Horizontal Pathways | TIA-569-B

The horizontal pathways are the paths that horizontal cable takes between the wiring closet and the work area. The most common place in which horizontal cable is routed is in the space between the structural ceiling and the false (or drop) ceiling. Hanging devices such as J hooks should be secured to the structural ceiling to hold the cable. The cable should be supported at intervals not greater than 60 inches. For long runs, this interval should be varied slightly so that structural harmonics (regular physical anomalies that may coincide with transmission frequency intervals) are not created in the cable, which could affect transmission performance.

Shake, Rattle, and Roll

A company that a friend worked for was using metal racks and shelving in the equipment rooms and telecommunications rooms. The metal racks were not bolted to the floors or supported from the ceiling. During the 1989 San Francisco earthquake, these racks all collapsed forward, taking with them hubs, LAN servers, tape units, UPSs, and disk subsystems. Had the racks been secured to the wall and ceilings, some or all of the equipment would have been saved. If you live in an area prone to earthquakes, be sure to take seismic precautions.

Note

Cable installers often install cable directly on the upper portion of a false ceiling. This is a poor installation practice because cable could then also be draped across fluorescent lights, power conduits, and air-conditioning ducts. In addition, the weight of cables could collapse the false ceiling. Some local codes may not permit communications cable to be installed without conduit, hangers, trays, or some other type of pathway.

Warning

In buildings where the ceiling space is also used as part of the environmental air-handling system (i.e., as an air return), plenum-rated cable must be installed in accordance with Article 800 of the NEC.

Other common types of horizontal pathways include conduit and trays, or wireways. Trays are metal or plastic structures that the cable is laid into when it is installed. The trays can be rigid or flexible. Conduit can be metal or plastic tubing and is usually rigid but can also be flexible (in the case of fiber-optic cable, the flexible tubing is sometimes calledinner duct). Both conduit and trays are designed to keep the cable from resting on top of the false ceiling or being exposed if the ceiling is open.

Other types of horizontal pathways include the following:

• Access floor, which is found in raised-floor computer rooms. The floor tile rests on pedestals, and each tile can be removed with a special tool. Some manufacturers make cable management systems that can be used in conjunction with access floors.
• Under floor or trenches, which are in concrete floors. They are usually covered with metal and can be accessed by pulling the metal covers off.
• Perimeter pathways, which are usually made of plastic or metal and are designed to mount on walls, floors, or ceilings. A pathway contains one or more cables. Many vendors make pathway equipment 

When designing or installing horizontal pathways, keep the following considerations in mind:

• Horizontal pathways are not allowed in elevator shafts.
• Make sure that the pathways will support the weight of the cable you plan to run and that they meet seismic requirements.
• Horizontal pathways should be grounded.
• Horizontal pathways should not be routed through areas that may collect moisture.

KEY TERM: Drawstring

A drawstring is a small nylon cord inserted into a conduit when the conduit is installed; it assists with pulling cable through. Larger conduits will have multiple drawstrings.