Backbone Pathways | TIA-569-B

Backbone pathways provide paths for backbone cabling between the equipment room, telecommunications rooms, main-terminal space, and entrance facility. The TIA suggests in TIA-569-B that the telecommunications rooms be stacked on top of one another from floor to floor so that cables can be routed straight up through a riser. They also recommend pathway diversity and redundancy. ANSI/TIA-568-C defines a few types of backbone pathways:

Ceiling pathways These pathways allow the cable to be run loosely through the ceiling space.

Conduit pathways Conduit pathways have the cable installed in a metallic or plastic conduit.

Tray pathways These are the same types of trays used for horizontal cabling.

KEY TERM: sleeves, slots, and cores

Sleeves are circular openings that are cut in walls, ceilings, and floors; a slot is the same but rectangular in shape. A coreis a circular hole that is cut in a floor or ceiling and is used to access the floor above or below. Cores, slots, and sleeves cut through a floor, ceiling, or wall designed as a firestopping wall must have firestopping material inserted in the hole after the cable is installed through it.

Some points to consider when designing backbone pathways include the following:

• Intercloset conduit must be 78(3) trade size (3″ or 78 mm sleeve).
• Backbone conduit must be 103(4) trade size (4″ or 103 mm sleeve).
• Firestopping material must be installed where a backbone cable penetrates a firewall (a wall designed to stop or hinder fire).
• Trays, conduits, sleeves, and slots need to penetrate at least 1″ (25 mm) into telecommunication rooms and equipment rooms.
• Backbone cables should be grounded per local code, the NEC, and ANSI/TIA-607-B.
• Backbone pathways should be dry and not susceptible to water penetration.

Warning

Devices such as cable trays, conduit, and hangers must meet requirements of the NEC with regard to their placement. For example, flexible-metal conduit is not allowed in plenum spaces except under restricted circumstances.

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.

TIA-569-B

Although the ANSI/TIA-568-C standard describes the subsystems of a structured cabling system, the TIA has published a more thorough document called TIA-569-B Commercial Building Standard for Telecommunications Pathways and Spaces. The purpose of the TIA-569-B standard is to provide a flexible and standardized support system for a structured cabling system, along with the detail necessary to design and build these facilities. The detail pertains to both single and multitenant buildings.

Note

This TIA-569-B document is especially important because network managers, architects, and even cable installers often don't give enough forethought to the spaces and infrastructure that will support structured cabling systems or data communications equipment.

Although repetitive to large degree with respect to ANSI/TIA-568-C, TIA-569-B does define and detail pathways and spaces used by a commercial cabling system. The elements defined include:

• Entrance facility
• Equipment room
• Main terminal space
• Telecommunications rooms and enclosures
• Horizontal pathways
• Backbone pathways
• Work areas
• Data centers

Warning

When planning telecommunications pathways and spaces, make sure you allow for future growth.

TIA-569-B provides some common design considerations for the entrance facility, equipment room, and telecommunications rooms with respect to construction, environmental considerations, and environmental controls:

• One of the key features of TIA-569-B is the necessity for pathway diversity and redundancy to assure continuous operation in the case of a catastrophic event.
• The door (without sill) should open outward, slide sideways, or be removable. It should be fitted with a lock and be a minimum of 36 inches (.91 meters) wide by 80 inches (2 meters) high.
• Electrical power should be supplied by a minimum of two dedicated 120V-20A nominal, nonswitched, AC-duplex electrical outlets. Each outlet should be on separate branch circuits. The equipment room may have additional electrical requirements based on the telecommunications equipment that will be supported there (such as LAN servers, hubs, PBXs, or UPS systems).
• Sufficient lighting should be provided (500 lx or 50′ candles). The light switches should be located near the entrance door.
• Grounding should be provided and used per ANSI/TIA/EIA-607 (the Commercial Building Grounding and Bonding Requirements for Telecommunications Standard) and either the NEC or local code, whichever takes precedence.
• These areas should not have false (drop) ceilings.
• Slots and sleeves that penetrate firewalls or that are used for riser cables should be firestopped per the applicable codes.
• Separation of horizontal and backbone pathways from sources of electromagnetic interference (EMI) must be maintained per NEC Article 800.154.
• Metallic raceways and conduits should be grounded.

Based on our own experiences, we recommend the following:

• Equip all telecommunications rooms, the entrance facility, and the equipment room with electrical surge suppression and a UPS (uninterruptible power supply) that will supply that area with at least 15 minutes of standby AC power in the event of a commercial power failure.
• Equip these areas with standby lighting that will last for at least an hour if the commercial power fails.
• Make sure that these areas are sufficiently separated from sources of EMI such as antennas, medical equipment, elevators, motors, and generators.
• Keep a flashlight or chargeable light in an easy-to-find place in each of these areas in case the commercial power fails and the battery-operated lights run down.

Note

For full information, consult the TIA-569-B standard, which may be purchased through Global Engineering Documents on the Web at www.global.ihs.com.

Note

The Canadian equivalent of ANSI/TIA/EIA-568-B is CSA T529.