For many years, cable technicians have used
“air jetting” (cable blowing) to install fiber
optic cable over great distances in long-haul
applications. The process involves using
compressed air (or nitrogen gas) to propel
the cable through pipe-like structures called
Cable jetting works well in long-haul applications because the cable is installed in a relatively straight line, typically within buried cable ducts. In premise environments, cable jetting is more challenging because of bends and curves in the cable run. Also, most buildings and campuses don’t yet have the required ductwork in place.
Nonetheless, many network operators dream of the day when cable jetting can be used to more easily install fiber within premise environments. This article highlights recent advancements that promise to make these “pipe dreams” a reality.
TRADITIONAL INSTALLATION METHOD
Installing fiber optic cable within
a building or campus traditionally
involves “pulling” cable. The
process begins by sending a
pull line through a cable duct
or other available pathway. The
cable is then attached to the line
and pulled into place manually
or by mechanical means. Some
cable ducts come with pull lines
One of the problems with cable pulling is that it forces the cable to be pulled tightly against the surface of every inside curve in the cable run. This greatly increases resistance on the cable and limits the distance over which it can be pulled. The process also risks damaging the cable because more pulling force is required as the cable pull progresses. The problem is the same whether the cable is installed in metal conduit or run through wooden wall studs.
Getting Your Ducts in OrderThere are various types of ducts and conduits used in cable jetting, some of which have similar-sounding names. To avoid confusion, it is important to understand the difference between Innerducts, Microducts and Conduits.
Innerducts are designed for Air Blown Cable (ABC) applications that involve jetting relatively thick fiber optic cable. Innerducts are often placed inside larger cable pathways such as Conduits, which may hold other types of cabling. Note that innerducts have been used for cable pulling for decades. However, these older corrugated innerducts are not well suited for cable jetting, unless they are retrofitted with newer innerducts and/or microducts specifically designed for cable jetting.
Microducts are used in Air Blown Fiber (ABF) applications for jetting small diameter micro cable and “loose tube” fibers. Microducts can be installed within innerduct or purchased as a self-contained “sheathed microduct bundle” (below).
CABLE PULLING VS. JETTING
In contrast to pulling, cable jetting typically employs a pushing mechanism, such as capstans, in conjunction with compressed air to move the cable through a dedicated cable duct. Because there is little or no pulling involved there is less resistance to the cable as it is installed around curves. In some cases a blowing tip is attached to assist in the installation of the cable.
Cable Jetting Benefits
After the initial cost of ductwork and equipment (which can be amortized), fiber upgrades can result in savings of up to 90%. Cable jetting requires fewer installers and reduces the number of splices, manholes, handholes and access points required.
Cable can be jetted 4,000 feet or more between jetting locations. Typically, pulled cable can be installed over a maximum distance of only 600 feet between pulling locations.
Jetted fiber can be installed at speeds of 200 feet per minute. Typically, pulled fiber can be installed at a rate of only 100 feet per minute.
With cable jetting, fiber upgrades can be accomplished without disrupting the workplace.
ELIMINATES DARK FIBER
When installing ductwork forjetting, some microducts can be left empty to accommodate new fiber when required. This eliminates the need to install dark fiber, which can become obsolete.
BETTER CABLE PROTECTION
Cable jetting requires that fiber optic cables be installed within their own cable ducts. After jetting, the cables remain in the ducts,which affords continued protection for the fiber.
ELIMINATES ORPHANED FIBER
Cable installed by traditional methods can be difficult or impossible to remove. Old cable is typically abandoned in place, which takes up valuable space in cable pathways. In contrast, fiber installed by cable jetting is easy to remove by using the same jetting process that installed it. The removal process is relatively gentle, so the extracted fiber can often be used in other applications.
Recent advances in materials and equipment are making cable jetting a viable solution for installing fiber optic cable in premise environments.
New cable lubricants are available that are made specifically for cable jetting. Some ducts have low friction materials embedded within the interior wall of the duct.
Ducts are available with special ribbing and other surface features that reduce drag by minimizingcontact between the cable and the duct.
Many of the new ducts are made of high density polyethylene (HDPE), offer low-smoke zero-halogen options, and are available with riser and/or plenum ratings.
Almost any type of fiber optic cable can be jetted. However, cables that are too stiff require more force to carry them through bends in the cable path. If cables are too flexible, the capstans pushing the cable may cause them to bunch up. To ensure success, use cables that are made for cable jetting.
THINNER OPTICAL FIBER
Optical fibers are now available that have thinner cladding, which greatly reduces the diameter of the fiber. Thinner fiber increases the number of fibers that can be installed in a given innerduct, and provides cable with more flexibility to negotiate curves and bends.
Cable Jetting ApplicationsToday, cable jetting can be used almost anywhere conventional fiber is deployed, including:
• Corporate Campuses
• Data Centers
• Manufacturing Facilities
• Government Facilities
• Sports Arenas
• Production/Broadcast Studios
Some cables designed for cable jetting have a rough or textured jacket that enables jetted air to better “grip” and propel the cable.
COMPACT JETTING EQUIPMENT
Compared to traditional jetting equipment, new equipment designed for premise applications is easier to use, less expensive and less intrusive in the workplace.
LET US KNOW WHAT YOU THINK
Not everyone agrees that cable jetting is a better alternative to cable pulling for premise applications. Detractors point out that cable jetting standards haven’t yet been fully developed, the jetting process is relatively complex, and there are significant upfront costs for jetting equipment and ductwork. In reply, advocates of cable jetting say these costs can be amortized, and that the future savings afforded by cable jetting are far greater than the upfront costs.
What’s your opinion?
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