S Paul Kish is Director, Systems and Standards at Belden

TIA has recently published a new ANSI/TIA-607-B-2011 Bonding and Grounding (Earthing) Standard for Customer Premises. This is a major revision of the standard and contains a lot of new material. For this months article, I wanted to provide a brief overview of its main components as well as the main differences compared to the previous edition of the standard. The primary purpose of telecommunications bonding and grounding infrastructure is to create a low resistance (low impedance) path to ground and thereby to equalize ground potentials and to reduce the problems associated with ground potential differences. In order to understand the structure of a bonding and grounding system for telecommunications, it is first necessary to learn the terminology of the components that comprise the system, as follows: TMGB Telecommunications Main Grounding Busbar is connected to the buildings main ground, which is also referred to as a building grounding electrode system. The TMGB is the central attachment point for the TBB(s) and equipment. TBB Telecommunications Bonding Backbone is a conductor that originates at the TMGB and follows the backbone pathways to connect to the TGBs in various distributors (telecommunications rooms) throughout the building. The TBB conductor size depends on the length and shall be a minimum of 6 AWG for lengths up to 4 meters and should increase in size at 2 kcmil per linear foot of conductor all the way up to 750* kcmil for lengths greater than 91 meters. (*Note: This is new. The maximum conductor size for the TBB in the J-STD-607-A standard was a 3/0 conductor.) TGB Telecommunications Grounding Busbar is the grounding connection point for telecommunications systems and equipment in the area served by a distributor. GE Grounding Equalizer is used within a multistory building to interconnect multiple TBBs at the top floor and at a minimum of every third floor in between to the lowest floor level. As a minimum, the GE shall be the same size as the largest TBB. BCT Bonding Conductor for Telecommunications is used to bond the TMGB to the service equipment (power) ground. As a minimum, the BCT shall be the same size as the largest TBB. Clause 6 of the TIA 607-B standard provides more detailed information on the materials and the construction of the TMGB and the TGB. The TIA 607-B standard now allows the use of copper alloys having a minimum of 95% conductivity in addition to copper or electrotin-plated copper for the TMGB and TGB. Clause 7 of the TIA 607-B standard provides information on how to design a telecommunications bonding and grounding infrastructure for bonding of metallic pClause 7 of the TIA 607-B standard provides information on how to design a telecommunications bonding and grounding infrastructure for bonding of metallic pathways, cable shields, racks, enclosures and equipment in telecommunications rooms, equipment rooms, and entrance facilities. The TIA 607-B standard also provides guidance in several Annexes on the design of Grounding Electrodes, Grounding Systems for Towers and Antennas and Electrical Protection of Telecommunications Circuits. One of the most notable additions to the TIA 607-B standard compared to the previous edition is the bonding and grounding of equipment in computer rooms. For example, the standard states that a computer room should also contain a supplementary bonding network, such as a mesh-BN, that is bonded (and thus becomes grounded) to the TGB or TMGB. A mesh-BN as the name implies consists of a bonding grid of conductors, either flat conductors or bare round wire, joined together via proper welding, brazing, listed compression connectors, or listed grounding clamps at each of the crossing points.

Metallic enclosures, including telecommunications cabinets and racks, shall be bonded to the mesh-BN, TGB, or TMGB using a minimum sized conductor of No. 6 AWG. A new term Telecommunications Equipment Bonding Conductor (TEBC) is used for the conductor that connects the equipment racks and cabinets to the TMGB/TGB. The standard also provides information on how to establish the connections to a TEBC and how to bond the equipment in a rack or enclosure. In summary, the main difference in the new TIA 607-B Bonding & Grounding Standard is that it does not stop at the busbar (TGB), but extends all the way out to the equipment. It provides design requirements on how to build and test a bonding and grounding infrastructure to ensure a reliable, low resistance path to ground. The recommended maximum value for resistance between any point in the telecommunications bonding and grounding system and the buildings electrical grounding electrode system is 100 milliohms. There is a lot more to bonding and grounding for telecommunications than meets the eye. There are a lot of nuances and procedures that are not well understood. The reader is encouraged to consult the TIA 607-B standard on how to properly design and implement a telecommunications bonding and grounding system for customer premises.

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A structured cabling system is a complete system of cabling and associated hardware, which provides a comprehensive telecommunications infrastructure. This infrastructure serves a wide range of uses, such as to provide telephone service or transmit data through a computer network. It should not be device dependent.

We further define a structured cabling system in terms of ownership. The structured cabling system begins at the point where the service provider (SP) terminates. This point is the point of demarcation (demarc) or Network Interface Device (NID).

For example, in a telephone system installation, the SP furnishes one or more service lines (per customer requirements). The SP connects the service lines at the point of demarcation.

The U.S. cabling industry accepts the American National Standards Institute (ANSI), in conjunction with TIA/EIA, as the responsible organization for providing and maintaining standards and practices within the profession. It has published a series of standards to design, install, and maintain cabling installations. These help to ensure a proper cabling installation.

The benefits of these standards include:

Consistency of design and installation;

Conformance to physical and transmission line requirements;

A basis for examining a proposed system expansion and other changes; and

Uniform documentation.

