OSHA’s NRTL requirement and UL508A Supplement SB

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pisani168

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To abide by OSHA all electrical devices must be NRTL listed. Let me say I have a UL508A listed Industrial Control Panel. The SCCR is 5kA but the available fault current is 15kA.
I decide to use supplement SB and increase the SCCR to 100kA by installing some current limiting fuses.
I know that I just lost my UL listing and even tbough I remediated a code violation in term and of 110.10, I created another one per 110.3(C).
I assume, I need a UL508A MTR and a UL Field Engineer to have my panel relabeled. Does anybody have experience with listings? OSHA can be a real trip.
 
pisani168 said:
To abide by OSHA all electrical devices must be NRTL listed. Let me say I have a UL508A listed Industrial Control Panel. The SCCR is 5kA but the available fault current is 15kA.
I decide to use supplement SB and increase the SCCR to 100kA by installing some current limiting fuses.
I know that I just lost my UL listing and even tbough I remediated a code violation in term and of 110.10, I created another one per 110.3(C).
I assume, I need a UL508A MTR and a UL Field Engineer to have my panel relabeled. Does anybody have experience with listings? OSHA can be a real trip.
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Only a UL field evaluation can help you unless you want to send the control panel back to be reworked by a UL508A shop. We do this once in a blue moon but it usually ends up being more cost-effective to pay UL to come out.
 
UL is not the only NRTL. I used a few different outfits when I was working. UL was always the most expensive when asking for quotes or rates.
 
Mfg might have information whether it has been series tested and what device its been tested with. That sort of documentation should be adequate with use of the listed combination to get you where you need to be.
If not available you are back to what others suggested.
The suggestion of the mfg testing to your needs might be an option as once they've tested they can continue to use that as part of their listing. A benefit to them and you.
 
Fred B said:
Mfg might have information whether it has been series tested and what device its been tested with. That sort of documentation should be adequate with use of the listed combination to get you where you need to be.
If not available you are back to what others suggested.
The suggestion of the mfg testing to your needs might be an option as once they've tested they can continue to use that as part of their listing. A benefit to them and you.
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It is possible that the manufacturer of the equipment might be able to modify the drawings to add a note to the drawings indicating that externally supplied current limiting fuses increase the short circuit current rating of the panel. I think this would have to be marked on the cabinet though. They might be able to send you a nameplate you could add to the cabinet. Not 100% sure this is completely legit but it's possibly a solution.
 
Fred B said:
Mfg might have information whether it has been series tested and what device its been tested with. That sort of documentation should be adequate with use of the listed combination to get you where you need to be.
If not available you are back to what others suggested.
The suggestion of the mfg testing to your needs might be an option as once they've tested they can continue to use that as part of their listing. A benefit to them and you.
Click to expand...
So to be clear, even if you go for a field evaluation, UL will need to see that all of the components in your power circuits ARE ALREADY SERIES LISTED in combination with the fuses you choose. UL is not going to list it at a higher SCCR just because you used current limiting fuses. Then if not, doing series listing requires destructive testing and boatloads of cash so the less expensive option is to change the components that were used. That’s why it is less expensive to send it back to the supplier to have it labeled.

Once you get this project sorted out, learn from the experience. Tell your clients (or your buyer) to ALWAYS specify an SCCR value on equipment prior to purchase, it’s far far far cheaper to deal with it up front than to try to fix it after the fact. If you are just bidding as a contractor, you can indirectly do that by quoting them a separate much higher contract price for having to install equipment that is not suitably rated for the available fault current, knowing that it causes major delays and considerable extra work in dealing with the complexities. What that will do is get their attention and if they have no clue, ask you what that means and why, so that hopefully they can go back to their suppliers and demand that they pay attention.

The reality here is that it is really NOT difficult to attain a descent SCCR by simply choosing components that are series listed together up front. The only limitation is usually that you cannot shop around to mix and match the cheapest parts possible because one mfr is not going to spend the money to series list their parts with a competitor. The 5kA value is just the “courtesy” maximum level that UL allows to be shown on the label for those who don’t want to pay any heed to the process, no matter how simple it is.
 
