In the past, buildings could have several different cabling systems for different communications systems, for example; block wiring for voice, coaxial for Ethernet, multi-pair for RS232 etc. The ideal solution is to install a standard cable and connector type throughout a building, which could, with additional equipment, be used to support all, or most of the different type of systems in use. This is known as Generic Cabling.

Also, for true flexibility, it would be desirable to have this generic cabling installed and ready for use at all possible locations within a site. This would allow a department to expand or to move to another buildings with a minimum disruption and more importantly saving costs. This is commonly known as Flood Wiring. The industry standard is to provide two connections for every 3 square metres of office space.

Finally to save costs on the provision of network hubs and to allow different outlets to be used for dissimilar systems a Patch Panel is used.

These three attributes: Generic cabling, flood wiring and patch panels are the essential characteristics of a structured wiring system.

A structured cabling system consists of outlets, which provide the user with an RJ45 presentation. User outlets are usually supplied as either one or two RJ45 connectors mounted in a standard single gang face plate, or as single snap in modules, which can be fitted into floor boxes, single gang face plates (up to two modules) or dual gang face plates (up to four modules).

Each user outlet is cabled back to a Telecommunications Closet (TC) using an individual cable containing four twisted pairs, this cabling is known as the ‘horizontal cabling’. In most cases, cable which meets the Category 5e specification is used for the horizontal cabling, the cable can be either unshielded, known as UTP (Unshielded Twisted Pair) or shielded, known as STP (Shielded Twisted Pair)

The cable is connected to the back of the user outlet by means of an IDC (Insulation Displacement Connection) connector.

The maximum length of cable between the hub and any outlet must be 90 metres to comply with EIA/TIA and ISO requirements. (This is for Class D applications on category 5 cable). The standards allow a further 10 metres for connecting leads and patch leads, making a total drive distance of 100 metres. (Note that some suppliers will warrant systems with longer drive distances, depending on the protocol being used).

In a true structured cabling system, the horizontal cabling and user outlets are the same for all services, so that any outlet can be configured for voice, Ethernet, RS232, video or other service. As user requirements change, simply changing the patching configuration in the equipment room can change the service provided on the outlets. If necessary, an adapter is used in the outlet to convert it to the service being provided.

When a structured cabling system is installed, the floors are usually ‘flood wired’, with outlets being installed on a grid layout to a specified density, rather than to individual user positions. This allows for more flexibility, without having to re-cable, when changes are made to the layout of the building in the future.

At the TC, the individual 4 pair cables from the user outlets are terminated on patch panels. These patch panels usually have IDC (Insulation Displacement Connection) connectors on the rear for terminating the 4 pair cables, and provide an RJ45 presentation on the front for patching. Patch panels are usually mounted in standard 19inch racks, either wall mounted or free standing. RJ45 patch panels usually come in panels containing 16, 24 and 48 RJ45 connectors.

The hubs or switches are connected together and to the main computer or equipment room using ‘riser’ or ‘backbone’ cables, these can either be copper or optical. In most systems, optical cables are used for the data backbone cables and multi-pair copper cables are used for the voice backbone cables.

The equipment cabinets usually also contain equipment for the data network. Depending on the equipment used, the data channels may be presented in one of two different ways.

Each data channel on the equipment may be fitted with an RJ45 connector, so that channels can be patched directly to the patch panels terminating the horizontal cables. Alternatively, the equipment may be fitted with ‘Telco’ connectors; these are 25 pair connectors each of which carries several (usually 12) data channels.

The biggest user benefits of structured cabling is that it allows you to do integrated voice & data wiring and it is extremely simple to add, move or change applications and services. Typically structured cabling costs 10-15% of the entire networking cost but play the most important role in it’s uptime and performance. Keep that in mind when choosing your structured cabling system.

(The article was written by the businessgyan editorial team with inputs from Netcom.)

Issue BG7 Oct01

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