Electrical Duct Banks and Service Entrances

Underground work gets one chance to be right. Once a duct bank is encased, backfilled and paved over, moving it means breaking concrete, and an owner who discovers a missing spare conduit after the parking lot is done pays several times what it would have cost to include it in the first pour. That is why we treat duct banks and service entrances as a design discipline, not a trenching job.

A data center depends on a few large, protected pathways. The utility service comes in through one or more entrances, usually from different directions for redundancy. From the entrance, concrete-encased duct banks carry medium-voltage feeders to transformers and switchgear, and low-voltage banks carry power to the generators, the cooling plant and the building. Separate banks carry fiber and communications. All of them have to be located, sloped, spaced and marked correctly.

We install these systems for Oklahoma data centers from the property line to the building wall. The sections below describe the scope, the field conditions that decide the cost, and the way we protect the work from weather, water and future digging.

The work begins with a utility survey and a coordination drawing that shows every duct bank, vault, handhole and manhole in three dimensions, with crossings and clearances noted. We excavate, set conduit on spacers, tie reinforcing where required, pour the encasement, and install handholes and pull boxes at the designed intervals. Marker tape and surface markers go in before backfill.

The service entrance is the point where the utility and the owner meet. Depending on the arrangement, we build a pad-mounted transformer foundation, a metering enclosure foundation, and a switchgear pad. Where the owner builds a yard, the duct banks begin inside the substation, as described in utility substation site work.

Vaults and large pull points deserve special attention. Medium-voltage cable has a minimum bending radius and a maximum pulling tension, so we place vaults where the electrical engineer's pull calculations say they belong, not where the grading happens to be convenient. We set them on compacted stone, seal the joints, and cast the lids at a grade that sheds water away from the opening.

Groundwater and floodplain conditions drive the design. The Caney River flooded in October 1986 and split Bartlesville for several days, and Arcadia Lake in eastern Edmond exists because its flood-control dam was built to protect the Deep Fork River Basin. Sites near creeks and rivers need duct banks that are watertight, sloped to drain to handholes with sumps, and located above or protected from high water where required.

Crossings are the other complication. Existing gas lines, water mains, fiber and drainage structures cross the route, and each crossing is a potential damage. We locate and pothole them before digging, mark them on the drawings and adjust the route when needed. Our fiber and telecom trenching service handles the carrier side of the same corridor.

The crews that dig and pour the duct banks work from a plan we coordinate. That lets us control the depth and slope of each run, the spacing of conduits, the quality of the concrete and the backfill compaction. We pull a mandrel through every conduit after the pour and leave a pull line in it.

We also keep spares. For every bank, we recommend extra conduits, and we place them in the same pour so there is no new trench later. Owners who plan to grow, whether through a second hall or a heavier load, benefit most from that practice. Large campuses with growth plans are described in hyperscale campus construction.

A newer National Electrical Code has been adopted in Oklahoma, and it governs the customer-owned portions of the service, including conduit fill, burial depth and grounding. The utility's own standards govern its portion, including transformer pads and clearances. Local jurisdictions can enforce a different edition, so we confirm the one that applies.

Licensed electricians must install the conductors and perform the connections, and the state's trade licensing rules apply. We coordinate our civil work with the electrical contractor's drawings so conduit sizes, bends and routes match the pull calculations the electrical engineer has done.

Length, depth, number of conduits and the amount of rock or water in the trench decide the price. A route that is shorter and straighter costs less, but the shortest route is not always the best one, since it may cross a drainage way or a future building. We review alternatives with the owner and show the cost of each.

Concrete encasement and reinforcement add cost but protect against future damage. Where the design allows direct-buried or sand-encased conduit, the price is lower, and we explain the tradeoff. Early pricing during preconstruction and estimating allows these choices to be made before they are drawn.

The same corridors often carry fiber, cooling water and stormwater, and we plan them together. See cooling water supply and reuse lines for the water side, and central utility plant for the buildings that these banks serve.

Utilities and developers who need an entrance finished before a service date, a situation covered on our page for utilities and power developers, can have us work directly from the utility's drawings.

Send the utility service plan and the building layout. We will draw the duct bank routes, price the options and show where spare conduits are worth the cost.

How many spare conduits should we install?

More than seems necessary. The cost of a spare conduit in the original pour is small compared with trenching later. We typically recommend spares in every bank and often suggest an empty spare bank on large sites. The right number depends on your growth plan.

Should the utility service come from two directions?

It is a common choice for resilience, but it costs more and depends on what the utility can offer. We build the entrances to the utility's design and keep them physically separated so one dig-in does not take out both.

How do you protect underground work from future digging?

With marker tape, surface markers, as-built drawings and, where the design calls for it, concrete caps over the encasement. We give the owner survey-grade as-builts at turnover, so future contractors know where the banks are.

What if we hit rock?

It changes the cost and sometimes the route. We review the geotechnical report before pricing, set an allowance for rock, and keep a unit price in the contract so the owner knows the cost per foot before the problem appears.

How does wet weather affect this work?

Open trenches and heavy rain do not mix. We stage excavation so that only what can be encased in a day is opened, pump water out, and protect the open ends of conduits from silt and debris. Cleaning and testing the conduits before turnover catches anything that got in.