ANSI/TIA -568-C Wiring Schemes T568A and T568B

ANSI/TIA-568-C does not sanction the use of the USOC scheme. Instead, two wiring schemes are specified, both of which are suitable for either voice or high-speed LAN operation. These are designated as T568A and T568B wiring schemes.

Both T568A and T568B are universal in that all LAN systems and most voice systems can utilize either wiring sequence without system errors. After all, the electrical signal really doesn't care if it is running on pair 2 or pair 3, as long as a wire is connected to the pin it needs to use. The TIA/EIA standard specifies eight-position, eight-contact jacks and plugs and four-pair cables, fully terminated, to facilitate this universality.

The T568B wiring configuration was at one time the most commonly used scheme, especially for commercial installations; it is shown in Figure 1. The TIA/EIA adopted the T568B wiring scheme from the AT&T 258A wiring scheme.

 
Figure 1: The T568B wiring pattern

The T568A scheme (shown in Figure 10.9) is well suited to upgrades and new installations in residences because the wire-termination pattern for pairs 1 and 2 is the same as for USOC. Unless a waiver is granted, the U.S. government requires all government cabling installations to use the T568A wiring pattern. The current recommendation according to the standard is for all new installations to be wired with the T568A scheme.

 
Figure 2: The T568A wiring pattern

The wire colors and the associated pin assignments for the T568B wiring scheme look like this:

Pin	Wire Color
1	White/orange
2	Orange
3	White/green
4	Blue
5	White/blue
6	Green
7	White/brown
8	Brown

The pin assignments for the T568A wiring schemes are identical to the assignments for the T568B pattern except that wire pairs 2 and 3 are reversed. The T568A pattern looks like this:

Pin	Wire Color
1	White/green
2	Green
3	White/orange
4	Blue
5	White/blue
6	Orange
7	White/brown
8	Brown

Note that when you buy eight-position modular jacks, you may need to specify whether you want a T568A or T568B scheme because the jacks often have IDC connections on the back where you punch the pairs down in sequence from 1 to 4. The jacks have an internal PC board that takes care of all the pair splitting and proper alignment of the cable conductors with the pins in the jack. Most manufacturers now provide color-coded panels on the jacks that let you punch down either pinout scheme, eliminating the need for you to specify (and for them to stock) different jacks depending on which pinout you use.

Tip

Whichever scheme you use, T568A or T568B, you must also use that same scheme for your patch panels and follow it in any cross-connect blocks you install. Consistency is the key to a successful installation.

Be aware that modular jacks pretty much look alike even though their performance may differ dramatically. Be sure you also specify the performance level (e.g., Category 3, Category 5e, Category 6, Category 6A, etc.) when you purchase your jacks.

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Tips for Terminating UTP Connectors

Keep the following points in mind when terminating UTP connectors:

• When connecting to jacks and plugs, do not untwist UTP more than 0.5″ for Category 5e and not more than 0.375″ for Category 6.
• Always use connectors, wall plates, and patch panels that are compatible (same rating or higher) with the grade of cable used.
• To "future-proof" your installation, terminate all four pairs, even if the application requires only two of the pairs.
• Remember that the T568A wiring scheme is compatible with USOC wiring schemes that use pairs 1 and 2.
• When terminating ScTP cables, always terminate the drain wire on both ends of the connection.

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When working with ScTP wiring, the drain wire makes contact with the cable shield along its entire length; this provides a ground path for EMI energy that is collected by the foil shield. When terminating ScTP, the drain wire within the cable is connected to a metal shield on the jack. This must be done at both ends of the cable. If left floating or if connected only on one end, instead of providing a barrier to EMI the cable shield becomes a very effective antenna for both emitting and receiving stray signals.

In a cable installation that utilizes ScTP, the plugs, patch cords, and patch panels must be shielded as well.

ANSI/TIA-570-B

ANSI and TIA published ANSI/TIA-570-B-2004, or the Residential and Light Commercial Telecommunications Cabling Standard, to address the growing need for "data-ready" homes and multidwelling residential buildings. Just a few years ago, only the most serious geeks would have admitted to having a network in their homes. Today, more and more homes have small networks consisting of two or more home computers, a cable modem, and a shared printer. Even apartment buildings and condominiums are being built or remodeled to include data outlets; some apartment buildings and condos even provide direct Internet access.

Cabling @Work: An Example of Poor Grounding

One of the best examples we can think of that illustrates poor grounding practices was a very large building that accidentally had two main grounds installed, one on each side. (A building should only have one main ground.) A telecommunications backbone cable was then grounded to each main ground.

Under some circumstances, a ground loop formed that caused this cable to emit EMI at specific frequencies. This frequency just so happened to be used by air traffic control beacons. When the building cable emitted signals on this frequency, it caused pilots to think they were closer to the airport than they really were. One plane almost crashed as a result of this poorly grounded building. The FAA (Federal Aviation Administration) and the FCC (Federal Communications Commission) closed the building and shut down all electrical systems for weeks until the problem was eventually found.

