standards and guidelines for communication sites - Radio And ...
standards and guidelines for communication sites - Radio And ... standards and guidelines for communication sites - Radio And ...
GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4: EXTERNAL GROUNDING (EARTHING) TABLE 4-3 EXTERNAL GROUND BUS BAR SPECIFICATIONS (WHEN REQUIRED) Item Specification Material Bare, solid Alloy 110 (99.9%) copper bus bar or plate of one piece construction. May be tin-plated. Minimum Dimensions (ANSI-J-STD-607-A-2002 and NFPA 70-2005, Article 250.64) Mounting brackets Stainless steel IMPORTANT: For improved lightning protection at the site, the RF transmission line entry point and EGB should be installed as low to the ground as practical; 610 mm (2 ft.) is the recommended maximum height for the RF transmission line entry point. (United States National Weather Service Manual 30-4106-2004, “Lighting Protection, Grounding, Bonding, Shielding, and Surge Protection Requirements”.) See “Design Considerations to Help Reduce Effects of Lightning” on page 2-19. 4.4.3.1 TOWER GROUND BUS BAR The purpose of the tower ground bus bar (TGB) is to provide a convenient termination point on the tower for multiple transmission line (coaxial) grounding (earthing) conductors. The tower ground bus bar should be an integral part of the tower construction. If the tower ground bus bar is not part of the tower construction, it shall be constructed and minimally sized in accordance with Table 4-4 on page 4-34, ensuring the ground bus bar is large enough to accommodate all coaxial cable connections and connection to the grounding electrode system. The requirements for installing tower ground bus bars are as follows: Height: 51 mm (2 in.) Thickness: 6.35 mm (0.25 in.) Length: Variable to meet the application requirements and allow for future growth. 305 mm (12 in.) is recommended as the minimum length. Insulators Polyester fiberglass 15 kV minimum dielectric strength flame resistant per UL 94 VO classification Conductor mounting holes Number dependent on number of conductors to be attached Holes to be 11 mm (0.4375 in.) minimum on 19 mm (0.75 in.) centers to permit the convenient use of two-hole lugs. Method of attachment of grounding electrode conductor Exothermic welding Irreversible crimp connection • Where a galvanized tower is not protected against precipitation run-off from copper and copper alloys, the tower ground bus bar (TGB) shall be constructed of tinned copper. See “Methods To Help Reduce Corrosion” on page 4-38. • The tower ground bus bar shall be installed below the transmission line ground kits, near the area of the tower at the point where the antenna transmission lines transition from the tower to the shelter. • The tower ground bus bar shall be connected to the tower grounding electrode system with a 35 mm 2 csa (#2 AWG) or coarser, bare, solid, tinned, copper conductor. 4-32 68P81089E50-B 9/1/05
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS • For reduced impedance to earth, the tower ground bus bar may be directly bonded to the tower, using hardware of materials suitable for preventing dissimilar metal reactions, if possible and allowed by the tower manufacturer. This is in addition to the required grounding conductor as described above. • The grounding conductors shall be run as short, straight, and smoothly as possible. See “Bending And Routing Grounding (Earthing) Conductors” on page 4-29. • The grounding conductor may be sleeved in PVC for protection if desired (ANSI T1.313-2003, section 11.4). This may be required in order to keep the grounding conductor from making incidental contact with the tower. For reduced impedance to the grounding electrode system, the TGB can be connected to the external grounding electrode system using solid copper strap. Relatively small copper strap has significantly less inductance (impedance to lightning) than large wire conductors. For example, 38.1 mm (1.5 in.) copper strap has less inductance than 70 mm 2 csa (#2/0 AWG) wire. To further reduce the inductance to ground, several copper straps can be installed across the entire length of the tower ground bus bar and routed down to the external grounding ring. Additional ground bus bars may be installed at different heights along the vertical length of the tower