limiting short circuit at chiller, part 2

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malachi constant

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See here for original thread:
http://forums.mikeholt.com/showthread.php?t=163026

Short version: two 208V ~300A chillers were installed with control enclosures rated 5kAIC. Actual available ISC is greater than 5k. Inspector flagged it, it was a new one for me and a lesson learned that won't happen again. That said have to fix it.

The manufacturer is providing parts and installation to field modify the two chiller controls enclosure with parts that will result in a 65kAIC rating. They need the Owner (who I am consulting to) to line up:
1. An electrician to disconnect/reconnect at the lugs (easy enough).
2. An inspector to field inspect that the new installation meets UL standards equipment.

It is the second one that I am having trouble with. I have not been able to talk directly with the factory to see what UL listing we are trying achieve, and the local "engineering inspectors" I talk to seem unsure what I am asking. I am trying to get contact information for someone within the factory but until that occurs I would appreciate any insight this community has to offer.

FYI - we have dismissed adding impedance as I understand that option to entail either adding hundreds of feet of coiled-up wire (expensive and impractical) or a 208V:208V transformer (also expensive - would need to be (2) 112kVA transformers, (2) 400A disconnects, 60' of above-grade 300A feeders, everything weatherproof, and none of it would fit inside the tidy new chiller enclosure we constructed). I suppose it is possible when all the costs are added up we could end up with the chiller being an option, but it would run about ~$50K, so I'm pursuing the above-mentioned factory fix above until I find out what those costs are.

If there is another solution I'm all ears. Someone in the above thread mentioned a line reactor, which I am not familiar with. Is it relatively small and cheap? I think of it as a medium voltage component - can it be added to a 208V system? Not sure how to model added impedance in SKM either - right now I've got 27kA available and need to get down to 5kA. (Also: I did quite a bit of research and couldn't find an appropriate fuse that would come close to limiting to that amount.)

Any and all thoughts are appreciated!
 
Part 2 may well be a major stumbling block.
I think before making any attempt to address it your best bet is to talk with the inspector and see what he will accept.
As I understand it, the only way you can maintain a UL listing on an altered piece of equipment is by a UL field evaluation... performed by UL.. not cheap :)
I would be willing to bet that most inspectors that knew enough to flag the original problem are not going to accept less than a NRTL listing, however, I do know a few areas that will accept a letter of compliance by a Professional Engineer.
Bottom line, it boils down to "acceptance by the AHJ" so, as noted, step one would be to see what he will accept.
 
I have seen 5kA control cabinets on chillers as well. I feel as if I should know this but does the magnetic trip setting on a MCCB effectively limit the SCCR? E.g. a 600A breaker (22kAIC) with a magnetic multiplier of 5 would be 3kA SCCR? Or is it not that simple?
 
A line reactor is just an inductor wired in series in each of the phases. It limits fault current.

The enclosure will be much smaller than a transformer and can be installed outside; i.e. NEMA 3R enclosure.

You just have to watch voltage regulation.

I believe the inspector is wanting verification that the cabinet with components, added/swapped, is done properly such that the assembly is still UL. I would think having the factory guys come out and do it would suffice.
 
send the control panel back to be reworked. it is the cheapest and simplest answer. then there is no fiddling around with field evaluations.

or just buy a new control panel.
 
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