Conduit Installation

Why the Duct Matters More Than the Cable In It

Conduit outlives everything you put in it. Fiber counts change, electronics get replaced, and routes get rebuilt, but the duct in the ground stays where you left it. Every one of those future changes is either a blow through an existing path or a new excavation, and the duct you place today decides which one your successor is buying.

That makes conduit the highest stakes decision on most builds and also the easiest one to under specify. A run placed one size too small, jointed with the wrong coupling, or left without tracer wire still passes a visual inspection on the day it goes in. The cost shows up years later, on somebody else's schedule and somebody else's budget.

The marginal cost of doing it correctly is small while the equipment is already on the route. Adding a spare duct to a bore that is being pulled anyway, or installing tracer wire properly the first time, costs a fraction of returning to the same corridor with a new permit, a mobilized crew, and another restoration obligation.

A finished conduit run has to do five things at once:

• Stay continuous, with joints that will not separate under load or come apart during a later cable installation.
• Stay clean and round through its full length, proven with a mandrel rather than assumed from the surface.
• Stay sealed at every termination so water, silt, and roots stay outside the duct.
• Stay locatable, with tracer wire that reads on an 811 ticket years after your crew leaves the corridor.
• Stay documented, with route, depth, footage, and test results in a package your engineering group can actually use.

Choosing the Duct: Size, Wall, and Inside Surface

High density polyethylene is the default for fiber duct because it arrives on long reels, bends without cracking, ignores corrosion, and can be fused into a continuous run with no joint weaker than the pipe itself. For most fiber distribution work the sizes in play run from roughly 1 inch through 2 inch, with larger diameters on backbone routes and anywhere multiple innerducts have to share one path.

Wall thickness is expressed as SDR, the ratio of outside diameter to wall thickness, so a lower SDR number means a thicker wall, more crush resistance, and more tensile capacity during pullback. SDR 11 and SDR 13.5 cover most communications work. The choice is driven by pull length, bore conditions, cover depth, and what will be driving over the route once it is backfilled.

The inside surface matters as much as the outside dimension if you intend to blow fiber. Smoothwall duct is the baseline. Ribbed and prelubricated interiors reduce friction and extend the distance a jetting head can push cable in one shot, which is the difference between a single blow and an extra intermediate access point you then have to build, permit, and maintain forever.

Color and print line are not cosmetic details. Orange identifies communications duct to the next excavator who opens that ground, and sequential footage printed on the duct gives you a measured position at every access point, which is the fastest way to convert an optical distance into a dig location during a fault.

• Duct size chosen for the cable diameter you will install plus the fill ratio your blowing or pulling method requires.
• Wall rating selected for pullback tension, crush load, and cover depth, not defaulted across an entire job.
• Smoothwall, ribbed, or prelubricated interior chosen against the planned blowing distance.
• Long coil lengths used to keep joint count low on continuous runs.
• Footage marked duct so every access point has a known position on the route.

How Deep Does Conduit Go, and Who Decides

The permitting authority decides, not the contractor and not the standard detail in your drawing set. State roads follow the Florida Department of Transportation utility accommodation requirements, county roads follow the county public works standard, and municipal streets follow the city. Each has its own minimum cover, its own placement zone inside the right of way, and its own review time.

The number itself changes with what sits above the duct. Cover under a paved travel lane is greater than cover in a grass utility strip, cover at a drainage crossing is measured from the ditch flow line rather than the top of the bank, and crossings under railroads, canals, and airport property are separate cases with their own reviewing authority. Agricultural ground and areas subject to future grading get extra depth because the surface is not permanent.

Separation from other utilities is the second half of the requirement. Horizontal and vertical clearance from gas, water, sewer, and electric is specified so a future excavator working one system does not find yours by accident. On a bore we confirm separation at the actual crossing, not on the plan sheet, by potholing the foreign utility and tracking the drill head past the exposed point.

