Best Practices for Copper Installation

Based on our experience installing copper cabling, we created guidelines for you to follow to ensure that your UTP cabling system will support all the applications you intend it to. These guidelines include the following:

• Following standards
• Making sure you do not exceed distance limits
• Good installation techniques

Following Standards

One of the most important elements to planning and deploying a new telecommunications infrastructure is to make sure you are following a standard. In the United States, this standard is the ANSI/TIA-568-C Commercial Building Telecommunications Cabling Standard. It may be purchased from Global Engineering Documents on the Internet atwww.global.ihs.com. We highly recommend that anyone designing a cabling infrastructure own this document.

Tip

Have you purchased or do you plan to purchase the ANSI/TIA-568-C standard? We recommend that you buy the entire TIA/EIA Telecommunications Building Wiring Standards collection on CD from Global Engineering (www.global.ihs.com). This is a terrific resource (especially from which to cut and paste sections into an RFP) and can be purchased with a subscription that lets you receive updates as they are published.

Following the ANSI/TIA-568-C standard will ensure that your cabling system is interoperable with any networking or voice applications that have been designed to work with that standard.

Standards development usually lags behind what is available on the market, as manufacturers try to advance their technology to gain market share. Getting the latest innovations incorporated into a standard is difficult because these technologies are often not tested and deployed widely enough for the standards committees to feel comfortable approving them.

Tip

If a vendor proposes a solution to you that has a vendor-specific performance spin on it, make sure it is backward-compatible with the current standards. Also ask the vendor to explain how their product will be compatible with what is still being developed by the standards workgroups.

Cable Distances

One of the most important things that the ANSI/TIA-568-C standard defines is the maximum distance that a horizontal cable should traverse. The maximum distance between the patch panel (or cross-connection, in the case of voice) and the wall plate (the horizontal portion of the cable) must not exceed 90 meters (285′). Further, the patch cord used in the telecommunications closet (patch panel to hub or cross-connection) cannot exceed 5 meters (16′), and the patch cord used on the workstation side must not exceed 5 meters (16′).

You may find that higher-quality cables will allow you to exceed this distance limit for older technologies such as 10Base-T Ethernet or 100VG-AnyLAN. However, you are not guaranteed that those horizontal cable runs that exceed 90 meters will work with future technologies designed to work with TIA/EIA standards, so it is strongly recommended that you follow the standard and not "customize" your installation.

Some tips relating to distance and the installation of copper cabling include:

• Never exceed the 90-meter maximum distance for horizontal cables.
• Horizontal cable rarely goes in a straight line from the patch panel to the wall plate. Don't forget to account for the fact that horizontal cable may be routed up through walls, around corners, and through conduit. If your horizontal cable run is 90 meters (295′) as the crow flies, it's too long.
• Account for any additional cable distance that may be required as a result of trays, hooks, and cable management.
• Leave some slack in the ceiling above the wiring rack in case re-termination is required or the patch panel must be moved; cabling professionals call this a service loop. Some professional cable installers leave as much as an extra 10′ in the ceiling bundled together or looped around a hook (as seen in Figure 1).
  
   
  Figure 1: Leaving some cable slack in the ceiling

Wiring Patterns

The ANSI/TIA-568-C standard recommends one of two wiring patterns for modular jacks and plugs: T568-A and T568-B. The only difference between these wiring patterns is that pin assignments for pairs 2 and 3 are reversed. However, these two wiring patterns are constantly causing problems for end users and weekend cable installers. What is the problem? Older patch panels and modular wall-plate outlets came in either the T568-A or T568-B wiring patterns. The actual construction of these devices is exactly the same, but they are color coded according to either the T568-A wiring standard or the T568-B wiring standard. Newer connecting hardware is usually color coded so that either configuration can be used. The confusion comes from people wondering which one to use. It doesn't matter—they both work the same way. But you have to be consistent at each end of the cable. If you use T568-A at one end, you must use it at the other; likewise with T568-B.

The cable pairs are assigned to specific pin numbers. The pins are numbered from left to right if you are looking into the modular jack outlet or down on the top of the modular plug. Figure 2 shows the pin numbers for the eight-position modular jack (RJ-45) and plug.

 
Figure 2: Pin positions for the eight-position modular plug and jack

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Which Wiring Pattern Should You Choose?

The T568-A wiring pattern is most prevalent outside of the United States and in U.S. government installations. T568-B used to be more prevalent in private installations in the United States. This has changed, however. The recommended pattern to use for new installations is T568-A. It is the only pattern recognized by ANSI/TIA-570-B, the residential wiring standard. The reason for recommending T568-A is that pairs 1 and 2 are configured the same as a wiring pattern called Universal Service Order Code (USOC), which is prevalent in voice installations.

The wiring pattern chosen makes no difference to the applications used. The signal does not care what color wire it is running through.

The most important factor is to choose one wiring configuration and stick with it. This means when you're purchasing patch panels, 110-blocks, and wall plates, they should all be capable of using the same wiring pattern.