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Bonding to the External Grounding (Earthing)

1. The following general observations can be made from Table 4 5 Copper clad steel or solid copper ground rods are one of the better and commonly used materials for grounding electrodes However the adverse effect of dissolved salts organic acids and acid soils generally should be noted BS 7430 1998 clause 11 Copper or copper clad ground rods should not be used in soils where organic acids are present unless protective measures are taken such as encasing the ground rods in a grounding electrode encasement material Organic acids are commonly found in poorly drained and poorly aerated soils See Grounding Earthing Electrode Encasement Materials on page 4 27 Galvanized ground rods should not be used in soils with a redox potential below 200 mV unless protective measures are taken such as encasing the ground rods in a grounding electrode encasement material See Grounding Earthing Electrode Encasement Materials on page 4 27 Galvanized ground rods should not be used in acidic soils with a pH below 6 4 5 2 GALVANIC CORROSION Galvanic corrosion also called dissimilar metals corrosion refers to corrosion damage induced when two dissimilar metals are electrically connected and coupled through an electrolyte such as soil When a metal is electrically connected to a dissimilar metal a difference of potential exists between the two metals If the dissimilar metals are also in contact with a low resistivity soil a complet
2. Properly dry all metal parts and molds prior to welding The exothermic welding process is shown in Figure 4 28 CRUCIBLE MOLD CLAMPED TO TOWER FIGURE 4 28 EXOTHERMIC WELDING MOLD LEFT AND PROCESS RIGHT 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES BONDING TO THE EXTERNAL GROUNDING EARTHING ELECTRODE SYSTEM 4 6 2 2 68P81089E50 B 9 1 05 EXOTHERMIC WELD 7 EXOTHERMIC WELD Nu E FIGURE 4 29 EXAMPLES OF COMPLETED EXOTHERMIC WELDS IRREVERSIBLE HiGH COMPRESSION FITTINGS Warne Wear safety glasses hard hat and steel toes shoes when working with high compression fittings When using irreversible high compression fittings always use the compression tool recommended by the manufacturer in accordance with the instructions provided by the manufacturer Use fittings made of the same material as the materials being bonded to avoid dissimilar metal reactions See Figure 4 30 for examples of high compression fittings e Use fittings properly sized for the conductors being bonded e Use fittings and compression tools rated at 13 3 tonnes 12 tons of force e Use only UL listed connectors e To ensure good contact clean conductors using a wire brush before crimping e Coat all crimped connections with a listed conductive antioxidant compound before crimping 4 43 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 7
3. CONNECT FENCE BONDING CONDUCTOR TO EXTERNAL GROUNDING ELECTRODE SYSTEM USING EXOTHERMIC WELD OR IRREVERSIBLE HIGH COMPRESSION FITTING FIGURE 4 49 FENCE FABRIC AND DETERRENT WIRING BONDING EXAMPLE 4 69 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING All gate posts on both sides of the gate shall be bonded to the nearest location of the building ground ring using 35 mm csa 2 AWG or coarser bare solid or stranded tinned copper conductors The grounding conductors shall be buried to the same depth as the building ground ring whenever practical ANSI T1 313 2003 figure 3 a e gates shall be bonded to the gate supporting fence post with 16 mm csa 6 AWG or coarser stranded copper conductors This jumper wire should be constructed with a highly flexible conductor ANSI T1 313 2003 figure 3 a See Figure 4 50 for an example FLEXIBLE BONDING JUMPER FIGURE 4 50 GATE BONDING EXAMPLE If the site has non electrified entry deterrent fence headers of barbed wire razor wire or other metallic wiring the headers shall be grounded bonded as follows e The deterrent wiring near each corner fence post shall be bonded to the nearest location of the building ground ring using 35mm csa 2 AWG or coarser bare solid or stranded tinned copper conductor This bond may be made using the same grounding
4. FIGURE 4 3 COMMON GROUNDING EXAMPLE 68P81089E50 B 9 1 05 4 6 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 4 4 68P81089E50 B GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 9 1 05 Warne To prevent accidental damage to underground utilities always have the local utility company or utility locator service locate the underground utilities before excavating or digging at a site The external grounding earthing electrode system may consist of but is not limited to the following components shown in Figure 4 4 e Ground rods or other grounding electrodes e Concrete encased electrode Building or shelter ground ring e Tower ground ring e Grounding conductors e Radial grounding conductors Guy wire grounding conductors guyed towers only e Tower ground bus bar e External ground bus bar e Fence grounding conductors GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING lt NENNE NENENEN NNN A PASADA D WAWATA TATATATA NATAT V A CG N e SD amp FIGURE 4 4 TYPICAL EXTERNAL GROUNDING ELECTRODE SYSTEM 4 8 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 4 4 1 68P81089E50 B
5. on page 4 22 e The tower ground ring shall consist of at least two ground rods installed on opposite diametrically opposed sides ANSI T1 313 2003 section 10 3 1 ANSI T1 334 2002 section 5 2 and ANSI TIA EIA 222 F R2003 section 12 e Ground rods shall meet the specifications and be installed in accordance with Ground Rods on page 4 11 e bottom plate of a guyed tower shall be bonded to the tower ground ring using three equally spaced grounding conductors or each leg shall be bonded to the tower ground ring using grounding conductors of 35 mm See Figure 4 35 csa 2 AWG or coarser bare solid tinned copper conductor e tower grounding conductors shall be exothermically bonded to the tower unless specifically directed otherwise by the tower manufacturer e tower s support piers concrete footings should have the rebar electrically connected to the tower holding bolts ANSI T1 313 2003 section 10 3 1 e Install radial grounding conductors if needed See Radial Counterpoise Grounding Conductors on page 4 24 GROUND RING c GROUND ROD EXOTHERMIC WELD OR IRREVERSIBLE HIGH COMPRESSION FITTING FIGURE 4 35 EXAMPLE OF GUYED TOWER GROUNDING 68P81089E50 B 9 1 05 4 53 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 54 4 7 6 2 1 Guy ANCHOR POINTS Grounding earthing guy anchor points requires special attenti
6. All tower guy anchors that are attached directly to the building shall be bonded to the main roof perimeter lightning protection ring ANSI T1 313 2003 section 10 3 3 conductors shall meet the installation requirements of Grounding Earthing Conductors on page 4 28 e Conductor bonding shall be made using exothermic welding listed irreversible high compression fittings or other fittings listed for use in lightning protection systems See Bonding to the External Grounding Earthing Electrode System on page 4 40 See Figure 4 57 for an example of a typical rooftop tower grounding system 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING APPLICATIONS MAIN ROOF PERIMETER ROOFTOP TOWER LIGHTNING PROTECTION RING GROUND RING AIR TERMINAL TOWER GROUNDING CONDUCTOR BONDED WITHIN 24 INCHES OF THE GROUNDING DOWN CONDUCTOR ROOFTOP TOWER TOWER GROUNDING CONDUCTOR 1 OF 2 MINIMUM BUILDING GROUND RING E PART OF THE COMPLETE GROUNDING ELECTRODE SYSTEM GROUNDING DOWN CONDUCTOR 1 OF 4 SHOWN FIGURE 4 57 TYPICAL ROOFTOP TOWER GROUNDING RING 4 10 SPECIAL GROUNDING EARTHING APPLICATIONS Some communications site locations and or applications require special consideration for effective grounding earthing The following sections describe the grounding techniques for some common communications applications Consultation
7. FIGURE 4 12 RESISTANCE TO EARTH DUE TO GROUND ROD LENGTH 4 15 GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 4 1 2 4 EFFECT OF PARALLEL GROUND RODS Figure 4 13 below shows the effects of adding additional ground rods 15 9 mm 0 625 in diameter by 3 10 ft long together in parallel As seen in the figure the addition of one ground rod to the first ground rod for a total of two rods significantly reduces the resistance to earth of the ground rod system Each subsequent ground rod added in parallel has less of an effect on the resistance to earth of the ground rod system 35 30 4 25 20 4 Approximate Resistance to Earth in Ohms 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Number of 3 m 10 ft Ground Rods Installed 6 1 m 20 ft apart in 10 000 ohm cm soil FIGURE 4 13 RESISTANCE TO EARTH DUE TO PARALLEL GROUND RODS 4 4 1 3 ELECTROLYTIC GROUND RODS At sites where due to poor soil conductivity high resistivity and or limited space an acceptable grounding earthing electrode system resistance cannot be achieved using standard ground rods commercially available electrolytic ground rods should be considered See MIL HDBK 419A Volume I section 2 9 5 and UL 467 2004 section 9 2 7 for additional information Electrolytic ground rods Figure 4 14 are available in straight or L shaped versions and in various lengths fro
8. GROUND LUG LOCKWASHER FIGURE 4 27 PROPER LOCATION OF WASHER WHEN CONNECTING GROUNDING LUG NOTE In some instances exothermic welding may not be possible or may be prohibited by the specific component manufacturer such as towers or fences in these cases other suitable means for bonding is allowed 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES BONDING TO THE EXTERNAL GROUNDING EARTHING ELECTRODE SYSTEM 4 6 2 4 6 2 1 68P81089E50 B 9 1 05 Connecting hardware shall be listed for the purpose for the type of conductor and for the size and number of conductors used All mechanical connections shall be coated with a listed conductive anti oxidant compound NFPA 70 2005 Article 250 70 All exothermic and irreversible compression connections for use on external grounding applications shall be UL 467 listed Copper connectors shall maintain minimum 88 conductivity rating Compression systems shall include crimped die index and company logo for purposes of inspection Aluminum shall not be used for connection purposes Bonding shall be performed so that a suitable and reliable connection exists The following requirements shall be observed when bonding grounding connections Paint enamel lacquer and other nonconductive coatings shall be removed from threads and surface areas where connections are made to ensure good electrical continuity NFPA 70 2005 Article 250 12 Use of a star washer doe
