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What do relay racks, cabinets, bridle rings, D-rings, J-hooks, plywood backboards, cable trays, conduits, slots, and sleeves have in common? They are all supporting structures that help you install wire, cable, connecting hardware, and associated apparatus. Why are they important? Because proper design of these components leads to successful installations and allows for future additions or rearrangements. Failure to adhere to such requirements may cost you hours or even days of delay as well as additional work.
When planning and installing this infrastructure, make sure you review American National Standards Institute (ANSI), Telecommunications Industry Association (TIA), and Electronic Industries Alliance (EIA) Standards 568-A, 569-A, 606, and 607. The key to a smooth installation is knowing the function of each piece of support equipment.
Telecommunications closets and equipment rooms. There are two types of spaces where the termination of cabling permits cross-connection and interconnec tion: equipment rooms and telecommunications closets. These two spaces share some of the same basic purposes. They both support the installation of cables, connecting hardware, cross-connects, and electronic equipment.
Equipment rooms are designed to house large pieces of equipment such as telephone cabinets, mainframe computers, uninterruptible power supplies, and/or video head-end equipment. The floor loading of equipment rooms must be rated higher than for telecommunications closets because of the anticipated high concentration of equipment in a confined space. The heating, ventilation, and air conditioning requirements for these spaces are also greater.
Telecommunications closets are designed for only limited equipment and floor loading. They may house splice cases, termination hardware, and relay racks. You can also find small items, such as hubs, multiplexers, and key telephone systems in telecommunications closets.
At least one telecommunications closet or equipment room serves every building, and each building should have a minimum of one telecommunications closet per floor. The types of cabling facilities you may find in a telecommunications closet include:
• Horizontal cables and their connecting hardware;
• Backbone cables and their connecting hardware;
• Building entrance cables and their connecting hardware;
• Telecommunications equipment;
• Data processing equipment;
• Public network equipment;
• Video head-end equipment;
• Paging systems; and
• Intelligent building systems.
You can find cross-connects between horizontal and backbone systems in telecommunications closets. Work area outlets must be cabled to the connecting hardware in telecommunications closets, thereby providing connection between them and the backbone system. You should also terminate horizontal cabling in a telecommunications closet on the same floor as the area you plan to serve.
According to the ruling standards, telecommunications closets should have three-quarter in. plywood backboards installed on at least two walls of the closet. You should paint the backboard with two coats of nonconductive, fire-retardant paint of a light color. The plywood provides a space for wall-mounting connecting hardware. You should mount a 300 mm (12 in.)-wide cable tray or ladder rack above and on the same wall(s) as the backboard.
The telecommunications designer''s documents will indicate the size, location, quantity, and nomenclature of the equipment you''re installing in the closet, along with a routing diagram of the cables that pass through it. They will also show the location of the pathways entering or leaving the space and who is responsible for installing them.
Always maintain appropriate clearances around all pieces of equipment. In the absence of a specified distance, plan for a minimum of 1m (3.3 ft) work and aisle space. If you''re not given a telecommunications closet layout, prepare one. You can find details for laying out a telecommunications closet in the most current edition of the BICSI "Telecommunications Distribution Methods Manual."
D-Rings. D-rings support small bundles of cables as they route from one termination point on the plywood backboard to another. However, do not substitute them for a cable tray.
D-rings are available in many sizes, shapes, materials, and colors. Traditionally, D-rings come in metal (aluminum) in the shape of the letter D. However, plastic versions are also available. Used to provide support and management primarily where cross-connect jumpers turn at a 90 degree angle, a half-D-ring is available in both metal and plastic.
An alternate to the half-D-ring is the "mushroom." This plastic piece contains a centermounted screw for attachment to plywood backboards. It is also available with threaded bolts for installation on equipment racks.
