our inspector requires panels mounted in basements to be seperated from the concreate wall by plywood. Does anyone know in the code where it requires this? Also, If the wall is studed and the panels are mounted to the studs with the concrete behind them, would this still require the plywood?

Not an NEC requirement.

I would ask the AHJ wich article in the NEC he is referring to if he's requiring you to do this. I did some looking around at article 408, and from there one of the articles referred me to 312.2 (A). As long as the panel is elevated 1/4" off the concrete wall I don't believe there is a violation. However, unless a panel is mounted between two studs I ALWAYS use a sheet a plywood as a barrier from the concrete wall. Think corrosion.

thanks alot, It's probably just a local requirement due to the corrosion like you stated.

I have seen the 1/4" rule before, I guess with no studs the plywood gives the 1/4" and the corrosion.

I had an inspector once who wanted sheet metal placed behind the plywood!

Anyone have any idea why?

Termite shield...you wouldn't want those termites to eat the plywood and get corrosion on their little bodies would you!

The sheet metal protects the plywood (vapor barrier) and the plywood protects the panel?
I would think VisQueen would do the same thing. If the basement walls are damp you can make the 312.2 (1/4") rule work.

I figured the sheetmetal was for some sort of protection for corrosion, but why isn't it in the code somewhere?

Or maybe the AHJ was using 300.6 as his justification.

Anyway, I only did it a few times and no one has enforced it since.

Gfretwell, you're an inspector, right? Do you enforce this?

I didn't do that much residential. In commercial the enclosures were usually on strut. Also we don't have basements.

I forgot that basements are non-existant in some areas of the country. I just got back from the Carolina's and they didn't have any down there either. I've become so accustomed to them that I could not imagine not having one. Where would I store all my crap? LOL.

By the way, isn't all concrete considered to be a damp location? And why don't inspectors enforce 4x4 metal boxes on concrete walls be mounted on some sort of wood? If we do it for panels, we should also do it for any metal electrical box.

I always use a PT 2X4 and mount that to the concrete then mount my plywood to the 2x4's.

Emt straps also corrode, as do the mounting screws for the panels, and so forth and so on.

New PT is copper-treated and will create corrosion problems of its own!

Those plastic panelboard enclosures look better every day.
If this is above ground, a stucco'ed concrete wall is pretty dry. A galvanized 1900 box should last forever.
Before you stucco a block wall you can blow water through it with a garden hose. We never hang drywall before stucco.

Here in this area basements are poured concrete with code required damp proofing applied to the outside.

In general most modern basement walls in this area are not damp once the concrete cures.

In the commercial jobs usually the specs will require a water proofing membrane be applied to the outside of the concrete.

Once cured these walls will not be damp again.


My own basement is made of stones, very damp and very tough to hang panels on, I built a plywood wall about 4" off the stone to let air flow behind.

Bob, that was my thinking too. When I set the "way-back" machine to when I was living in the frozen subterrainian north I remember basemenmt walls were parged and painted with black tar.

Up here in Canada we used to have to put drywall behind the panel in basements. Not anymore. I think it was for fire protection?

I always use unistrut when mounting a panel to a poured concrete or block wall in a basement or above grade.

Fred, do you use the strut to mount a sheet of plywood?

Or do you use the strut to mount the panel directly to the strut?

Don't mind me asking, I'm always interested in new ways of doing things to better improve my work.

I mount the panel to the strut, usually. I have used unistrut to mount a 4x4 sheet of plywood for mounting the panel, video and phone equipment. It was a request from the homeowner and over-kill in my opinion.

Mounting the panel is required in some areas around here (local amendment). The idea being the basement wall is colder then the load center and could condence moisture. They say those ark faults get warm so the problem may be worse in the future. IMO panels mounted on wood tend to look cleaner after some years (little or no corrosion & etc.)