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How To Install Large Underground Enclosures?

Enclosures sized 24” x 36” and larger can be safely and securely installed by following these five simple steps:

Site Selection

Select an appropriate site or location that is suitable for an underground enclosure. Suitability evaluation of a particular site should include:

  • Slope — Ideal location is level, but some grade is acceptable depending on soil conditions and expected drainage.
  • Existing underground utilities — Make necessary preparations for avoiding all existing utility lines and equipment.
  • Traffic — Hubbell enclosures are load rated and designed for non-deliberate traffic.


After line trenches are complete, excavate an area approximately 1- to 2-feet larger than the width and length dimensions of the box, and 6- to 8-inches deeper than the overall height of the box.

  • Add rodent barrier if necessary.
  • Cover bottom of hole with 6-inches of gravel or crushed rock and level.

Lifting & Placement

  • Remove cover from box.
  • Attached lift straps to lift positions on box.
  • Position box on leveled gravel in bottom of hole. Adjust for level or to match grade.
  • Prepare incoming conduit paths into the box. Any necessary box modifications (i.e. knockout holes) should be added.
  • Stub conduit into box.


  • Add bracing inside enclosure as described in the Internal Bracing section of this reference guide.
  • Using proper lifting techniques, replace cover onto box and bolt down.


  • Wrap box with rodent barrier if necessary.
  • Begin backfilling around perimeter of box and manually tamp, every 6- to 8-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. Finish with grass seeding and/or additional erosion control. Enclosures Reference Guide
Large Enclosures Installation