NM Cables leaving panel
#11
I'm in the process of installing a new sub panel in my shop. I have the house's main panel opened up and have noticed something that gives me a question. I'm wondering what is the proper way to have 30 or so NM 12-2 cables exit the top of a panel. Both panels are flush mounted, with the NM in the walls and distributed across the attic. (House panel is this way, new panel is headed this way).

My house main panel has all of the NM clustering out a single 2" or 3" opening. The knockout is protected by what looks like a blue bushing. I can't see what it looks like behind the drywall just above the panel, but I know the cables penetrate the wall's top plates into the attic as a cluster of free cables. The NM insulation only protrudes about 1/2" into the panel, and the blue bushing does not appear to be a clamp or threaded conduit fitting.

So I go to Lowes looking for a blue bushing thingy. Can't find one. Nothing in the fittings aisle looks like it. Hanging off the rack near the panels is a Square D brochure with a picture of a panel that looks just like mine, it has the blue bushing.

So I turn to the interweb, and end up finding a lot of websites that claim that this type of cluster is common, but does not meet NEC. Apparently NEC only allows such a cluster if the panel is surface mounted, enters a 1.5' to 10' conduit that is sealed at the top and does not enter a structural ceiling.

Also, according to the interweb, each NM should have its own knockout with its own clamp. This is 42 space panel. There isn't that many knockouts around the whole box. There is no way you could put 30-40 clamps in one of the panels. Something doesn't add up.

What is the proper way to get a boatload of branch circuits out of a flush mounted panel, into a wall, properly anchored and safe from sheet metal nicks?
Shame on the men who can court exemption from present trouble and expense at the price of their own posterity's liberty! - Samuel Adams
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#12
The way it's done is just how you have seen. A bushing then a crap load of wires through it. I personally don't like the method but it's how it's done. If you can't find the bushing stop into an electric supply and they will have it. If not just use a 2" pvc nipple.

I like how the Canadians put their panel horizontally. It's not common here and only a few ways it's allowed by code in the us. And it only works well if you are lucky enough to have a basement. Course canada still sells and uses the old federal pacific stab lock panels. They are now white and a different name but still the same thing. Sad as its square d that makes the stuff...
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#13
I use the metal bushing cable clamps. Inspector has not had an issue with it though he did question whether the nut should be on the inside or the outside of the box. It was a retrofit situation and I could not get to the outside so he allowed it to be installed with the nut on the outside before installing the panel box.
WoodNET... the new safespace
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#14
Robert Adams said:


The way it's done is just how you have seen. A bushing then a crap load of wires through it.




So, does that mean that the websites Mandrake has seen which claim that it doesn't comply with the NEC are wrong? Or is everyone ignoring the NEC?
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#15
Mandrake said:


Also, according to the interweb, each NM should have its own knockout with its own clamp. This is 42 space panel. There isn't that many knockouts around the whole box.




Not an NEC wizard by any stretch, but I was under the impression that you could run more than one NM cable thru a knockout clamp.
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#16
Mandrake said:

What is the proper way to get a boatload of branch circuits out of a flush mounted panel, into a wall, properly anchored and safe from sheet metal nicks?




I don't know the proper way.

I find that using conduit to leave the box acceptable. There is no need for cable clamps where cables enter conduit.

At the exit follow the usual protection and support rules.
Economics is much harder when you use real money.
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#17
A Squared said:


Not an NEC wizard by any stretch, but I was under the impression that you could run more than one NM cable thru a knockout clamp.




According to my research, you can go with multiple cables only if the clamp is designed by its manufacturer for that duty. The kicker is that the multi-cable label is usually on the packaging and not the clamp itself.
Shame on the men who can court exemption from present trouble and expense at the price of their own posterity's liberty! - Samuel Adams
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#18
Is this what you're looking for?;

http://www.garvinindustries.com/conduit-...22dUaAoYn8P8HAQ
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#19
Robert Adams said:


The way it's done is just how you have seen. A bushing then a crap load of wires through it. I personally don't like the method but it's how it's done. If you can't find the bushing stop into an electric supply and they will have it. If not just use a 2" pvc nipple.

I like how the Canadians put their panel horizontally. It's not common here and only a few ways it's allowed by code in the us. And it only works well if you are lucky enough to have a basement. Course canada still sells and uses the old federal pacific stab lock panels. They are now white and a different name but still the same thing. Sad as its square d that makes the stuff...




My understanding is that the horizontal mounted panels are to make them usable by people in wheel chairs. Was told it was code, but am not sure. Maybe Blackhat would know more.

Mel
ABC(Anything But Crapsman)club member
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#20
Mandrake said:


[blockquote]A Squared said:


Not an NEC wizard by any stretch, but I was under the impression that you could run more than one NM cable thru a knockout clamp.




According to my research, you can go with multiple cables only if the clamp is designed by its manufacturer for that duty. The kicker is that the multi-cable label is usually on the packaging and not the clamp itself.


[/blockquote]

It was my understanding the limit was two 14-2 or 12-2 cables in a single 1/2" or 3/4" knock-out cable clamp.

When I installed my 40 slot panel, there were not enough knock-outs to go one cable per.
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