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INTRODUCTION CHAPTER 5: INTERNAL GROUNDING (EARTHING) Safety of personnel and protection of sensitive electronics equipment from ground faults, lightning, ground potential rise, electrical surges, and power quality anomalies is of utmost importance at any communications site. Though unexpected electrical events like lightning strikes and power surges cannot be prevented, this chapter provides design and installation information on communications site grounding (earthing) systems that may help minimize damage caused by these events. WARNING Grounding and bonding alone are not enough to adequately protect a communications site. Transient voltage surge suppression (TVSS) techniques, using appropriate surge protection devices (SPD), shall be incorporated at a communications site in order to provide an adequate level of protection. See Chapter 7 for details and requirements. WARNING The AC power system ground shall be sized appropriately for the electrical service and shall be approved by the authority having jurisdiction. An internal grounding system shall have low electrical impedance, with conductors large enough to withstand high fault currents. The lower the grounding system impedance, the more effectively the grounding electrode system can dissipate high-energy impulses into the earth. All site development and equipment installation work shall comply with all applicable codes in use by the authority having jurisdiction. Grounding systems shall be installed in a neat and workmanlike manner (NFPA 70-2005, Article 110.12 and NFPA 780-2004, section 1.4). Where conflicting, the more stringent standard should be followed. Government and local codes shall take precedence over the requirements of this manual. Unusual site conditions may require additional effort to achieve an effectively bonded and grounded (earthed) site. See Chapter 2, “Site Design and Development”. In these instances, consultation with Motorola Engineering or with an engineering firm specializing in grounding system design is recommended. Some of the benefits of a properly designed and installed low-impedance grounding system are described below. See ANSI T1.333-2001, section 4; ANSI T1.334-2002, section 5.1; IEEE STD 142- 1991, section 1.3; IEEE STD 1100-1999, section 3.3.1; and NFPA 70-2005, Article 250.4 for additional information. • To help limit potential differences between conductive surfaces caused by electrical disturbances such as electrical power faults, lightning strikes and electrostatic discharges. • To help provide fault current paths of sufficient current carrying capacity and low impedance to allow overcurrent protection devices to operate. • To help limit the voltage caused by accidental contact of the site AC supply conductors with conductors of higher voltage. • To help dissipate electrical surges and faults, to minimize the chances of injury from grounding system potential differences. • To help dissipate the voltages caused by lightning. • To help maintain a low potential difference among exposed metallic objects. 5-2 68P81089E50-B 9/1/05
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES COMMON GROUNDING (EARTHING) • To contribute to reliable equipment operation. • To provide a common signal reference ground. 5.2 COMMON GROUNDING (EARTHING) At a communications site, there shall be only one grounding (earthing) electrode system. For example, the AC power system ground, communications tower ground, lightning protection system ground, telephone system ground, exposed structural building steel, underground metallic piping, and any other existing grounding system shall be bonded together to form a single grounding electrode system. Underground metallic piping systems typically include water service, well castings located within 7.6 m (25 ft.) of the structure, gas piping, underground conduits, and underground liquefied petroleum gas piping systems. (ANSI T1.313-2003; ANSI T1.333-2001; ANSI T1.334-2002; IEC 61024-1-2, section 2.4.4; IEEE STD 1100-1999; NFPA 70-2005, Articles 250.58, 250.104, 250.106, 800.100, 810.21, and 820.100; and NFPA 780-2004, Section 4.14). Interconnection to a gas line shall be made on the customer's side of the meter (NFPA 780-2004, Section 4.14.1.3). See Chapter 6, “Power Sources” for additional information on grounding and bonding requirements of power sources. The objective of grounding and bonding system components to a single point is to minimize any difference of potential that may develop between individual components within the system and within the equipment site or area. To reach this objective a low-impedance internal single-point ground system is required for all communication equipment, support equipment, power systems, and other items and materials located within the building, shelter, room or area of the same building. A single point ground system is defined as a single point, typically a master ground bus bar (MGB), within a shelter, equipment building or room, where all communications equipment, ancillary support equipment, antenna transmission lines, surge protection devices (SPDs), and utility grounds are bonded. The single point ground system must be effectively connected to a grounding electrode system as described in this chapter and in Chapter 4, “External Grounding (Earthing)”. The system is defined as all equipment required for proper communications system functionality at the site, and includes but is not limited to: • Communications and support equipment • Power systems • Power distribution systems • Voice, data and video circuits • Antenna systems • Global Positioning System (GPS) • Surge protection devices • Support components and material. The equipment site or area is defined as the equipment building, shelter, room or area within another room where communications equipment or systems may be located and includes but is not limited to: • Heating, ventilation and air conditioning (HVAC) systems • Fire suppression systems • Power distribution systems • The building structure 68P81089E50-B 9/1/05 5-3
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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 4 EXTERNAL 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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