Cable Placement, Pulling and Air-Blowing Installation Methods
The placement domain tests the methods that get cable into duct, air or trench: pulling, lashing, direct burial and air-blowing/jetting, plus the tension, lubrication and bend control that keep the fiber alive. Questions often ask why a pull stalled or how a long duct run should be installed.
Methods
- Direct burial: trench or plow, cable on a bed of suitable backfill, warning tape and markers; armored cable or conduit where required.
- Aerial: lash cable to messenger or install ADSS; maintain sag and NESC clearance.
- Duct pull: rod and rope the duct, attach a pulling grip and swivel, lubricate, pull steadily. Pull speed is typically kept to about 30 m/min or less.
- Air-blowing/jetting: compressed air carries the cable through the duct; water mist or a foam piston helps. It suits long, continuous duct runs and avoids high pulling tension.
Pulling mechanics
- Measure tension at the puller with a dynamometer and stay below the cable rating.
- Use a swivel so twist does not build up; use sheaves and rollers that respect the 20x OD bend radius.
- Figure-8 the cable when the pull is long or must reverse direction; use a figure-8 machine to avoid kinks.
- Use a water-based lubricant compatible with the polyethylene jacket.
Air-blowing specifics
- Duct must be clean, continuous and pressure-tested; blow a foam piston through first to prove it and remove debris.
- Air volume (CFM) matters more than static pressure; high pressure with low flow stalls.
- Jetting runs of several hundred meters are routine; longer runs need boosters, larger duct or lower cable mass.
Worked example
A 33 mm ID duct and a 12 mm OD cable: area ratio = (12/33)^2 = 0.132, or 13%. Three such cables give 3 x 0.132 = 40%, acceptable under a common 40-50% design limit but close enough that a fourth cable would overfill the duct. Confirm the fill before ordering cable, then check tension and bend radius at every vault.
Traps
- Overfilling duct or ignoring a collapsed section.
- Pulling dry or too fast, or with an incompatible lubricant.
- Sharp duct transitions and sheaves below the bend radius.
- Forgetting the pull rope for the next cable.