In Part I of this series, I covered the basics of copper cabling for voice and data. In Part II, I covered copper cable categories, certification and ratings. Part III discussed optical fiber. All of this information now provides the foundation for us to learn about Structured Cabling Systems.
Structured Cabling refers to a set of standards governing telecommunications cable installation in commercial buildings. Fair warning: learning about structured cabling involves a lot of vocabulary and abbreviations. Learning the lingo will help you communicate with contractors and electrical designers. OK, let’s get started.
Just the Standard Stuff
The goal of structured cabling is to standardize design and construction practices for telecommunications cabling. This should provide a telecommunications support system that is maintainable and adaptable to change during the life of the facility. The over-arching standard for Commercial Building Telecommunications Cabling is ANSI/TIA/EIA-568-B. The standard lays out the acceptable topology for the building cable, acceptable cable lengths and types as well as connectors, patch cords, etc. The standard addresses several regions of cabling within the building, including:
- Equipment Room (ER) containing the Main Cross-Connect (MC),
- Backbone Cabling connecting Equipment Room to Telecom Room (TR),
- Telecom Room containing the Intermediate Cross-Connect (IC) and/or Horizontal Cross-Connect (HC),
- Horizontal Cabling connecting the Telecom Room to the Work Area (WA) and
- the Work Area (including open office areas).
Let’s take a look at each of these areas:
Equipment Room
Every building is different and not all architects are aware of (or follow) structured cabling standards, so your building may be different. But the Equipment Room would typically include entrance facilities and backbone cable distribution panels for the entire building. This is where telecom and data services enter the building and terminate. Equipment such as CSU/DSUs, network interface units (NIUs), fiber muxes, etc. might be located here. At this point, outside plant cable bringing those services into the building transition to inside cable for distribution throughout the building. This is also typically where a building electrical ground is established.
Backbone Cabling
The backbone cabling system provides interconnections between Telecom Room, Equipment Room, main terminal space, and entrance facilities. It includes backbone cables, intermediate and main cross-connects, mechanical terminations, and patch cords or jumpers used for backbone-to-backbone cross-connections. The backbone also extends between buildings in a campus environment. The backbone cabling is configured in a star topology with each Horizontal Cross-connect tied to a Main Cross-connect (possibly through an Intermediate Cross-connect). No more than one Intermediate Cross-connect may exist between a Main and any Horizontal Cross-connect. The primary cable types allowed in the backbone are 100Ω UTP (Unshielded Twisted Pair) (as we discussed in Part I) and 50/125μm or 62.5/125μm multimode fiber (as we discussed in Part III). Typically, these cables will be high capacity, consisting of hundreds of pairs of copper or dozens of pairs of fiber each. Maximum backbone cable length is 800m for UTP and 2000m for fiber.
Many smaller commercial buildings combine the Equipment Room with the Telecom Room, thus eliminating any backbone cabling.
Telecom Room
The Telecom Room (TR) is where the horizontal cable connects to the backbone cable. So, there are terminal blocks or patch panels where backbone and horizontal cables terminate, plus any jumpers or patch cables to connect the two. The Customer Premises Equipment (CPE) is typically located in the Telecom Room. CPE may include the telephone system / PBX and data network equipment including routers, firewalls, switches, etc. The backbone cable connects that equipment back to the entrance services and the horizontal cable connects it out to the work areas.
Horizontal Cabling
Horizontal cabling connects from the Telecom Room out to the Telecom Outlet (TO) in the Work Areas. Horizontal cabling is configured in a star topology so that each workstation outlet is connected directly to a Horizontal Cross-connect in the Telecom Room. 
Horizontal cabling includes the patch cables in the Telecom Room(B,C) and out at the Work Area(G), as well as up to 90m of cable (D) and the telecom outlet (F). Again, 100Ω UTP and multi-mode fiber are the primary cable types allowed here. Standards require a minimum of two outlets at each workstation, the first being 100Ω UTP and the second being either 100Ω UTP or multi-mode fiber. A Consolidation Point “CP” (E in the figure above) is allowed, but is not common. Maximum horizontal cable length is 90 meters. Always provide adequate distance between telecom cable pathways and your electrical distribution. It is OK for telecom cable to run perpendicular to an electrical cable, but not horizontal to it.
Work Area
The Telecom Outlet serves as the work area interface to the cabling system. Telecom Outlet connectors and patch cables must be the same performance category as the horizontal cable. Additional specifications exist for horizontal cabling in areas with moveable furniture and partitions. These specs allow multi-user telecommunications outlet assemblies (MUTOAs) which provide flexibility in cubical areas that require frequent reconfiguration.
The Benefits of Structure
Structured Cabling Systems are easier to maintain and easier to understand. Moves, adds and changes will be easier and less expensive over the life of the cable plant. What many people don’t realize is that a structured cable system design can substantially reduce the cost of the initial installation as well. Learn the basics of the standards and make sure that your vendor complies with them in all your cabling installations.
Is your building cable ‘structured’ or a bit random? How hard or easy is it to maintain? What have you done to move to a structured cabling system? Share your thoughts in the comments.
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