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Thread: Nonmetallic conduit and direct burial

  1. #1
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    Nonmetallic conduit and direct burial

    OK, I'm trying to run power to a couple of outdoor lights. There will be turns and angles, and I'm not too sure I want to stick multiple pieces of schedule 40 together.

    So, I've been looking at this product, https://www.hubbell.com/hubbell/en/P...1075/p/1674826

    It says it's direct burial, but no one around my neck of the woods has used it that way. Has anyone used it for direct burial conduit? Any negatives?

    Thx

  2. #2
    Sure you can use that conduit. That kind of application is what it's made for.

  3. #3
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    My first choice on burial conduit is to use black polyethylene pipe. It's available in long, continuous lengths, so you can pull wires both ways with no worry of hangups on the joints. The plastic conduit will work too, but you just have to remember which way the joints run. You can still pull wires both ways, but it can be a little more aggravating one way. I pull nylon mason's line through the black poly with a vacuum cleaner, and every time you pull a wire, pull another line along with it for the next thing. It can be harder to suck a line through if something is already in there. It is also a lot cheaper than what you linked to.

    I've probably put miles of that stuff in the ground. When I used to build new, spec houses, I always put some in from the street to the house. I've had second and third owners thank me for doing that. It saves getting a lawn plowed up.

    I'd still run UF wire though. UF is for direct burial, so it doesn't really matter what it's in anyway.

  4. #4
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    I used the black water pipe that Tom mentions for the communication cables to my shop building not that long ago. It was easy to join to the regular non-metallic conduit section that was above ground at the house. I used it for exactly the reason he mentioned. But I also agree with him that you should use UF cable within the conduit for underground runs. Buried conduit of any kind can get damaged and therefore, get "wet" inside. Using cable that's designed for that condition insures no issues should the conduit get compromised.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  5. #5
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    Most anywhere in the world buried conduit will gradually condense water and get filled with liquid water.
    Bill D

  6. #6
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    Very much like they say about boats, "If you put it in the water, it's going to get wet". They aren't talking about the outside.

  7. #7
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    Because the black polyethylene pipe is not approved as conduit, you MUST use direct burial wire or cable in it.

    I've got lots of experience with underground installations, both with polyethylene and PVC conduit. The poly is harder to pull wire through than PVC. That's sort counter intuitive, because PE is a pretty low friction material. But years of experience have taught me to use PVC. It's been at least a couple of decades since we installed anything in PE pipe.

  8. #8
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    I've worked around miles of the linked 'liquidtight' conduit. As Tom has pointed out, it rarely keeps water out, but it does a good job of simplifying convoluted conduit runs. The transitions to end-fittings are prone to damage if there is any traffic nearby (mowers, large dogs, even people). I think it does a great job preventing mechanical damage to the contents but I would not use it for burial, despite the mfgr's claims. (Note: This is an opinion, not NEC code interpretation. Consult an expert to maintain safety/resale value.)

    I would use PVC conduit for burial of power lines, even if you plan low voltage and/or run direct-burial cable inside it. And use good judgement around trees - - long term planning is a good thing!

    ***************
    Not included in you request, but maybe this will help....
    Previous owners here had tree lights installed with PVC conduit run to junction boxes (JB) mounted low ON the tree trunk. Trees grow; PVC does not; trees win (I could post pics to prove it). If this is in your plan, sink a 4x4 PT post 16-24" deep & 2-3ft out from the trunk (or at least, outside the existing root ball), then run buried PVC conduit to this JB from your power source, then use BX or liquidtight above ground as a loose flex line to a JB on the tree, then suitable conductor on to a light, etc.. You can even leave the post a little long and mount a low voltage transformer on it as well - the less 'in' the tree, the better.

    Make sure all penetrations to JBs, etc. are on the bottom. Water is insidious.

    (Even better than the PT4x4 for long-term peace of mind is a 24"L stick of grip-strut embedded in concrete, then mount JBs & other devices to this.)
    Molann an obair an saor.

  9. #9
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    Regardless of what you end up pulling the wire through, it will save a lot of headaches if you rig up something for the wire to unspool off of. 500', and up rolls come on nice spools that you only need to have a supported rod through the middle of. The 250 rolls in boxes will need something more planned out. If you just pull the wire out of the middle of the roll, through a hole in the box, the wire will get all sorts of twists in it, and be extra trouble in all sorts of ways. It's better to take it out of the box, and rig up something that it can unspool off of. If you just stick something through the large hole, in the middle of the roll, it will close in on the spindle, and be difficult.

    We have just rolled it out on the ground, but that's nowhere nearly as easy, all through the process, as wire on a nice spool.

    Wire is much cheaper from dedicated electrical supply stores than box stores, as are all the devices. Free shipping might seem like a good deal online, but the cost always gets added in.

  10. #10
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    When using sch 80 grey PVC, I pull the wire as I go, pushing it one section at a time, avoiding having to use a pull string. Last couple of projects included RG 11 from the pole to house, sprinkler valve control wire and 4-#10 above ground for a generator plug. The generator wire was on 50' spools from Menards so we did as Tom suggests. Apparently they don't cut that wire like HD does so had to buy spools.
    Last edited by Ole Anderson; 09-16-2019 at 7:42 AM.
    NOW you tell me...

  11. #11
    It wouldn't hurt anything for a wire to get wet inside the conduit. The conduit is there to prevent accidentally cutting the insulation off the wire by someone perhaps digging where they didn't know there was a buried wire.

  12. #12
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    It's a good practice to bury a strip of yellow caution tape in the dirt a few inches above anything you bury. It can alert an operator.

  13. #13
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    Why not 14g uf and forget the conduit?

    edit: the stub out will need protection and support. Not sure of your terminations, but if just a junction box the protection must be different than the support, that is, conduit can not be the only means of support. If the conduit is prone to abuse (mowers, weed whackers, others) I think you need sch.80.
    Last edited by Charlie Velasquez; 09-17-2019 at 11:31 PM.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  14. #14
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    Quote Originally Posted by Edward Dyas View Post
    It wouldn't hurt anything for a wire to get wet inside the conduit. The conduit is there to prevent accidentally cutting the insulation off the wire by someone perhaps digging where they didn't know there was a buried wire.
    Edward, that's only true if the insulation is rated for use in wet areas.

    For example where I live T90 is not allowed in wet locations..............Rod.

  15. #15
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    Quote Originally Posted by Rod Sheridan View Post
    Edward, that's only true if the insulation is rated for use in wet areas.

    For example where I live T90 is not allowed in wet locations..............Rod.
    As Bill said, anything under the ground is considered a wet location, even if in conduit. So you need wire rated for wet location no matter what your method of installation.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

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