Number of Penetrations in a NEMA enclosure

[DM2]

I'm trying to determine what standard specifies the number of holes I can drill into one side of a NEMA enclosure.

I'm pretty sure I read this somewhere but can't remember where.

Imagine you've got a NEMA (lets say a NEMA 4) enclosure and you're either not permitted or can't make penetrations on any side of the enclosure except the bottom. Theoretically I couldn't make enough penetrations to exceed the fill of the box per NEC, but I could make enough penetrations where I'd weaken the structural integrity of the box causing the bottom side to bend.

I thought I read somewhere that the maximum square area of penetrations couldn't exceed 40% of the surface area I'm making the penetrations in.

Any help?

 

[itsmoked]

I have never heard of such a thing. Your penetrations need to maintain the NEMA level but that's it. The NEMA rating is just an environmental rating. You can knock out large bazaar shapes just as long as they maintain the correct integrity.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[DonPhillips]

I would think the listing literature would address the number and size of openings.

Don Phillips

http://worthingtonengineering.com

 

[jraef]

Nothing in UL508 that says this specifically, but it does say that any penetrations must be "covered" with devices that meet or exceed the original enclosure rating. So for instance your NEMA 4 enclosure would need sealing conduit hubs with a UL listed type 4 rating for each conduit going in or out, and they are going to be large compared to the conduit size, probably twice as big. So that alone will effectively limit the number of possible holes, as well as prevent you from making them too close to the edge. UL-508 does reference UL-50 as the design spec for the enclosures themselves, but I don't have a copy of that.

19 Enclosure Openings
19.1 All openings provided for conduit connections in the field shall be of standard dimensions. When
provided, conduit fittings shall comply with UL 514B, Standard for Fittings for Cable and Conduit. For
enclosures other than Type 1, as noted in column 1 of Table 19.1, the conduit openings and fittings shall
additionally comply with the requirements specified in column 2 of Table 19.1.
...
19.3 Openings provided in enclosures for mounting components shall be covered with components
intended for such mounting. For an enclosure type specified in column 1 of Table 19.2, openings provided
for components, including ventilation openings, or observation windows, shall be closed with components
that have been evaluated for one of the enclosure Types in column 2 of Table 19.2.
...balance snipped, but it goes on similarly