Direct Buried Conduits – Substation Below Grade Engineering

Inside the substation, conduits route the cables from the yard equipment to the control house. These conduits are directly buried and are routed to the cable ladder near the control room or are terminated at the nearest cable trench.

When showing a detail of the direct buried conduits on the design drawings, indicate

  1. Depth of burial.
  2. Location of ground grid relative to conduits.

    Direct Buried Conduit - PEguru - Power Systems Engineering
    Direct Buried Conduit
  3. Fire retardant material to bury conduits in. Example, sand.
  4. Clear dirt for back fill, on top of FR material.
  5. Mechanical tamping of the back fill.
  6. Cable markers or 2inch wide tape along the length of conduit.
  7. Crushed rock to top it off and installed flush with the adjacent rock

Sometimes these details are covered in the standard specifications pertaining to conduits and may not be shown on the drawings at all.

Aleen Mohammed

Aleen Mohammed

Registered Professional Engineer | MSEE
Skillset: Substation Design | Power System Studies | Arc Flash Study
DISCLAIMER: ALL VIEWS EXPRESSED IN THIS ARTICLE ARE MINE ALONE.

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Looking at your graphic it appears that the grounding grid is buried too deep or the conduit is not buried deep enough if it was placed per NEC at 60cm below finished grade.

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