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Chapter 4

Trench and You must provide a 12-inch layer of sand above and a 4-inch layer of sand bedding
backfill below the utilities before backfilling (see Figure 22). If native backfill is completely free of
requirements foreign objects and rocks in excess of 8 inches in diameter, sand shading over utilities
for primary can be reduced to 6 inches after compaction.
electric line You are responsible for the following:
extension
trenches (with • Completing backfill as soon as practical after facilities are placed and inspected.
PSE gas) • Carefully placing backfill to prevent damage or movement of the cables or conduit.
• Cost of damages to PSE facilities caused by improper backfill or compaction.
• Relocation costs due to change in grade or alignment.
CAUTION: Do not use a compactor directly over the power conduit(s) until at least
30 inches of backfill is in place so that the compactor will not damage the cables or
conduit. Do not penetrate the soil deeper than 3 inches during compaction with a
backhoe compactor.

Vaults

PSE is responsible for furnishing and installing all primary vaults and secondary
handholes required for your electric service.

Vault 1. Locate the vault according to PSE’s work sketch drawing.
excavation 2. Determine a suitable place to put the spoils (at least 2 feet from the edge of the
procedure excavation).
3. Excavate so the vault is in correct alignment with the trench and so that conduits
for primary voltage cables (if required) can be brought straight into the front half of
the vault.
4. Dig a hole large enough to accommodate the transformer or junction box vault and
allow for easy installation and compaction (see Figures 23 through 26).
5. Remove debris and level the bottom of the excavation.
6. Prepare the bottom of the excavation so that the vault will rest on solid undisturbed
earth with a 6-inch base of crushed rock. This prevents vault settling.

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Electric Service Handbook 2017 — Single-Family Residential Projects 41