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I have a 1-gang box that I'm installing a switch in, for my wood shop. I need to make it dust-resistant, if not absolutely dustproof. I can't use a waterproof box because I don't think they're made for the depth I need (3.5") to fit the switch. Do they sell covers for the screw holes of j boxes, like they sell knockout covers? If so, what are these things called? If not, what are some other possible approaches?

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  • Does this absolutely need to be an ordinary light switch, or can it be a "safety switch" type of device? Oct 30, 2020 at 0:00
  • Also, what wiring method is used for the wires coming into this box, and is the existing box surface-mounted or flush-mounted? Oct 30, 2020 at 0:10
  • The switch is not a light switch. It is a safety paddle switch. The cord entry points are not a problem. I'm using waterproof cable glands. The only problem I have is sealing the screw holes.
    – user278411
    Oct 30, 2020 at 1:02
  • Can you link the make and model of the switch then please? Oct 30, 2020 at 1:19
  • 1
    Can you provide a picture of the switch?
    – MonkeyZeus
    Oct 30, 2020 at 12:48

3 Answers 3

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Use a weatherproof box and a weatherproof extension ring (or rings if you need a lot of depth) if you cannot find a weatherproof box to suit.

Or, just seal up the box with duct seal (non-hardening electrical putty for sealing up conduits.)

Unless you use a weatherproof switch enclosure (which may not be compatible with whatever absurdly deep switch you have chosen if it's not like a normal toggle switch at the mounting end) the switch itself will be an entry for dust into exactly the places you most don't want it.

Depending on the nature/purpose of the switch, enclosing the entire switch behind a gasketed door might be appropriate - but not if it's something that requires immediate access, like an emergency stop (though most of those are dust-resistant and/or waterproof, or available that way, anyhow.)

Addressing dust collection/control is another approach. It's not good to breathe that stuff, so getting it out of the air ASAP is good for you AND your electrical items.

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Look for switch/outlet insulators, like this one (Note: just the first one I found in a search, no recommendation of vendor or retailer implied.)

It's a thin foam gasket designed to go under the cover plate to keep cold air from coming in through the box, but should do a reasonably good job of keeping much larger dust particles from getting into the box, too.

Also, they're dirt cheap. (I found one source for receptacle gaskets for 10¢ each.)

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In the US, NEMA (the National Electrical Manufacturers Association) is the standards body which establishes standards for this type of thing.

It looks like you want a NEMA type 5 box: Wikipedia Article on NEMA Enclosure Types

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  • The OP's issue is that NEMA enclosures are a completely separate thing from standard wall boxes (and not generically compatible with wallbox devices, of course); "safety switches" are made in NEMA 4X or 12/3R combo enclosures for industrial work, but are rather different beasts than a wall switch Oct 30, 2020 at 0:01
  • I believe that a NEMA type 5 box isn't much more than a normal box with dust-proof foam gaskets. It's when you get into types 7, 8, and 9 (for example, dust-proof enough to use in an explosive environment like a flour mill) that things get complicated. Then again, I haven't cared about this in about 30 years so I may be completely off base.
    – Flydog57
    Oct 30, 2020 at 0:07
  • Yeah -- I believe a normal wallbox + coverplate is roughly equivalent to NEMA 1, but nobody ever bothers assigning NEMA ratings to those, either :P Oct 30, 2020 at 0:09
  • I was thinking something like this (though it doesn't seem to have a NEMA rating): amazon.com/Hubbell-5123-0-Weatherproof-Vertical-Decorator/dp/…. I use Sealproof brand covers for my outside plugs/switches. I suspect "weatherproof" will likely be dustproof enough for this application (again, not a flour mill)
    – Flydog57
    Oct 30, 2020 at 0:18
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    @ThreePhaseEel Sorry, I misread your original comment. In any case, I think OP should really consider a proper NEMA or IP rated switch. It's a different beast, yes, but it's the right tool for the job in a dusty woodworking shop.
    – J...
    Oct 31, 2020 at 11:12

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