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How To Install Small Underground Enclosures?

Enclosures sized smaller than 24” x 36” can be safely and securely installed by following these four simple steps.

Site Selection

Select an appropriate site or location that is suitable for an underground enclosure. Consider the following:

  • Slope — Level is ideal, but some grade is acceptable depending on soil conditions and expected drainage.
  • Existing underground utilities — Call 8-1-1 and avoid all existing lines
  • Traffic — Select the enclosure type and ANSI/TIER load rating based on application.


  • Excavate six inches to one foot larger than enclosure size.
  • Excavate six to eight inches deeper than enclosure height.
  • Cover bottom of hole with six-inches crushed rock.
  • Level gravel prior to setting enclosure.


  • Remove cover from box.
  • Manually position box on leveled gravel in bottom of hole.
  • Adjust for level or to match grade.
  • Trim/prepare any incoming conduit paths.


  • Begin backfilling around perimeter of box and manually tamp, every six- to eight-inches of backfill. Proper backfilling will minimize settling and potential frost heave of the enclosure.
  • Where ribbing exists on exterior of enclosure, carefully work backfill into voids and tamp.
  • Bring backfill to desired grade.  Enclosures Reference Guide
Excavation – Placement – Backfill