Trenching/Montana 811

The purpose of this section is to clearly outline the requirements for the installation of vaults and conduits used in the Flathead Electric Cooperative (FEC) electrical distribution system. FEC requires all new underground line extensions to install a conduit and vault system. Guidelines in this section must be followed. Any deviation from these requirements must be approved by FEC prior to construction. Failure to do so may result in the rejection of the installation. Please contact FEC at (406) 751-4483 and ask for the distribution design department with any questions.

Member Trenching

For logistical and cost-saving purposes, it is FEC’s policy to allow members to supply trench and conduit for electrical services on their own property. Know whose property you are on, and be sure you have the legal right to dig on the property. To excavate on private property other than your own, an FEC-approved contractor shall be used. Contact FEC for a list of excavation and boring contractors. To excavate in public right-of-ways (i.e. county and city), you may use a licensed and insured contractor of your choice. Your contractor will be required to obtain any permits and bonding from the appropriate government agency. The following pages illustrate the member’s responsibility when providing trench and conduit for electrical service. FEC reserves the right to reject any trench and conduit system that does not meet FEC requirements. It is the member’s/member contractor’s responsibility to perform excavation and install conduit safely and to adhere to any and all state, local, and FEC requirements.

Call 811 Before You Dig

Montana 811 LogoRegardless of where you live or conduct your business, the gas, electric, cable, water, and sewer lines that serve you may very likely be underground. It doesn’t matter how deep you plan to dig, if you’re planning a project that requires digging, state law requires you to notify Montana 811 at least three working days in advance. They’ll come to the location that you’d like excavated to mark the buried utilities on your property. Whether you are planning to do it yourself or hire a professional, smart digging means Call 811 or visit the Montana 811 website before each job.

If the designed route requires that you parallel or cross existing FEC locates, any excavation required within 18 inches of the locate mark must be done by hand or vacuum truck. It is not FEC’s responsibility to cross existing lines. If you do not feel comfortable crossing the line, you may hire a professional excavation contractor or request an FEC representative to be present when the line is crossed. For crossing non-FEC lines, please contact the appropriate utility.

  • Red: Electric
  • Yellow: Gas/oil/steam
  • White: Proposed excavation
  • Orange: Communications CATV
  • Blue: Water
  • Green: Sewer
  • Pink: Temporary survey mark

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Typical Trenching Specifications & Procedures

Trench Requirements

  • The depth requirement for all trenches is 36 inches in addition to the size of conduit.
  • The bottom of the trench must be smooth and level. This prevents “bridging” of the conduit, which can cause the conduit to flatten or pull apart when the trench is backfilled.
  • The trench must be free of sharp rocks, concrete waste, and other construction debris. In extremely rocky areas, sand bedding may be required.
  • Trench width should be sufficient to allow safe installation of conduit and provide proper separation from power and other utilities.
  • 1 foot of separation is required between power and communication company conduits. 3 feet of separation are required between power and gas lines.
  • The trench must be a minimum of five feet from septic tanks and a minimum of 10 feet from a drain field.
  • FEC requires inspection of all trenches and conduit installations prior to backfilling.
  • Any variations to these trench requirements must be preapproved by an FEC distribution designer.

Conduit Installation

  • Keep the inside of the conduit clean and free of foreign materials.
  • The use of primer is recommended when gluing conduit.
  • Special care needs to be taken to insure that conduits do not block any other knockouts in the vault.
  • A new quarter-inch nylon pull rope (no splices) is required in all conduit runs. Installing pull rope after backfilling will help validate the integrity of conduit installations against pipe breakage and disjointing.
  • To prevent wire damage, file and smooth the inside edge of all cut conduits.
  • FEC-supplied red caution tape should be placed approximately 2 feet above conduit.
  • See our section on Extending Conduits for secifications on extending conduit into FEC enclosures.

Conduit Specifications

  • Conduit size and number of conduits will be determined by the FEC distribution design department. Be sure you know what size and how many conduits are required for your installation. If you use the wrong size or too few conduits, your installation will be rejected.
  • Buried conduits must be schedule 40 gray electrical PVC.
  • Any exposed conduits must be schedule 80 gray electrical PVC.


  • All sweeps must be wide radius sweeps. In conduit runs of less than 200 feet and 270° of bend, PVC sweeps may be used. On runs in exceeding 200 feet, you must use steel or burn-proof fiberglass wide radius sweeps. In no case may you exceed 270° of bend in a single conduit run.
  • Heating and bending of conduits is discouraged but may be allowed and shall be inspected by FEC before backfilling. Be careful not to flatten the conduit when bending. This decreases the ability to pull the conductor through the conduit.
  • See section on Extending Conduit up to FEC poles on sweeping conduit at FEC poles.


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Typical Trenching Detail

typical trenching detail showing: the rock-free seed and fertilizer per county specifications, the red caution tape supplied by FEC placed two feet above conduit, native backfill as the steps, and rock-free backfill at bottom step of trench. The rock-free backfill has no rocks greater than 1.5 inches, and six inches below and six inches above conduit. The typical trench depth is 36 inches to top of conduit. There is 12 inches between the 2 conduits.


  • All areas of excavation must be restored to their original condition.
  • Any surplus material not suitable for spreading along the road to widen the shoulder or raise the grade shall be disposed of.
  • Seeding: Any right-of-way that is disturbed in any manner must be reseeded by the contractor to the satisfaction of the Flathead County Weed Control District.*

*See the Flathead County Weed Control District Re-vegetation Policy for seed and fertilizer specifications.

