I don't generally bother to run the numbers unless someone asks for something specific. Why spend money on something that the customer has not asked for and did not pay for.
These days it is not real hard to get to 65kA SCCR, but a lot of the old design practices such as use of distribution blocks gets in the way of that.
I agree. As a general rule, most mfrs have received the message and offer up combinations of their devices that are pre-certified under their UL listing to work together in series for high(ish) SCCRs. The kicker is, the overall SCCR cannot be any higher than the lowest rated power component or combo in the circuit, so if even one device, such as the distribution block, is not rated, then the default rating becomes 5kA for that device, and consequently 5kA for the panel. The other gotcha is when a panel builder uses the least expensive components in a string, regardless of whether or not they have been series listed, ie a Square D breaker ahead of an AB contactor; neither of those mfrs would have tested those in series, why would they? So think of these issues collectively as a weakest link in the chain. One bad device or combo and the whole thing gets pulled down.
The original panel builder that labeled the panel can redo this, IN THEIR SHOP, but their listing authority does not extend beyond their own walls so the panels would need to be sent back. Another panel builder could do ot too, but the same will apply. An NRTL can do a field evaluation, I just saw someone do that recently, $20k after the all expense paid trip for the NRTL (Intertek/ETL) inspector. If allowed in your jurisdiction, you might be able to get a local PE to crunch all the numbers inside of the panel and provide a letter certifying the SCCR, or so I've heard, that seems to be a local issue. But no matter what, none of those methods gets around the weakest link issue so it might also mean changing components, which if done in the field, invalidates the UL listing of the panel and you are back to square one. So bottom line, it's usually best to have the original panel shop redo it in the fist place. An alternative is to find and hire a local PE to come up with a way for him to certify that there is only 5kA available at the terminals of your panel as it is now, which is debatable as to whether that can really be done (but is done nonetheless).
That said, Bob has a point. The panel shop should not be expected to bear the cost if it was not in the procurement spec. Were it me when I had my shop, I would have warned the buyer ahead of time and asked the question, but only out of professional courtesy. Technically, the panel shop has no way of knowing if 5kA is fine with you or not. I see specs all the time, even written by PEs, where SCCR is not mentioned and I will bring it up to them because it's a nasty little surprise later when the AHJ red tags it.
I have a huge one going on right now where the owner and his PE have specified re-use of some enclosures and specialized (18 pulse) transformers on 12 400-450HP drives that are existing, they just want the VFDs themselves replaced inside the box. That would be doable of they don't want to have it done by a contractor who is pulling a permit (by calling it maintenance), but they want it permitted too, and they want UL listing, and there is 62kA available on the bus feeding these panels, but no mention of an SCCR at over 62kA. Trying to get the owner and PE to understand that nobody will be able to get a better than 5kA SCCR on the panel using old parts they have never evaluated is proving to be a much bigger challenge than shoehorning in the new added components to a box that is already there. The SCCR requirement is not in the spec, so everyone is bidding it without it, I am the only one warning them of the impending doom. Their response so far is to just tell me I don't have to bid on it, they have 3 other bids already. So this job is going to blow up in someone's face in about 6 months when the AHJ does the final inspection, and in my opinion the fault is going to lie with the engineering firm who is refusing to listen to my warnings. Unfortunately the poor contractor will likely bear most of the brunt of that, not the engineer, because during the inevitable finger pointing session, the contractor will not be getting paid...
