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I believe it is prudent to use pressure-treated plywood when mounting a residential electrical panel against a concrete basement wall. I am in the Northwest USA where concrete basement walls often have quite a bit of moisture.

But I never understood what kind of fastener to use. Usually the plywood is only 3/4" thick, meaning I can't use most any exterior-rated screw due to being too long. I could use small stainless screws, but then I have stainless in contact with a bunch of plain steel. Probably not a huge deal, but it would still be nice to avoid it.

On top of all of that, and most importantly, I have nowhere to staple my cables. Every staple or cable fastener I've seen uses a plain or zinc-coated fastener (eg, NM-B staples), which I assume would corrode readily when in contact with pressure-treated plywood.

What exactly are you supposed to do when seemingly all electrical equipment is not meant to be in contact with pressure-treated wood, yet it is often required to use it?

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  • Use brass or bronze screws.
    – FreeMan
    Oct 6, 2023 at 15:06
  • There's always washers....
    – Mazura
    Oct 7, 2023 at 1:36

3 Answers 3

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Use aluminum or nylon spacers (or squares of the PT plywood) to set your plywood off the wall. It's getting harder to find stainless NM-B staples, but there's always screw mounted cable ties where you can supply your own hot dip galvanized screws.

Huesmann: Or use plastic NM staples (e.g. Gardner Bender PS-175ZN) and swap stainless nails for them.

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    Or use plastic NM staples (e.g. Gardner Bender PS-175ZN) and swap stainless nails for them.
    – Huesmann
    Oct 6, 2023 at 12:55
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Mount pressure-treated 2x4s to the basement wall then attach the plywood to the 2x4s with PT lumber compatible fasteners (like these). The 1-1/2" air space between the plywood and the foundation should solve the moisture problem. Should be no worse than regular lumber wall framing on top of PT sole plates on a basement floor.

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I hang LCs with 1/4 tapcons, substrate notwithstanding. If it stands off, then you actually have to drill some hole, but impact drivers help make it not care about what's behind it for that last quarter inch.

Exterior screws and tapcons only go down to 1-1/4", but on a tapcon that last 1/4" is all tip anyway; it'll go. Whereas exterior screws stop when they meet masonry. Also, it's 1/8 thick to begin with, or 1/4" if there's raised holes in the enclosure.

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