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PVC Conduit and Frost Line

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    PVC Conduit and Frost Line

    I'm involved in a project in MN, that will be require direct burial of Sch 80 PVC. The Frost Line in the area is 54", other than the vertical transitions into and out of the ground. Will the PVC conduit have to be buried below the Frost Line?
    I find a few references in the NEC about expansion characteristics of conduits in the ground, but nothing that specifically says it has to be below the Frost Line.
    I'm also checking the local authorities.

    #2
    I believe standard rules apply.
    Master Electrician
    Electrical Contractor
    Richmond, VA

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      #3
      Nothing in the NEC requires that it be buried according to the frost line. If it had water running through it then it would be a concern.
      Rob

      Moderator

      All responses based on the 2014 NEC unless otherwise noted

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        #4
        Once you arrive in Minnesota, ask the locals. They have a LOT of experience with frost.
        (and frost heaves, which I presume is the real concern)

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          #5
          Expansion couplings

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            #6
            If it is PVC I have no issues with it being installed above the frost line. There is no code rule, but I don't like to see rigid or concrete encased PCV above the frost line. I have replaced conductors and fiber optic that were damaged from the crushing force of the water when it turns into ice where there is no "give" in the raceway.
            Don, Illinois
            (All code citations are 2017 unless otherwise noted)

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              #7
              Same discussion with PVC factory reps years ago.
              My understanding was "BELOW" frost line or "Concrete Encase".
              Not sure which company sent me the NEMA document.
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