SCCR in the feeder

I have been going over my notes from a UL class from years ago and was trying to see what effect on SCCR a power distribution block would have in a feeder going to multiple branch circuits in a panel.
Just ignoring figuring any branch circuit SCCR for this question and it being assumed at 65kA, If you had a 30kA power distribution block downstream from a feeder with 200 amp 100kA rated fuses with 29kA let through current , would the SCCR have to be lowered to 30kA or would the fact that the power distribution block rating is over the let through current allow the panel to keep the 65kA rating?

Thanks

If I understand your question right, the 29kA of let-through is less than the 30kA rating of the PDB so the panel retains its 65kA rating.

Thanks, That's what I was thinking, I just wasn't sure if the rules were different because it was in a feeder instead of a branch circuit.

I wasn't aware of there being a difference, but I could be wrong. Maybe someone else can check me on that.

rupej said:

If I understand your question right, the 29kA of let-through is less than the 30kA rating of the PDB so the panel retains its 65kA rating.

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That only counts if the PDB is tested and listed in series with the fuse in question. It might be, but you have to check.

jraef said:

That only counts if the PDB is tested and listed in series with the fuse in question. It might be, but you have to check.

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Are you saying that PDBs have different SCCR ratings for different fuses, and that a blanket "30kA" rating doesn't cover all situations?

rupej said:

Are you saying that PDBs have different SCCR ratings for different fuses, and that a blanket "30kA" rating doesn't cover all situations?

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No. If it's rated for 30kA without fuses, that's what it's rated. But if you want to use it at a higher value by using current limiting fuses ahead of it, then it has to be listed in series with the fuses, and it will be specific fuses, maybe breakers. Every manufacturer has (should have) a list of what OCPD you must use ahead of the PDB in order to get more than 10kA SCCR.


Here is Bussman's data sheet on this. You will notice that they say 200kA SCCR right up front, but if you look on the next page they show the list of acceptable OCPDs that are necessary to get there. In this case, because Bussman is not owned by Eaton, they listed their PDBs with Eaton breakers at 65kA. PDB mfrs that don't make OCPDs usually only list them with fuses because their are less expensive to get the Series listing.
https://www.eaton.com/content/dam/e...n-and-terminal-blocks/bus-ele-pp-3134-pdb.pdf

Interesting, thanks for the detailed response. I learned something new.

In the past, when I saw things like the brochure you linked, I assumed that the manufacturer was being disingenuous- that the "200kA" rating was only due to the current limiting effect of the OCPD, and it's actual rating was lower, and nothing out of the ordinary.

Just to make sure I understand correctly- the following is a PDB we use often: https://www.erico.com/part.asp?part=UD-80A
It's listed SSCR is 100kA according to the specifications, with no further details on required OCPD to achieve that on any document that I can find. So in this case, any panel that this PDB is used in can never be rated to more than 100kA since to do so would require using a current limiting OCPD- is that correct? Assuming this is not behind a control transformer, of course.

rupej said:

Interesting, thanks for the detailed response. I learned something new.

In the past, when I saw things like the brochure you linked, I assumed that the manufacturer was being disingenuous- that the "200kA" rating was only due to the current limiting effect of the OCPD, and it's actual rating was lower, and nothing out of the ordinary.

Just to make sure I understand correctly- the following is a PDB we use often: https://www.erico.com/part.asp?part=UD-80A
It's listed SSCR is 100kA according to the specifications, with no further details on required OCPD to achieve that on any document that I can find. So in this case, any panel that this PDB is used in can never be rated to more than 100kA since to do so would require using a current limiting OCPD- is that correct? Assuming this is not behind a control transformer, of course.

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Needs Class J or T fuses ahead of it.... You have to look on the instruction sheet. Not the best way to let you know if you ask me, but technically, they do...

*For Short Circuit Current Rating up to 100kA see UL file E198301
NOTE:
1. Tighten screws of all unused galleries to the specified torque above.
2. For multiple phase assemblies, join blocks together before installing on DIN Profile.
3. When protected by 200 ampere Class J or T fuse, this terminal block is rated for use on a circuit capable of delivering no more than 100kArms symmetrical amperes, 600 volts maximum.
4. The conduit ends shall be provided with a plastic conduit bushing.

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I learned this the hard way. UL inspectors are well aware of it, ESPECIALLY when it comes to PBDs.

Wow- thanks again for sharing this. I'm really struggling with their wording, though- it seem like that could be interpreted a number of different ways.

So if NOT protected by a J or T fuse, does the PDB default to the standard non-listed SCCR? 10kA or so?

rupej said:

Wow- thanks again for sharing this. I'm really struggling with their wording, though- it seem like that could be interpreted a number of different ways.

So if NOT protected by a J or T fuse, does the PDB default to the standard non-listed SCCR? 10kA or so?

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Yes. 10kA is what is allowed as a "courtesy" level for things like PDBs and terminal blocks that have not been tested for higher values without being in series with an OCPD. For most other devices it's actually 5kA, so in comparison, 10kA is "generous". Still useless in most cases at 480V though.

jraef said:

Yes. 10kA is what is allowed as a "courtesy" level for things like PDBs and terminal blocks that have not been tested for higher values without being in series with an OCPD. For most other devices it's actually 5kA, so in comparison, 10kA is "generous". Still useless in most cases at 480V though.

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Interesting. The phrasing is so oddly specific- it says "when protected by a 200A Class J or T fuse". What about a 60A Class J? One would assume that would be fine, but it seems strange that they leave so much up to interpretation.

rupej said:

Interesting. The phrasing is so oddly specific- it says "when protected by a 200A Class J or T fuse". What about a 60A Class J? One would assume that would be fine, but it seems strange that they leave so much up to interpretation.

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With SCCR listings, they are always listing the MAX size fuse. They know that, they just did (again) a poor job of communicating it.


The issue of SCCR of components only very recently has become an issue. Despite the fact that it was first introduced in the 2005 code, it's taken a long time for this to filter down into the inspector community, then that forced it back up into the panel builder world. For a lot of years panel builders were simply slapping the "courtesy" 5kA SCCR label on their panels and nobody really understood, or cared, what that meant. About 10 years ago, inspectors started getting more cognizant of it and what it means, red tagging people for trying to install 5kA panels in places where the Available Fault Current was higher than that. But even then, it took a while for contractors to catch on and start insisting that the panels they buy have the right values, which happened when it started costing them money.