Fiber Splicing & Installation
Fiber Pulling
TLDR
Fiber pulling installs cable through conduit with a winch and rope, governed by pulling tension, bend radius, and lubrication. Strilla Communications pulls with a swivel and grip matched to the cable, sheaves at every direction change, and a monitored tension limit, so the cable arrives inside the manufacturer rating rather than past it and damaged.
Tension Is the Whole Job
Every fiber cable carries a maximum tensile load for installation and a lower one for long term residence in the duct. Exceed the installation rating and you can stretch the strength members, stress the glass, and produce attenuation that no amount of splicing recovers. The damage often does not appear on a 1310 nm trace and does appear at 1550 nm.
Friction is what builds tension, and it accumulates. Every foot of duct adds some, and every bend multiplies what came before it. That multiplying effect is why a pull with several direction changes can exceed the rating at a distance where a straight pull would not come close.
We monitor tension during the pull rather than inferring it afterward. A rising reading means something has changed in the duct, and the correct response is to stop and find out what, not to add power. A breakaway rated to the cable is set so the rope fails before the cable does.
Rigging: Swivels, Grips, Sheaves, and Blocks
The pulling grip has to transfer load into the cable strength members, not into the jacket. A grip that is undersized, misapplied, or reused past its life slips or bunches the jacket, and a jacket pulled off its core in the middle of a duct run is not a recoverable situation.
A swivel sits between the rope and the grip so rope torsion does not transfer into the cable. Rope under load unwinds, and without a swivel that rotation twists the cable inside the duct, adding friction and putting torsion into buffer tubes that were never designed to take it.
At the entry and at every direction change, sheaves and quadrant blocks keep the cable on a radius instead of dragging it across a duct lip or a vault wall. A cable bent past its rating for even a moment during a pull can carry that damage permanently, and the mark on the jacket is often the only evidence at the surface.
Lubrication and Duct Friction
Lubricant is not optional on a pull of any length. It reduces the coefficient of friction between jacket and duct wall, which lowers tension along the whole run, and the effect compounds through every bend behind the cable head.
The lubricant has to be compatible with both the jacket material and the duct material, and it has to be applied continuously as the cable enters rather than dumped at the start. A front loaded application coats the first section and leaves the rest of the pull running dry at exactly the point tension is highest.
Duct condition changes the friction picture too. Sand and grit act as an abrasive under a moving jacket, and a duct with a joint offset or a partially collapsed section produces a hard spot the tension reading will show. Proofing the duct before a pull is as valuable here as it is before a blow.
Backfeeding, Figure Eight, and Long Pulls in Sections
A long route does not have to become a long pull. The cable can be pulled from an intermediate access point in one direction, then the remaining length figure eighted at that access point and pulled in the other direction, so the whole route is placed as one continuous cable with no added splice.
Figure eighting keeps twist out of the cable while it is on the ground between pulls. Coiling would accumulate a turn per loop and put every one of those turns into the duct on the second pull. The figure eight pattern pays back out neutral, which is why it is worth the ground space it takes.
Choosing where to break a pull is a route decision made with the vault and handhole layout in hand. We look at bend count between structures, available working space, traffic exposure at each access point, and the reel length actually delivered, then set the pull plan before anything is rigged.
Pulling Into Occupied Duct
Adding cable to a duct that already carries one is routine and it deserves more care than an empty duct. Clearance is reduced, friction is higher, and there is a live cable in there that belongs to someone, sometimes to you.
The risk is a wrap. A new cable can spiral around an existing one during the pull, and once that happens tension climbs sharply and both cables are at risk. Correct rope setup, a swivel, generous lubrication, and steady controlled speed reduce it, and a tension reading that climbs without explanation is a reason to stop.
Where an existing cable is in service, we treat the pull as work on live plant: confirm what is in the duct before starting, coordinate with your NOC on the window, and stop on any anomaly rather than finishing the run and hoping. An outage caused during a routine placement is more expensive than the delay of stopping to check.
What Happens at Each Vault and Handhole During a Pull?
Every structure along a pull is a place where the cable changes direction, can be damaged, or can be stored. At an intermediate handhole the cable has to be guided from one duct entry to the next on a radius, not dragged across the concrete edge or the lip of the duct. Quadrant blocks or a guide setup at that structure keep it there.
Someone should be watching each intermediate structure the cable passes through on a long pull. They see a cable riding against an edge, a duct entry starting to pull out of its knockout, or lubricant running dry, and they can stop the pull by radio before the damage is done. A pull run blind through three handholes relies on luck.
When the cable reaches a structure where it will be stored or spliced, the slack is pulled out and coiled before the next section starts. That length is measured, recorded, and secured off the floor so it is still there, undamaged, when the splice crew arrives.