9. GROUNDING EARTHING ELECTRODES Grounding earthing electrodes are the conducting elements used to connect electrical systems and or equipment to the earth The grounding electrodes are placed into the earth to maintain electrical equipment at the potential of the earth Grounding electrodes may be ground rods metal plates concrete encased electrodes ground rings electrolytic ground rods the metal frame of building or structure and metal underground water pipes NFPA 70 2005 Article 250 III NOTE Metallic underground gas piping shall not be used as a grounding electrode NFPA 70 2005 Article 4 4 1 1 9 1 05 250 52 but shall be bonded upstream from the equipment shutoff valve to the grounding electrode system as required by NFPA 70 2005 Article 250 104 and NFPA 780 2004 section 4 14 1 3 GROUNDING EARTHING ELECTRODE RESISTANCE CHARACTERISTICS AND SPHERE OF INFLUENCE Around a grounding earthing electrode such as a driven ground rod the resistance of the soil is the sum of the series resistances of virtual concentric shells of earth located progressively outward from the rod The shell nearest the ground rod has the smallest circumferential area or cross section so it has the highest resistance Successive outward shells have progressively larger areas therefore progressively lower resistances IEEE STD 142 1991 section 4 11 and MIL HDBK 419A Rod Length EN 2X Rod Length Concentric Shells FIGURE 4
10. Typically this will include a grounding point or multiple grounding points with at least two direct connections to the building s grounding electrode system The direct connection to the building s grounding electrode system may be made using effectively grounded structural building steel preferred and or down conductors Other engineered antenna mast and support structure grounding systems may include metallic antenna support structures that are directly and effectively bonded to effectively grounded structural building steel When a lightning protection system is installed on the building roof mounted antenna masts and support structures shall be bonded to the lightning protection system IEC 61024 1 2 and NFPA 780 2004 section 4 17 The conductor shall be of the same size as the Main Roof Perimeter Lightning Protection Ring FAA STD 019d 2002 section 3 7 9 4 Conductor bonding shall be made using exothermic welding listed irreversible high compression fittings or other fittings listed for use in lightning protection systems See Bonding to the External Grounding Earthing Electrode System on page 4 40 No additional grounding shall be required of roof mounted antenna masts and support structures when bonded to a lightning protection system 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ROOF MOUNTED ANTENNA MASTS AND METAL SUPPORT STRUCTURES 68P81089E50 B 9 1 05 When a ligh
11. below the surface of the earth NFPA 70 2005 Article 250 53 If soil conditions do not allow the ground plate to be buried at this depth see Shallow Topsoil Environments on page 4 97 for additional information Where practical a ground plate shall be embedded below permanent moisture level BS 7430 1998 clause 10 and NFPA 70 2005 Article 250 53 Ground plates should be installed vertically to allow for minimum excavation and better contact with the soil when backfilling BS 7430 1998 clause 10 and IEEE STD 142 1991 section 4 2 4 See Figure 4 16 SERRATED EDGES PROVIDE MORE STRAIGHT EDGES EDGE SURFACE FIGURE 4 15 TYPICAL GROUND PLATES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 20 4 4 1 5 TOP EDGE OF PLATE 762 mm 30 IN BELOW GRADE 2 AWG BARE COPPER WIRE BACKFILL MATERIAL GROUND RING 152 mm MINIMUM 6 IN MINIMUM ON ALL SIDES GROUND PLATE 1 5mm 0 06 in EXOTHERMIC CONNECTION SITE SOIL FIGURE 4 16 TYPICAL GROUND PLATE INSTALLATION e grounding electrode encasement material should be used to backfill around the ground plate to help insure effective contact with the earth BS 7430 1998 clause 10 See Grounding Earthing Electrode Encasement Materials on page 4 27 CONCRETE ENCASED ELECTRODES Though concrete encased electrodes also known as Uf
12. 2 AWG OR COARSER BARE COPPER CONDUCTOR ROUTED ON OPPOSITE SIDE FROM TRANSMISSION LINE GROUND KITS TRANSMISSION LINE TO SHELTER GROUND RODS FIGURE 4 39 WOODEN POLE GROUNDING 4 58 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 4 7 7 4 7 7 1 68P81089E50 B 9 1 05 DEDICATED COMMUNICATIONS BUILDING GROUNDING EARTHING All dedicated communications buildings shall have a properly installed external grounding earthing electrode system The grounding electrode system resistance shall meet the requirements of Grounding Earthing Electrode System Resistance Requirements on page 4 46 A typical site grounding electrode system layout is shown in Figure 4 4 on page 4 8 The building grounding electrode system requirements are listed below and shall also include any additional grounding electrode system components required to achieve the resistance requirements of the site See Minimum Site Grounding Earthing Requirements on page 4 44 e Installation of concrete encased electrodes as part of new construction See Concrete Encased Electrodes on page 4 20 e building shall be encircled by a ground ring installed in accordance with External Building and Tower Ground Ring on page 4 22 e The building ground ring shall have a ground rod installed near the external ground bus bar EGB a
13. 53 It is recommended to install the ground rods so the upper end of the rod is buried to a minimum depth of 610 mm 24 in below the surface of the earth NFPA 780 2004 section 4 13 2 3 See Figure 4 8 for typical single ground rod installations 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS GROUNDING CONDUCTOR GROUNDING CONDUCTOR TOP OF ROD JUST BELOW SOIL SURFACE RECOMMENDED DEPTH MINIMUM DEPTH FIGURE 4 8 TYPICAL SINGLE GROUND ROD INSTALLATION e Ground rods shall not be installed closer than 1 8 m 6 ft from other ground rods and grounding electrodes NFPA 70 2005 Article 250 56 See Figure 4 31 on page 4 49 for an example Unless otherwise stated in this chapter ground rods shall not be installed closer to one another than the sum of their respective lengths when possible This is especially important for the ground rods associated with tower ground rings See Grounding Earthing Electrode Resistance Characteristics and Sphere of Influence on page 4 9 e See External Building and Tower Ground Ring on page 4 22 for ground rod installation requirements on ground rings method of bonding grounding conductors to ground rods shall be compatible with the types of metals being bonded See Dissimilar Metals and Corrosion Control on page 4 34 e Ground rods that cannot be driven straight do
14. 7 mm 0 5 in in diameter e Concrete encased electrodes shall be bonded to any other grounding electrode system at the site See Common Grounding Earthing on page 4 5 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 25 mm CSA 4 AWG OR COARSER BARE COPPER GROUNDING ELECTRODE CONDUCTOR OR STEEL CONDUCTOR REINFORCING BAR OR ROD NOT LESS THAN 12 7 mm 0 5 in NONMETALLIC DIAMETER AND AT LEAST 6 1 m PROTECTIVE SLEEVE 20 ft LONG CONNECTION LISTED FOR THE PURPOSE 51 mm 2 in MINIMUM FOUNDATION IN DIRECT CONTACT WITH EARTH CLAMP SUITABLE FOR ENCASEMENT OR EXOTHERMIC WELD MINIMUM 6 1 m 20 ft SIDE VIEW i END VIEW 12 7 mm 0 5 in REBAR TYPICAL 25 mm csa 4 AWG COPPER CONDUCTOR MINIMUM 6 1 m 20 ft SIDE VIEW END VIEW FIGURE 4 17 TYPICAL CONCRETE ENCASED ELECTRODES 68P81089E50 B 9 1 05 4 21 GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 22 4 4 1 6 EXTERNAL BUILDING AND TOWER GROUND RING The buried external ground rings building and tower provide a means of bonding ground rods together and bonding other grounding earthing electrode system components together improving the overall grounding electrode system The ground rings also help to equalize potential in the earth surrounding the
15. AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING PPLICATIONS 4 10 3 3 68P81089E50 B 9 1 05 4 10 3 2 1 SIDE MOUNTED Access points and wireless routers mounted to the side of a building shall be bonded directly to the building s common grounding earthing electrode system using a 16 mm csa 6 AWG or coarser solid or stranded copper conductor grounding conductors installed partially below ground shall be 35 mm csa 2 AWG or coarser Connection to access points and wireless routers shall be made to an adequately sized dedicated grounding point in accordance with the device manufacturer requirements The grounding conductor shall meet the specifications and installation requirements of Grounding Barthing Conductors on page 4 28 4 10 3 2 2 ROOF MOUNTED Access Points and Wireless Routers mounted on the roof a building shall be bonded directly to an available location of the building s common grounding earthing electrode system using 16 mm csa 6 AWG or coarser solid or stranded copper conductor grounding conductors installed partially below ground shall be 35 mm csa 2 AWG or coarser Connection to access points and wireless routers shall be made to an adequately sized dedicated grounding point in accordance with the device manufacturer requirements The grounding conductor shall meet the specifications and installation requirements of Grounding Earthing Conductors on page 4 28 An
16. And Routing Grounding Earthing Conductors on page 4 29 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 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 e Bolting a tin plated bus bar directly to the tower structure using stainless steel hardware In this case a grounding conductor is not required e Securing a bus bar to the tower using appropriate mechanical hardware Electrically bonding the bus
