An underground conduit system is a network of buried pipes — single runs or multi-pipe duct banks — that carries and protects electrical, fiber, and communication cables, with long-radius sweeps for turns, pull boxes and handholes for access, and spare ducts left empty for future cables. Utilities and inspectors increasingly require conduit instead of direct-burial cable, and for good reason: the pipe protects the cable for decades and turns every future upgrade into a pull instead of a dig. Here is how these systems are put together, where they are used, and how conduit placement works when the path runs under a driveway or a road.
What Is an Underground Conduit System?
A conduit system has four building blocks: the conduit itself (one pipe or a bundled duct bank), sweeps that let cable turn corners without kinking, pull boxes and handholes that break long runs into manageable pulls, and spare ducts installed empty against future needs. Get those four right and the system serves the property for fifty years.
Conduit Runs and Duct Banks
The pipe itself — typically Schedule 40 PVC in open ground, Schedule 80 or HDPE where it crosses under pavement. A single residential feeder might be one 2-inch pipe; a commercial service entrance is often a duct bank of four, six, or more conduits placed together in one trench or bore so power and communications each get a dedicated pathway.
Sweeps
Long-radius bends that carry the conduit up out of the ground at each end and around any change of direction. Cable cannot be dragged around a sharp elbow without damaging its jacket, so utility specs call for large-radius sweeps — commonly 24-inch or 36-inch radius on service work — and limit how many total degrees of bend a run can contain between access points.
Pull Boxes and Handholes
Ground-level access boxes set where runs get long or change direction. They break a pull into shorter, lower-tension segments, give crews a place to feed and lubricate cable, and leave a permanent access point for whoever services the line in twenty years. On long site-lighting or fiber routes, boxes are spaced so no single pull exceeds what the cable can safely take.
Spare Ducts
Empty conduits placed alongside the live ones while the trench or bore is already open, each with a pull string inside. A spare duct costs a fraction of the install while the ground is open — and saves the entire cost of a second dig the day the property needs fiber, a second feeder, or an EV circuit. It is the cheapest insurance in underground work.
Why Do Utilities and Inspectors Require Conduit Instead of Direct Burial?
Direct-burial cable works until something touches it — a rock settling against the jacket, a root, a rodent, or a shovel. Conduit is required more and more often because it solves three problems at once: physical protection, replaceability, and code compliance.
Protection
A buried pipe takes the abuse the soil dishes out so the cable jacket does not have to. In Upstate red clay, that matters most at rock contact points and wherever fill was compacted over the line. Under driveways and roads, Schedule 80 PVC or HDPE handles the loading that would eventually work a direct-burial cable apart. A cable inside conduit also stays dry enough that a nicked jacket is an inconvenience instead of a fault.
Future Pulls
This is the argument that wins with every utility engineer: when a cable in conduit fails or needs upsizing, the fix is to pull the old cable out and pull a new one through — no excavation, no landscape damage, no second bore. A direct-burial failure means locating the fault and digging. It is also why damaging a buried line during unrelated digging is so much costlier when there is no conduit; our post on what happens when you hit an underground utility covers that scenario in detail.
Code and Utility Specifications
The electrical code sets minimum burial depths that vary by wiring method, and conduit generally earns a shallower minimum than direct-burial cable. Beyond code, most power companies publish their own underground service specs — conduit material, diameter, sweep radius, depth, and a pull string in every duct — and the meter will not be set until the inspection passes. Detached-structure feeders permitted through the county face the same review. Building to the spec the first time is faster than arguing with it.
What Are the Most Common Uses for Underground Conduit?
Most of the conduit we place falls into five buckets — residential power feeders, site lighting, EV charging circuits, fiber and communications, and commercial duct banks.
- Power to detached garages, shops, and outbuildings. The classic residential job: a feeder from the main panel to a sub-panel in the new building, run in conduit under the yard. Our underground electric line installation service handles these runs across the Upstate.
- Site and landscape lighting. Parking-lot poles, pathway lighting, and landscape circuits all ride in conduit with handholes at each pole base, so one damaged fixture never means trenching the whole loop.
- EV chargers. A Level 2 charger at a detached garage or a bank of chargers in a commercial lot needs a dedicated circuit — and because charging loads tend to grow, this is the use case where a spare duct pays for itself fastest.
- Fiber and communications. Fiber is never direct-buried on private property work; it goes in its own duct, usually with a locate wire or toning capability. Our fiber optic installation page and our guide to fiber optic cable installation in South Carolina cover these projects end to end.
- Commercial multi-duct banks. Service entrances, campus interconnects, and utility road crossings bundle many conduits into one placement — power in one group, communications in another, spares throughout — so the site never has to be opened twice.
Why Duct Banks Beat Repeat Trenching
Opening the ground is the expensive part of underground work — the pipe inside is comparatively cheap. That is the whole logic of the duct bank: mobilize once, place every pathway the site will plausibly need, and cap the spares. On commercial sites in Greenville and across the Upstate, we routinely place power, communications, and spare ducts in a single bore or trench for less than what two separate mobilizations would cost.
How Is Conduit Installed Under Driveways and Roads?
Where a conduit route crosses a driveway, parking lot, or public road, the pavement does not have to be cut — horizontal directional boring steers the conduit underneath it. A drill rig launches from a small pit on one side, bores a guided pilot path beneath the pavement, and then pulls the conduit (or the whole duct bundle) back through the bore in one continuous piece.
