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GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4: EXTERNAL GROUNDING (EARTHING) • Grounding electrode encasement material shall be packaged for the purpose of grounding electrode encasement. • Grounding electrode encasement material shall be environmentally safe and approved by the environmental authority having jurisdiction. • Grounding electrode encasement material shall be used in accordance with the manufacturers' instructions. • Grounding electrode encasement material shall not have a corrosive effect on the grounding electrode system components. • The use of charcoal or petroleum based coke breeze is not recommended as it may result in rapid corrosion of copper electrodes and copper conductors (BS 7430:1998, clause 8.5; BS 6651:1999, clause 18.4.2; and FAA STD 019d-2002, section 3.8.3.5). Charcoal and petroleum based coke typically contains high levels of sulfur, which in the presence of moisture will accelerate corrosion. Coke breeze derived from coal in coke ovens is generally considered acceptable; all the corrosives and volatiles have been cooked off at extremely high temperatures (FAA STD 019d-2002, section 3.8.3.5). Per MIL-HDBK-419A, the suggested grounding electrode encasement (backfill) material is a mixture of 75 percent gypsum, 20 percent bentonite clay, and 5 percent sodium sulfate. The gypsum, which is calcium sulfate, absorbs and retains moisture and adds reactivity and conductivity to the mixture. Since it contracts very little when moisture is lost, it will not pull away from the ground rod or surrounding earth. The bentonite ensures good contact between the ground rod and earth by its expansion, while the sodium sulfate prevents polarization of the ground rod by removing the gases formed by current entering the earth through the ground rod. This mixture is readily available from cathodic protection distributors as standard galvanic anode backfill. The backfill mixture should be covered with 305 mm (12 in.) of excavated soil. See MIL-HDBK-419A Volume I, section 2.9 for additional information. 4.4.2 GROUNDING (EARTHING) CONDUCTORS Grounding (earthing) conductors are the conductors used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or grounding electrode system. These conductors may connect grounding electrodes together, form buried ground rings, and connect objects to the grounding electrode system. See BS 7430:1998, clause 3.17 and NFPA 70-2005, Article 100 for additional information. 4.4.2.1 GENERAL SPECIFICATIONS General specifications for grounding (earthing) conductors are listed below. • Unless otherwise stated, all below-ground, or partially below-ground, external grounding electrode system conductors shall be 35 mm2 csa (#2 AWG) or coarser, bare, solid, tinned or un-tinned, copper conductors (ANSI T1.313-2003 and ANSI T1.334-2002, section 5.3). For areas highly prone to lightning, and/or military installations, larger conductors, such as 50 mm2 csa (#1/0 AWG) or coarser, should be considered (MIL-HDBK-419A); stranded conductors may be used in this application. Tinned conductors are recommended for stranded conductors. • Solid, bare, tinned, copper conductors should be used to help minimize galvanic corrosion between tower legs and other parts of the grounding electrode system (ANSI T1.313-2003, section 10.7). See “Dissimilar Metals and Corrosion Control” on page 4-34. 4-28 68P81089E50-B 9/1/05
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS • Grounding electrode conductors shall be installed in one continuous length without a splice or joint, unless spliced using irreversible compression-type connectors listed for the purpose or by exothermic welding (NFPA 70-2005, Article 250.64). See “Bonding Methods” on page 4-41 for additional information. • Above-ground conductors used for bonding individual metallic objects shall be 16 mm2 csa (#6 AWG) or coarser, tinned or un-tinned, copper conductors (ANSI T1.334, section 5.3.3). See “Metallic Objects Requiring Bonding” on page 4-67 for additional information. • Above-ground conductors used for bonding multiple metallic objects (used as a ground bus conductor) shall be 35 mm2 csa (#2 AWG) or coarser, tinned or un-tinned, copper conductors. See “Metallic Objects Requiring Bonding” on page 4-67. • Above-ground bonding conductors should be jacketed, whenever practical (ANSI T1.334-2002, section 5.1). • Solid straps or bars may be used as long as the cross-sectional area equals or exceeds that of the specified grounding conductor. WARNING The AC power system grounding conductors shall be sized appropriately for the electrical service and shall be approved by the authority having jurisdiction. 4.4.2.2 BENDING AND ROUTING GROUNDING (EARTHING) CONDUCTORS Grounding (earthing) conductors shall be run in a direct manner with no sharp bends or narrow loops (ANSI T1.313-2003, section 11.3, and ANSI T1.334-2002, section 13.4). Sharp bends and/or narrow loops increase the impedance and may produce flash points (also see NFPA 780-2004, section 4.9.5). The following requirements apply when installing grounding system conductors: • Sharp bends shall be avoided (ANSI T1.334-2002, section 13.4). • Grounding conductors shall be run as short, straight, and smoothly as possible, with the fewest possible number of bends and curves (ANSI T1.313-2003, section 11.3; ANSI T1.334-2002, section 13.4; and NFPA 70-2005, Articles 800.100, 810.21, and 820.100). • A minimum bending radius of 203 mm (8 in.) shall be maintained, applicable to grounding conductors of all sizes (ANSI T1.313-2003, section 11.3; MIL-STD-188-124B; and NFPA 780- 2004, section 4.9.5). A diagonal run is preferable to a bend even though it does not follow the contour or run parallel to the supporting structure. See Figure 4-22. • All bends and curves shall be made toward the ground location (grounding electrode system or ground bar). Radius The radius of any bend shall not be less than 203 mm (8 in.) 90 degrees minimum The angle of any bend shall not be less than 90 degrees. FIGURE 4-22 MINIMUM BENDING RADIUS FOR GROUNDING CONDUCTORS 68P81089E50-B 9/1/05 4-29
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© 2005 MOTOROLA, INC. ALL RIGHTS R
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TABLE OF CONTENTS Chapter 1. Introd
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STANDARDS AND GUIDELINES FOR COMMUN
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CHAPTER 1 INTRODUCTION 1 This manua
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CHAPTER 2 SITE DESIGN AND DEVELOPME
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CHAPTER 3 COMMUNICATION SITE BUILDI
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CHAPTER 5 INTERNAL GROUNDING (EARTH
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CHAPTER 6 POWER SOURCES 6 6.1 LOCKO
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CHAPTER 7 SURGE PROTECTIVE DEVICES
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CHAPTER 8 MINIMIZING SITE INTERFERE
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CHAPTER 9 EQUIPMENT INSTALLATION 9
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APPENDIX A ELECTROMAGNETIC ENERGY I
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APPENDIX B SOIL RESISTIVITY MEASURE
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APPENDIX C PROTECTING AGAINST ELECT
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APPENDIX D GROUNDING (EARTHING) ELE
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APPENDIX E GENERAL CONVERSIONS AND
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APPENDIX F R56 COMPLIANCE CHECKLIST
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I NDEX Index Index AC power cabling
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