12-29-2015, 11:09 AM
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?
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