Pulling Through Bored Conduit
Much of the conduit we pull into was installed by directional drill, and the bore determines how the pull goes. A bore profile with gentle curves gives an easy pull. A bore that had to steer hard around a conflict leaves a tighter bend in the conduit, and that bend adds friction to every cable pulled through it afterward.
Pull line is usually placed with the conduit during pullback, often as a measuring tape style line marked in footage. That line is used to pull a rope or the cable itself, and its footage markings give a quick check on conduit length against the design before any cable is committed.
Because we drill and place cable, the bore logs and the pull plan come from the same company. If a bore had a tight section, the pull crew knows about it before rigging and can plan a shorter section or extra lubrication through it, rather than discovering it on the tension readout.
Key takeaways
- Pulling tension builds with every foot of conduit and multiplies at every bend, so pull sections are planned around bend count as well as length.
- A swivel between the rope and the pulling grip keeps rope rotation from twisting the fiber cable inside the duct.
- Lubricant has to be applied continuously as the cable enters, because tension is highest at the end of the pull, not the start.
- Cable overtensioned during a pull can pass a 1310 nm test and still show damage at 1550 nm.
Key terms
- Pulling tension
- The tensile load placed on a cable while it is drawn through conduit. Every fiber cable has a maximum installation rating from the manufacturer, and exceeding it can stretch strength members and stress the glass, causing permanent attenuation.
- Breakaway swivel
- A rigging link between the pulling rope and the cable grip that rotates freely to stop twist and is built to separate at a set load. It is chosen to fail below the cable's installation rating, so the rigging gives way before the cable is damaged.
- Pulling grip
- A woven or mechanical fitting that attaches the pulling rope to the cable. A correct grip transfers load into the cable's strength members rather than the outer jacket, so the jacket does not slip or strip off the core during the pull.
- Quadrant block
- A curved guide made of rollers that holds cable on a controlled radius where it changes direction, such as at a vault entry or a duct turn. It keeps the cable from bending past its rating or dragging across a hard edge under load.
- Pull line
- A rope or flat tape left inside a conduit so cable can be pulled through later. Lines placed during directional drill pullback are often marked in footage, which gives a quick check on conduit length before cable placement begins.
| Component | Purpose | What goes wrong without it |
|---|---|---|
| Pulling grip | Transfers load into the strength members | Jacket slips or strips off the core |
| Swivel | Lets rope rotate without twisting the cable | Torsion in buffer tubes and higher friction |
| Breakaway | Separates below the cable rating | Cable is overtensioned before anyone notices |
| Entry sheave | Holds radius where cable enters the duct | Cable bends sharply over the duct lip |
| Quadrant blocks | Hold radius at vaults and direction changes | Bend damage and jacket wear at edges |
| Lubricant | Lowers friction along the whole run | Tension climbs fast toward the end of the pull |
| Tension readout | Shows load live during the pull | Damage is discovered only at testing |
What this means for your project
Cable damaged during a pull is one of the most expensive problems on a fiber project because it is often invisible until testing. A span that fails at 1550 nm after the splices are made may need a section replaced, a new splice point added, and closures re-entered. Planned pull sections, correct rigging, and live tension monitoring are how that risk is kept off your schedule.
Pull planning also affects cost directly. Breaking a long route into sections at the right structures, and using figure eight staging to keep the cable continuous, avoids splice points that would otherwise add material, labor, and loss. Those choices are made from the handhole layout and the bore logs before rigging begins.
For documentation, expect placed footage reconciled against reel footage, slack lengths at each structure, and any conduit condition issues found during the work. If an existing cable shares the duct, the record should also show the coordination with your operations team, which protects both parties if a question comes up later.
Related reading
- Fiber blowing and jettingLow tension placement for long runs in clean duct and microduct.
- Pullback operationsHow conduit and pull line are installed during directional drilling.
- Handhole placementThe access structures that set where pull sections break.
- Conduit proofing and verificationConfirming conduit is clear before cable is pulled.
- Handholes and vaults in fiber networksHow access structures shape placement, splicing, and repair.
- Fusion splicingJoining the cable sections once placement is complete.
What's Included
- Pull planning from the vault and handhole layout, bend count, and delivered reel lengths.
- Duct proofing and cleaning before rigging where the duct condition is unknown.
- Pulling grip and swivel selected and applied for the specific cable construction.
- Sheaves and quadrant blocks at the entry and at every direction change.
- Continuous lubricant application compatible with the jacket and duct materials.
- Monitored pulling tension with a breakaway rated below the cable installation limit.
- Backfeed and figure eight staging to place long routes without added splice points.
- Slack measured and stored at each structure, with duct entries sealed after placement.
