MCC UL Rating

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NikolaP

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Minnesota
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Electrical Engineer
Hello everyone,
I'm trying to understand how UL Rating works on this particular example. You got MCC built with VFDs, Starters and breakers inside, and it's UL Rated. Let say in a couple of years you need to replace one of the VFDs and you can not replace it with the same one because it's obsolete. If you put a different one inside do you lose UL rating of the MCC? I'm having with discussion with my boss, and my opinion is until the new one is UL rated you are good. His opinion is unless you replace it with the exactly the same you are loosing UL rating. How is this usually done in practice?

Thank you,
Nikola
 
If by 'UL Rated' you mean the MCC was listed as an assembly, then I agree with your boss on the legality of it.

As far as how it's usually done in practice, my wild guess is that a few people diligently look for an exact replacement part, while many others pay no attention to these issues until something goes wrong and there's a lawsuit. Another option would be to have the MCC field listed by UL with the different VFD. Probably not hard to get UL sign-off, but you have to pay them so I doubt it happens much.
 
There are companies that rebuild MCC's and can put a UL label on a rebuild MCC.

The UL thing only matters if you care about it having a valid UL listing.
 
You cannot replace a component in a UL listed MCC bucket with anything other than the original components it was built and listed with and still maintain the UL-845 listing of that bucket. Full stop.

Then if any bucket of an MCC is not UL-845 listed, it voids the UL listing if the entire lineup. Full stop.

Now that said, there are two issues requiring UL-845 listing:

1. Upon initial installation in which it will be inspected by an AHJ who will look for UL labels on the MCC.

2. Your business’ insurance carrier may (will likely) require that all electrical equipment have valid UL listings.

You may get into the validity of “Who is going to know?” or the “We’ve done it like this for years and nobody noticed / cared.” aspects of this all you like, I’m just stating the facts.

OFFICIALLY, if you must replace an obsolete VFD in an MCC and maintain the UL listing, the most valid option is to buy a new bucket with whatever new VFD the MCC mfr offers. As a general rule (although not guaranteed), new VFDs tend to be smaller than older versions, so bucket size is often not an issue, but it depends on a lot of factors. Only the MCC mfr can tell you for sure.

The biggest issues with MCCs are Short Circuit listing and what’s called a “heat rise testing” requirement. You cannot just willy-nilly stuff something in an MCC without having been listed for the same or higher Short Circuit level or having test results on the effect it will have on the temperature of everything around it in the section and adjacent sections.

There ARE a select few companies that can build new retrofit MCC buckets and apply a special UL “Reconditioned” certification to it, when built to specific UL standards. Regular UL-508A “panel shops” cannot do this, it is a separate and specific program for MCCs that is required. For the most part, the companies that have this capability are the MCC mfrs themselves just because the required investment is substantial. Yes, “field evaluation” is another option, but get out your big wallet for that…
 
Thank you for your detailed response and clarification, now I'm sure I understand what is the right way to do it. Thanks everyone!
 
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