Depth gets verified while the duct is going in, because after backfill the only honest answer is to dig. On directional bores the head is tracked and depth is logged at intervals along the shot. In open trench and plowed sections, depth is measured before backfill. Both end up in your as-built instead of in a field memory that leaves when the crew does.

• Cover requirement pulled from the governing permit for each road class along the route.
• Deeper placement under pavement, ditch bottoms, and ground subject to future grading.
• Horizontal and vertical separation from foreign utilities confirmed by potholing at crossings.
• Depth logged during placement and reported with the as-built rather than estimated afterward.

Innerduct, Microduct, and Buying Capacity Before You Need It

A single large conduit with one cable in it wastes most of what you paid to install. Innerduct subdivides that space into separate, individually usable paths so a second and third cable can go in later without disturbing the first. Rigid innerduct, fabric innerduct, and microduct bundles each accomplish this differently and belong on different jobs.

Fabric innerduct is a woven divider pulled into an existing conduit, commonly with several cells in one pull, and it is the usual way to recover capacity in a legacy duct that already carries a cable. It occupies very little of the cross section itself, which is exactly why it works in duct that is already partly occupied.

Microduct is the current default on new fiber builds. Small ducts bundled together are placed as a unit, either direct buried in a jacketed bundle or pushed into a larger host conduit, and each one carries a single blown cable. The value is that a new service area, a new customer segment, or a second operator can be added later with a jetting machine instead of an excavator and a permit.

The planning question is simple: what is the cheapest moment to add capacity to this route? It is almost always the moment the bore is already reamed and the crew is already there. We size the bore for the duct bank you may want in five years rather than the single cable you need this quarter, and we hand you a record of which duct is occupied and which is spare.

Proofing: Proving the Duct Before Fiber Goes Near It

Proofing means pulling a mandrel through the finished run to prove the duct is continuous, round, and clear for its full length. The mandrel is sized close to the duct inside diameter, so anything that reduces the bore stops it: a crushed section, an oval spot, a partially separated coupling, an intruding rock. If the mandrel passes, cable of the design size will pass.

Proofing is scheduled before the fiber crew mobilizes, and that sequence is the entire point. A blow that stalls partway down a run is an expensive way to discover a defect, because the crew is on site, the reel is cut in, and the duct now has to be located, exposed, repaired, and reproofed while a splice schedule slides behind it.

The failures proofing catches are ordinary. Duct pulled oval on a hot day by a hard pull. A coupling that separated during pullback and left a step in the path. A section flattened where a steel plate sat over a shallow trench. Silt and standing water in a run left open overnight. None of these are visible from the surface, and every one of them stops a cable.

When a run fails, the mandrel position tells you roughly where it stopped. Rodding, a duct camera, or a locate on the tracer wire narrows that to a single dig point, the section is repaired with a rated coupling rather than tape, and the run is proofed again end to end. The result goes in the closeout, both the pass and the record of what it took to get there.

• Mandrel pull on every completed run, full length, in the direction the cable will travel.
• Pull tape or mule tape left in place after proofing, with footage readable at the access points.
• Rodding or camera inspection whenever a mandrel stops short of the far end.
• Repair with a rated coupling and a full length reproof, never a partial retest of the suspect section.

Locatability: Tracer Wire, Marker Tape, and Marker Balls

HDPE duct is invisible to the electromagnetic equipment locators use. Without tracer wire your conduit cannot be found on an 811 ticket, which means the next excavator in that corridor is working blind over the top of your route. Locatability is not a finishing touch, it is the difference between a documented utility and a hidden one.

Tracer wire is installed with the duct, never added afterward. Copper clad steel with a high density polyethylene jacket is the common choice because it survives the tensile load of a bore pullback or a plow without stretching apart, and the jacket resists the abrasion of sand and shell. Wire that breaks during installation and is never tested reads exactly the same as no wire at all.

Splices are where tracer systems fail. Twisted wire and electrical tape corrode within a season in wet Florida ground. Direct bury waterproof connectors, brought up to test stations at handholes, vaults, and pedestals, keep the circuit continuous and give a locate technician somewhere to connect years after your project closed out.