There are a lot of things that you can just put a current limiting fuse in the feeder circuit and get some benefit from it. About the only thing it doesn't help is with fuses and circuit breakers, unless they are tested combinations. But most of the time anything over about 30 amps rating on the CL fuses it really doesn't help much because the let through is enough that it doesn't do much good.
 
But adding the fuses in the field does not change the 5kA SCCR now listed on the panel, nor does it officially change the Available Fault Current. That’s why the devices need to have been series listed AND the panel labeled as such. I agree it would not have been that difficult for the panel builder to have shown a higher SCCR, even (I believe) by just saying “…when protected by xyz fuses”, which would have allowed someone to put them in a disconnect ahead of the panel. But they didn’t bother.
 
Jraef said:
But adding the fuses in the field does not change the 5kA SCCR now listed on the panel, nor does it officially change the Available Fault Current.
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So on the last part, is that for technical reasons (there are no fuses that can guarantee a lower downstream AFC) or regulatory reasons (there probably are such fuses, but they are only officially recognized if the destructive series testing is done)? Is the only official way to lower AFC to add impedance?

Cheers, Wayne
 
Jraef said:
But adding the fuses in the field does not change the 5kA SCCR now listed on the panel, nor does it officially change the Available Fault Current. That’s why the devices need to have been series listed AND the panel labeled as such. I agree it would not have been that difficult for the panel builder to have shown a higher SCCR, even (I believe) by just saying “…when protected by xyz fuses”, which would have allowed someone to put them in a disconnect ahead of the panel. But they didn’t bother.
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I'm not sure you can't add the label in the field. You can't add the UL sticker.

It doesn't have anything to do with the available fault current. The UL supplement on calculating the short circuit current rating allows you to put current limiting fuses in the feeder circuit and then use the let through current as the available short circuit current for devices other than over current protection devices. These fuses are not required to be in the listed panel, as long as it is marked. I don't recall exactly where it is required to be marked.
 
wwhitney said:
So on the last part, is that for technical reasons (there are no fuses that can guarantee a lower downstream AFC) or regulatory reasons (there probably are such fuses, but they are only officially recognized if the destructive series testing is done)? Is the only official way to lower AFC to add impedance?

Cheers, Wayne
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How do you know the current limiting fuse is reducing the amount of fault current below the 5kA value shown on the label?

Look at the definition of a current limiting device. It will reduce the total let-through current not the available current and the fault will be cleared within a 1/4 cycle. If there is not enough available fault current the current limiting device may not perform as intended.
A series rating may allow a larger amount of let-through current than a current limiting device, as defined, but it clears the fault before the protected equipment is destroyed.
 
jim dungar said:
How do you know the current limiting fuse is reducing the amount of fault current below the 5kA value shown on the label?

Look at the definition of a current limiting device. It will reduce the total let-through current not the available current and the fault will be cleared within a 1/4 cycle. If there is not enough available fault current the current limiting device may not perform as intended.
A series rating may allow a larger amount of let-through current than a current limiting device, as defined, but it clears the fault before the protected equipment is destroyed.
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There is a chart in the UL508a supplement that gives you dispensation. I don't personally care how they came up with it but that's the way they do it.
 
petersonra said:
There is a chart in the UL508a supplement that gives you dispensation. I don't personally care how they came up with it but that's the way they do it.
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I know the UL table, and I too do not know how it was derived. My point was that there is no evidence that the let through fault current is reduced below 5kA. All we know is it provides an acceptable series rating.
 
jim dungar said:
I know the UL table, and I too do not know how it was derived. My point was that there is no evidence that the let through fault current is reduced below 5kA. All we know is it provides an acceptable series rating.
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As far as I'm concerned as long as UL provides a means of creating a short circuit current rating, as long as one follows that set of rules, all is good.
 
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