The industry standard term for a network installation that serves a relatively small area (such as a structured cabling installation serving a building) is a local area network (LAN). There are also metropolitan area networks (MANs) and wide area networks (WANs).

Structured cabling installations typically include: entrance facilities; vertical and horizontal backbone pathways; vertical and horizontal backbone cables; horizontal pathways; horizontal cables; work area outlets; equipment rooms; telecommunications closets; cross-connect facilities; multi-user telecommunications outlet assemblies (MUTOA); transition points; and consolidation points.

The entrance facility includes the cabling components needed to provide a means to connect the outside service facilities to the premises cabling. This can include service entrance pathways, cables, connecting hardware, circuit protection devices, and transition hardware.

An entrance facility houses the transition outside plant cabling to cabling approved for intrabuilding construction. This usually involves transition to fire-rated cable. The entrance facility is also the network demarc between the SP and customer premises cabling (if required). National and regional electrical codes govern placement of electrical protection devices at this point.

The location of the entrance facility depends on the type of facility, route of the outside plant cabling (e.g. buried or aerial), building architecture, and aesthetic considerations. The four principal types of entrance facilities include underground, tunnel, buried, and aerial. (We will cover only aerial entrances in this article.)

In an aerial entrance, the SP cables provide service to a building via an overhead route. Aerial entrances usually provide the lowest installation cost, and they're readily accessible for maintenance. However, they're subject to traffic and pedestrian clearances, can damage a building's exterior, are susceptible to environmental conditions (such wind and ice), and are usually joint-use installations with the power company, CATV company, and telephone or data service providers.

Backbone cabling.From the entrance facility, the structured cabling network branches out to other buildings, as well as from floor to floor within a building on the backbone cabling system. We use the term backbone to describe the cables handling the major network traffic.

The ANSI/TIA/EIA-568-A standard defines backbone cabling as follows: "The function of the backbone cabling is to provide interconnections between telecommunications closets, equipment rooms, and entrance facilities in the telecommunications cabling system structure. Backbone cabling consists of the backbone cables, intermediate and main cross-connects, mechanical terminations, and patch cords or jumpers used for backbone-to-backbone cross-connection. Backbone cabling also includes cabling between buildings."

Interbuilding and intrabuilding are two types of backbone cables. Interbuilding backbone cable handles traffic between buildings. Intrabuilding backbone cable handles traffic between closets in a single building.

This standard identifies two levels of backbone cabling. First-level backbone is a cable between a main cross-connect (MC) and intermediate cross-connect (IC) or horizontal cross-connect (HC). Second-level backbone exists between an IC and HC.

The main components of backbone cabling are:

Cable pathways: shafts, conduits, raceways, and floor penetrations (such as sleeves or slots) that provide routing space for the cables.

The actual cables: optical fiber, twisted-pair copper, coaxial copper, or some combination of these. (Note: You should avoid areas where potential sources of EMI or electromagnetic interference may exist when planning the routing and support structure for copper cabling.)

Connecting hardware: connecting blocks, patch panels, interconnections, cross-connections, or some combination of these components, and

Miscellaneous support facilities: cable support hardware, firestopping and grounding hardware. Note: The terms horizontal and backbone (previously called riser) evolved from the orientations typical for functional cables of these types. However, the physical orientation of the cabling has no bearing on classifying the cable as horizontal or backbone.

The useful life of a backbone cabling system consists of several planned growth periods (typically three to 10 years). This is shorter than the life expectancy of the premises cabling system.

Cabling connectors.A connector is a mechanical device you use to interface a cable to a piece of equipment or one cable to another. The role of the connector is to provide a coupling mechanism that keeps loss to a minimum.

In the case of fiber, it allows light impulses to transfer from one connector to another. For copper, it allows electrical signals to transfer from one connector to another.

A good connection requires aligning the connectors, preventing the connectors from unintentional separation, and efficient transferring of light or electricity from one connector to the other.

A connector demonstrates durability by withstanding hundreds of insertion and withdrawal cycles without failing. We calculate this as mean time between failures (MTBF).

Connectors are as essential to the integrity of the entire telecommunications network as is the cable itself. Connectors align, attach, and decouple the media to a transmitter, receiver, another media of same or similar type, an active telecommunications device, or a specified passive telecommunications device.

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THE SUCCESS OR FAILURE OF A RADIO ANTENNA SYSTEM OFTEN (PERHAPS USUALLY) hangs on whether or not it has a good RF ground. Poor grounds cause most antennas to operate at less than best efficiency. In fact, it is possible to burn up between 50 and 90 percent of your RF power heating the ground losses under the antenna, instead of propagating into the air. Ground resistances can vary from very low values of 5 , up to more than 100 (5 to 30 is a frequently quoted range). RF power is dissipated in the ground resistance. The factors that affect the ground resistance include the conductivity of the ground, its composition, and the water content. The ideal ground depth is rarely right on the surface, and depending on local water table level might be a couple meters or so below the surface.