for bonding multiple transmission line ground kits to the tower, if not already included as part of the tower structure. The additional ground bus bars shall be bonded directly to the tower using tower manufacturer approved methods. Bonding to the tower may include the following options: • Bolting a tin-plated bus bar directly to the tower structure using stainless steel hardware. In this case, a grounding conductor is not required. • Securing a bus bar to the tower using appropriate mechanical hardware. Electrically bonding the bus bar to the tower using a grounding conductor. The grounding conductor should bond to the tower using appropriate hardware, such as stainless steel beam clamps, or stainless steel band/strap type clamp. The grounding conductor shall bond to the bus bar using exothermic weld, irreversible compression connectors, or listed compression two-hole lugs. TOWER GROUND RING (UNDERGROUND) FIGURE 4-25 TYPICAL TOWER GROUND BUS BARS TOWER GROUND BUS BAR TRANSMISSION LINES TO BUILDING 68P81089E50-B 9/1/05 4-33
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GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4: EXTERNAL GROUNDING (EARTHING)<br />
TABLE 4-3 EXTERNAL GROUND BUS BAR SPECIFICATIONS (WHEN REQUIRED)<br />
Item Specification<br />
Material Bare, solid Alloy 110 (99.9%) copper bus bar or plate of one piece<br />
construction. May be tin-plated.<br />
Minimum Dimensions<br />
(ANSI-J-STD-607-A-2002 <strong>and</strong> NFPA 70-2005, Article 250.64)<br />
Mounting brackets Stainless steel<br />
IMPORTANT: For improved lightning protection at the site, the RF transmission line entry point <strong>and</strong><br />
EGB should be installed as low to the ground as practical; 610 mm (2 ft.) is the<br />
recommended maximum height <strong>for</strong> the RF transmission line entry point. (United States<br />
National Weather Service Manual 30-4106-2004, “Lighting Protection, Grounding,<br />
Bonding, Shielding, <strong>and</strong> Surge Protection Requirements”.) See “Design Considerations<br />
to Help Reduce Effects of Lightning” on page 2-19.<br />
4.4.3.1 TOWER GROUND BUS BAR<br />
The purpose of the tower ground bus bar (TGB) is to provide a convenient termination point on the<br />
tower <strong>for</strong> multiple transmission line (coaxial) grounding (earthing) conductors. The tower ground bus<br />
bar should be an integral part of the tower construction. If the tower ground bus bar is not part of the<br />
tower construction, it shall be constructed <strong>and</strong> minimally sized in accordance with<br />
Table 4-4 on page 4-34, ensuring the ground bus bar is large enough to accommodate all coaxial cable<br />
connections <strong>and</strong> connection to the grounding electrode system.<br />
The requirements <strong>for</strong> installing tower ground bus bars are as follows:<br />
Height: 51 mm (2 in.)<br />
Thickness: 6.35 mm (0.25 in.)<br />
Length: Variable to meet the application requirements <strong>and</strong> allow<br />
<strong>for</strong> future growth. 305 mm (12 in.) is recommended as the<br />
minimum length.<br />
Insulators Polyester fiberglass 15 kV minimum dielectric strength flame<br />
resistant per UL 94 VO classification<br />
Conductor mounting holes Number dependent on number of conductors to be attached<br />
Holes to be 11 mm (0.4375 in.) minimum on 19 mm (0.75 in.)<br />
centers to permit the convenient use of two-hole lugs.<br />
Method of attachment of grounding electrode conductor Exothermic welding<br />
Irreversible crimp connection<br />
• Where a galvanized tower is not protected against precipitation run-off from copper <strong>and</strong> copper<br />
alloys, the tower ground bus bar (TGB) shall be constructed of tinned copper. See “Methods To<br />
Help Reduce Corrosion” on page 4-38.<br />
• The tower ground bus bar shall be installed below the transmission line ground kits, near the area<br />
of the tower at the point where the antenna transmission lines transition from the tower to the<br />
shelter.<br />
• The tower ground bus bar shall be connected to the tower grounding electrode system with a<br />
35 mm 2 csa (#2 AWG) or coarser, bare, solid, tinned, copper conductor.<br />
4-32 68P81089E50-B 9/1/05
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