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Cutting into sheathing for exterior electric outlet; recommendations?

Cutting into sheathing for exterior electric outlet; recommendations?


Old 03-31-17, 09:45 PM
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Cutting into sheathing for exterior electric outlet; recommendations?


I'm installing Hardie plank and will be installing an electrical outlet within a mounting block. My question is; how big of a hole do I cut into the sheathing? Do I make a hole; just big enough for the Romex to fit through? big enough for the wire clamp? or big enough for the entire box to be recessed into the wall?
I've made a few sketches (side-view cutaway) to help illustrate what I mean.
Note: I do understand that I need to add an "in-use" cover, but, for simplicity I did not include the cover in the sketches:

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The option shown in the sketch above only requires a small hole in the sheathing for the Romex.

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The option shown above requires a hole just large enough for the Romex clamp (arounc 1 1/2" diameter).

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This final option requires a hole large enough to recess the entire outlet box.

From an insulation/air sealing perspective, I think that the first option (hole just enough for the Romex) is best, but, with the large protrusion of the box, it looks the worst.
The second option (hole for the wire clamp) has a nice snug fit of back of the box to the face of the sheathing, but the protrusion is still evident.
The third option (box recessed within the wall) will look the best, but from an insulation/air sealing perspective, it's probably the worst. With just 2x4 exterior walls, I can't get much insulation behind a box that is sunk 2" within the wall.

So, which of the options is best? Or, should I spring for a prefab'd recessed box like this one: Arlington | DBVM1C Product Information ?

Thanks in advance for your help.
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Old 04-01-17, 06:43 AM
Tolyn Ironhand's Avatar
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You will need to cut a hole large enough to fit the cable clamp, otherwise you will not be able to secure the box to the sheathing.

You are also required to install a in use cover on the box so that it is water tight even when it is being used. I highly recommend the Arlington boxes you posted. They will sit back in the wall, they are easy to side to, and are code compliant.

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