Fortunately, there are some fixes that will help your situation. We can reduce the ground resistance by either altering the composition of the earth surrounding the ground point, or by using a large surface area conductor as the ground point. Figure 29-1 shows the traditional ground rod used on small radio stations, including amateur stations. Use either a copper (or copper-clad steel) rod at least 6 ft long (8 ft preferred). Electrical supply houses, as well as amateur radio and communications equipment suppliers, also sell these ground rods. Do not use the nonclad steel types sold by some electrical supply houses. They are usable by electricians when making a service entrance ground on your home or workplace, but RF applications require the low skin resistance of the copper-clad variety. The rod need not be all copper, because of skin effect forcing the RF current to flow only on the outer surface of the rod. Try to use an 8-ft rod if at all possible, because it will work better than the shorter kind. Do not bother with the small TV-antenna 4-ft ground rods; they are next to useless for HF radio stations. Drive the ground rod into the earth until only 6 in or so remains above the surface. Connect a ground wire from your station to the ground rod The ground wire should be as short as possible. Furthermore, it should be a lowinductance conductor. Use either heavy braid (or the outer conductor stripped from RG-8 or RG-11 coaxial cable) or sheet copper. You can buy rolls of sheet copper from metal distributors in widths from 4 in up to about 18 in. Some amateurs prefer to use 7-in-wide foil that is rated at a weight of 1 lb/linear ft. Sweat-solder the ground wire to the rod. You can get away with using mechanical connections like the electricians use, but you will eventually have to service the installation when corrosion takes its toll. I prefer to use soldered connections, and then cover the joint with either petroleum jelly or acrylic spray lacquer. Another alternative is to use a copper plumbing pipe as the ground rod. The pipe can be purchased in 8-ft through 16-ft lengths from plumbing supply shops or hardware stores. The pipe selected should be 3 4 in or larger. Some people report using up to 2-in pipe for this application. The surface area of the hollow pipe is greater than that of a solid rod of the same diameter. Because of certain current flow geometries in the system, however, the ground resistance is not half the resistance of a rod of the same diameter, but is nonetheless lower. Driving a long pipe into the ground is not easily done. Unlike the copper-clad steel rod, the pipe has no compression strength and will deform when you hit it with a hammer or other driving tool. To overcome this problem.

Altering soil conductivity The conductivity of the soil determines how well, or how poorly, it conducts electrical current (Table 29-1). Moist soil over a brackish water dome conducts best (southern swamps make better radio station locations), and the sand of the western deserts makes the worst conductor.

grounds Radials/counterpoise The effectiveness of the ground system is enhanced substantially by the use of radials either above ground or buried under the surface. Figure 29-5 shows a vertical

antenna with three different forms of radials: aboveground, subsurface, and ground rod. It is not unreasonable to use both radials and a ground rod. Note (from Chap. 7) that vertical antennas are relatively ineffective unless provided with a good ground system, and for most installations that requirement is best met through a system of ground radials. An effective system of radials requires a large number of radials. Although as few as two quarter-wavelength resonant radials will provide an improvement, the best performance is to use more. Broadcasters in the AM band (550 to 1640 kHz) are advised to use 120 half-wavelength radials. Installing more than 120 radials is both expensive and time-consuming, but does not provide any substantial improvement. For amateur and small commercial stations, use a minimum of 16 quarter-wavelength radials. Above ground, the use of insulated wire is recommended, but not required. Below ground, noninsulated wire is preferred. Although some sources claim that any size wire from no. 26 up to no. 10 can be used, it is best to use larger sizes in that range (i.e., no. 14 through no. 10). Either solid or stranded wire can be used. The layout for a system of radials in a vertical antenna system is depicted in a view from above in Fig. 29-6. Here, the radials are laid out in a uniform pattern around the antenna element. This coverage provides both the lowest resistance and the best radiation pattern for the antenna. Solder all radials together at a common point, which might be the ground or mounting rod used to support the vertical antenna.

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Station grounding It does no good to provide a topflight ground system, such as those shown earlier in this chapter, if the connection between the station equipment and the ground system is substandard. Figure 29-7 shows a method used by the author to good effect. On the back of the operating position is a sheet of copper, 7 in wide, running the length of the equipment platform. This form of copper, in the 1-lb/sq ft weight, is used on older houses for roofing flashing. Each piece of equipment is connected to the ground sheet through a short length of braid harvested from RG-8 or RG-11 coaxial cable shield. RF accessories, such as the low-pass TV interference filter (if usedit should be) are mounted directly to the copper sheet. In one installation, the author was able to drop the copper sheet down from the table to connect directly to the ground system outside the building. The run was less than 40 in. But in other cases, a short length of braid wire will be more practical.

Tuning the ground wire An alternative that some operators use is the ground wire tuner. These instruments insert an inductor or capacitor (or a LC network) in series with the ground line. You adjust the ground line tuner for maximum ground current at the operating frequency. MFJ Electronics, Inc., Mississippi State, MS, makes one of these devices. Conclusion A high-quality, low-resistance ground might seem costly to install, but in reality it pays rich dividends in the functioning of your antenna. Dont overlook the quality of the ground, or you might be in the position of being penny wise and pound foolish.

7 Ground system inside shack