Waterproofing and Air-Sealing Electrical Penetrations
artisanfarms
| Posted in General Questions on
I’m in the process of bringing electric to my pole barn shop and will need to seal the points where the electric service enters, the mini-splits enter and for three outside lights and at least 3 outside GFCI receptacles.
What are good ways to seal the penetrations – both from weather and also air sealing to protect the fiberglass insulation batts in the walls?
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Replies
If you're bringing the electric service in from underground, I would come up on the exterior to a NEMA 3R (raintight) pull box on the exterior, then go through the back of that box (near the top, not the center) with a short conduit nipple to an interior box and then continue the conduit run to wherever it needs to go. Seal around that nipple going through the wall between the two boxes with caulk, then flash the top and sides of the box into the wall to keep an water sheeting down the wall from sneaking in behind the box. In this way you have two layers of protection: the flashing is the first, and primary layer, and the caulk around the conduit nipple is a secondary layer. This is how we do this kind of thing commerically.
For the devices, you can either surface mount boxes and caulk the top and sides (leave the bottom open to avoid any water accumulation behind the box), or recess them into the walls and flash/seal the devices. Keep in mind that if you're expecting a lot of rain exposure, the gaskets provided with fixtures and devices covers don't really seal very well and will all leak. Rain blown against the wall that sheets down will get behind stuff that isn't flashed or well caulked, and that includes anything with just the included gasket as a "seal".
For refrigerant lines, it's common to put a pipe sleeve through the wall, seal the pipe, then seal around the lines inside the pipe with canned foam and/or duct seal, similar to a pitch pot on a commercial roof if you're familiar with those. If you have a way to bring the lines out at a downward sloping angle through the wall, that will make the seal less important since water won't be prone to run inside that way.
If you want to be extra cautious, use mineral wool in any stud cavities with a wall penetration. Mineral wool won't hold water and get saturated if you do have any leaks.
Bill
Thanks for the detailed and informative response