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Maintenance & Repair

  • All contractors installing conduit and vaults for FEC use shall guarantee all work relating to the specifications for a period of two years from the date of acceptance of the work or project.
  • The contractor shall assume full responsibility and expense for all backfill settlement, and shall refill and restore the work as directed to maintain an acceptable surface condition. Any settlement of road surfaces in excess of one inch that are within the guarantee period shall be considered failure of the mechanical compaction. The contractor shall be required to repair such settlement at no additional cost to FEC.

Extending Conduit into FEC Enclosures

  • Members (or their contractors) shall not extend conduit into any enclosure without an FEC representative on site. Please schedule an appointment with a distribution designer before extending conduit into FEC enclosures. The distribution designer will instruct where the trench needs to be extended to, and determine if it is safe to extend conduit into the enclosure. If existing wires are in the way, an FEC serviceman will need to be scheduled to move the wires in order for the conduit to be extended.

Secondary Pedestal

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Extending Conduit

Extending Conduit into FEC Enclosures on Top of Vaults

  • It is not safe to extend into any enclosure without a trained FEC representative on site.
  • Extend the male end of the conduit straight and level through the bottom knockout. Belled ends must be cut. To prevent wire damage, file and smooth the inside edge of all cut conduits
  • Conduit angled toward the vault wall, floor, or other conduits will be rejected.
  • Only extend PVC into vaults. HDPE (bore pipe) will be rejected.
  • Sweeps will be rejected.

Vault showing to extend 3 to 4 inches maximum

Extending Conduit into FEC Enclosures on Top of Wells

  • A preconstruction meeting with an FEC distribution designer is required to determine the proper location for the conduit extension.
  • The trench depth may need to be altered to account for the large radius sweep.
  • Flex conduit, small radius sweeps, and conduits that extend too far into equipment will be rejected.
  • Extensions over 200 feet require burn-proof fiberglass sweeps. Verify sweep types with the distribution designer.

Extending Conduit into FEC Enclosures on Top of Wells

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Extending Conduit Up to FEC Poles

Schedule an appointment with an FEC distribution designer before extending conduit to FEC poles. The distribution designer will determine if the pole needs to be changed out. If the pole does not need to be changed out, the distribution designer will place a standoff bracket on the pole. The member will be responsible for sweeping the conduit up at the bracket keeping the conduit three to four inches away from the pole. If it is determined that the pole needs changed out, the conduit will need to be dug to within four to five feet of the existing pole with the end of the conduit capped and marked with a red top stake.


  • Contact FEC to place a standoff bracket on the pole
  • An FEC distribution designer will specify the size and type of large radius sweep required
  • Install sweep four inches from pole to side of bracket (as pictured)
  • Sweep shall be plumb and level
  • Call an FEC distribution designer for a trench inspection
  • Backfill
  • Sweeps located too far or close to the pole and sweeps that are not plumb will be rejected
  • See the Typical Trenching Specifications and Procedures section for general sweep requirements

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Installing Concrete Vaults

Vaults are used as foundations for FEC equipment and also as pulling points for long wire runs. The FEC distribution designer will determine the number, size, and type of concrete vaults required for your project. Vaults are prefabricated by local precast concrete companies, and it is the member’s responsibility to order and install them. There are 2 standard vault sizes (single-phase and three-phase) that may be required for underground line extensions. The distribution designer will determine which will be used for your application. These vaults are produced to FEC specifications and vaults will not be accepted from manufacturers without prior approval from FEC. FEC’s vault specifications are available upon request.

The manufacturers listed below are currently producing approved vaults:

Some applications may require specialty vaults. The specifications for the specialty vaults will be provided by FEC. FEC reserves the right to reject any vault that does not comply with FEC specifications.

Typical Conduit & Vault Installation

Conduit and vault set 2 to 4 inches above grade

Vault Location Requirements

Vaults will be placed according to the design provided by the FEC distribution design department. Any variation from the design must be approved by FEC prior to construction. Failure to follow these steps may result in the rejection of the installation:

  • A minimum clear zone of 10 feet from the centerline of the vault must be maintained in order for FEC to place and work on the equipment. Access to all vault locations must be maintained for maintenance and future line extensions. All vault locations must be accessible by a boom truck at the time of installation and into the future.
  • Whenever possible, vaults should be set in accessible areas at an elevation that is lower than the member’s meter base.
  • Transformer vaults will also need to be located to maintain the following minimum clearance:
  • 3-foot clearance from noncombustible walls (including brick, concrete, steel, and stone), provided the side of the wall facing the transformer does not have a door. Contact FEC for clearances from combustible walls (including stucco), doors, windows, vents, fire escapes, and other building openings.
  • 15-foot clearance from the water’s edge of a swimming pool or any body of water.
  • 20-foot clearance from facilities used to dispense or store hazardous liquids or gasses such as gas tanks, propane tanks, gas pumps, etc.

Setting the Vault

FEC retains the right to reject all vaults that are not properly installed or are damaged. The
following procedures should be followed when setting and installing the vault:

  • All vaults will be set level on undisturbed earth.
  • Vaults will be set at a depth where the vault (without the lid) is 2 to 4 inches above final grade. This prevents water and dirt from entering the vault.
  • The orientation of the vault should be such that the copper wire that exits the concrete (UFER Ground) is in the back.
  • The floor drain that is located in the bottom of the vault shall be knocked out.
  • Holes that have been enlarged or knock outs that have been removed and not used need to be sealed with grout.
  • Minor damage or gaps around the conduit can be repaired with grout or spray foam.
  • Clean out the inside of the vault after it is set. Keep all dirt and construction debris out of the vault.
  • Secure aluminum cover to lid.


  • FEC must inspect all primary trenches prior to backfilling. The inspection can be scheduled by calling the distribution designer directly or by calling FEC’s distribution design department.
  • All trenches must be backfilled prior to the work order being released to the FEC operations department for scheduling.
  • Great care should be taken during backfilling to ensure the integrity of the conduit systems.

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