Our Process
- 01
Pull Planning
Access points, bend counts, reel lengths, and duct occupancy are reviewed to set where each pull starts, where it breaks, and which direction it runs. Pull sections are sized so calculated tension stays comfortably inside the cable rating rather than approaching it.
- 02
Rigging and Setup
The rope is placed, the grip and swivel are fitted to the cable, sheaves and blocks are set at the entry and every direction change, and the winch is anchored. Traffic control goes up at any structure sitting in a travel way before the lids come off.
- 03
The Pull
Cable is fed with lubricant applied continuously at the entry while tension is monitored throughout. Speed is kept steady, communication runs between the reel end and the winch end, and a rising tension reading stops the pull for diagnosis rather than triggering more power.
- 04
Slack, Storage, and Sealing
At each structure the cable is measured out for slack, racked or coiled at an acceptable radius, and secured off the floor. Duct entries are sealed, unused ducts are plugged, and placed footage is reconciled against reel footage before the location is closed.
Capability Overview
| Method | Winch and rope pulling with monitored tension and rated breakaway |
|---|---|
| Rigging | Cable specific pulling grip, swivel, entry sheave, quadrant blocks at direction changes |
| Tension control | Held inside the cable manufacturer maximum installation tensile rating |
| Bend radius | Held above the manufacturer dynamic radius under load at every guide point |
| Lubrication | Applied continuously at the entry, matched to jacket and duct material |
| Long route technique | Backfeed and figure eight staging at intermediate access points |
Frequently Asked Questions
- How do you keep from overtensioning the cable?
- Pull sections are planned from bend count and length so calculated tension stays inside the cable installation rating, then tension is monitored live during the pull with a breakaway rated below that limit. Lubricant is applied continuously, sheaves keep the cable on radius at every direction change, and a tension reading that climbs without explanation stops the pull for diagnosis instead of prompting more winch power.
- Why does a swivel matter on a fiber pull?
- Rope under load unwinds, and that rotation travels straight into the cable if nothing separates them. Torsion in the cable adds friction against the duct wall, twists buffer tubes that were not designed for it, and can damage fiber inside the tubes. A swivel between the rope and the grip lets the rope rotate freely while the cable stays neutral, which is why it is standard rigging on every pull.
- Can you pull a new cable into a duct that already has one in service?
- Yes, with additional precautions. We confirm what is in the duct, coordinate the window with your NOC where the existing cable is live, use generous lubrication and a steady controlled pull speed to reduce the chance of the new cable wrapping the existing one, and stop on any unexplained tension rise. Clearance is tighter and friction is higher in occupied duct, so pull sections are planned shorter.
- Do you pull or blow, and who decides?
- Duct condition and route geometry decide, and we bring the recommendation to you before mobilizing. Long, clean, correctly sized duct suits jetting, which places continuous runs at low tension and removes splice points. Short sections, occupied duct, vault transitions, and runs with an existing pull line are pulled. We are equipped for both, so the method follows the route rather than the equipment on hand.
- What pulling tension do you work to?
- The limit comes from the cable manufacturer's maximum installation tensile rating and from your project specification, whichever is lower. We plan pull sections so calculated tension stays well inside that limit, set a breakaway rated below it, and monitor tension live during the pull. If the reading climbs toward the limit without explanation, the pull stops for diagnosis. The exact figure depends on the cable construction you are placing.
- Does the conduit need a pull line before you arrive?
- It helps, but it is not required. Conduit installed by directional drill or trench usually has a pull line placed with it, and that saves a step. Where no line exists, we place one by rodding or by blowing a line through, which also tells us whether the conduit is clear. Either way, we proof questionable conduit before rigging so a hidden obstruction does not show up mid pull.
- Can you pull fiber through conduit another contractor installed?
- Yes. We pull into conduit regardless of who placed it, and we treat its condition as unknown until it is verified. That means checking the pull line, proofing where records are missing, and reviewing any bore logs or as builts available. If the conduit has a crushed section or a coupling that has pulled apart, we report it with its location so it can be repaired before cable goes in.
Related Services
- Conduit InstallationHDPE duct, innerduct, and microduct placed by bore, trench, or plow, proofed with a mandrel, and made locatable with tracer wire and marker tape.
- Fiber BlowingFiber blowing and jetting into HDPE duct and microduct across Florida. Duct proofing, low tension placement, and continuous runs with fewer splice points.
- Pullback OperationsControlled pullback of HDPE conduit, multi-duct, and cable on Florida bores. Monitored tension, swab passes, and proofing before the pits are closed.
- Handhole PlacementHandhole placement planned against pull tension, splice points and right of way limits, set to grade and load rated for the location.
- Conduit VerificationConduit verification in Central Florida: mandrel proofing, rodding, camera inspection, obstruction location, and a pass record before fiber goes in.
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