The ANSI/TIA-570-B standard provides requirements for residential telecommunications cabling for two grades of information outlets: basic and multimedia cabling. This cabling is intended to support applications such as voice, data, video, home automation, alarm systems, environmental controls, and intercoms. The two grades are as follows:

Grade 1 This grade supports basic telephone and video services. The standard specifies twisted-pair cable and coaxial cable placed in a star topology. Grade 1 cabling requirements consist of a minimum of one four-pair UTP cable that meets or exceeds the requirements for Category 5e, a minimum of one 75-ohm coaxial cable, and their respective connectors at each telecommunications outlet and the DD. Installation of Category 6 cable in place of Category 5e cable is recommended.

Grade 2 Grade 2 provides a generic cabling system that meets the minimum requirements for basic and advanced telecommunications services such as high-speed Internet and in-home generated video. Grade 2 specifies twisted-pair cable, coaxial cable, and optionally optical fiber cable, all placed in a star topology. Grade 2 cabling minimum requirements consist of two four-pair UTP cables and associated connectors that meet or exceed the requirements for Category 5e cabling; two 75-ohm coaxial and associated connectors at each telecommunications outlet and the DD; optionally, two-fiber optical fiber cabling. Installation of Category 6 cabling in place of Category 5e cabling is recommended.

The standard further dictates that a central location within a home or multitenant building be chosen at which to install a central cabinet or wall-mounted rack to support the wiring. This location should be close to the telephone company demarcation point and near the entry point of cable TV connections. Once the cabling system is installed, you can use it to connect phones, televisions, computers, cable modems, and EIA 6000-compliant home automation devices.

ANSI/TIA-607-B

The ANSI/TIA-607-B Commercial Building Grounding and Bonding Requirements for Telecommunications Standard covers grounding and bonding to support a telecommunications system. This document should be used in concert with Article 250 and Article 800 of the NEC. ANSI/TIA-607-B does not cover building grounding; it only covers the grounding of telecommunications systems.

ANSI/TIA-607-B specifies that the telecommunications ground must tie in with the building ground. Each telecommunications room must have a telecommunications grounding system, which commonly consists of a telecommunications bus bar tied back to the building grounding system. All shielded cables, racks, and other metallic components should be tied into this bus bar.

ANSI/TIA-607-B specifies that the minimum ground-wire size must 6 AWG, but, depending on the distance that the ground wire must cover, it may be up to 3/0 AWG (a pretty large copper wire!). Ground-wire sizing is based on the distance that the ground wire must travel; the farther the distance, the larger the wire must be. ANSI/TIA-607-B supplements (and is supplemented by) the NEC. For example, Article 800-100 specifies that telecommunications cables entering a building must be grounded as near as possible to the point at which they enter the building.

Warning

When protecting a system with building ground, don't overlook the need for lightning protection. Network and telephone components are often destroyed by a lightning strike. Make sure your grounding system is compliant with the NEC.

Grounding is one of the most commonly overlooked components during the installation of a structured cabling system. An improperly grounded communications system, although supporting low-voltage applications, can result in, well, a shocking experience. Time after time we have heard stories of improperly grounded (or ungrounded) telecommunications cabling systems that have generated mild electrical or throw-you-off-your-feet shocks; they have even resulted in some deaths.

Grounding is not to be undertaken by the do-it-yourselfer or an occasional cable installer. A professional electrician must be involved. He or she will know the best practices to follow, where to ground components, which components to ground, and the correct equipment to be used. Further, electricians must be involved when a telecommunications bus bar is tied into the main building ground system.

Warning

Grounding to a water pipe may not provide you with sufficient grounding, as many water systems now tie in to PVC-based (plastic) pipes. It may also violate NEC and local-code requirements.

American National Standards Institute (ANSI) | Standards and Specification Organizations

Five engineering societies and three U.S. government agencies founded the American National Standards Institute (ANSI) in 1918 as a private, nonprofit membership organization sustained by its membership. ANSI's mission is to encourage voluntary compliance with standards and methods. ANSI's membership includes almost 1,400 private companies and government organizations in the United States as well as international members.

ANSI does not develop the American National Standards (ANS) documents, but it facilitates their development by establishing a consensus between the members interested in developing a particular standard.

To gain ANSI approval, a document must be developed by a representative cross section of interested industry participants. The cross section must include both manufacturers and end users. In addition, a rigorous balloting and revision process must be adhered to so that a single powerful member does not drive proprietary requirements through and establish a particular market advantage.

Through membership in various international organizations such as the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC), ANSI promotes standards developed in the United States. ANSI was a founding member of the ISO and is one of the five permanent members of the ISO governing council and one of four permanent members on the ISO's Technical Management Board.

ANSI standards include a wide range of information-technology specifications, such as SCSI interface specifications, programming language specifications, and specifications for character sets. ANSI helped to coordinate the efforts of the Electronic Industries Alliance (EIA) and the Telecommunications Industry Association (TIA) to develop ANSI/TIA/EIA-568, the cabling specification in the United States. ANSI/TIA-568-C is discussed in more detail later in this chapter. You can find information on it and links to purchase the documents on ANSI's website at www.ansi.org.