design.

thumperbs said:

Thanks..........As far as getting forceful with them, it’s somewhat complicated however I do have one portion of the bill still outstanding for leverage...........

Click to expand...

I’ve worked as a System Integrator for over 30 years and even if we submit something and it is approved that does not mean we were off the hook if it turns out the product did not actually meet the spec’s. If you can show that their panel is not designed properly for the load then you should be on firm ground for rejecting it.

The most important thing to start with is does their design match your requirements for the # of motors, sizes, & sequence of operation.

All that being said, it will be time to look at the fine print of your contract.

In the section of UL508A in industrial machinery, it says the supply terminals should be sized based on

1. 125% of all heater loads, and
2. 125% of the largest motor, and
3. Fla of all other motors and loads that are simultaneously operable

So it is possible that they are doing it right but their attitude sounds wrong.

Their “attitude” may have been the result of your nor accepting the first (or second or third or fourteenth) answer when they told you it was fine; we were not there so we don’t know.

But one thing IS true: you were reading the NEC, which deals with INSTALLATIONS and would apply IF there is no other NRTL(Nationally Tecognized Testing Lab) listing of a system. But if it IS listed by an acceptable NRTL (such as UL), it’s true that the NEC is no longer applicable to what is INSIDE of that panel. And part of the NRTL listing process is for them to tell you, clearly and unambiguously, exactly what the OCPD must be, plus the FLA of the system as a WHOLE so that you can size the feeder conductors. So from that standpoint, they are correct.

Could they have handled it better? Maybe, but then again as I said, we weren’t there to hear just how much pushing you did on a subject that they likely understood better than you appear to. I too was a long time integrator / panel builder and I was in this unenviable position many times. It’s hard to keep it together when someone refuses to accept that you know more than they do on a subject. Once you go through the rigors of attaining and maintaining a UL508A shop license, which you pay dearly for, you don’t appreciate novices stepping in and telling you your business.

jraef said:

Their “attitude” may have been the result of your nor accepting the first (or second or third or fourteenth) answer when they told you it was fine; we were not there so we don’t know.

But one thing IS true: you were reading the NEC, which deals with INSTALLATIONS and would apply IF there is no other NRTL(Nationally Tecognized Testing Lab) listing of a system. But if it IS listed by an acceptable NRTL (such as UL), it’s true that the NEC is no longer applicable to what is INSIDE of that panel. And part of the NRTL listing process is for them to tell you, clearly and unambiguously, exactly what the OCPD must be, plus the FLA of the system as a WHOLE so that you can size the feeder conductors. So from that standpoint, they are correct.

Could they have handled it better? Maybe, but then again as I said, we weren’t there to hear just how much pushing you did on a subject that they likely understood better than you appear to. I too was a long time integrator / panel builder and I was in this unenviable position many times. It’s hard to keep it together when someone refuses to accept that you know more than they do on a subject. Once you go through the rigors of attaining and maintaining a UL508A shop license, which you pay dearly for, you don’t appreciate novices stepping in and telling you your business.

Click to expand...

JRef,

This seems never more true than when I have to explain to someone that I HAVE to put J fuses in front of their VFD because the Manufacturer’s manual says I have to use J fuses for a UL application. And by the way, it now won’t fit in the small box you want me to shove everything into because of those fuses and the spacing I have to allow at the feeder for UL compliance. “But our other panel builder did it!” -
At this point it would be very satisfying to just say their other builder is wrong but we usually just point back to the code and say we can’t control what other people do. I have definitely turned down a few jobs because ppl wanted us to list designs that are not to code. It also helps to know that no code is perfect and it doesn’t always have to make sense to you but each part has a reason for someone or some application.
Also, you can call UL and ask questions. For the VFD fusing issue it talked to the group that handles control panels and the group that handles drives. I learned that nothing would prevent a VFD mfg from recommending some other type of fusing for their devices like circuit breakers or smaller CC fuses but almost all chose J fuses when testing their drives because it likely lead to a higher SCCR rating of the drive. Since testing is expensive, unless there is a large demand from the market, the VFD manufacturers will not retest with other short circuit devices to see what SCCR they end up with.

ndzied1 said:

JRef,

This seems never more true than when I have to explain to someone that I HAVE to put J fuses in front of their VFD because the Manufacturer’s manual says I have to use J fuses for a UL application. And by the way, it now won’t fit in the small box you want me to shove everything into because of those fuses and the spacing I have to allow at the feeder for UL compliance. “But our other panel builder did it!” -
At this point it would be very satisfying to just say their other builder is wrong but we usually just point back to the code and say we can’t control what other people do. I have definitely turned down a few jobs because ppl wanted us to list designs that are not to code. It also helps to know that no code is perfect and it doesn’t always have to make sense to you but each part has a reason for someone or some application.
Also, you can call UL and ask questions. For the VFD fusing issue it talked to the group that handles control panels and the group that handles drives. I learned that nothing would prevent a VFD mfg from recommending some other type of fusing for their devices like circuit breakers or smaller CC fuses but almost all chose J fuses when testing their drives because it likely lead to a higher SCCR rating of the drive. Since testing is expensive, unless there is a large demand from the market, the VFD manufacturers will not retest with other short circuit devices to see what SCCR they end up with.

Click to expand...

Yep, been there, done that, got the T-shirt and the hat.

ONE time in my career, I knuckled under to the "Well the other guys will do it..." argument. It was a VFD going on a rock crusher that would be operating at 10,000ft elevation from a portable generator. Knowing that VFD bus caps will freeze and if even just energized when frozen can explode, I proposed a solution. A line side side contactor controlled by a thermostat so that the drive would not get power until AFTER the panel was 40F inside, because when the generator was shut down at night, there was no power for space heaters either. The customer complained about my price and I pointed out that the other guy didn't think of that. The customer insisted that it was unnecessary and I was over thinking it, because if it ever got that cold, they wouldn't operate the crusher anyway. I agreed to match the other price and built it without the contactor, even though I KNEW better. Sure enough, the owner forget to tell the operator not to power up the system when it was that cold (-12F), so the first time he fired it up in the morning, the VFD caps exploded like a hand grenade! Sure, I got paid to go out there to replace it, but that was a week of my life (including travel time) I will never get back.

jraef said:

Yep, been there, done that, got the T-shirt and the hat.

ONE time in my career, I knuckled under to the "Well the other guys will do it..." argument. It was a VFD going on a rock crusher that would be operating at 10,000ft elevation from a portable generator. Knowing that VFD bus caps will freeze and if even just energized when frozen can explode, I proposed a solution. A line side side contactor controlled by a thermostat so that the drive would not get power until AFTER the panel was 40F inside, because when the generator was shut down at night, there was no power for space heaters either. The customer complained about my price and I pointed out that the other guy didn't think of that. The customer insisted that it was unnecessary and I was over thinking it, because if it ever got that cold, they wouldn't operate the icrusher anyway. I agreed to match the other price and built it without the contactor, even though I KNEW better. Sure enough, the owner forget to tell the operator not to power up the system when it was that cold (-12F), so the first time he fired it up in the morning, the VFD caps exploded like a hand grenade! Sure, I got paid to go out there to replace it, but that was a week of my life (including travel time) I will never get back.

Click to expand...

Oh *****, you did it just like I told you to.

jraef said:

Their “attitude” may have been the result of your nor accepting the first (or second or third or fourteenth) answer when they told you it was fine; we were not there so we don’t know.

But one thing IS true: you were reading the NEC, which deals with INSTALLATIONS and would apply IF there is no other NRTL(Nationally Tecognized Testing Lab) listing of a system. But if it IS listed by an acceptable NRTL (such as UL), it’s true that the NEC is no longer applicable to what is INSIDE of that panel. And part of the NRTL listing process is for them to tell you, clearly and unambiguously, exactly what the OCPD must be, plus the FLA of the system as a WHOLE so that you can size the feeder conductors. So from that standpoint, they are correct.

Could they have handled it better? Maybe, but then again as I said, we weren’t there to hear just how much pushing you did on a subject that they likely understood better than you appear to. I too was a long time integrator / panel builder and I was in this unenviable position many times. It’s hard to keep it together when someone refuses to accept that you know more than they do on a subject. Once you go through the rigors of attaining and maintaining a UL508A shop license, which you pay dearly for, you don’t appreciate novices stepping in and telling you your business.

