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Thread: MV cable in PVC Conduit

  1. #1
    Join Date
    Oct 2008
    Posts
    661

    MV cable in PVC Conduit

    We are looking at a project that is considering running 4.16kV cable in a single underground PVC pipe without a concrete encased ductbank. I am used to seeing PVC conduits run in concrete encased ductbank however that does not appear to be a requirement but rather perhaps a good practice in some applications.

    This application is simply running a cable between an existing pad mounted transformer and an skid located across an open field so there doesn't really seem to be a necessity for concrete encased ductbank.

    Per 300.50 it appears that at 4.16kV the PVC conduit would be required to be 18" below grade. I'm curious is this is simply putting in a PVC pipe and backfilling with soil or if there is a typical backfill or other details that are typically used specified.

    If anyone has any comment, suggestions, or a typical detail it would be much appreciated.

  2. #2
    Join Date
    Dec 2008
    Posts
    468
    In my opinion ,National Electric Safety Code IEEE/ANSI C2 [the latest edition is 2017, I think] states this more clear.
    According to 2007 Edition[only that what I have]:
    NESC Section 32. Underground conduit systems. Rule322. Ducts and joints.
    A3. The conduit system shall be designed to withstand external forces to which it may be subjected by the surface loadings set forth in Rule 323A, except that impact loading may be reduced one third for each 300 mm (12 in) of cover so no impact loading need be considered when cover is 900 mm (3 ft) or more.
    Rule 323A
    2. In designing structures not subject to vehicular loading, the design live load shall be not less than 14.5 kPa (300 lb/ft2).

  3. #3
    Join Date
    Oct 2008
    Posts
    661
    Quote Originally Posted by Julius Right View Post
    In my opinion ,National Electric Safety Code IEEE/ANSI C2 [the latest edition is 2017, I think] states this more clear.
    According to 2007 Edition[only that what I have]:
    NESC Section 32. Underground conduit systems. Rule322. Ducts and joints.
    A3. The conduit system shall be designed to withstand external forces to which it may be subjected by the surface loadings set forth in Rule 323A, except that impact loading may be reduced one third for each 300 mm (12 in) of cover so no impact loading need be considered when cover is 900 mm (3 ft) or more.
    Rule 323A
    2. In designing structures not subject to vehicular loading, the design live load shall be not less than 14.5 kPa (300 lb/ft2).
    This installation occurs on secondary of utility transformer so NESC doesn't really apply.

    There is a consideration to go with direct bury cable vs cable in conduit so I was looking for opinions or best installation practices for either.

  4. #4
    Join Date
    May 2017
    Location
    Richland, WA, Benton County
    Posts
    10
    In my utility life, we installed 5kV MV concentric neutral all the time in SCH40 PVC Conduit, probably since 1990+/-. We typically installed it in a 4' deep trench and used native soils for backfill.

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