Exterior Wall Light Electrical Box
rodrob15
| Posted in Mechanicals on
For outdoor coach lights, are special exterior rated electrical boxes needed? Or are standard interior rated electrical boxes generally used since the light fixture has a gasket that will seal out any moisture?
In my application, the electrical box will be outside the sheathing and house wrap (I have exterior insulation) if this makes a difference.
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Replies
HI Rod or Rob (always good to have a name in a community like GBA) -
I must admit that I wired my own home here in Vermont without an electrical inspection but I was working under the "adult supervision" of a licensed electrician - I did not use anything other than a standard box.
For bulk water protection for the light installation, though, I did install all exterior light fixtures on mounting blocks, which were flashed including drip cap to the mounting block.
Hopefully, we will get some electrical "adult supervision" here on this GBA Q&A...
Peter
You only need a real outdoor rated box (commonly known as a “bell box” by electrical contractors) when the bo itself will be exposed to the weather. Bell boxes are generally of cast metal or thick molded plastic so they’re pretty durable. Bell boxes are also very limited in mounting options compared to “regular” indoor boxes.
A regular box mounted within an exterior wall is ok to use for an exterior fixture when the exterior fixture is rated to be exposed to the weather and provides protection to the box within the wall. The assembly doesn’t have to be waterproof, just “drip tight”, which basically means it’s unlikely that water in the form of rain will enter the assembly. This “drip tight” assembly is usually implemented with a combination of a foam gasket and a bent flange a bit like flashing, but there are lots of ways to do it so don’t worry if your fixture is a bit different.
I’d recommend using a regular box in the wall installed so that the fixture will mount flush with the wall surface. On some types of siding, you need to use a piece of trim to give the fixture a vertically flat mounting surface. The important thing for weather sealing is that the box in the wall shouldn’t stick out past the wall surface, or the surface of the trim piece you use, and the fixture you mount should mount tight to the wall so that rain is unlikely to enter the assembly. If you think water might sheet down the side of the wall in a heavy storm, a bead of caulk to seal the top maybe 2/3 of the fixture to the wall (leaving the bottom 1/3 open for drainage) is a good idea.
Note that octagon boxes are usually standard for wall mounted light fixtures.
Bill