Steve Hovey, Senior Vice President of Sales & Marketing
Proper Installation (Pulling) of Fiber Optic Cable
Correct installation of fiber optic cable is one of the first and most important steps to ensure that the optical fiber network performs properly. Incorrect methods can lead to reduced light passing through the fibers (high attenuation), cable stretching and cosmetic irregularities in the cable, or in the worst case broken or “dark” fibers when tested … just to name a few. Incorrect “pulling” of the cable can and will have detrimental effects on the cable’s performance. Below are some general guidelines for proper optical cable installation.
Do not pull directly on cable: One of the biggest mistakes an installer can make with fiber optic cable is pulling the cable from the outer jacket. Cable should never be pulled directly by the jacket. Most fiber optic cable contains strength members; either a central strength member (usually a fiberglass rod) or aramid yarn(sometimes referred to as “Kevlar”). Installers should always pull the cable by attaching directly to one or both of these components as they have much higher pull strength values. Using a pulling eye or pulling grip installed at the end of the fiber cable and directly connected to the strength members is a very efficient and safe method of installing fiber optic cable. These devices have the ability to swivel which prevents additional pulling tension caused by twisting of the cable.
Adhere to pull load specs: Exceeding the maximum pulling load rating should also never be done. On long runs proper lubricant compatible with the cable jacket may be used and, whenever possible, pull from the middle of the cable out to both ends. Some installers may find that using an automated electric puller is helpful in reducing the cable tension during traditional installation.
Adhere to Bend Radius specs: Always verify, and never exceed the manufacturer’s published minimum bend radius of the fiber optic cable being installed. Glass fiber is actually stronger than steel when pulled straight. Fiber can also break very easily when bent too tightly. Exceeding the minimum bend radius of a fiber optic cable can reduce its performance immediately in the short term, or it can be much subtler and cause deterioration of performance over time. Either way, not adhering to published bend radius specs can have detrimental effects on the transmission performance of the cable.
Roll fiber optic cable off the spool: Rolling, as opposed to pulling, prevents putting twists in the cable. When preparing the fiber optic cabling for a long installation, it is recommended that the cable is rolled from the spool to form a “Figure 8” on the ground. This technique puts a half twist on one side of the 8 and takes it out on the other.
Vertical Fiber Optic Cable runs for “premises” or “indoor” installations: Whenever possible, the best method of installing vertical runs is to drop the cable down rather than pulling the cable up. Supporting the fiber optic cable at frequent intervals prevents excess stress and helps keep the performance integrity intact. This type of support can be accomplished by using cable ties. When using cable ties, it is important to tighten snugly, but not too tightly, so as to not deform or damage the cable. Any excess length of the cable tie should be removed to prevent further tightening. Hook-and-loop fastener ties are preferred for fiber optic cables as they are unable to apply enough crushing force to damage the cable. All vertical cables must be secured at the top of the run.
General “premise” or “indoor” installations: Optical fiber cable can be installed directly as well as the fairly common consideration of running the cable inside innerduct. Innerduct provides
1) A good way to identify cable and
2) Protection for the cable during and after installation.
Innerduct is available with a pulling tape which allows for the cable to be easily pulled through. If further protection and crush resistance is needed, fiber optic cable with Aluminum Interlocking Armor (AIA) applied is a common solution. AIA is used in place of conduit. Benefits are not only superior protection but lower overall installation cost when compared to installing cable and conduit separately.
Plan the Installation: Proper planning can eliminate many installation problems. The detailed plan should include cable specifications, lengths, and locations, proper equipment needed as well as a detailed schedule as to when each cable is being installed among other things (safety, testing parameters, personnel, etc.). Ensure that proper cable lengths are verified (with service loops etc.) prior to cutting.
Pull, don’t push: Unless otherwise designed (see “Jetted Cable” section below), Fiber Optic Cables should be pulled and not pushed. Pushing cables can snag causing bend radius violations or in extreme cases permanent damage to the cable.
Proper training of installation personnel: Installers properly trained in the techniques of fiber optic cable installation greatly reduce potential installation issues.
Observe and adhere to manufacture’s specifications of operating temperature ranges: Violations of published temperature range parameters can result in diminished cable performance of the fiber itself and may also cause cracking or breaking of the cable jacketing.
Test for continuity and attenuation: Verifying cable performance throughout the installation process can save time, effort, and money in the long run. These cable checks should be performed prior to running the product, after the cable is run, and after splicing and connector installation. Having cable installed and then discovering performance problems can be very expensive if repair or replacement is needed.
Make cable runs and pulls as straight as possible: A good rule of thumb is that the more bends that are recognized in a fiber optic cable installation the more chances there are of cable damage and performance problems. Also, offset or “fleeting angle” pulls are not recommended as they can damage the cable. Every effort should be made to recognize and follow the straightest paths possible when installing.
Store Fiber Optic Cable on ends of both flanges: Avoid placing or storing fiber optic cable spools on their side or on the flat side of the spool flange. Cable spools left on their side can lead to the “cascading” of the cable which causes snagging, tangling, and possible fiber breakage when paying off the spool. ALWAYS store fiber optic cable upright on both flanges of the spool. This will help ensure that the fiber is deployed properly.
Follow all Building Codes: Though it should go without saying, all local and national fire and building codes must be followed. Using “firestop” methods for penetrating firewalls, riser/plenum ratings where applicable, following correct installation distance limits when using unrated cables are a few of the basics. Always check local ordinances and laws prior to fiber optic cable installations.
Cable Blowing or "Jetting" as a Fiber Optic Cable Installation Solution
What is Jetting technology?
As opposed to traditional cable installations in which cables are pulled through pathways, Jetted or Blown cable installation uses compressed air to push the cable through a tube to its intended destination. Much like a puck on an air hockey table, the compressed air not only pushes the cable but the positive air pressure greatly reduces the friction that may otherwise occur between the cable and the sides of the conduit. The cable easily “slides” through the tube.
Jetting Tests: Testing should be performed to determine the maximum push force as over pressurizing or over pushing can cause a “corkscrew” effect, twisting the cable, and potentially causing cable damage and diminished performance. Jetting equipment manufacturers should be consulted to recommend that the proper equipment is being used (jetting machine w/compressor, duct, and duct size, etc.).
Jetting paths: Consider the cable path to determine the most desirable path possible, keeping in mind that straighter is better. Maintaining proper airflow is paramount to the success of cable jetting. Any and all cable lubricants, if needed, should only be recommended or approved by the equipment and cable manufacturers.
Infrastructure Future Proofing: Duct manufacturers offer many products for the jetting market. It is important to determine not only the present need but also what the installation landscape will look like in the future. If more cables are to be jetted in similar paths and instances, installing the proper duct system upfront will save time and money down the road.
“Jettable” cable: Though many types and brands of cable can be blown or jetted, some perform better than others do. If “Jetting” performance results can be obtained, an easier decision can be made as to the best fiber optic cable to use in specific jetting installations.
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