Section 8.1 General Cable Trench Requirements
- Customer Provided
All trenches shall be provided by the Customer. Inspection and acceptance by the utility’s representative is required - Definition
Trench shall be defined to mean trenching, bedding, backfilling, restoration, and maintenance of subsequent ditch settling for electrical cables and conduits. - Notification
The District, all participating utilities, and the Underground Locating Center, shall be notified a minimum of 48 hours in advance of the date and time for the right-of-way trenching and facility placement. Locating services notification is required by state law.
Section 8.2 Root & Rock Restrictions
The trench shall be free of rocks or roots greater than 2 inches in diameter
Section 8.3 Specification Drawings
The trench shall be dug to the specifications shown on Drawings #30, 31, and 32, unless otherwise approved by a District representative.
Section 8.4 Water-Free Trench
The Customer is responsible for installing well points, pumping, or other measures to provide reasonably water-free trenches.
Section 8.5 Access, Construction
To facilitate installation, the Customer shall place all excavated material in a manner, which allows the District’s installation vehicle to drive on the opposite side of the trench the full length of the project unless other specific arrangements are approved by the District representative.
Section 8.6 Sloping and Shoring
Any area where District personnel must enter the trench shall be excavated in accordance with Chapter 296-155 WAC of the Washington State Safety Code. The Code requires that the excavated material be at least 2 feet from the edge of the trench and that any trench over 4 feet deep be sloped, shored, sheeted, or otherwise adequately protected.
Section 8.7 Joint Use of Trenches (See Drawing #30)
Section 8.7.1 Direct Buried Cable Separation
A minimum vertical and horizontal separation of one foot must be maintained between direct buried electric cables and communication cables.
Section 8.7.2 Electric Cable in Conduit, No Separation Required
Electric cables installed in conduit and communication cables may be buried together at the same depth with no deliberate separation between facilities if both utility owners concur.
Section 8.7.3 Water and Sewer Lines
A water service line, up to 1½ inches may be installed at 18 inches above District cables. No sewer lines or water mains will be allowed in any electrical trench.
Section 8.8 Permanent Access
All surface areas above direct-buried cable and cable in conduit must be accessible for future District operations including, but not limited to, maintenance, location, repair, and replacement. The Customer shall not construct any building, fence, landscaping device, or other obstruction over the direct-buried cable route that restricts said access. In addition, customers should consider that cable in conduit routes may also need to be accessed in the event the conduit system fails or otherwise needs to be repaired or maintained. All transformers and other aboveground devices must remain accessible to District vehicles at all times and the opening side of the device must have at least 10 feet of clearance from any obstruction. The District handout on padmounted equipment requirements provides more details. (See Drawings #34 and 35). Failure by the customer to maintain accessibility to all District facilities may result in delays in repairs and the restoration of service to the customer.
Section 8.9. Cable Pulled Into Continuous Conduit
When service cable is installed in continuous conduit, the cable shall be pulled into conduit after it has been assembled (conduit shall not be installed by slipping over cable as it introduces rock and dirt into the conduit and does not allow for an adequate sealing procedure). See Chart #1 for minimum conduit and sweep sizes allowed for conductor sizes.
Section 8.9.1 PVC Joints Must Be Glued
Each PVC conduit joint must be permanently glued, prior to cable installation.
Section 8.9.2 Maximum Number of Bends in Service Conduit
Total number of bends in a service run shall not exceed 360 degrees. All bends shall be long radius type (24-inch minimum). See Chart #1 for minimum sweep dimensions for various conduit sizes.
Section 8.9.3 Conduit Under Buildings
No structure may be built over District facilities except when it is absolutely unavoidable. Written approval of the Manager of the District is required.
- The required conduit(s)shall be paralleled by an equal spare conduit(s) from the pole to the vault or between vaults
- Conduits shall not pass through nor conflict with the building’s foundation walls.
- Conduit(s) shall be encased in concrete. Minimum encasement shall be 2 inches thick on all sides of the conduit.
- Exception: The concrete encasement requirement can be waived if the building will have a minimum 4-inch thick concrete slab first floor and no basement.
- A Hold Harmless Clause will become part of the power line easement.
- Total number of bends shall not exceed 180 degrees.
- Continuation and restoration of service cannot be assured if a structure is built over District lines. 1 of the following remedies shall apply:
- Removal of the structure(s).
- Payment to reroute the line(s) around the structure(s).
- Customer acknowledgement that additional restoration expense caused by the structure(s) shall be billed to the customer. This will generally apply when a cable fault occurs under the structure and the raceway, if available, is unusable.
Section 8.10 Equipment Locations Permanent
The Customer is responsible for establishing the location and grade of the cable trench route and transformers, junction boxes, or secondary pedestals that are shown on the sketches provided by the District. The transformer, junction box, and pedestal locations are considered permanent and moving them is difficult and expensive. In the event any of these facilities need to be relocated, the entire cost will be at the Customer’s expense. We recommend that a licensed surveyor be used to determine the lot lines, property corners, right-of-way, and easements to ensure that the facilities are properly located
Section 8.11 the Customer Shall Provide Final Grade
The Customer shall provide final grade at the site of a transformer or other aboveground devices. After installation, the Customer shall not change the cable depth by cutting or filling without the express consent of the District.
Section 8.12 Backfill Bedding Material
Bedding material for backfill will be subject to approval by a District representative. The Customer will provide the appropriate bedding material when native material is unsuitable. The Customer shall place the approved bedding material in the trench in sufficient quantity to protect the conduit, prior to installation. The Customer shall place an equal amount of approved bedding material over the installed conduit prior to backfilling with native materials. The typical requirement is 6 inches of bedding below and 6 inches above the conduit.
Section 8.13 Backfill Compaction
All trenches shall be compacted to the satisfaction of the District in the following manner:
- Compacted sufficiently to prevent later settling of the fill material.
- For Trenches compact in lifts to attain 95% compaction. The Customer shall provide compatible 1 inch minus granular material (i.e. sand, screen reject, or pit run) should the District determine that native material is unsuitable for backfill. The surface material shall be replaced with material equal to existing surface (crushed rock, asphalt, concrete, etc.).
- For beneath transformers, pedestals, and above-grade devices - Compact in lifts to attain 95% compaction. The Customer shall provide compatible 5/8 inch to 3/4 inch minus granular material.
Section 8.14 Road Bores
All road bores should begin at a depth of 42 inches to the bottom of the bore hole and exit or end with a depth of no less than 36 inches or no more than 48 inches below grade. Lesser or greater depth will not be accepted without the approval of a District representative. In addition, a gradual transition from the end of the bore into the 42 inch trench or excavation must be provided by the contractor
Section 8.15 Requirements Before Construction
The District will schedule the Customer’s project only after required easements are received and necessary monies are paid. Trenching should not be started before consultation with a District representative and a date scheduled for the work. At this consultation, any special requirements for the trench will be outlined. The trench shall then be dug prior to the arrival of a District crew on the scheduled date.