17. and or military installations longer rods such as 3 m 10 ft should be considered for the minimum length MIL HDBK 419A and MIL STD 188 124B Ground rods shall have a minimum diameter of 15 9 mm 0 625 in ANSI T1 313 2003 section 10 3 1 and ANSI T1 334 2002 section 5 3 2 unless otherwise allowed by the UL listing of the ground rod UL 467 See NFPA 70 2005 Article 250 52 for additional information Ground rods shall be free of paint or other nonconductive coatings NFPA 70 2005 Article 250 53 and NFPA 780 2004 section 4 13 2 4 4 1 2 2 GROUND ROD INSTALLATION Where practical ground rods shall be buried below permanent moisture level MIL HDBK 419A and NFPA 70 2005 Article 250 53 Where practical ground rods shall penetrate below the frost line MIL HDBK 419A Ground rods longer than the minimum required 2 4 m 8 ft may be required to maintain contact with permanently moist unfrozen soil MIL HDBK 419A When part of a ground ring system the upper end of the ground rods shall be buried to the depth of the ground ring typically 762 mm 30 in minimum below finished grade The upper end of the ground rods should be buried to the same depth as the ground ring to allow for easy bonding to the ground ring See External Building and Tower Ground Ring on page 4 22 When not part of a ground ring system such as in a Type A site the entire length of the rod shall be in contact with soil NFPA 70 2005 Article 250
18. 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 E cum om TOWER GROUND BUS BAR TRANSMISSION LINES TO BUILDING TOWER GROUND RING UNDERGROUND FIGURE 4 25 TYPICAL TOWER GROUND BUS BARS 4 33 DISSIMILAR METALS AND CORROSION CONTROL CHAPTER 4 EXTERNAL GROUNDING EARTHING TABLE 4 4 TOWER GROUND BUS BAR SPECIFICATIONS Item Specification Material Bare solid Alloy 110 99 9 copper bus bar or plate of one piece construction Should be tin plated if installing on a galvanized tower See Dissimilar Metals and Corrosion Control on page 4 34 for information regarding tower corrosion related to copper bus bars Minimum Dimensions ANSI J STD 607 A 2002 and NFPA 70 2005 Article 250 64 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 Mounting brackets Stainless steel 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 convenien
19. bonded to the grounding conductor at both ends NFPA 70 2005 Article 250 64 and NFPA 780 2004 section 4 9 11 1 e grounding conductor or its enclosure shall be securely fastened to the surface on which it is carried NFPA 70 2005 Articles 250 64 and 810 21 and NFPA 780 2004 section 4 10 e Grounding conductors shall be secured using appropriate hardware intended for the purpose e When metallic fasteners are used on bare grounding conductors fasteners of the same material shall be used or approved bonding techniques shall be observed for the connection of dissimilar metals See Dissimilar Metals and Corrosion Control on page 4 34 See NFPA 780 2004 section 4 10 2 for additional information e Above ground grounding conductors shall be securely fastened at intervals not exceeding 91 cm 3 ft where practical ANSI T1 334 2002 section 8 3 and NFPA 780 2004 Section 4 10 EXTERNAL GROUND BUS BAR The purpose of the external ground bus bar EGB is to provide a convenient grounding earthing termination point for antenna transmission lines coaxial cables and other cables prior to their entry into a building or shelter ANSI T1 313 2003 Antenna transmission lines and other communications cables with metallic sheaths shall be grounded as close as practical to their point of entry into the building or shelter NFPA 70 2005 articles 770 93 800 100 810 20 820 93 and 820 100 Requirements for external ground bus bars w
20. communications tower ground lightning protection system ground telephone system ground exposed structural building steel underground metallic piping that enters the facility and any other existing grounding electrode system shall be bonded together to form a single grounding electrode system 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 All grounding media in or on a structure shall be interconnected to provide a common ground potential This shall include but is not limited to the AC power system ground communications tower ground lightning protection system ground telephone system ground exposed structural building steel and underground metallic piping systems Underground metallic piping systems typically include water service well castings located within 7 6 m 25 ft of the structure gas piping underground conduits underground liquefied petroleum gas piping systems and so on Interconnection to a gas line shall be made on the customer s side of the meter NFPA 780 2004 Section 4 14 1 3 CHAPTER 4 EXTERNAL GROUNDING EARTHING COMMON GROUNDING EARTHING TO SUPPLY TRANSFORMER BUILDING SERVICE STEEL EQUIPMENT GROUNDED TO LIGHTNING CONDUCTOR PROTECTION SYSTEM CONCRETE ENCASED ELECTRODE GROUND RING GROUND ROD
21. conductors shall be sized as follows e The conductor shall be a 35 mm csa 2 AWG or coarser bare copper or equivalent for buildings not exceeding 22 9 m 75 ft in height NFPA 780 2004 Table 4 1 1 1 A conductor shall be a 70 mm csa 42 0 AWG or coarser bare copper or equivalent for buildings equal to or exceeding 22 9 m 75 ft in height NFPA 780 2004 Table 4 1 1 1 B Available effectively grounded structural building steel can typically be used as a grounding down conductor The conductor used to bond the main roof perimeter lightning protection ring to the structural building steel shall be sized as required in this section for down conductors See Figure 4 53 on page 4 75 for an example of acceptable structural building steel bonding connections e Structures exceeding 76 m 250 ft in perimeter shall have a down conductor for every 30 5 m 100 ft of perimeter or fraction thereof NFPA 780 2004 section 4 9 10 1 4 79 GROUNDING EARTHING ROOFTOP MOUNTED TOWER STRUCTURES CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 80 Other metallic objects on the roof shall be bonded to the roof perimeter lightning protection system ring as required by BS 6651 1999 IEC 61024 1 2 NFPA 780 2004 or other standard in effect and recognized by the local authority having jurisdiction All grounding electrodes at the building shall be bonded together to form a single grounding electrode system See Common Groun
22. follow the contour or run parallel to the supporting structure See Figure 4 22 e All bends and curves shall be made toward the ground location grounding electrode system or ground bar I 90 degrees minimum 4 f ll ll The radius of any bend shall not The angle of any bend shall not be less than 203 mm 8 in be less than 90 degrees FIGURE 4 22 MINIMUM BENDING RADIUS FOR GROUNDING CONDUCTORS 4 29 GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 4 3 4 30 4 4 2 3 PROTECTING AND SECURING GROUNDING EARTHING CONDUCTORS Above ground external grounding earthing conductors including straps are exposed to movement by wind and other physical forces that can lead to damage or breakage over time The following requirements shall apply when installing grounding conductors e Grounding conductors shall be protected where exposed to physical damage NFPA 70 2005 Articles 250 64 800 100 810 20 820 100 and NFPA 780 2004 section 4 9 11 e Grounding conductors exposed to physical damage shall be protected for a minimum distance of 1 8 m 6 ft above grade level NFPA 780 2004 section 4 9 11 2 Such areas may include but are not limited to runways driveways school playgrounds cattle yards public walks NFPA 780 2004 section 4 9 11 Metallic guards and or conduits used to protect grounding conductors shall be
23. of the building within 1 8 m 6 ft of the building shall be bonded to the nearest practical location on the grounding earthing electrode system as shown in Figure 4 40 on page 4 60 using a 16 mm csa 6 AWG or coarser copper conductor ANSI T1 334 2002 section 5 3 3 Grounding conductors routed below ground or partially below ground shall be a 35 mm csa 2 AWG or coarser bare solid tinned or un tinned copper conductor External generator grounding shall comply with the following e Bonding to the generator chassis shall be done in accordance with the manufacturer s requirements 4 59 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 60 grounding conductors shall meet the requirements of Grounding Earthing Conductors on page 4 28 e Bonding to the grounding electrode system shall be made using exothermic welding or listed irreversible high compression fittings See Bonding to the External Grounding Earthing Electrode System on page 4 40 Generators installed more than 1 8 m 6 ft away from the building shall be bonded to the nearest practical location on the grounding electrode system as describe above for generators within 1 8 m 6ft of the building In addition the generator shall have a ground rod installed nearby and bonded to the generator ANSI T1 313 2003 See Figure 4 40 Installation of the addition generator ground rod shall comply with
24. on page 4 27 See MIL HDBK 419 A Volume I section 2 11 2 for additional information 4 99 SPECIAL GROUNDING EARTHING SITUATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING THIS PAGE INTENTIONALLY LEFT BLANK 4 100 68P81089E50 B 9 1 05
