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Community and Q&A

Electrical Entrance Through Slab vs. Wall

idahobuild | Posted in Energy Efficiency and Durability on

Hey all,

I’m working on design details for what I hope to be a fairly well built and efficient house (Pretty Good House).  In considering the electrical entrance, I am thinking that coming in to the utility room through the slab foundation would help with the air-tightness details.  It seems like most details that I find just come through the exterior wall.

The water will come in through the foundation, but that just seems easier to pull off.

Does bringing the electrical through the foundation (sleeve, etc.) over complicate the build?  Should I just come through the wall and pay special attention to detailing the transition through the air barrier?


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  1. joenorm | | #1

    Up through the foundation for sure

    1. kbentley57 | | #4

      I second this opinion. Fewer penetrations, and more importantly, less hole saws.

  2. Expert Member
    BILL WICHERS | | #2

    You may find that your electric utility will have some requirements as to how you have to do this. Those requirements will usually be in what I like to jokingly call “thou shalt” form — as in “thou shalt build thy electric service THIS WAY”. Biblical style authority, absolutely zero wiggle room or deviations or the utility won’t hook you up. Find out about these requirements before you get too far into your project.

    The first thing I can think of is that the meter can will have to go somewhere. It sounds like you probably have underground service, but is the meter going to be on your house, or on a pedestal somewhere? If the meter will be on your house, there will be requirements as to where it has to go. You will need to bring your service up to the meter can on the exterior of the home. You now have to check with your local building dept people if they have any restrictions as to how you run cable between the meter can and your panel, which is required to be a short run (typically under ten feet). You gain some flexibility with cable placement if you mount a main disconnect (breaker or fuse) at the meter, then you run four conductor cable from there to the panel without distance limits. I would try to put the breaker next to the meter using a close nipple (very short threaded conduit section), then go out the back of the main disconnect box into the wall and from there to the panel, concealing the cabling in the wall.

    If you have a remote mounted meter, you could enter through the foundation, but that does make moisture ingress through the conduit more of a risk. You can mitigate that risk somewhat by coming into a large pull box first, then going out the top of that box up to the ceiling and down to wherever the panel is after running the run along the ceiling. You can use the pull box as an access to the outdoor conduit, and you can seal it at that location as well.


    1. idahobuild | | #3

      Thanks Bill.

      I'm definitely having conversations with the Utility (Idaho Power) regarding placement of service handhole and meter. Though the county that I'm in is using the 2018 NEC, which doesn't require an exterior service disconnect, I am now going to include one (solar power later, your suggestion, etc.). That disconnect will help in many ways.

      To facilitate the transition from exterior to interior, I'm thinking that an exterior hand-hole/j-box will help by serving as a common tie back for the various conduit runs (see atch'd image). If I get the conduit in the exterior handhole that goes into the house up high in the box that should keep gravity on my side; plus I am thinking that the elevation of the branch-circuit panel inside would help with the water as well. I wonder if maybe a wall mounted j-box might be better. Though the turns would be quite tight from the exterior to the interior (see atch'd image 2).


      1. Expert Member
        BILL WICHERS | | #5

        That's probably not going to work. The utilities don't want the wires on "their" side of the meter to be mixed with the wires on "your" side of the meter anywhere except INSIDE the meter can. The reason is that they don't want it to be easy to tap into "their" side of the meter, which would let you get power without them billing you for it!

        I would just go out the back of the disconnect box and through the wall, which avoids the foundation penetration and the risk of water ingress.

        Precast handholes are pretty expensive too, so if you don't absolutely have to have one (which you don't here), save the money and don't put one in.


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