Available fault current vs. SCCR

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GoldDigger

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You found that in the device specs, I assume. So the inspector would have to accept that as a supplement to the nameplate info.
Regarding LA, would they accept this as alternative rating rather than directly relying on the fuse let thru rating and main device rating separately?
Are they concerned that the fuses and holders may be replaced at some time in the future?

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JDBrown

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GoldDigger said:
You found that in the device specs, I assume. So the inspector would have to accept that as a supplement to the nameplate info.
Regarding LA, would they accept this as alternative rating rather than directly relying on the fuse let thru rating and main device rating separately?
Are they concerned that the fuses and holders may be replaced at some time in the future?

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I'm not sure how LADBS would respond to that; I've never had a need to find out. Nearly all the work I do in LA is at LAX, and the Port Authority there doesn't even allow series ratings, much less things like fuse let-thru. I just remembered seeing it on the plan check form.

And who knows where most of these rules come from? I certainly don't know what their worry is, although your guess that it has to do with the possibility of replacement with a different fuse seems to be the most logical answer.

The specific quote from the LADBS plan check form is "Provide short circuit analysis including motor contribution. Fuse let-thru is not acceptable." So you can't use the fuse let-thru to reduce your calculated fault current. If you're able to get some kind of alternative rating, then I guess it would be worth a shot to see if they'd accept it. I'd definitely run it by them before starting work, though.
 
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overkill94

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California
winnie said:
Take a look at http://www.ab.com/en/epub/catalogs/...04-D-100S-C-104S-C-100S-D-Specifications.html

Look about 3/4 of the way down, under "Short-Circuit Coordination Data"

There they describe the maximum fuse or breaker permitted given various available short circuit conditions, including under UL requirements. They list a value at 5kA available, and then have blanks for higher ratings (10kA, 18kA, 30kA....) but have ratings for 100kA. There is even a rating for 25kA available in series with an inverse time breaker....

Like I said, I am out of my element here, so take the above as my research due to my curiosity, not my expertise!

-Jon
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We have a winner! Thanks a bunch, I'm sure the client will be thrilled although probably still bitter that I didn't agree with their let-thru argument.
 
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overkill94

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For the future though, it seems that you just have to go by the calculated available fault current when comparing to a panel's SCCR, correct? I'd like to have a solid answer if this comes up again.
 
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petersonra

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GoldDigger said:
You found that in the device specs, I assume. So the inspector would have to accept that as a supplement to the nameplate info.
Regarding LA, would they accept this as alternative rating rather than directly relying on the fuse let thru rating and main device rating separately?
Are they concerned that the fuses and holders may be replaced at some time in the future?

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I think you are missing a critically important issue here.

The control panel has a rating nameplate on it. That is the rating of that piece of equipment. It does not matter much what an EC or EI says the rating is or if some calculation or scheme someone puts in place makes that rating different.

Someone has to put a new label on the control panel that says what the new SCCR is. I think that will either have to be the people who made the panel or some NRTL field inspector.
 
Jraef

Jraef

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petersonra said:
I think you are missing a critically important issue here.

The control panel has a rating nameplate on it. That is the rating of that piece of equipment. It does not matter much what an EC or EI says the rating is or if some calculation or scheme someone puts in place makes that rating different.

Someone has to put a new label on the control panel that says what the new SCCR is. I think that will either have to be the people who made the panel or some NRTL field inspector.
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I think some panel builders get sloppy about this issue and just slap on the "courtesy" 5kA label they are allowed to apply without testing or thought, based on that being the lowest level of most power components. Had they thought it through even a little in this case they would have seen what we see, that simply using some 50A Class J fuses in the main disconnect would have made it all so much easier for the installer. Did the panel NEED a fused main disconnect? Maybe not, but when discussing it with the customer (you in this case overkill94), had they said "Without a fused main disconnect you will be responsible for making sure there is no more than 5kA AFC." you may have opted to just pay the extra few hundred more it would have cost to not have to deal with it. It's pretty difficult to find an installation on something like this that will have 100kA AFC, which means this would have been a non-issue.

But some of that blame lies at the feet of the purchasers as well. Many will shop pricing only, and XYZ Panel Shop is $100 less than ZYX Panel Shop, so they give them the order paying no attention to this detail, which may cost them a LOT more when the panel arrives on site with a label that says 5kA.
 
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GoldDigger

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Retired PV System Designer
A very useful discussion, thanks.
For the OP, however, it is not a big help since it only discusses use of fuses inside a UL listed component.
I am still having a problem with just how a given component can have one SCCR on the label and supplemental documentation stating a different SCCR rating when used with EXTERNAL fuses.

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