Screwing nameplates on NEMA 4X-rated enclosure

[cmlr]

Hi,

Our client requires us to mount phenolic nameplates to some NEMA 4X rated enclosures using stainless steel screws.

According to us any penetration with an unrated component (in this case the screws) violates the NEMA-rating of the enclosure.
Does anybody know whether our reasoning is correct, or is the client right and is the enclosure still rated NEMA 4X after mounting the nameplates.

Thanks in advance for your answers,
Caspar

 

[jraef]

I don't have my copy of UL508 any longer but as I remember it, screws (and other fasteners) don't count, as long as the screw is there. In fact, I think UL even requires that the rating plate be screwed or riveted on IIRC. From a corrosion standpoint (the X in 4X), the corrosion resistance of the fasteners must be equal to or greater than that of the enclosure. I know that because I discovered (by virtue of failing an inspection) that you cannot use aluminum rivets if the enclosure is stainless steel or fiberglass.

Remove the screw and leave a hole, then[i/] you have a problem.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[cmlr]

Hi jraef,

Thanks for your response.

Since I have a copy of UL 508A I did a search, but could not find anything that said screws and other fasteners don't count for the NEMA rating (to be fair, I also didn't find anything saying they do...)

Paragraph 52.4 of UL 508A specifies that markings shall be "permanently attached to the industrial control panel by rivets, screws, or adhesive", so you are right in that.
Of course using screws or rivets on a NEMA 1 panel does not de-rate it any further, so maybe this applies to NEMA 1 panels only.

I guess I will have to ask our local UL inspector what he thinks about it.

Thanks again,
Caspar

 

[jraef]

Ultimately, he s the one you must convince anyway. Good luck with that.

I have had some really good UL inspectors and some really bad ones. The ones I consider bad are those who simply read and act on what is printed in a book without thinking through the application presented. I have had one look over a very large soft starter in the field and apply a label, then ask after the fact what it was! I have also had one that was a stickler for every tiny detail and bounced me because an octal socket for a relay was not the same brand as the relay (which is technically correct but realistically impractical).

On the other hand, I had a great one here in California who looked at what we had done on customizing some MV switchgear and said, even though it had not been specifically tested in that configuration, that what we did was so well beyond the requirements to be considered safe and labeled it.

You just never know.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376