25. parallel rods and or ground radials See Radial Counterpoise Grounding Conductors on page 4 24 and Figure 4 65 on page 4 90 See Interpreting Test Results on page B 10 to determine the number of rods and rod spacing required to achieve the resistance requirements of the site STONE MOUNTAIN TOPS Some sites are located on mountaintops because of their RF propagation characteristics In the instances where there is no or very little top soil at the site special designs will be needed Some options for an effectively grounded earthed site are listed below reasonable attempts should be made to use as many options as possible and as needed to meet the ground resistance requirements of the site e Consult with Motorola Engineering or other engineering firm e Installation of concrete encased electrodes as part of new construction See Concrete Encased Electrodes on page 4 20 e Installation of radial grounding conductors from the tower and building throughout the property Install the radial grounding conductors to a depth allowed by the soil preferably 457 to 762 mm 18 to 30 in Encasing the radial grounding conductors in a grounding electrode encasement material can further increase the effectiveness of the grounding electrode system See Radial Counterpoise Grounding Conductors on page 4 24 e Installation of ground rings around the building and tower with the ground rings buried as deep as the soil wil
26. section 2 2 2 1 If the design goal of 25 ohms cannot be achieved throughout the year with a single grounding electrode then the grounding electrode shall be augmented by at least one additional grounding electrode NFPA 70 2005 Article 250 56 See Soil Resistivity Variability and Factors Affecting Soil Resistivity on page B 1 for information regarding the seasonal variations in grounding electrode resistance 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS NOTE It is recommended to use two grounding electrodes as the minimum installation even if 25 ohms is achieved with a single grounding electrode Type A sites typically have the following characteristics e tower associated with the site e Non critical installation Not part of a larger system infrastructure e Single control station e RF alarm reporting site e Small telemetry cabinet utilizing an existing utility pole to support the antenna Single voting receiver site e be located in a commercial office or residence 4 7 4 2 SITES STANDARD DUTY Type B sites shall have a grounding earthing electrode system resistance design goal as low as practical and not over 10 ohms AS 3516 2 1998 BS 6651 1999 FAA STD 019d 2002 MIL HDBK 419A and MIL STD 188 124A Motorola recommends a design goal of 5 ohms or less also see the International Association of Elec
27. shall be installed as needed to limit the distance between 2 4 m 8 ft ground rods from 3 m to 4 6 m 10 to 15 ft ANSI T1 334 2002 if longer ground rods are used a larger separation proportional to the increase in rod length may be used See Grounding Earthing Electrode Resistance Characteristics and Sphere of Influence on page 4 9 for additional information SELF SUPPORTING TOWERS INCLUDING MONOPOLES Self supporting towers shall minimally be grounded earthed as follows e tower shall be encircled by a ground ring ANSI T1 334 2002 section 5 and MIL HDBK 419A e tower ground ring shall be installed at least 610 mm 2 ft from the tower structure base or footing ANSI T1 334 2002 section 5 3 1 e The tower ground ring shall be installed in accordance with External Building and Tower Ground Ring on page 4 22 e tower ground ring shall be bonded to the building ground ring in at least two points using a 35 mm csa 2 AWG or coarser bare solid tinned or un tinned copper conductor ANSI T1 334 2002 figure I and MIL STD 188 124B See External Building and Tower Ground Ring on page 4 22 and Figure 4 18 on page 4 23 e For towers not exceeding 1 5 m 5 ft in base width including monopoles the tower ground ring shall consist of at least two ground rods installed on opposite diametrically opposed sides ANSI T1 313 2003 section 10 3 1 ANSI T1 334 2002 section 5 2 and ANSI TIA E
28. structure using guy insulators may help reduce the transmission of stray currents from outside sources therefore minimizing electrolytic corrosion TIA EIA 222 F R2003 section 4 1 Guy isolators should only be installed under the advice of a professional engineer Galvanic corrosion due to the presence of copper ground rods is greatly reduced if the ground wires are connected on the tower side of the isolation point TIA EIA 222 F R2003 section 4 1 A ground rod shall be installed at each guy anchor point ANSI TIA EIA 222 F R2003 Ground rods shall meet the specifications and be installed in accordance with Ground Rods on page 4 11 In order to reduce galvanic corrosion from the galvanized guy anchor point to a nearby copper ground rod this ground rod shall be constructed of galvanized steel unless a guy insulator is used TIA EIA 222 F R2003 section 4 1 4 55 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING COPPER GROUND ROD 1 CORROSION FROM STEEL ANCHOR SHAFT TO COPPER GROUND ROD AND OTHER COPPER GROUNDING ELECTRODE SYSTEM COMPONENTS 2 CORROSION FROM STEEL ANCHOR SHAFT TO THE PORTION OF ANCHOR SHAFT ENCASED IN CONCRETE STEEL ENCASED IN CONCRETE IS SIMILAR TO COPPER FIGURE 4 37 GUY ANCHOR GALVANIC CORROSION EXAMPLE e All guy wires at a guy anchor point shall bond to the ground rod ANSI T1 313 2003 section 10 3 1 and ANSI TIA EIA 222 F R2003 using a grounding condu
29. system from opposite sides of the roof whenever practical ANSI T1 334 2002 section 8 2 Down conductors shall be physically separated from one another as much as practical ANSI T1 334 2002 section 8 2 Additional requirements for down conductors are as follows e Grounding down conductors shall be sized as follows conductor shall be a 35 mm csa 2 AWG or coarser bare copper or equivalent for buildings not exceeding 22 9 m 75 ft in height NFPA 780 2004 Table 4 1 1 1 A e The conductor shall be a 70 mm csa 82 0 AWG or coarser bare copper or equivalent for buildings equal to or exceeding 22 9 m 75 ft in height NFPA 780 2004 Table 4 1 1 1 B e Grounding down conductors shall be protected from physical damage NFPA 70 2005 Article 810 21 d and NFPA 780 2004 section 4 9 11 See Protecting and Securing Grounding Earthing Conductors on page 4 30 e Grounding down conductors shall be permitted to be run either outside or inside the building or structure NFPA 70 2005 Article 810 21 g 4 75 GROUNDING EARTHING ROOF MOUNTED ANTENNA MASTS AND METAL SUPPORT STRUCTURES CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 76 NOTE NOTE e Grounding down conductors shall not be required to be insulated NFPA 70 2005 Article 810 21 b Insulated conductors are recommended when the grounding conductor may come into incidental contact with other metallic objects Incidental contact with other metall
30. system shall be constructed of only listed components The lightning protection system shall meet the requirements of BS 6651 1999 IEC 61024 1 2 NFPA 780 2004 or other standard in effect and recognized by the local authority having jurisdiction As a minimum the lightning protection system shall contain the following e The lightning protection system shall contain a grounding conductor installed around the roof perimeter to form the main roof perimeter lightning protection ring The main roof perimeter lightning protection ring shall be sized as follows conductor shall be a 35 mm csa 2 AWG or coarser bare copper or equivalent for buildings not exceeding 22 9 m 75 ft in height NFPA 780 2004 Table 4 1 1 1 A conductor shall be a 70 mm csa 2 0 AWG or coarser bare copper or equivalent for buildings equal to or exceeding 22 9 m 75 ft in height NFPA 780 2004 Table 4 1 1 1 B e Strike termination devices also known as air terminals are typically installed along the length of the main roof perimeter lightning protection ring typically every 6 1 m 20 ft or as otherwise required by the standard in effect and recognized by the local authority having jurisdiction e The main roof perimeter lightning protection ring shall contain at least two down conductors connected to the grounding electrode system The down conductors shall be physically separated from one another as much as practical The down
31. throughout the world These figures are for general informational and educational purposes only and are not indicative of current or future lightning activity The average amount of lightning that occurs in any given area varies significantly from year to year EUROPE AMERICA AFRICA SOUTH AMERICA FIGURE 4 1 LIGHTNING ACTIVITY THUNDERSTORM DAYS PER YEAR 68P81089E50 B 9 1 05 4 3 LIGHTNING ACTIVITY AND EXPOSURE CHAPTER 4 EXTERNAL GROUNDING EARTHING TT ca 270 p nre yit d 1 FIGURE 4 2 LIGHTNING ACTIVITY FLASH DENSITY FLASHES PER SQUARE KILOMETER PER YEAR Table 4 1 provides a relationship between thunderstorm days per year and lightning flashes per square kilometer per year BS 6651 1999 table 6 TABLE 4 1 RELATIONSHIP BETWEEN THUNDERSTORM DAYS PER YEAR AND LIGHTNING FLASHES PER SQUARE KILOMETER PER YEAR Flashes per square kilometer Flashes per square mile per per year year Thunderstorm days per year Mean Limits Mean Limits 5 0 2 0 1 to 0 5 0 5 0 25 to 1 35 10 0 5 0 15 to 1 1 29 0 38 to 2 59 20 1 1 0 3 to 3 2 84 0 77 to 7 77 30 1 9 0 6 to 5 4 92 1 55 to 13 40 2 8 0 8 to 8 7 25 2 to 20 7 50 3 7 1 2 to 10 9 58 3 1 to 25 9 60 4 7 1 8 to 12 12 17 4 66 to 31 80 6 9 3 to 17 17 87 7 8 to 44 100 92 4 to 20 23 82 10 36 to 51 8 NOTE Information obtained from BS 6651 1999 Table 6 4 4 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES
32. using heavy duty tinned pipe clamps designed for fence grounding and stainless steel hardware or equivalent Residential grade and or preexisting fencing will not typically withstand exothermic welding Fences around tower guy anchor points shall be bonded to the guy anchor ground rod using 35 mm csa 2 AWG or coarser bare solid tinned copper conductors and bonded as outlined above Guy anchor fence gates shall be bonded as described above AN caution Braided straps shall not be used because they corrode too quickly and can be a point for RF interference CABLE BRIDGE ICE BRIDGE GROUNDING EARTHING Cable bridges and ice bridges are used to protect and support RF transmission lines between the tower structure and the equipment building shelter When present cable bridges and ice bridges shall be bonded to the grounding earthing electrode system Grounding of self supported cable bridges ice bridges shall be completed as follows Figure 4 51 e support post shall bond to the grounding electrode system using 35 mm csa 2 AWG or coarser bare tinned copper conductor e Conductor bonding to the grounding electrode system shall be made using exothermic welding or listed irreversible high compression fittings See Bonding to the External Grounding Earthing Electrode System on page 4 40 e Conductor bonding to the support posts shall be made using exothermic welding See Bonding to the External Gro
