This chapter discusses the elements of a structured wiring system and the critical standards that need to be considered. In the past, wiring systems were designed to meet the vendor’s preference and to interface with each new piece of equipment. The resulting mixtures of low-quality and specialized wiring:

• clogged conduit and installation corridors
• was unacceptable for high-speed data transfer
• was haphazardly labeled
• was subject to cross talk

In the early 1990s, the Electronic Industries Association (EIA) and the Telecommunications Industries Association (TIA) collaborated to develop standards for a structured wiring system that would allow users to choose a complete solution for wiring phones, workstations, PCs and LANs throughout a building, campus, network, or company. A structured wiring system includes both the overarching plan for connectivity, and the standards for each component. Although local building codes usually do not require these standards, it is in the best interest of companies to implement them to ensure quality, reliability, connectivity and compatibility.

The benefits of a structured wiring system include:

• The owner of equipment is assured of compatibility with future applications.
• Standard layout and documentation methods enhance problem isolation and detection.
• Wiring complies with distance limits in a structured wiring system.
• Technicians can easily install a standardized system.
• Network segmentation is easier because network interfaces for LANs are provided.
• Moves, adds, and changes are easier.

To realize these benefits, the installation must also be of high quality, and the wire terminations must be according to manufactures’ standards. EIA/TIA developed 5 wiring standards:

A structured wiring system serving a multi-building campus contains the following elements:

• Equipment rooms (ER) – building areas intended to house telecommunications equipment; can also serve as a telecommunications closet
• Telecommunications closets (TC) – rooms in which wiring is terminated
• Backbone wiring (riser cable) – the wire that connects ERs to TCs
• Work area (WA) – the user’s workspace; telecommunications outlets (TO) are located in the work area
• Horizontal wiring – the wiring from the EC or TC to the work area
• Entrance facility (EF) – the physical structure and cable connecting the main ER to the common carrier’s facilities

The major objective is to ensure that the structured wiring system will support future broadband applications. The rule of thumb is that the greater the bandwidth, the shorter the distance the wire can support. Structured wiring standards specify an upper distance limit of 90 M for horizontal wiring (with 10 M for patch cords).

Three main variables affect the quality of a structured wiring system:

• Attenuation - the decrease in the power of a signal as a result of absorption, reflection, diffusion, scattering, deflection, or dispersion
• Impedance - the total opposition, or resistance to flow, of electrical current in a circuit
• Crosstalk - the amount of coupling between adjacent wiring pairs; highly dependent on good installation practice and quality of twist

All are functions of wire gauge, capacitance and the quality of connections.

There are two kinds of crosstalk that cause concern:

• Near-end crosstalk (NEXT) - from an adjacent channel; most important because the signal is at its highest level for transmission
• Far-end crosstalk (FEXT) - travels along a circuit in the same direction as the signals

Four parts of the EIA/TIA Standards must be considered in structured wiring systems:

• Wiring
• Pathways
• Grounding and bonding
• Administration

Wire is installed in a star configuration with horizontal wiring extending from the work area to the TC or ER with no splices or bridged tap. Wire is specified in levels and categories (level 1-2, followed by categories 3-5). Most companies install:

• One or more category 3 wire (for voice), plus;
• At least one category 5 wire (for data) – these 2 wires are minimum configuration
• Four-pair wire used to accommodate future higher speed data requirements

If bandwidth needs exceed 100-155 Mb/s, use fiber-optic cable, shielded twisted pair or coax.

Shielding is a metallic braid or layer of foil surrounding all or some of the conductors in the cable. The purpose of the shield is to reduce electromagnetic interference (EMI) by attenuating the electrical energy radiated from the cable and minimizing energy coupled from outside sources. Shielded cables include a drain wire for grounding. Shielding reduces electromagnetic interference (EMI), but it increases signal attenuation, especially at high frequencies.

UTP is adequate for balanced network equipment (receives its signal across 2 wires of a pair) since the EMI affects both wires equally. Some services are unbalanced and benefit from shielded wiring.

Shielding is often chosen for the following reasons:

• The equipment manufacturer specifies it
• It seems the most conservative approach

Shielding is sometimes avoided because:

• Shielded wiring is significantly more expensive than unshielded
• More difficult to install and terminate
• Has higher loss – sometimes 50% or more.

In the TC and the ER, two methods are available for terminating wire:

• Punch-down connectors - preferred for voice wiring
• Patch panels - preferred for data wiring

Cross-connect of category 5 wires should be avoided – use patch cords. In voice, however, jumper wire is fine – less expensive and usually used from horizontal wiring to riser cable.

Category 5 wire designed for up to 100Mb/s. Since ATM is at 155Mb/s, and gigabit Ethernet is 1000Mb/s and requires bi-directional transmission on all four pairs, manufacturers are building enhanced category 5 and TIA is considering standards for categories 6 and 7.

EIA/TIA 569 standards cover commercial building telecommunications pathways and spaces. Pathway choices are also regulated by fire and building codes. The use of plenum space for wiring requires plenum wiring, which has a Teflon (or other smokeless) sheath. The outdoor cable sheath that is brought into the building cannot exceed 50 feet unless in a conduit. Since the major cost for backbone cable installation is digging the trench, an inner duct for future fiber optic cable and extra conduit for future growth should be installed, if cost permits.

Pathways include:

• Ceiling area – above suspended ceiling; must be connected to building structure
• Floor cells – cells under the floor accessed by core drilling
• Raised flooring – built on metal framework; cable is brought up through holes in tile

• Cable trays and raceways – effective where esthetics are not as important; raceways attempt to conceal wire and blend into decor

Spaces include:

• Telecommunications Closets (TCs) – limit TCs, but keep maximum distance in mind; large enough for terminating horizontal and backbone cables; may also contain hubs, routers, and other relay-mounted equipment
• Work area – place where user equipment is installed; horizontal wiring terminates in modular jacks, usually with modular cords or sometimes modular-to-EIA adapter

TIA/EIA 606 covers administration of telecommunications wire. Wire and terminations must be numbered, labeled, color-coded, and designated in a manner that is easy to follow. Separate designations are used for backbone, grounding and horizontal paths. TIA/EIA also provides record keeping specifications.

Records that must be kept:

• Identifiers – the designations that are assigned to items such as cables, manholes, conduits, and bonding and grounding locations
• Linkages – logical connections between identifiers and their corresponding records

EIA/TIA 607 standard specifies bonding and grounding requirements in commercial buildings:

• A single grounding point called the telecommunications main grounding bus bar (TMGB) must be bonded securely to building’s metal framework and electrical power ground.
• Each TC and ER must contain a telecommunications grounding bus bar (TGB) that is connected to the TMGB over the telecommunications bonding backbone (TBB).
• The purpose of the TBB is to equalize the ground potential of the various building locations housing telecommunications equipment.

The NEC specifies fire-resistance standards for communications cables that protect people and property from fire hazards. This code addresses methods for limiting the hazards of cable-initiated fires and cable-carried fires. All telecommunications cables must meet these standards.

The application should always dictate the type of telecommunications wiring. A properly installed structured wiring system should last at least 10 years. The telecommunications wiring design must be part of the architecture in new buildings, just as the electrical wiring is. Managers may want to purchase a manufacturer’s warranty that ensures that the installation meets the manufacturer’s specifications – not just on the materials, but also on the installation itself.