Control Enclosure Subplate Requirements

[familyman412000]

I have gone through NFPA 79 and UL 508A and can not find an answer to a seemingly simple question. Is a subpanel required for all components in a machine control enclosure and which surfaces inside the enclosure can components be mounted on? The most common example I see is an existing control enclosure with too little spare space on a machine that we need to add some component. Can I mount this equipment directly to the interior side wall? I have seen this many times but having trouble finding code that expressly addresses this issue. There is of course the issue of possibly compromising the IP rating of the enclosure. But I'm interested in specifically where components can, or can not, be mounted.

 

[Jraef]

Back panels are made thicker than side walls so that they can hold a minimum of 2 threads when drilled and tapped, which effectively eliminates sheet metal screws. As I recall the 2 thread minimum is a requirement in NFPA79 and was part of the original JIC standards that NFPA79 came from, so it has been an industry expectation for decades even if not dictated elsewhere.

If your box walls are 16ga or less, as some enclosures are, you cannot get 2 full threads in tapping that.

PS:

12.2.1.5 Threaded fasteners with machine threads shall be
used to attach components to a subplate and shall provide
sufficient thread engagement to maintain secure mounting.
12.2.1.5.1 Steel subplate thickness shall provide engagement
of at least 2 full threads.