Electrical Duct Banks and Underground Power for Denver Industrial Sites

Electrical service is the item a new Adams County plant waits on the longest, and the duct bank is the first piece of it that can be built. Thornton enforces the 2023 NEC alongside the 2024 IBC, and Lakewood, Wheat Ridge and Broomfield list the 2023 NEC as well. The conduit under a site must meet that code edition, and it must also meet the utility's own construction standards, which vary by provider.

We install underground power for industrial customers: concrete-encased duct banks from the utility transformer to the main switchgear, feeders to remote buildings, yard lighting circuits, security and data conduits, handholes and pull boxes. Each of these has to be located accurately in three dimensions, because the building slabs, foundations and pavement will bury them for decades.

A duct bank that is wrong by two feet can mean a cut-in through a new floor. Surveying, spacing and inspection discipline are what we sell.

Why Power Controls the Schedule in the Metro

Industrial growth along I-25, E-470 and the DIA corridor draws on the same electric infrastructure. Large buildings such as the 855,000 square foot, three-level fulfillment center announced for I-25 and 144th Avenue in Thornton, and campuses like the six-building Crossroads 25, call for transformers and services of a size that requires utility engineering and lead time.

We therefore engage the electric provider at the first site plan, gather the load letter from the electrical engineer and file the service application as early as the utility accepts it. The duct bank is designed and built in the knowledge that the provider will set the transformer location and energization date.

NEC, Local Amendments and State Electric-Ready Rules

Colorado HB22-1362 requires jurisdictions that update their building codes to adopt the state model electric and solar ready code, which can add spare conduits, panel space and roof provisions for new buildings. Local electrical amendments differ, as do inspection practices and utility specifications for depth, spacing, warning tape and marker placement.

We read the electrical engineer's drawings against all three layers of requirements and raise conflicts before pouring concrete. If a spare conduit is required for a future vehicle charging yard or rooftop solar array, it is installed now, while the trench is open and the cost is a fraction of what it would be later.

Duct Bank Construction Details

A typical duct bank uses schedule 40 or 80 PVC conduit set on spacers, with specified separation between power circuits and between power and communications. The bank is encased in red-dyed or plain concrete, reinforced where required, and covered with warning tape and backfill. Pull boxes, manholes and handholes are located at changes in direction and at intervals determined by pull tension and cable length.

Roads and truck courts above the bank require extra consideration. We check cover depth, concrete strength and compaction so that heavy trucks do not damage the system. Transformer pads, generator pads and switchgear pads are poured as part of the same package.

Surveying, Spacing and Proofing

We stake conduit runs from the electrical drawings and coordinate with storm sewer, water and gas lines to avoid conflicts. Conduit spacers and rebar chairs set the geometry, and the layout is surveyed before concrete placement. After the pour, each conduit is cleaned and proven with a mandrel, and then fitted with a pull line and cap.

The frost depth documented in Lakewood's design handout, 36 inches, is a reminder that cover requirements are determined by climate as well as by electrical rules, and we make sure the depths we build satisfy both.

Concrete and Excavation Managed Together

Because we schedule the excavation, forming and concrete placement as one sequence, the duct bank is built as a single operation rather than handed from excavator to conduit installer to concrete supplier. This shortens the time a trench stays open and lets the same superintendent take responsibility for alignment, cover and survey control.

Our equipment pads and foundations work gives us a direct route to transformer, generator and switchgear pads, and our yard lighting and electrical site work work extends the system to poles and cabinets.

Working Near Energized Lines

Underground electric work involves locating existing lines, protecting them during excavation and sometimes working next to energized facilities. We rely on locate tickets, potholing, insulated tools, observers and clearance procedures that comply with the utility's requirements. Duct banks that tie into live switchgear are scheduled for planned outages with lockout and tagout procedures.

Trench safety, confined-space entry into manholes, and vehicle control around open excavations are covered in a project safety plan reviewed with the owner and the electrical subcontractor. Energization dates are agreed in writing with the utility, and no one touches gear until the utility confirms the circuit is released to us.

Power in the Larger Picture

Underground power connects to nearly everything else on the site. It feeds the dock aprons and loading zones through door operators and lighting, and it supports data center buildings and data center construction with redundant paths.

It also serves utilities and power customers with their own substation yards. When the project is the first on a parcel, we plan the duct bank alongside site utilities so that trenches are shared and crossings are resolved on paper.

Plan the Power Path First

Send us the electrical one-line and the utility letter. We will lay out the duct bank, price the pads and map the order of work.

Common Questions

Who designs the duct bank, the utility or the engineer?

Both have a role. The electrical engineer designs the owner side, from the meter to the building, while the utility specifies its own transformer pad, primary conduit and metering. We coordinate the handoff point and make sure the two designs match in the field.

How many spare conduits should we install?

More than you think you need. Conduits are cheap while the trench is open and expensive after the paving goes in. A good rule is to add spares for future power, data and security circuits, and to account for state electric-ready provisions that apply to new buildings.

Can a duct bank be built before the building permit?

In some jurisdictions, under a site utility permit. This can save weeks if the electrical service is the longest-lead item, but it requires a stable design for the service entrance and the building location.

What happens if we hit an unknown line?

We stop, protect the line, identify the owner and coordinate a repair or relocation. Potholing in advance reduces the odds, and a contingency in the budget keeps a surprise from becoming a dispute.

How do you protect a duct bank under a truck court?

With adequate cover, reinforced concrete encasement where needed and compaction control over the trench. Pavement design accounts for the extra stiffness, and we place the bank away from joints and drains where possible.

Related