33. 1 e Installation of tower radial grounding conductors in a trench extending away from the tower and building The radial grounding conductors shall be buried as deep as the soil will allow The radial grounding conductors shall bond to the tower ground ring using exothermic welding or listed irreversible high compression fittings The radial grounding conductors should be encased in a grounding electrode encasement material A conductive concrete may be the best grounding electrode encasement material for use in shallow topsoil environments since the conductive concrete would not require a covering of topsoil for protection Each radial grounding conductor may have ground plates installed every 1 8 to 4 9 m 6 to 16 ft along its length See Figure 4 71 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING SITUATIONS 4 11 7 68P81089E50 B COMMUNICATION SITE UFER GROUND VERTICAL GROUND PLATE GROUND RADIAL FIGURE 4 71 GROUNDING ELECTRODE SYSTEM WITH GROUND PLATES AND RADIALS GROUNDING EARTHING IN ARCTIC REGIONS It may be difficult to achieve an effective low resistance grounding earthing electrode system at sites located in arctic regions or similar cold climates In these cases consultation with an engineering firm is recommended The primary issue with achieving an effective grounding electrode system in arctic regions is making good contact with frozen high resistivity
34. 2 Buried 457 mm 18 in in 10 000 ohm cm soil Approximate Resistnce b Earth in Ohms 5 Buried 762 mm 30 in in 10 000 ohm cm soil 10 20 30 40 50 60 70 80 Radial Grounding Conductor Length feet Radial Grounding Conductor Resistance AWG 2 0 Buried 457 mm 18 in in 10 000 ohm cm soil Approximate Resistance to Earth in Ohms Buried 762 mm 30 in in 10 000 ohm cm soil 10 20 30 40 50 60 70 80 Radial Grounding Conductor Length feet FIGURE 4 20 RESISTANCE CHARACTERISTICS OF A RADIAL GROUNDING CONDUCTOR 4 26 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 4 4 1 8 4 4 1 9 68P81089E50 B 9 1 05 GROUND TEST WELLS Ground test wells are not required but may be desired for troubleshooting and or inspecting the grounding earthing electrode system components Ground test wells are typically constructed of PVC tubing 203 mm 8 in or more in diameter and have a detachable cover to keep debris out A typical PVC ground test well is shown in Figure 4 21 Cover typically metal removable for inspection of grounding electrode Test Well Ground Rod Exothermically Welded to Ground Ring Ground Rod FIGURE 4 21 TYPICAL GROUND TEST WELL GROUNDING EARTHING ELECTRODE ENCASEMENT MATERIALS The resistance to earth of a grounding earthing
35. 2002 section 5 4 If it is not practical to bond all conductors to the tower the tower shall have additional grounding conductors bonding it to the tower ground ring 70 mm 2 0 AWG or coarser conductor is recommended in this case e Conductor bonding shall comply with Bonding to the External Grounding Earthing Electrode System on page 4 40 conductors shall be constructed of 35 mm csa 2 AWG or coarser bare solid tinned or un tinned copper See Grounding Earthing Conductors on page 4 28 for conductor specifications and installation requirements ANSI T1 334 2002 section 5 4 conductors shall be buried at least 457 mm 18 in below ground ANSI T1 334 2002 section 5 4 When topsoil conditions allow it is recommended to bury the conductors to a depth of at least 762 mm 30 in ANSI J STD 607 A 2002 section C 9 2 this is especially important in areas where the frost line may reach 457 mm 18 in e minimum length of each conductor shall be 7 6 m 25 ft If the desired resistance to earth is not achieved at 7 6 m 25 ft the radial conductor may be extended to help obtain the desired resistance ANSI T1 334 2002 section 5 4 The maximum effective length for a single radial conductor is generally considered to be approximately 24 4 m 80 ft Adding additional conductors is generally more effective than extending the length of a single conductor When multiple radial conductor
36. 4 68 MOUNTAINTOP SYSTEMS INSTALLATION OF GROUND PLATES 4 93 SPECIAL GROUNDING EARTHING SITUATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 94 e Installation of down conductors to a lower area where there is usable soil for the installation of vertical ground rods The down conductors would be more effective if buried below ground like a radial grounding conductor wherever possible The down conductors shall be sized according to length as shown below in Table 4 8 based on MIL HDBK 419A See Figure 4 69 on page 4 96 TABLE 4 8 GROUNDING CONDUCTOR SIZING Conductor length in Conductor size in linear m ft mm csa AWG MCM Less than 10 Less than 33 33 62 2 10 36 12 5 34 41 42 4 1 12 8 16 42 53 52 1 0 16 5 20 54 66 67 4 2 0 20 4 25 6 67 84 85 3 0 25 9 32 85 105 107 4 0 32 3 38 1 106 125 126 70 250 MCM 38 4 45 7 126 150 152 300 MCM 46 53 34 151 175 177 350 MCM 53 76 1 176 250 253 4 500 MCM 76 4 91 39 251 300 300 600 MCM Greater than 91 39 300 380 750 MCM 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING SITUATIONS TABLE 4 9 STANDARD WIRE SIZES AVAILABLE FOR INTERNATIONAL MARKET Conductor size in mm csa Conduct
37. 4 7 1 4 44 MECHANICAL HYDRAULIC BATTERY POWERED FIGURE 4 30 HIGH COMPRESSION CONNECTORS AND TYPICAL CRIMPING TOOLS MINIMUM SITE GROUNDING EARTHING REQUIREMENTS This section provides the minimum grounding earthing requirements for installing a grounding electrode system at a communications site and for bonding site equipment to the grounding electrode system Reasonable attempts shall be made to achieve the grounding electrode system resistance design goal as defined in Grounding Earthing Electrode System Resistance Requirements on page 4 46 The requirements for installing a typical grounding electrode system are as follows Perform a soil resistivity test at the site as described in Appendix B Soil Resistivity Measurements Calculate the resistance of a single ground rod as described in Interpreting Test Results on page B 10 Determine the resistance requirement of the grounding electrode system based on the site type Light Duty or Standard Duty site See Grounding Earthing Electrode System Resistance Requirements on page 4 46 TYPE A SITE LIGHT DUTY Determine if the single ground rod will meet the minimum 25 ohm requirement If the single ground rod does not meet the 25 ohm requirement an additional ground rod or other grounding earthing electrode will be required See Type A Site Grounding Earthing on page 4 48 for additional information Install th
38. 5 4 45 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 7 4 4 46 NOTE 4 7 4 1 GROUNDING EARTHING ELECTRODE SYSTEM RESISTANCE REQUIREMENTS In order to disperse lightning energy into the earth without causing dangerous over voltage the shape and dimensions of the grounding earthing electrode system are more important than a specific resistance value of the grounding electrode system However a low resistance grounding electrode system is generally recommended IEC 61024 1 2 Attempts should be made to reduce the grounding electrode system resistance to the lowest practical value MIL HDBK 419A section 2 2 3 Although grounding electrode system resistance is important and should be met whenever possible it alone does not determine the suitability of the grounding electrode system to properly dissipate and control lightning energy The resistance of the grounding electrode system is only a general measure of merit Proper design and installation of the grounding electrode system installation of ground rings ground rods radial grounding conductors and the bonding of systems and equipment is as important as the resistance to earth Effective grounding electrode system shape and dimensions are achieved through the proper installation of the required and recommended grounding electrode system components listed throughout this chapter The required and recommended grounding electrode sys
39. 5 GROUNDING ELECTRODE SPHERE OF INFLUENCE The effect of the concentric shells is that it takes a finite amount of earth for a ground rod to fully realize its resistance value This finite amount of earth is commonly known as the ground rod s sphere of influence The sphere of influence for a ground rod is commonly thought of to be a radius around the ground rod equal to its length the ground rod achieves approximately 94 of its resistance value at this radius 100 is achieved at approximately 2 5 times the rod length IEEE STD 142 1991 section 4 1 See Figure 4 5 GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING Optimum Spacing 2X Rod Length 2X Rod Length 94 of the resistance to remote earth occurs within a radius equal to the length of the ground rod This radius is commonly used as the ground rod s sphere of influence Ground rod resistance at a radius from a 3 m x 16 mm 10 ft x 0 625 in ground rod From IEEE STD 142 1991 Table 9 4 10 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS NOTE In a given area more ground rods installed closer together such as one length apart from one another will achieve a lower resistance to earth than fewer rods installed further apart such as twice the length apart from one anothe