Click to expand...

Well I have to admit, the one person I was hoping would chime in in fact does and then proceeds to essentially dunk my head in the toilet. Here is a little more information for you so that you hopefully don’t have to be such a jackass.

As I stated before, it’s complicated. I inherited this project mid cycle, I say this not as a means for an excuse but to help fill the history lesson. Since coming on board this is the sixth time I have needed to step in and question this integrator. The other five were extremely justified. What qualifies as “extremely”? How about sending me used and damaged parts in another supposed UL install? Perhaps writing code in the wrong literal language is a better explanation? I don’t want to get too descriptive but there were other used parts scenarios as well.

I’ll be the first to admit that I am a novice when it comes to UL hierarchy however I am no slouch when it comes to doing my homework. Besides reaching out here, I’ve set in motion some UL education for myself so I am better prepared next time. All of that said, I do know quality when I see it and this company gives any others I have met thus far a bad name. If I had it my way I would have designed every facet myself but it was not an option in this case and I’m working through my issues. I’ve kept it as professional as I can while still trying to gather some advice because for all I know the same folks in question frequent this forum.

In close, if you think for a second that it’s a safe assumption that a little sticker gives anyone the benefit of the doubt in regards to builds, then you must deal with some pretty poor end users. Yes I’m learning but I live by the motto of “expect what you inspect” and if I question your build as a customer then I expect you to back it up entirely. Not provide some BS answer like I was given. I really am grateful for all the knowledge shared within this group but after reading today I just feel like an outcast from the privileged *******s. I think I’m ok with that......

jraef said:

Their “attitude” may have been the result of your nor accepting the first (or second or third or fourteenth) answer when they told you it was fine; we were not there so we don’t know.

But one thing IS true: you were reading the NEC, which deals with INSTALLATIONS and would apply IF there is no other NRTL(Nationally Tecognized Testing Lab) listing of a system. But if it IS listed by an acceptable NRTL (such as UL), it’s true that the NEC is no longer applicable to what is INSIDE of that panel. And part of the NRTL listing process is for them to tell you, clearly and unambiguously, exactly what the OCPD must be, plus the FLA of the system as a WHOLE so that you can size the feeder conductors. So from that standpoint, they are correct.

Could they have handled it better? Maybe, but then again as I said, we weren’t there to hear just how much pushing you did on a subject that they likely understood better than you appear to. I too was a long time integrator / panel builder and I was in this unenviable position many times. It’s hard to keep it together when someone refuses to accept that you know more than they do on a subject. Once you go through the rigors of attaining and maintaining a UL508A shop license, which you pay dearly for, you don’t appreciate novices stepping in and telling you your business.

Click to expand...

Well I have to admit, the one person I was hoping would chime in in fact does and then proceeds to essentially dunk my head in the toilet. Here is a little more information for you so that you hopefully don’t have to be such a jackass.

As I stated before, it’s complicated. I inherited this project mid cycle, I say this not as a means for an excuse but to help fill the history lesson. Since coming on board this is the sixth time I have needed to step in and question this integrator. The other five were extremely justified. What qualifies as “extremely”? How about sending me used and damaged parts in another supposed UL install? Perhaps writing code in the wrong literal language is a better explanation? I don’t want to get too descriptive but there were other used parts scenarios as well.

I’ll be the first to admit that I am a novice when it comes to UL hierarchy however I am no slouch when it comes to doing my homework. Besides reaching out here, I’ve set in motion some UL education for myself so I am better prepared next time. All of that said, I do know quality when I see it and this company gives any others I have met thus far a bad name. If I had it my way I would have designed every facet myself but it was not an option in this case and I’m working through my issues. I’ve kept it as professional as I can while still trying to gather some advice because for all I know the same folks in question frequent this forum.

In close, if you think for a second that it’s a safe assumption that a little sticker gives anyone the benefit of the doubt in regards to builds, then you must deal with some pretty poor end users. Yes I’m learning but I live by the motto of “expect what you inspect” and if I question your build as a customer then I expect you to back it up entirely. Not provide some BS answer like I was given. I really am grateful for all the knowledge shared within this group but today after reading today I just feel like an outcast from the privileged *******s. I think I’m ok with that......