Ground wires. Ground wires and bonding conductors play an important role in ensuring a safe and reliable building communications system. You should install ground wires and a ground bus soas not to obstruct cable trays, cables, or terminating equipment. Always install ground wires and bonding wires in the straightest and shortest route between the origination and termination point. A sharp bend may interfere with the effectiveness of the grounding system, since it will modify the characteristics of the grounding path.
Floor-mounted relay racks. Relay racks are metal frames equipped with a large number of vertically arranged, closely spaced, mounting holes. These racks support all of the equipment housed within the telecommunications closet. These racks are typically 1.83 m (6 ft) or 2.1 m (7 ft) in height. Custom-sized racks are also available. The common widths are 19 in. and 23 in. For building telecommunications systems, most installations require the 483 mm (19 in) wide by 2.1 m (7 ft) high racks. Always use double-sided racks, with mounting holes on the front and rear, when installing equipment to meet ANSI/TIA/EIA-568-A standards.
Make sure racks are accessible from the front and rear. A rack lineup (consisting of two or more racks) will require accessibility on one side of the line up for walk space. This will facilitate the installation of cable management devices used to support the cables as they route to the rear of the patch panels for termination. Note: Refer to EIA-310C for hole spacing requirements for racks.
Racks are available in two common depths: 100 mm (4 in) and 152 mm (6 in). Depending on the requirements for an installation, you may need deeper racks to support a larger number of cables routed to the patch panels. These deeper racks may also offer additional physical stability when you attach several pieces of electronic equipment to the racks.
Never route cables on the rear sides of the rack using cable management accessories. Attach them to the rear of the rack''s vertical channels or in cable management channels mounted vertically on the sides of the rack.
Where relay racks are separated some distance from a wall, install cable trays from the wall to the top of the relay racks. This provides a pathway for cables to be routed to and from the relay racks. Without a cable tray, no means of support is available, and the cables may incur damage. At minimum, degradation of signal will result. Conduits do not offer sufficient cross-sectional area for large numbers of cables and are not easily attached to the tops of the racks.
Floor-mounted cabinets. In lieu of relay racks, cabinet enclosures are available to house connecting hardware. They are basically enclosed relay racks with additional specialized hardware installed. Cabinets are available with standard or specialized components. You can order most cabinets with clear-paneled doors at front and rear. The vertical mounting hole spacing on the racks inside of the cabinets is the same as for relay racks. Sometimes the designer will specify cabinets containing power strips, fans, or other electrical apparatus. Follow manufacturer''s grounding and bonding instructions.
Knockouts typically provide cable access to the cabinet. Cable trays and ladder racks provide the means of routing cables to the cabinet. Make sure cabinets fit the footprint allocated for them prior to installation. If there is a question about space, review the drawings or contact the designer for clarification.
Wall-mounted racks and cabinets. When floor space is at a premium or when other equipment is occupying all available floor space, floor-mounted relay racks and cabinets may not fit in the room. Wall-mounted racks are available in several depths, with or without easy rear access (hinged brackets). If you need to install electronic equipment on the wall-mounted rack, allow for equipment depth when ordering and installing them. For example, LAN hubs may require a depth of as much as 355 mm (14 in.) when installed on a rack. In this instance, you''d specify a rack of at least 457 mm (18 in.) in depth.
Wall-mounted racks and wall-mounted cabinets are available in various heights up to 72 in. and in widths of 21 in. and 26 in. with a depth of 6 in., 12 in., or 18 in. Wall-mounted cabinets may be either vented or unvented and can come with clear plastic or metal doors. Some manufacturers also offer cabinets featuring power strips and fans. You must use fans only when the equipment installed in the cabinets generates a significant amount of heat. Power strips should provide both overvoltage and overcurrent protection and should provide a minimum of six positions.
Always ground the cabinets using a minimum of 6 AWG, green-insulated copper wire. Install the ground wire from the special ground lug on the cabinet chassis to the ground bus bar located in the telecommunications closet.
Next month, we''ll discuss the proper techniques to use when installing datacom cable.
