Number of Penetrations Permitted in an Enclosure

[DM2-Inc]

Somewhere I thought I read there was a limit to the number of penetrations permitted in an enclosure. I thought you couldn't exceed 40% or something like that.

I looked at NEMA 250 but I didn't see it in there.

Anybody know where I can find this answer?

 

[al hildenbrand]

This isn't a NEC issue, as the focus is on the conductor and the box volume and dimensions each conductor requires.

Nothing in the NEC prevents me from oversizing the raceway. Small conductors allow a small required volume. The raceway end fittings will space the penetrations.

 

[DM2-Inc]

This has nothing to do with oversizing the raceway but rather how many holes can you drill in to a NEMA enclosure (say a NEMA 4 for example). NEC is silent about this (i'm pretty sure).

While I could drill as many holes as could fit into one side of the enclosure, too many and the enclosure will loose it's structural integrity and the side with all of the holes would start to bend.

I also don't believe the limiting factor is the number of conductors one can fit in a box either. Imagine if I were able to put up to 100 conductors in a box (as determined by NEC) and bring them all in using multiple conduits, or cables in my case. I'd be smart to bring them in on all 4 sides of the box, but if other obstructions to entry limit me from using the other 3 sides, I may elect to penetrate the bottom of the enclosure. At some point I'm going to have to use a box with a larger surface area on the 1 side.

I'm pretty sure I read somewhere where there was a limit.

 

[e57]

Conductor fill can be limited to 40%...

 

[iwire]

While I could drill as many holes as could fit into one side of the enclosure, too many and the enclosure will loose it's structural integrity and the side with all of the holes would start to bend.

Really?

Considering the support requirements for all those raceways IMO the side would only get stronger.

I have never heard anything about a limit, often with NEMA 4 enclosure the hubs that are used with them will limit the spacing.

 

[weressl]

Really?

Considering the support requirements for all those raceways IMO the side would only get stronger.

I have never heard anything about a limit, often with NEMA 4 enclosure the hubs that are used with them will limit the spacing.

The manufacturer MAY limit the locations and number of openings and defenitely will limit it in the case of NEMA 7&9 enclosures.

In EU and other parts of the world it is taken care by so called "gland-plates" where you can buy interchangeable standard gasketed plates that fit the standard size opening on enclosures and they have pre-weakened holes of various size combinations. You just need to pop it out and install your CGB like connector.
I didn't say it was cost effective, but it falls along with the approach where little field fabrication is required, but knowledge and savy to figure out how these systems work. Typical methodical approach to engineering.

 

[iwire]

Laszlo, the OP mentioned NEMA 4.

Lets not make this more painful then it has to be. :smile:

 

[weressl]

Laszlo, the OP mentioned NEMA 4.

Lets not make this more painful then it has to be. :smile:

Not in the Original Post and even later on he used NEMA 4 as "for example". I am not sure what your point is though. My point is that IF the manufacturer specifies the location and size of openings the installer has to follow it.

It isn't painful untill you start banging my head against the monitor.......

 

[DM2-Inc]

Laszlo,
You're reply is appreciated. We work outside of the US and I've dealt with these Gland Plates before.

I've called both Hoffman and B-Line but no reply as of yet.

I've seen enclosures with too many entries (cables, not Conduit) and the enclosure began to deform to the point the door would no longer close.

I currently have a project where I've been asked to repeat such a task. The holes will physically fit, but it will make installation difficult and i'm concerned that the enclosure will start to deform with all of these cable penetrations. I'm insisting on a larger enclosure yet others are telling that wall space is limited. There are other locations nearby that will support a larger enclosure but I'm getting some resistance.

I'm trying to avoid purchasing a UL standard, such as 509 although I don't think the answer is in there.

Maybe I'm dreaming all of this up and it was something I heard of in a conversation with another engineer as a "Best Practice". Still if anyone has any suggestions...

 

[weressl]

Laszlo,
You're reply is appreciated. We work outside of the US and I've dealt with these Gland Plates before.

I've called both Hoffman and B-Line but no reply as of yet.

I've seen enclosures with too many entries (cables, not Conduit) and the enclosure began to deform to the point the door would no longer close.

I currently have a project where I've been asked to repeat such a task. The holes will physically fit, but it will make installation difficult and i'm concerned that the enclosure will start to deform with all of these cable penetrations. I'm insisting on a larger enclosure yet others are telling that wall space is limited. There are other locations nearby that will support a larger enclosure but I'm getting some resistance.

I'm trying to avoid purchasing a UL standard, such as 509 although I don't think the answer is in there.

Maybe I'm dreaming all of this up and it was something I heard of in a conversation with another engineer as a "Best Practice". Still if anyone has any suggestions...

Why don't you review the ROX products http://www.roxtec.com/. They may be just what you need. We had succesfully used them for DCS field enclosures where not only the number of cables were an issue, but the flexibility to add cables during construction and after, in service. We only permit bottom entry and the number of cables would have been impossible to accomodate with CGB's.

 

[DM2-Inc]

These are cable transits and would not be permitted for use in an enclosure where you're stripping the wire back to land on terminals.

To brink cables into an enclosure you'd be required to use a Hawk gland, or Myers Hub.

 

[weressl]

These are cable transits and would not be permitted for use in an enclosure where you're stripping the wire back to land on terminals.

To brink cables into an enclosure you'd be required to use a Hawk gland, or Myers Hub.

Are you entering with conduits or with cables. If cables, please look again as their cabinet entry products are for multiple cable entries where the cable glands take up too much space.