General Cabling Guidelines

All transition points should be kept smooth while you are pulling cable in conduit. You may keep the cable from resting on a sharp edge with the addition of a piece of conduit beyond the transition, though there are also bushings designed to fit the ends of the conduit. You can prevent the cable from scraping on rough edges or pressure against the cable by placing flexible conduit in the boxes or at interfaces.

Some cabling applications may present conditions in which the equipment configuration can cause overbending, which will damage the cable without taking precautions. You must check conduit bends, pull boxes, and joints to ensure that the bend radius is large enough. If you need to ease or sweep cable around tight corners, you can use inner-duct or flexible conduit. You need to make sure the inner radius of the fiber-optic cable bends is at least ten times the diameter of the cable and to back-feed any bent elbow fixtures before pulling them through tightly. To put it another way, never pull cable from end to end – always pull to and from an opened junction box, with the cable coiled loosely on the ground to be fed through the rest of the way.

The minimum bend radius must also be monitored for tray and rack installations, due to cable being routed around corners or through transitions. Flexible conduit should be used for protection when raceway or rack transitions expose the cable.

While intrabuilding conduit can be run through ceilings, walls, or under floors, there are limits due to the lack of flexibility in conduit systems. These systems should only be used for permanently-located workstations and when there is no wiring flexibility and low outlet density.

Because in-floor conduits are often embedded in concrete, it is difficult to move, add, or change the conduit. Conduit can be made of metallic tubing or rigid polyvinyl-chloride plastic, according to the National Electrical Code.

Your conduit run should be no longer than 100 feet with no more than two 90 degrees bends between pull points or boxes. Electronic Industries Association/Telecommunications Industry Association 569, the commercial building standard for tele-communications pathways and spaces, details many of the requirements for conduit installation and sizing, and the NEC lists appropriate conduit types.

There are several reasons to install pull boxes, including fishing the run and looping cable for the next length of conduit, though they are not used for splicing cable. Conduit installation can be made easier by placing fish tapes or pullcords, or by using innerduct, which can also protect the cable.

Sometimes, plenum runs or runs in dropped ceilings or raised floors are the easiest to install, due to easily removed panels for fast access. It is important to use plenum-rated cable in areas used for environmental air handling. So long as there is not a lot of equipment in the air space, there will be ample room to work, and the cables in these spaces should be supported in easy-maintenance trays, wireways, or racks, or at least I-hooks or bridle rings.

Cable trays and ladder racks are convenient, safe, and efficient locations for installing optical-fiber cable. While they can be installed in ceilings, below floors, or in riser shafts, there are trays designed to be aesthetically pleasing, allowing them to be placed in the line of vision. Since trays can be used for many types of cable, installation precedes pulling the fiber cable. This means that existing tray distribution systems may be used for installing new cable if the system supports the appropriate locations.

Even though a tray provides support and protection for cable, the cable is still subject to stresses, which is why optical-fiber cable should be run in trays to avoid as much tension, crushing, and bending as possible. You should inspect routes for sharp turns, snags (even from other cables), or rough surfaces. You should run the fiber cable without pulling it under or between heavier cable and multiple cables that can stress the cable.

This also goes for moving or adding cable; the cable should be secured to the tray and attached at least every three feet to avoid damage when changes are made.

You should apply the same guidelines when installing cable in vertical shafts or risers, using only cable rated OFNR, at a minimum. Optical-fiber cables for vertical applications are assigned a calculated maximum vertical rise, which is the distance the cable may be pulled vertically before they are supported, determined by the weight of the cable and its ability to resist buckling or kinking.

In order to pull cable vertically, you should use split wire mesh grips, which work like basket or finger grips to support the cable without crushing its core. The cables should then be supported by cable ties, straps, or clamps in wiring closets, and you should begin the installation from the top whenever possible, to allow the weight of the cable rather than adding more load.

Handling procedures vary from product to product, so you should abide by specific handling procedures in the manufacturer’s instructions However, some general observations can be made on the situations most often encountered in pulling and terminating this medium.

