Major Cable Components for Transmitting Data

Written by Julianus Yu

Here we describe the components involved in transmiting data from the work area to the wiring closet, the component are horizontal cable, backbone cable, and patch cable.

Horizontal cables run between a cross-connect panel in a wiring closet and a wall jack. Backbone cables run between wiring closets and the main cross-connect point of a building (usually referred to as the equipment room).

Horizontal runs are most often implemented with 100-ohm, four-pair, unshielded twisted-pair (UTP), solid-conductor cables, as specified in the ANSI/TIA/EIA-568 Standard for commercial buildings. The Standard also provides for horizontal cabling to be implemented using 62.5/125-micron or 50/125-micron multimode optical fiber. The Standard recognizes 150- ohm shielded twisted-pair (STP) cable, but does not recommend it for new installations, and it is expected to be removed from the next revision of the Standard. Coaxial cable is not a recognized horizontal cable type for voice or data installations. Backbone cables can be implemented using 100-ohm UTP, 62.5/125-micron or 50/125- micron multimode optical fiber, or 8.3/125-micron single-mode optical cable. Neither 150- ohm STP nor coaxial cable is allowed. Optical fiber is the preferred installation medium because of distance limitations associated with copper wiring. Another plus for running a fiber backbone is that glass does not conduct electricity and is thus not subject to electromagnetic interference (EMI) like copper is.

Modular patch cables (patch cords) are used to provide the connection between field-terminated horizontal cables and network-connectivity devices such as switches and hubs and connections between the wall-plate jack and network devices such as computers.  Whereas horizontal UTP cables contain solid conductors, patch cords are made with stranded conductors because they are more flexible. The flexibility allows them to withstand the abuse of frequent flexing and reconnecting. Although you could build your own fieldterminated patch cords, we strongly recommend against it. The manufacture of patch cords is very exacting, and even under controlled factory conditions it is difficult to achieve and guarantee consistent transmission performance.

At first glance, modular patch cords may seem like a no-brainer, but they may actually be the most crucial component to accurately specify. When specifying patch cables, you may also require that your patch cords be tested to ensure that they meet the proper transmission performance standards for their category.

Professional cable installers and cable-plant designers are called upon to interpret and/or draft cable specifications to fulfill businesses’ structured-cabling requirements. We should now have adequate information to specify the proper cable for our installation.

First, you must know the installation environment and what the applicable NEC and local fire-code requirements will allow regarding the cables’ flame ratings. Your second decision on cabling must be on media type. The large majority of new installations use fiber-optic cable in the backbone and UTP cable for the horizontal. Make sure that you specify that patch cords be rated in the same category as, or higher than, the horizontal cable.