40. CHAPTER EXTERNAL GROUNDING EARTHING This chapter provides requirements and guidelines for designing and installing the external 4 1 68P81089E50 B grounding earthing electrode system at a communications site This chapter provides information on the following topics Lightning Activity and Exposure on page 4 3 Common Grounding Earthing on page 4 5 Grounding Earthing Electrode System Component and Installation Requirements on page 4 7 Dissimilar Metals and Corrosion Control on page 4 34 Bonding to the External Grounding Earthing Electrode System on page 4 40 Minimum Site Grounding Earthing Requirements on page 4 44 Grounding Earthing Roof Mounted Antenna Masts and Metal Support Structures on page 4 74 Grounding Earthing Rooftop Mounted Tower Structures on page 4 79 Special Grounding Earthing Applications on page 4 81 Special Grounding Earthing Situations on page 4 88 NOTE Throughout this chapter the terms grounding and earthing are used synonymously INTRODUCTION 9 1 05 The requirements and guidelines in this chapter are derived from a compilation of local and national codes widely accepted industry codes and standards and good engineering practices Such codes and standards are from but not limited to the following standards organizations Alliance for Telecommunications Industry Solutions ATIS American National Standards Instit
41. DUCTOR BACKFILL WEEP HOLES COVERED TEST WELL GRADE 35 csa 2 AWG OR COARSER COPPER CONDUCTOR BREATHER HOLES EXOTHERMIC WELD BACKFILL WEEP HOLES L SHAPED FIGURE 4 14 ELECTROLYTIC GROUND RODS 4 18 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 4 4 1 4 68P81089E50 B 9 1 05 GROUND PLATE ELECTRODES Ground plates Figure 4 15 may be used in special cases or if specifically engineered into the design of the grounding earthing electrode system Requirements for the use of ground plate electrodes are listed below Ground plates should only be used if soil conditions prohibit the use of standard ground rods or if specifically engineered into the grounding electrode system Ground plates should be UL listed or equivalent Ground plates shall be constructed of copper or copper clad steel Ground plates shall expose not less than 0 37 m 2 ft2 of surface to exterior soil MIL HDBK 419A section 2 5 5 NFPA 70 2005 Article 250 52 and NFPA 780 2004 section 4 13 6 1 Ground plates shall have a minimum thickness of 1 5 mm 0 06 in MIL HDBK 4194A section 2 5 5 and NFPA 70 2005 Article 250 52 Ground plates shall be free of paint or other nonconductive coatings NFPA 70 2005 Article 250 53 and NFPA 780 2004 section 4 13 2 2 Ground plates shall be buried not less than 762 mm 30 in
42. E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES DISSIMILAR METALS AND CORROSION CONTROL The least aggressive soils tend to be those having a high resistivity The resistivity of soil can be measured which provides an indication of corrosiveness under aerated conditions BS 7430 1998 See Performing Soil Resistivity Test on page B 6 for measurement details Soil with a resistivity below 2 000 ohm centimeters Q cm is generally considered to be highly corrosive TIA EIA 222 F R2003 More details about the aggressiveness of soils can be obtained by measuring the redox from the words reduction and oxidation potential of the soil which indicates the risk of corrosion due to the presence of anaerobic bacteria BS 7430 1998 Test equipment required to measure redox potential is commercially available The procedure required to test the redox potential can be found in ISO 11271 2002 E A geotechnical firm may be required to measure the redox potential of the soil General guidance on the corrosiveness of some grounding electrode system metals in relation to soil composition is given below in Table 4 5 BS 7430 1998 A geotechnical firm may be required to determine all of the listed soil parameters TABLE 4 5 CORROSION RESISTANCE PROPERTIES OF COMMON GROUNDING ELECTRODE SYSTEM METALS AS RELATED TO SOIL COMPOSITION Grounding Electrode Metal Austenitic Stainless
43. FOR COMMUNICATION SITES COMMON GROUNDING EARTHING 4 3 68P81089E50 B Communications facilities located at elevations significantly above the average elevation of the surrounding terrain such as hilltops fire towers airport control towers and high rise buildings shall be considered exposed to lightning regardless of thunderstorm activity and soil resistivity ANSI T1 313 2003 section 5 1 1 Communications facilities with a tower shall be considered as exposed regardless of thunderstorm activity and soil resistivity By their very construction radio antennas towers are considered exposed to the possible damaging effects of lightning Tall structures such as towers buildings and antenna masts provide a favorable discharge point for lightning strokes ANSI T1 313 2003 section 5 2 3 Some communications facilities may be classified as unexposed if the building and tower are within the zone of protection of a higher structure Only a qualified engineer should determine if the communications facility is unexposed The following standards can be used by the engineer to help determine if the communications facility is unexposed BS 6651 1999 IEC 61024 1 2 NFPA 780 2004 or other applicable standard in effect and recognized by the local authority having jurisdiction COMMON GROUNDING EARTHING 9 1 05 At a communications site there shall be only one grounding earthing electrode system For example the AC power system ground
44. IA 222 F R2003 section 12 e Ground rods shall meet the specifications and be installed in accordance with Ground Rods on page 4 11 e For towers equal to or exceeding 1 5 m 5 ft in base width the tower ground ring shall consist of at least one ground rod per tower structure leg ANSI T1 313 2003 section 10 3 1 and ANSI TIA EIA 222 F R2003 section 12 e Ground rods shall meet the specifications and be installed in accordance with Ground Rods on page 4 11 e monopole towers equal to or exceeding 1 5 m 5 ft in base width the tower ground ring shall consist of four equally spaced ground rods e Ground rods shall meet the specifications of and be installed in accordance with Ground Rods on page 4 11 e monopole towers shall be bonded to the tower ground ring using at least four equally spaced grounding conductors of 35 mm csa 2 AWG or coarser bare solid tinned copper conductor 4 51 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING e leg of a self supporting tower shall be bonded to the tower ground ring using grounding 2 conductors of 35 mm csa 2 AWG or coarser bare solid tinned copper conductor See Figure 4 33 tower grounding conductors shall be exothermically bonded to the tower unless specifically directed otherwise by the tower manufacturer e tower s support piers concrete footings should have t
45. INEER FIGURE 4 36 Guv ANCHOR POINT GROUNDING FOR NEW CONSTRUCTION 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 68P81089E50 B 9 1 05 A ground rod shall be installed at each guy anchor point ANSI TIA EIA 222 F R2003 Ground rods shall meet the specifications and be installed in accordance with Ground Rods on page 4 11 All guy wires at a guy anchor point shall bond to the ground rod ANSI T1 313 2003 section 10 3 1 and ANSI TIA EIA 222 F R2003 using a grounding conductor of 35 mm csa 2 AWG or coarser bare solid tinned copper conductor Do not use un tinned wire The grounding conductor shall be connected to each guy wire using stainless steel or other approved clamps Each connection shall be coated with a listed conductive anti oxidant compound AN caution Do not attempt to exothermically weld to tower guy wires The grounding conductor shall be connected to the guy wires above the turnbuckles The grounding conductor shall maintain a continuous vertical drop from the guy wire attachment point to the grounding electrode Existing Anchor Points If possible backfill around the embedded anchor with a high resistivity soil such as gravel This may be beneficial in reducing the rate of corrosion between the guy anchor point and copper grounding electrode system components TIA EIA 222 F R2003 Isolation of anchors from the
46. NG FIGURE 4 60 BONDING TWO STRUCTURES ADJACENT TO THE TOWER ACCESS POINT AND WIRELESS ROUTER GROUNDING EARTHING Access points wireless routers and similar equipment are typically installed in a variety of different locations Such locations may be on communications towers building rooftops or utility light poles These typical locations are addressed in this section TOWER MOUNTED Tower mounted access points and wireless routers shall be bonded to the tower using a 16 mm csa 6 AWG or coarser solid or stranded tinned and or jacketed copper conductor Connection to access points and wireless routers shall be made to an adequately sized dedicated grounding earthing point in accordance with the device manufacturer requirements Connection to the tower shall be made using tower manufacturer approved methods typically a type of mechanical clamp The grounding conductor shall meet the specifications and installation requirements of Grounding Earthing Conductors on page 4 28 The tower shall be grounded as described in Tower Grounding Earthing on page 4 50 BUILDING MOUNTED Building mounted access points and wireless routers are typically mounted on the side of the building or on the roof of the building Access points and wireless routers installed inside the building shall be grounded earthed as required for electronic equipment in Chapter 5 Internal Grounding Earthing 68P81089E50 B 9 1 05 STANDARDS
47. PROPER GROUNDING OF NON SELF SUPPORTING ICE BRIDGE 68P81089E50 B 9 1 05 4 73 GROUNDING EARTHING ROOF MOUNTED ANTENNA MASTS AND METAL SUPPORT STRUCTURES CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 7 11 IMPORTANT In ice prone areas if isolating the cable bridge ice bridge from the tower creates an unprotected area on the RF transmission lines some type of ice shield shall be installed above the isolation point in order to protect the RF transmission lines The ice shield shall be bonded to the tower only METALLIC BUILDING SIDING GROUNDING EARTHING Although metallic building siding is not required to be grounded by this standard grounding the metallic siding can provide additional safety at the site NFPA 70 2005 Article 250 116 FPN It is recommended to bond the metallic building siding in at least one location on the building preferably near the electrical service entrance 4 8 GROUNDING EARTHING ROOF MOUNTED ANTENNA MASTS AND METAL SUPPORT STRUCTURES NOTE 4 74 All roof mounted antenna masts and metal support structures shall be grounded earthed NFPA 70 2005 Article 810 15 Rooftop mounted towers are not covered in this section See Grounding Earthing Rooftop Mounted Tower Structures on page 4 79 for information about rooftop tower grounding requirements In new construction provisions shall be engineered into the building design for effective roof mounted antenna mast and support structure grounding
48. RTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 4 2 4 28 4 4 2 1 e Grounding electrode encasement material shall be packaged for the purpose of grounding electrode encasement e Grounding electrode encasement material shall be environmentally safe and approved by the environmental authority having jurisdiction e Grounding electrode encasement material shall be used in accordance with the manufacturers instructions e Grounding electrode encasement material shall not have a corrosive effect on the grounding electrode system components e 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 an
49. Soil Parameter Copper Galvanized Steel Steel lt 700 Slightly Reduced Moderately Reduced Slightly Reduced Resistivity 700 to 4000 Slightly Reduced Moderately Reduced Generally Unaffected gt 4000 Generally Unaffected Generally Unaffected Generally Unaffected lt 200 Moderately Reduced Considerably Reduced Moderately Reduced Redox Potential mV 200 to 400 Slightly Reduced Slightly Reduced Generally Unaffected gt 400 Generally Unaffected Generally Unaffected Generally Unaffected lt 10 Generally Unaffected Generally Unaffected Generally Unaffected Moisture Content 101080 Slightly Reduced Moderately Reduced Slightly Reduced gt 80 Slightly Reduced Slightly Reduced Slightly Reduced Dissolved Salts Moderately Reduced Moderately Reduced Slightly Reduced Chlorides Moderately Reduced Moderately Reduced Moderately Reduced pH Acidic lt 6 Moderately Reduced Considerably Reduced Slightly Reduced Neutral 6 to 8 Generally Unaffected Generally Unaffected Generally Unaffected Alkaline gt 8 Slightly Reduced Moderately Reduced Generally Unaffected Organic Acids gt 8 Considerably Reduced Moderately Reduced Slightly Reduced Austenitic stainless steel Shall be formed from 18 chromium and 8 nickel 18 8 stainless steel per UL 467 2004 section 9 2 6 Table based on information from BS 7430 1998 68P81089E50 B 9 1 05 4 35 DISSIMILAR METALS AND CORROSION CONTROL CHAPTER 4 EXTERNAL GROUNDING EARTHING
50. TED IN FLEXIBLE NONMETALLIC CONDUIT N FIGURE 4 46 Bus BAR CONFIGURATION BOTTOM GROUND KIT ANGULAR TOWER TO GOUNDING ELECTRODE SYSTEM EXTERIOR INTERIOR FIGURE 4 47 TRANSMISSION LINE GROUNDING AT BUILDING ENTRY POINT 4 66 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 4 7 10 68P81089E50 B NOTE 9 1 05 METALLIC OBJECTS REQUIRING BONDING The objective of bonding metallic objects is to equalize the potential between conductive parts This is done for personnel safety and to prevent arcing between metallic components that might otherwise be at different potentials Bonding conductors shall be as short and straight as possible ANSI T1 313 2003 section 6 3 Metallic objects that are located within 1 8 m 6 ft of the external grounding earthing electrode system or within 1 8 m 6 ft of a grounded metallic item shall be bonded to the external grounding electrode system using 16 mm csa 6 AWG or coarser conductors as described in Grounding Earthing Conductors on page 4 28 ANSI T1 334 2002 section 5 3 3 Bonding to the metallic objects shall be made as allowed by the manufacturer In high lightning prone geographical areas or areas of high soil resistivity it is recommended to bond all metallic objects that are located within 3 m 10 ft of the external grounding electrode system or within 3 m 10 ft of a grounded metalli
51. ally 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 e 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 e 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 e tower ground bus bar shall be connected to the tower grounding electrode system with 2 35 mm csa 2 AWG or coarser bare solid tinned copper conductor 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 68P81089E50 B 9 1 05 e 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 e grounding conductors shall be run as short straight and smoothly as possible See Bending
52. available location to the building s common grounding electrode system may include the following e Effectively grounded structural building steel e An existing communications grounding system e An existing lightning protection system down conductor e A grounding down conductor e device s AC power receptacle conduit when no other ground source is available or practical When the AC power receptacle conduit is used the effectiveness of its grounding bonding connection shall be verified UTILITY POLE MOUNTED 4 10 3 3 1 METALLIC POLE MOUNTED Access points and wireless routers mounted to metallic utility poles are grounded earthed in the same manner as described above for tower mounted units Metallic utility pole mounted access points and wireless routers shall be bonded to the metallic utility pole using a 16 mm csa 6 AWG or coarser solid or stranded tinned and or jacketed copper conductor as shown in Figure 4 61 Connection to access points and wireless routers shall be made to an adequately sized dedicated grounding point in accordance with the device manufacturer requirements The grounding conductor shall meet the specifications and installation requirements of Grounding Earthing Conductors on page 4 28 Connection to the metallic utility pole shall be made using appropriate listed grounding hardware typically a type of mechanical clamp The metallic utility pole shall be effectively grounded or made to be effec
53. c item ANSI T1 313 2003 section 10 3 2 Metallic objects requiring bonding include but are not limited to the items listed below ANSI T1 313 2003 section 10 3 2 ANSI T1 334 2002 section 5 3 3 e Fences e Fence posts Fence gates e Cable Bridge Ice Bridge e Generator frame e Skid plate or metal support frame of a prefabricated shelter e Metallic members of all incoming telecommunications cables including paired conductor and optical fiber ANSI T1 313 2003 section 8 2 e Facility grounding electrode system e Main telephone company ground if external e Metallic entry points e Metallic conduits piping and raceways e HVAC units e Vent covers if not already grounded inside e Storage tanks above and below grade if allowed e External light fixtures or support masts e other grounding electrode systems at the site see Common Grounding Earthing on page 4 5 Bonding conductors installed underground shall be constructed of 35 mm csa 42 AWG or coarser conductor See Grounding Earthing Conductors on page 4 28 Series or daisy chain connection arrangements shall not be used See Figure 5 20 on page 5 34 for an example of a daisy chained ground connection 4 67 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 68 4 7 10 1 FENCE AND GATE GROUNDING EARTHING All site fencing including gates within 1 8 m 6 ft of the groundin
54. conductor used for bonding the fence fabric See Figure 4 49 for an example e individual run of the deterrent wiring shall be bonded using a listed bimetallic transition connector Each connection shall be liberally coated with a listed conductive antioxidant compound at the point of insertion into the connector e grounding conductor shall be routed so as not come into incidental contact with the deterrent wiring fence post fence fabric or support apparatus for the wire Incidental contact can create an RF interference point e grounding conductor shall follow the proper routing methods described in Bending And Routing Grounding Earthing Conductors on page 4 29 NOTE Consult with Motorola Engineering or other engineering firm for the grounding requirements recommendations of fence systems that extend well beyond the communications building and tower 4 70 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 4 7 10 2 68P81089E50 B 9 1 05 Grounding electrode system connections to commercial grade fencing and gates shall be made using the exothermic welding process where possible Coat all welded connections with zinc enriched paint to prevent rusting If exothermic welding is not possible use the methods described below for residential fencing If the site has residential quality fencing and or preexisting fencing it shall be grounded
55. csa 6 AWG or coarser copper conductor bonded to the External Ground Bus bar EGB Conductor bonding to the cable bridge ice bridge and EGB shall be made using exothermic welding or two hole lugs and stainless steel hardware See Bonding to the External Grounding Earthing Electrode System on page 4 40 Bonding of the cable bridge ice bridge to the grounding electrode system may also be accomplished using a 35 mm csa 2 AWG or coarser bare copper conductor bonded directly to the grounding electrode system Conductor bonding to the grounding electrode system shall be made using exothermic welding or listed irreversible high compression fittings Conductor bonding to the cable bridge ice bridge shall be made using exothermic welding or listed two hole lugs and stainless steel hardware See Bonding to the External Grounding Earthing Electrode System on page 4 40 At the tower Cable bridges ice bridges may be sufficiently grounded when an integral part of the tower construction and bonded directly to the tower through multiple metallic mechanical connections The metallic connections shall be of the same metals and shall provide direct metal to metal contact without any non conductive coatings such as paint When the cable bridge ice bridge is not effectively bonded to the tower additional bonding shall be required in order to effectively ground the cable bridge ice bridge The additional bonding shall be accomplished using
