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Thread: Rigid metal conduit

  1. #1
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    Default Rigid metal conduit

    Good evening,

    I found a couple of 10’ pieces of rigid metal schedule 40 galvanized 4” conduit on craigslist.


    The plan is to embed in concrete and use a specialized fitting to hold a 3” cross pipe, and some double 1 5/8”, and single strut to make a couple of 6 solar panel pole mounts. One east; one west. These will supplement the bigger ground mount array that is fixed and south facing.

    My question is whether there is an elegant way to run the wires down through the 4” main pipe and exit to an underground run of conduit? I can always run conduit along side but thought I’d check to see if one could pole holes in this stuff to run wires and still be code compliant (and safe).

    There is no regulatory authority on this job. Just common sense and fire safety.

    All I can think of is find a 4” 90 degree fitting and embed it in the concrete with a reducer out to the side to the start of the underground conduit run. Or maybe drill a 1” hole in the side and fit it with a compression fitting and conduit elbow.

    Anybody familiar with working with this stuff?

    Thanks

    Here are both ways of doing it.

    16774A91-AA75-4DC2-B7E1-E48C158BDB06.jpg

    F7C73517-8336-4AED-9F21-C99A3D0F2EB4.jpg
    Last edited by bluedog225; 06-27-2022 at 07:13 PM.

  2. #2
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    Default Re: Rigid metal conduit

    Rigid sweeps are pricey, why not join to pvc undergrond?

  3. #3
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    Default Re: Rigid metal conduit

    Now that I typed it all out, it seem pretty clear that is the way to do it. Come off the bottom with 4” pvc, out to a trench, then pour over the whole deal. I think I was subconsciously trying to avoid more digging. Thanks!

  4. #4
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    Default Re: Rigid metal conduit

    Though it’s going to be sketchy setting that heavy as heck pipe on a pvc elbow. Maybe a T capped would do better on the bottom.

  5. #5
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    Default Re: Rigid metal conduit

    What are you a data guy? No way you could possibly need 4" conduit. Depending on the wire size requirement for the panels you probably need an inch or less conduit. Drill a hole in the stand pipe and put a pvc 90 through it. you don't need your wire at the bottom of the hole, just even with your trench.

  6. #6
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    Default Re: Rigid metal conduit

    Maybe it is that simple. Agreed. Don’t need 4” for the run to the cabin. Still some undecided on the voltage and wire size. Need to make it big enough to pull the wire. I’ll do the calculations and probably go up to 2” anyway just to make things easy.

  7. #7
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    Default Re: Rigid metal conduit

    More is not always better. Calculate what you need and do the least amount of damage to the standpipe as possible.

  8. #8
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    Default Re: Rigid metal conduit

    Tom, what is your 'frost line' at the cabin ? You may not need to trench all that deeply, except to avoid hitting the power cable during future digging. As for the size of conduit needed to run to the cabin, do you know what wire size you will be running ?


    Rick
    Charter Member - - Professional Procrastinators Association of America - - putting things off since 1965 " I'll get around to it tomorrow, .... maybe "

  9. #9
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    Default Re: Rigid metal conduit

    As far as I know, there is no frost line. I’ve not known the ground to actually freeze. Even during the big cold snap that knocked out the grid. I’m pretty sure the frost line is 0”. Sort of like our tides are 6” (max).

    I don’t have the wire sized yet. I’m a little hesitant with the idea of high voltage DC (over 80 volts). But it seems to help (a lot) with the wire size and cost.

    And candidly, I’m not comfortable I’m doing the wire size calculations correctly.

    100 feet (round trip) at 20 amps, something like 6 awg? Didn’t find the chart for “in conduit” just now.

    6 wires for the three strings.

    I will have someone check this all out before I start putting up panels.

    If I go direct current to a string inverter, it looks something like this:

    2 strings of 9 panels (9*40.1=360.9V per string)
    4 strings of 7 panels (7*40.1=280.7V per string)
    6 strings total (46 panels and about 12,880 watts)
    Short-circuit current 9.52A
    Combined (2x) 9-panel strings=9.52A*2=19.04A (feeding 1 mppt input)
    Combined (4x) 7-panel strings=9.52A*4=38.08A (feeding 2 mppt inputs/19A each)



  10. #10

    Default Re: Rigid metal conduit

    The conduit is structural support for the panels no? That would explain the need for the 4" size--otherwise something smaller should be sufficient for wire handling, I would think. Not sure if rigid metal conduit is that great a material--especially in in shear--think wind loadings.

  11. #11
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    Default Re: Rigid metal conduit

    Yes, it’s the main post the panels will be resting on. I’m planning to bury about 4 feet of it with 6’ above ground.

  12. #12
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    Default Re: Rigid metal conduit

    Metal conduit is a bit passe over here. Why not just concrete in the support posts and use pvc to run the cables?

    Or have I missed something?

  13. #13
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    Default Re: Rigid metal conduit

    Mostly asthetics.

  14. #14
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    Default Re: Rigid metal conduit

    You could just put the (smaller) pvc conduit inside the 4" rigid
    How you keep rain water out will be interesting

  15. #15
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    Default Re: Rigid metal conduit

    Three things come to mind. These are my own opinions and I have given some thought to solar panel installations in the past.

    In this situation repairability and serviceability beats aesthetics. I'd definitely put the conduit and boxes on the outside where they can be easily accessed.

    Also I don't like embedding stuff in concrete as sooner or later it has to be accessed, in spite of the best designing and planning.

    Also 4" PVC pipe would make a poor choice for a single support stand like those in the pictures - it's subject to bending from wind load and subsequent breakage. I know that from using PVC guides on my boat trailer. As soon as the boat pressed on the guides they snapped off. If the PVC pipes were supporting the 4 corners of the panels - maybe ok. And some grades of PVC are susceptible to UV deterioration from sunlight.
    Will

  16. #16
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    Default Re: Rigid metal conduit

    Agreed on pvc not being suitable. And if I run any of this through the concrete, I’ll need a vault and easy access.

    Rigid metal schedule 40 galvanized 4” conduit. Pretty stout stuff.

    A couple of these are on the way. They will hold the 3” cross pipe. And keep the water out.

    I’m mostly convinced to just run emt on the outside. Will be easier all around.

    F295E344-DBC7-4EA4-A0AD-819DF7DD0223.jpg

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