The following contains information on the placement of fiber optic cables in various indoor and outdoor environments. In general, fiber optic cable can be installed with many of the same techniques used with conventional copper cables. Basic guidelines that can be applied to any type of cable installation are as follows:
Conduct a thorough site survey prior to cable placement.
Develop a cable pulling plan.
Follow proper procedures.
Do not exceed cable minimum bend radius.
Do not exceed cable maximum recommended load.
Document the installation.
Conduct a Site Survey
The purpose of a site survey is to recognize circumstances or locations in need of special attention. For example, physical hazards such as high temperatures or operating machinery should be noted and the cable route planned accordingly. If the fiber optic cable has metallic components, it should be kept clear of power cables. Additionally, building code regulations, like the National Electric Code (NEC)** must be considered. If there are questions regarding local building codes or regulations, they should be addressed to the authority having jurisdiction, such as the fire marshal or city building inspector.
Develop a Cable Pulling Plan
A cable pulling plan should communicate the considerations noted during the site survey to the installation team. This includes the logistics of cable let-off/pulling equipment, the location of intermediate access points, splice locations and the specific responsibilities of each member of the installation team.
Follow Proper Procedures
Because fibers are sensitive to moisture, the cable end should be covered with an end cap, heavy tape or equivalent at all times. The let-off reel must never be left unattended during a pull because excess or difficult pulls, center-pull or backfeeding techniques may be employed.
Do Not Exceed Cable Minimum Bend Radius
Every Belden® cable has an installation minimum bend radius value. During cable placement it is important that the cable not be bent to a smaller radius. After the cable has been installed, and the pulling tension removed, the cable may be bent to a radius no smaller than the long term application bend radius specification.
The minimum bend radii values still apply if the cable is bent more than 90 degrees. It is permissible for fiber optic cable to be wrapped or coiled as long as the minimum bend radius constraints are not violated.
Do Not Exceed Cable Maximum Recommended Load
While fiber optic cables are typically stronger than copper cables, it is still important that the cable maximum pulling tension not be exceeded during any phase of cable installation. In general, most cables designed for outdoor use have a strength rating of at least 600 lbs. Belden fiber optic cables also have a maximum recommended load value for long term application. After cable placement is complete the residual tension on the cable should be less than this value. For vertical installations, it is recommended that the cable be clamped at frequent intervals to prevent the cable weight from exceeding the maximum recommended long term load. The clamping intervals should be sufficient to prevent cable movement as well as to provide weight support.
Leave Extra Cable
A common practice is to leave extra cable at the beginning and at the end of the cable run. Also, extra cable should be placed at strategic points such as junction boxes, splice cases and cable vaults. Extra cable is useful should cable repair or mid-span entry be required.
Document the Installation
Good record keeping is essential. This will help to ensure that the cable plant is installed correctly and that future trouble shooting and upgrading will be simplified. All Belden fiber optic cables have a unique lot number shown on the shipping spool. It is important that this number be recorded. Cable pre- and post- installation test data should be recorded in an orderly and logical fashion.
In order to effectively pull cable without damaging the fiber, it is necessary to identify the strength material and fiber location within the cable. Then, use the method of attachment that pulls most directly on the strength material—without stressing the fiber.
As a general rule, it is best to install cable prior to connector attachment. After connectors have been attached, it becomes more difficult to protect the fiber from inadvertent stress. If a pull is to be made entirely in one direction, connectors may be pre-installed on one end, leaving the other end for pulling.
If the cable must be installed with connectors attached, every practical means must be taken to protect the connectorized end from damage or stress. Cushioned enclosures should be used to protect connectors during pulling.
The leading end of the cable should be sealed to prevent intrusion of water or other foreign material while pulling.
Bi-directional pulls are possible by laying the cable into large “figure-8”-shaped loops on the ground, from where it can feed from both ends.
For ease of cable installation, the area of the cable divided by the area of the duct or conduit should be less than 53% per a single cable. Permissible area to be occupied for 2 cables is 31%, for 3 or more cables it is 40%.
Direct Attachment: Strength member is tied directly to the pulling fixture. The cable end must be sealed to prevent intrusion of moisture while pulling.
With direct attachment, cable strength material is tied directly to the pulling fixture. Conventional cable tools may be used. Loose fiberglass threads are not suitable for direct attachment because they may break if knotted. Fiberglass epoxy rods are too rigid to tie, but may be secured to the pulling fixture by using tight clamping plates or screws.
Indirect Attachment: Pulling forces are distributed over the outer cable structure.
With indirect attachment, pulling forces are distributed over the outer portion of the cable structure. If cable strength materials are located directly beneath the jacket, this method will produce the least amount of stress on the fiber.
A popular type of pulling fixture for indirect attachment is the “Chinese Basket” or “Kellems Grip”.* The Kellems Grip is usually reliable for cables of 1/4″ diameter or more. Large pulling forces are possible with a Kellems Grip if the grip’s diameter and length are properly matched to cable characteristics.
A Kellem Grip should spread pulling forces over a 1-1/2 to 3-foot length of cable. For small cables, pre-stretching and taping the Kellems Grip to the cable helps to assure even pulling.
Many lubricants are available for lowering friction forces. These include greases, waxes, clay slurries and water-based gels. Fiber optic jacket materials are compatible with most of these. For new conduit, lubrication of the conduit before pulling is suggested—particularly if there are several bends.
Air Plenums, Trays, Raceways
Installation procedures for open placement of fiber optic cables are the same as for electrical cables. Care should be taken to avoid sudden, excessive force so as not to violate tensile load and radius limits. Sharp bending and scraping at entrances and covers should be avoided.
For indoor applications, NEC**-rated OFNR (riser) and OFNP (plenum) should be used to satisfy building code regulations. It is always recommended to check local authorities prior to cable installation.
Belden outdoor cables may be buried directly in the ground. Environmental hazards include freezing water, crushing forces from rocky soil, ground disruption from construction, and rodents. Burying the cable 36 to 48 inches deep may help prevent most of these hazards.
Direct plow-in installation requires a cable capable of withstanding uneven pulling forces. Loose tube cables are best suited for these types of installations.
Double jacketing, gel filling, metal sheathing and armoring are used as water barriers.
Use of double jacketed armored cables can sometimes be avoided by burying polyethylene pipe to form a simple conduit. The pipe makes a smooth passageway and may be curved to allow easy access at manholes and other pull points. Cables may be subsequently replaced without digging.
All Belden Loose tube cables are compatible with helical lashing.
Aerial lashing of a fiber optic cable.
It is frequently required to store cables prior to installation. Temperature ranges for cable storage are listed in the corresponding catalog pages. It is recommended that cable ends be sealed to prevent intrusion of moisture.
Polyethylene pipe can be used as a simple conduit. This allows use of less expensive cables in direct burial applications.
Harvey Hubbell Trademark.
** Trademark of National Fire Protection Association, Quincy, MA.
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