For any fiber-count cable or cable type, some of the outer jacket must be removed to expose the fibers. For simplex or duplex cables whose jackets fit within the connector, the length of jacket removed will be specified by the connector manufacturer. Typical values for outer jacket removal for these cables are 1.5 to 2 inches. Multi-fiber cables will have longer lengths of jacket removed. Outside-plant cables that will be terminated in trays may have more than six feet of jacket removed. Mark the cable with a piece of tape to show how far the jacket should be stripped.

Interconnect Cables: For simplex and duplex cables, no more than a few inches are removed from the point of termination, which can be easily done with a standard buffer or jacket strippers. For round interconnect cable jackets, round cable slitters or other tools can be used, so long as they do not damage the interior of the core.

Distribution Cables: Provided with ripcords for easier jacket removal, distribution cables may have dual ripcords for higher fiber-count unitized cables, requiring only the first few inches of the jacket to be removed. The ripcord can be exposed by removing the first four inches of jacket with a cable slitter or a hook knife, then you can grasp the cable end with one hand and use the other to pull the ripcords one at a time.

Heavy-Duty Breakout-Style Cables: All heavy-duty cables contain dual ripcords for jacket stripping and clear polyester tape wraps to maintain core symmetry and fiber protection. Once several inches of jacket have been taken off, the ripcords can be used.

Outside-Plant Cables: Outside-plant cables have ripcords and core wraps to aid in the removal of the rugged outer jacket, but use caution and don’t get the aramid strength members tangled with the ripcords.

You can cut the clear tape and ripcords can be cut back to the jacket after it has been removed to the required distance. In cables that have layers of aramid in the core – for example, interconnect and low-fiber-count distribution-style – trim the aramid to the necessary length as specified by the manufacturer. Aramid is most easily cut with utensils sold specifically for the purpose, although razor blades and scissors do work.

Central strength members must also be trimmed, with some cut back to the jacket so as to not interfere with termination, and other applications calling for the central strength member to be cut to a specific length and incorporated in termination (for example, in some breakout kits).

Central strength members that are made of fiberglass rod can be cut with almost any cutting tool, though those with aramid inners are more easily cut with aramid cutters. Unitized distribution cables contain aramid yard and jackets over the subunit, which must be cut back. This is why it may be easier to complete installation of a 6 or 12 fiber subunit at a time in order to avoid connecting the wrong fiber to the wrong termination point.

Buffer-tube cutters are designed specifically for the purposed of easy buffer-tube removal, but it can also be done with a razor blade. Score one side of the tube with the razor and bend the tube away from the score. As long as you don’t cut too deeply, the separated piece can be pulled off the end of the fiber.

There are many tools that can strip the buffer and coating off 900-micron tight-buffered fibers or the coating off loose-buffered fibers, with tight-buffered fibers being stripped in a one- or two-step process, depending on the tools you have. Taking the coating off loose-tube fibers can be done with the same tool used for the coating of tight-buffered fibers, and with some tools, the blades can be exchanged for the two functions.

The amount of buffer or coating you need to remove depends on the application and termination procedure. Many connectors will come with templates for this purpose, so be sure to check the hardware or connector manufacturer`s specific instructions for a detailed procedure.

For the removal of cable-filling gel, try Hydrasol solvent. Any gel remover used carelessly can mar the tube printing, but Hydrasol, used in moderation, will not affect the identification markings.

Fiber-optic cable installations, with some foresight and care, can be done in such a way as to secure maximum cable performance. Installation guidelines include the following:

• Never kink the cable.
• Never exceed recommended bend radiuses, during or after installation.
• Do not exceed recommended tensile loads. If you are ever concerned that you may be exceeding listed cable values or are not certain what they are, contact the manufacturer.
• Do not crush the cable; avoid impacts to it.
• Optical-fiber cable should not rest against sharp edges, and must be swept around corners.
• Monitor tensile loading during pulls, and avoid pulling long lengths in one direction.
• Plan to install extra cable protection in high-risk areas.
•  Do not exceed maximum vertical rise.
•  Secure cables in all installations. Do not let them run free over ceilings or under floors.
•  Plan all cable routes before beginning, ensuring the cable will not be unnecessarily exposed to hazards.
•  Comply with all regulatory requirements and fire codes.