UL508A sealing holes with washers and Type ratings

[Royalty]

Hi all,

I was wondering if all holes in a UL508A enclosure must be sealed with a UL Type rated component to maintain the UL Type rating. I'm am curious specifically about small hole used to attach a name plate or label. I have seen sealing washers, a screw and nut used for this purpose but was wondering if they all would have to be UL Type rated. I was referencing the link below before posting in the forum and noticed that someone mentioned that things like fasteners were an exception to this. I was wondering where that is in the code and why.

http://forums.mikeholt.com/showthread.php?t=140694

Thanks

 

[tom baker]

Hoffman 12R enclosures come with sealing washers to use under the fasteners.
Why not use self adhesive nameplates? Once the adhesive sets you have to break the nameplate to get it off.

 

[Jraef]

The way UL50 works is that if an enclosure is modified by adding holes, it must be marked to whatever standard it becomes. Types 1, 2 and 3R are not a problem because the standards allow for holes anyway. So it only matters for 4, 12, 13 and 6. In those cases, conduit entry can be addressed by the use of appropriate hubs or threaded connections and pilot devices if they carry the same UL environmental rating as the box. But little things like nameplate screws are not addressed specifically. However, there is an acceptable mounting screw standard for the enclosure basic design that states that anything with a minimum thread pitch of 32 is allowed without further mechanical strength testing. Although this does not specifically address the environmental integrity, the general interpretation by UL508A inspectors has been that as long as the screw is in place, the enclosure environmental rating is not violated. So for nameplates then, a 4-32 mounting screw is going to be OK, but a sheet metal screw will not (this was specifically pointed out to me by my UL inspector). That's why you typically see nameplates mounted with 4-32 machine screws. It never hurts to put a small dollop of RTV on the hole before screwing it ion though.

 

[Royalty]

Thank you, that is very helpful