Sloan Underground Construction has been in the underground business since 1965 — four generations of the same family — and runs Ditch Witch JT-520 and JT-2020 directional drills for exactly this work. The JT-520 handles tight residential crossings like a driveway or a narrow side yard; the JT-2020 takes on longer shots such as road crossings and commercial duct banks. William Sloan is on-site on jobs, and every project starts with utility locates before the drill head ever enters the ground. For a closer look at how a crossing works from setup to pull-back, read our walkthrough of how to bore under a road.
Boring also keeps the conduit at consistent depth under the crossing, which matters for inspection — a spec-depth bore under a driveway passes the same review a hand-dug trench would, without a saw cut or a patch line in the concrete.
How Should Conduit Be Sized — and How Much Spare Capacity Is Enough?
The short version of what we spec on jobs: size the conduit one trade size above the minimum the cable needs, keep the bend budget low, and place at least one spare duct any time pavement sits over the route.
Go One Size Up
Code fill limits cap how much of a conduit’s cross-section the conductors may occupy, but the practical constraint is the pull itself: a snug conduit on a long run with a couple of sweeps builds real tension on the cable. The cost difference between a 1.5-inch and a 2-inch pipe is small change against the cost of the bore; the difference at pull time — and at upgrade time years later — is large. When a homeowner tells us a shop feeder “might get a welder someday,” the answer is the bigger pipe, every time.
Respect the Bend Budget
Every degree of bend adds friction. Runs are planned to stay within a total bend allowance between access points — which is why routes are laid out with long, gentle sweeps and why a pull box goes in where the geometry gets complicated, rather than forcing one heroic pull.
Always Place the Spare
Anywhere the route passes under a driveway, a road, or finished hardscape, we recommend at least one spare duct with a pull string. The marginal cost while the bore is open is minor; re-mobilizing a drill rig to add one conduit later costs as much as the original job. On commercial work, spares in every duct bank are simply standard practice.
What Does Conduit Placement Cost Depend On?
There is no single per-foot price that covers every job honestly — placement cost moves with six variables, and two jobs of identical length can price very differently.
- Length of the run — the biggest driver, though short runs still carry mobilization minimums
- Diameter and duct count — one 2-inch conduit and a six-duct bank are different bores entirely
- Soil conditions — Upstate red clay drills predictably; rock shelves and cobble slow the bore and raise cost
- Depth and crossings — road crossings at utility-spec depth take longer than a shallow yard run
- Access points and boxes — pits, pull boxes, and handholes each add fixed cost
- Permits and traffic control — public road crossings can require encroachment permits and lane control
As an honest market range, single-conduit residential bores commonly land around $10 to $30 per foot installed, with multi-duct and commercial work priced per project — our breakdown of directional boring cost in South Carolina goes deeper on the numbers. Sloan Underground Construction serves the Upstate — Greenville, Spartanburg, Anderson, and surrounding counties — plus the Midlands and Western North Carolina. Call (864) 386-1649 for a free estimate, or start at our conduit placement page.
Frequently Asked Questions
What is the difference between conduit and direct burial cable?
Direct burial cable is rated to lie in the soil on its own, with nothing protecting it but depth. Conduit is a buried pipe — usually Schedule 40 PVC, Schedule 80 under drives and roads, or HDPE on bored crossings — that the cable is pulled through. Conduit shields the cable from rocks, roots, rodents, and shovels, and it means a failed or undersized cable can be pulled out and replaced later without digging the yard up again. That last point is why most utilities and inspectors now require it.
What size conduit do I need to run power to a detached garage or shop?
It depends on the feeder size, which depends on the loads you plan to run. As a rule of thumb from our jobs: a modest sub-panel feeder often fits a 1.5-inch or 2-inch conduit, and a 100-amp shop feeder is commonly run in 2-inch. Conduit fill limits in the electrical code cap how much of the pipe cross-section the conductors can occupy, and long runs need room to pull without damaging insulation. Your electrician sizes the wire; we typically recommend going one trade size up from the minimum so the pull is easy and an upgrade is possible later.
Can conduit be installed under a driveway or road without cutting it?
Yes — that is exactly what horizontal directional boring is for. A drill rig launches from a small pit on one side, steers a bore path beneath the pavement, and pulls the conduit back through the bore. The driveway, road, curbing, and landscaping above are never opened. Sloan Underground runs Ditch Witch JT-520 and JT-2020 drills for these crossings across the Upstate, the Midlands, and Western North Carolina.
Why do power companies require conduit for underground service?
Because the utility owns the problem when a buried service fails. Conduit protects their cable from mechanical damage and moisture, gives them a permanent pathway to pull a replacement cable through without re-trenching your yard, and standardizes their inspections. Most utility specifications for new underground service spell out the conduit material, diameter, burial depth, sweep radius, and pull-string requirements — and the trench or bore will not pass inspection without them.
How much does underground conduit placement cost?
It depends on length, conduit diameter and count, soil conditions, depth, and what the bore has to cross. In our market, a single residential conduit placed by directional bore commonly lands in the range of roughly $10 to $30 per foot, with short runs carrying minimum mobilization costs and hard rock or congested utility corridors pushing the number up. Multi-duct commercial duct banks are priced per project. Sloan Underground provides free estimates — call (864) 386-1649.
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