Above the duct, warning tape gives an excavator a visual warning before the bucket reaches the conduit, and marker balls set at critical points (crossings, sweeps, splice locations, and route changes) allow those specific features to be found even where the wire has been damaged. We test continuity end to end and walk the route with a locator before demobilizing, so the run is proven findable rather than merely wired.

Getting the Duct in the Ground: Bore, Trench, or Plow

Placement method is chosen by what is on the surface and what is under it. Directional boring wins wherever the surface is expensive or busy: pavement, driveways, mature landscaping, canals, and anywhere a permit will not allow an open cut. Open trench wins in soft, clear ground where restoration is cheap and the run is short. Vibratory plowing wins on long, open runs with clean soil and few foreign utilities.

Most routes use all three. A single mile of build can bore two road crossings, plow the long section between them, and trench the last stretch into a cabinet pad. Because the drills and crews are our own, the bored sections run on our schedule, and the breaks between methods are planned on one schedule for the route rather than negotiated between separate subcontractors.

Florida ground adds specific constraints. Sand caves and will not hold a trench wall for long. The water table sits high through much of Volusia County and along the coast, which means saturated soil, buoyant empty duct, and trenches that fill as fast as they open. Empty HDPE floats, so duct in a wet trench is weighted or backfilled promptly, and pullbacks are planned so a duct string is not left sitting in a flooded bore.

The duct itself needs handling discipline no matter which method places it. Reels are paid off under control rather than dragged, bend radius is respected at every sweep and every entry, and pull tension is monitored and limited by a breakaway swivel so a hung pull damages a connection instead of stretching the duct into an oval nobody can blow through later.

Terminations, Sealing, and the Record You Keep

Duct ends cause more trouble open than anything that happens in the middle of a run. Every entry into a handhole, vault, cabinet, or building gets a bell end or a proper terminator so cable never rests against a cut edge, gets racked in an order that matches the route, and gets plugged or sealed whether it is occupied or spare.

Water and silt are the long term enemy in Florida. A duct sealed at both ends stays workable. A duct left open fills, and the crew that arrives in three years to blow a cable spends a day jetting mud out of it first. Simplex and duplex plugs on occupied duct and blank plugs on spares are inexpensive insurance against that outcome.

Building and cabinet entries carry sealing requirements of their own. Conduits entering a structure are sealed at the wall penetration so the duct does not become a path for water, gas, or fire into an occupied space, and the seal is selected for the structure rather than improvised from what is on the truck.

The record you receive ties the physical work back to the map: route with measured offsets, depth at intervals, duct count and size, coupling and sweep locations, footage at each access point, mandrel proofing results, and tracer wire continuity readings. It arrives in a form your GIS and your maintenance group can use, because a duct nobody can find on paper is only slightly better than one that was never placed.

What Should a Conduit Bid Request Include?

A conduit bid is only as accurate as the scope behind it. The fastest way to get comparable numbers from several contractors is to send the same decisions to all of them, so nobody is pricing their own guess about duct count, wall rating, or test requirements.

Route drawings come first, with the placement method marked by section where your engineer has already decided it. Then the duct schedule: how many ducts, what size, what wall rating, and whether innerduct or microduct goes inside. Access point locations matter just as much, because handhole spacing sets shot length, pull length, and blow distance.

Permit status changes the price and the start date. Tell bidders which permits are approved, which are in review, and which authority owns each segment, whether that is FDOT, a county, or a city. Restoration requirements belong in the package too, since sod, sidewalk, and pavement repair can rival the cost of the duct itself.

Finally, spell out how the work will be accepted. Mandrel size, tracer wire and test station requirements, marker tape, and the as-built format all belong in writing before the bid, not in a punch list after it.

• Route drawings with method by section and known crossings marked.
• Duct schedule: count, size, wall rating, and any innerduct or microduct.
• Handhole and vault locations, with structure types if they are in scope.
• Permit status and the permitting authority for each segment.
• Restoration, testing, and as-built requirements stated up front.