5

I need to run conduit underground to a new garage. My problem is I don't understand the proper way to run the 2in PVC conduit outside to the sub panel. The wall sits on a 3ft 8in stem wall. The top of the footing is at grade level. It extends from the wall about 14 inches. The buried conduit will be 21 inches deep. Then it will have to rise to the edge of the footing, then on top of the footing to the stem wall and rise up to the wall.

If I used 90 degree bends,.. that will force me over the 360 degree rule. The cables are 1/0 THHN. so Pulling that through the 90s will be nearly impossible. Can I used LBs in the place of the 90 degree bends at the ground level? If I do, what is the proper way to secure them? Any input will appreciated. Thank you

It was pointed out that I should explain why I will be over the 360 degree code. The other end of the conduit. There are two more bends that have to be. From an outdoor box, on the corner of the house, it heads under ground, then at 21in, it makes a 90 to run to the back yard. There it's another 90 to run 65 feet to meet with what you see in the picture.

I have all of the wiring completed inside the garage, and this is the last piece of the puzzle before I call in for rough-in inspection.

enter image description here

4
  • 1
    I'll leave it to our more experienced electrical experts to provide answers, but you could eliminate the second and third bends from the bottom and run straight up from the footing. Wouldn't be as pretty, but it solves your problem. You'd probably need some sort of standoff for support at the LB.
    – isherwood
    Jun 7 at 14:40
  • 1
    Unfortunately, you appear to have missed the opportunity to simplify this by installing the conduit before the concrete. Sometimes planning ahead can really simplify things. One 90 degree sweep and you'd be there.
    – Ecnerwal
    Jun 7 at 14:42
  • I totally agree with that. I have no-one else to blame but myself for that. Jun 7 at 14:43
  • I would penetrate the stem wall and put a conduit body on the inside. Another option is to install a hand-hole adjacent to the footing so you can pull cable into the hand-hole. Jun 7 at 14:52
2

Wow -- that's a very substantial footing. First thing I'd look into is whether it'll be allowable to cut or break a notch in the footing. Doing so could allow the pair of 90's in the middle of the drawing to be replaced by 45's.

Another option is an in-ground pull box. You see them all around in the urban/suburban landscape -- the smallest options are the same sizes as a sprinkler valve box. Some are made of the same material and simply have a lid marked "ELECTRIC" instead of "IRRIGATION", but they're more commonly made of concrete instead. The zig-zag conduit rising up the wall could be brought into this box and the conduit crossing the yard brought in as well. I'd pull cable from the house to here, then feed the same cable up the zig-zag to the sub panel. No need to cut the cable and no need for splice blocks in the box.

Maybe your electrical inspector will tolerate a sprinkler valve box as a pull box. If not, call electrical distributors and ask for a "hand hole" or "flower pot" or "small cable vault" or "Quazite box" (the latter is a brand name). In my market 13x24 is the smallest commonly available size. They'll ask which "tier" you need. That's a rating for the weight the box and cover can bear (these boxes may be installed literally in a lane of traffic, or in a sidewalk/park strip/driveway where they'll see varying traffic impacts). Smaller numbers support less weight. The tier 15 I commonly use cost me about US$180 for the box and cover -- tier 8 or 5 or even non-rated may be suitable for your use.

4
  • Pro-tip. Enter the hand-hole with 45's, not 90's. In communications work, we like to leave a service loop (a little bit of extra cable coiled up) in each box, in case of any damage at the ends (so you can pull a bit more from the loop, rather than having to re-run the entire cable.) Look up "figure-8 coiling" to see how you pull enough cable to (and out of) the box, then flip the coil and pull from the box to the next thing, without snarls.
    – Ecnerwal
    Jun 7 at 15:13
  • You are correct, everyone who have seen this has said the same thing about the footing. I guess this is what happens when you have a known "National Shed" company build your garage. With a 12ft ceiling height requirement. To say I'm not happy with how they built it is an understatement What about using an LB conduit body on top of the footing? Will that be ok? not sure bout how it would be secured. I've thought about an in-ground box. I am hesitant bout a box but I'm not sure why I'm hesitant. Jun 7 at 15:14
  • The hand-hole can be anywhere convenient in the run from the last 90 to here. It does NOT need to be right next to the garage.
    – Ecnerwal
    Jun 7 at 15:15
  • 1
    You could actually do the "pair of 45's" (or 22.5's, for that matter) without a notch in the footing. I'd add a couple of bollards beyond the conduit and footing to prevent anything running into the exposed conduit, but it's less completely exposed than the straight-up-and-over method. Do recall that all the exposed conduit here has to be schedule 80 (which usually needs an electrical supply, since the big boxes don't seem to stock it, at least not in my area.) You could also raise the grade in that area (pile dirt against the stemwall for a couple of feet, still leaving 18" clear.)
    – Ecnerwal
    Jun 7 at 15:27
0

You can eliminate two 90 degrees bents by doing one of the two shown below. For option A, leave a clear distance of 1" - 2" between the bottom of the pipe and the foundation. For option B, the clear cover on the top of the pipe should be at least 2".

enter image description here

Also, using your configuration, I think it is possible to pull the wire through multiple stages rather than a one-shot pull.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.