56. cted to the 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 csa 2 0 AWG wire To further reduce the inductance to ground several copper straps can be installed across the entire length of the external ground bus bar and routed down to the external grounding ring See Figure 4 23 EXOTHERMIC WELD OR LISTED IRREVERSIBLE COMPRESSION 35 csa 2 AWG MINIMUM 2 Re FR COPPER STRAP PREFERRED RECOMMENDED FIGURE 4 23 TYPICAL EXTERNAL GROUND BUS BARS MASTER GROUND BUS BAR ON INTERIOR WALL INTERIOR WALL SURFACE EXTERNAL GROUND BUS BAR UNDERGROUND SI CONNECTION TO BUILDING GROUND RING FIGURE 4 24 INTEGRATED CABLE ENTRY PoRT WiTH GROUND STRAPS 68P81089E50 B 9 1 05 4 31 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 Height 51 mm 2 in ANSI J STD 607 A 2002 and NFPA 70 2005 Article 250 64 Thickness 6 35 mm 0 25 in Length Variable to me
57. ction 6 6 ANSI T1 313 2003 section 10 5 1 and MIL HDBK 419A e Transmission line ground kits shall be installed at the bottom of the tower near the vertical to horizontal transition point ANSI T1 313 2003 section 10 5 1 ANSI T1 334 2002 section 6 6 and MIL HDBK 419A The ground kits shall be bonded to the tower or tower ground bus bar TGB if installed e Ifthe tower is greater than 61 m 200 ft in height an additional ground kit shall be installed at the tower midpoint ANSI T1 334 2002 section 6 6 and MIL HDBK 419A Additional ground kits shall be installed as necessary to reduce the distance between ground kits to 61 m 200 ft or less e In high lightning prone geographical areas additional ground kits should be installed at spacing between 15 2 to 22 9 m 50 to 75 ft ANSI T1 313 section 10 5 1 and ANSI T1 334 2002 section 6 6 This is especially important on towers taller than 45 7 m 150 ft NOTE The use of down conductors on metallic towers is not recommended for grounding bonding transmission lines The down conductor has a much higher impedance to earth than the tower The use of down conductors does not provide equipotential bonding between the transmission lines and tower Transmission line ground kits shall be installed near the building shelter equipment housing or cabinet entry point ANSI T1 334 2002 section 6 6 MIL HDBK 419A and NFPA 70 2005 Articles 810 20 and 820 93 The ground kits shall bond to t
58. ctor of 35 mm csa 2 AWG or coarser bare solid tinned copper conductor Do not use un tinned wire e grounding conductor shall be connected to each guy wire using stainless steel or other approved clamps Each connection shall be coated with a listed conductive anti oxidant compound 4 56 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS Do not attempt to exothermically weld to tower guy wires e The grounding conductor shall be connected to the guy wires above the turnbuckles see Figure 4 38 e grounding conductor shall maintain a continuous vertical drop from the guy wire attachment point to the grounding electrode GUY WIRE CLAMPS 85 mm CSA 2 AWG TINNED COPPER ANCHOR SHAFT SURROUNDED BY 152 mm 6 IN OF GRAVEL PN CONCRETE ANCHOR GALVANIZED GROUND ROD 2 4 M 8 FT MINIMUM FIGURE 4 38 Guv ANCHOR POINT GROUNDING FOR EXISTING CONSTRUCTION 4 7 6 2 2 PROTECTION Additional corrosion control can be obtained through the use of Cathodic Protection See MIL HDBK 419A Volume I section 2 10 and TIA EIA 222 F R2003 section 4 4 for additional information Cathodic protection should only be installed under the advice of a licensed professional engineer spo WARNING Any type of corrosion control installation techniques does not eliminate the need for proper monitoring and maintenance over the life of the stru
59. ctrode system is installed it shall be bonded to the existing building grounding electrode system See Common Grounding Earthing on page 4 5 NOTE In order to maintain maximum efficiency of parallel ground rods the ground rods shall be separated from one another by twice the length of the individual ground rods CONDUCTOR EXTERIOR WALL PVC CONDUIT GUARD CABLE FASTENERS PVC EXTENDED 305 mm 1 ft EE BELOW FINISHED GRADE EXOTHERMICALLY WELDED OR HIGH COMPRESSION CONDUCTOR BOND GROUND ROD BOND F RECOMMENDED MINIMUM ge GROUND ROD SEPARATION IS 4 9 m 16 ft GROUND RING FIGURE 4 64 SMALL GROUND RING INSTALLATION 68P81089E50 B 9 1 05 32 mm 1 25 in x 2 1 m 7 ft INSTALLED EVERY 914 mm 3 ft BOND BETWEEN SMALL GROUND RING AND EXISTING GROUNDING ELECTRODE SYSTEM 4 89 SPECIAL GROUNDING EARTHING SITUATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING TOWER GROUND RODS 8 TOTAL COMMUNICATIONS SITE BUILDING lt SESCSISCSCSASNSCSCSCSCSENCN VPA 9 ADJACENT BUILDINGS FIGURE 4 65 TYPICAL LINEAR GROUNDING ELECTRODE SYSTEM 4 11 2 SITES WITH LIMITED SPACE FOR THE GROUNDING EARTHING ELECTRODE SYSTEM Some sites such as locations in metropolitan areas or areas close to adjacent buildings or property lines have very little space available for installing a grounding earthing electrode system One solution for achieving an accep
60. cture TIA EIA 222 F R2003 section 4 68P81089E50 B 9 1 05 4 57 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 7 6 3 WOODEN STRUCTURES POLES Wooden pole structure towers and other non metallic towers shall minimally be grounded earthed as follows e wooden pole shall have a vertical grounding conductor installed over the length of the wooden pole e vertical grounding conductor shall be constructed of 35 mm csa 2 AWG or coarser solid bare tinned or un tinned copper conductor ANSI T1 334 2002 section 6 5 e grounding conductor shall be installed in accordance with Grounding Earthing Conductors on page 4 28 e vertical grounding conductor shall terminate into a radial grounding conductor or tower ground ring with rods ANSI T1 334 2002 section 6 5 e The radial grounding conductor shall be installed in accordance with Radial Counterpoise Grounding Conductors on page 4 24 e The tower ground ring shall be installed in accordance with External Building and Tower Ground Ring on page 4 22 e Ground rods shall meet the specifications and be installed in accordance with Ground Rods on page 4 11 wooden pole grounding electrode system shall be bonded to the building grounding electrode system See Common Grounding Earthing on page 4 5 ANTENNA WOODEN POLE d 35 mm csa
61. d 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 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 GENERAL SPECIFICATIONS General specifications for grounding earthing conductors are listed below e Unless otherwise stated all below ground or partially below ground external grounding electrode system conductors shall be 35 mm 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 lightn
62. dance grounding electrode system are described below See ANSI T1 333 2001 section 4 ANSI T1 334 2002 section 5 1 BS 7430 1998 IEC 60364 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 e To help limit the voltage caused by accidental contact of the site AC supply conductors with conductors of higher voltage e To help dissipate electrical surges and faults to minimize the chances of injury from grounding system potential differences e To help limit the voltages caused by lightning e help maintain a low potential difference between exposed metallic objects 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES LIGHTNING ACTIVITY AND EXPOSURE e stabilize the AC voltage relative to the earth under normal conditions e contribute to reliable equipment operation e To provide a common signal reference ground 4 2 LIGHTNING ACTIVITY AND EXPOSURE Communications facilities shall be defined as exposed to lightning unless thunderstorm activity in the area is an average of five thunderstorm days per year or fewer and soil resistivity at the site is less than 10 000 ohm centimeters Q cm The soil resistivity shall be measured as described in ANSI IEEE STD 81 ANSI T1 313 2003 section 5 1 1 See Appendix B for soil resistivity measurement methods Figure 4 1 and Figure 4 2 are maps representing typical lightning activity
63. ding Earthing on page 4 5 4 8 1 SIDE MOUNTED ANTENNA GROUNDING EARTHING Typically a side mounted antenna may be grounded earthed with a single grounding conductor The use of two grounding down conductors may not always be practical However two down conductors should be used whenever practical this is especially important at buildings that are normally occupied such as dispatch centers When two grounding down conductors are not installed it is recommended to either use a copper strap or a larger sized grounding down conductor 68P81089E50 B 9 1 05 4 77 GROUNDING EARTHING ROOF MOUNTED ANTENNA MASTS AND METAL SUPPORT STRUCTURES CHAPTER 4 EXTERNAL GROUNDING EARTHING 35 mm csa ANTENNA ANTENNA 508 mm 2 in STRAP 2 AWG MOUNT RECOMMENDED TRANSMISSION 35 mm csa CONDUCTOR LINE GROUND KIT 2 AWG MINIMUM ELECTRICAL zj SERVICE DEPT ud GROUND RODS FIGURE 4 55 SIDE MOUNTED ANTENNA GROUNDING UsiNG COPPER STRAP DOWN CONDUCTOR When multiple side mounted antennas are installed together a single horizontal grounding conductor should bond all antenna masts together The horizontal grounding conductor should bond to the grounding electrode system from each side of the side mounted antennas with a grounding down conductor When several antennas are installed together therefore creating a long horizontal grounding conductor it is recommended to install intermediate grounding down conductors e
64. ding Earthing on page 4 5 The rooftop mounted tower shall be effectively grounded by bonding to the lightning protection system The rooftop mounted tower shall bond to the lightning protection system as follows The rooftop mounted tower support legs shall be interconnected with a conductor to form a roof tower ground ring A guyed tower base plate can be used in place of the roof tower ground ring The conductor shall be of the same size as the main roof perimeter lightning protection ring The roof tower ground ring shall be exothermically bonded to the tower unless specifically directed otherwise by the tower manufacturer The rooftop mounted tower ground ring or guyed tower base plate shall bond to the main roof perimeter lightning protection ring with a minimum of two opposing conductors at or within 610 mm 24 in of a grounding down conductor or other main grounding conductor as defined by NFPA 780 2004 such as effectively grounded structural building steel The conductor shall be of the same size and type as the main roof perimeter lightning protection ring conductors shall meet the installation requirements of Grounding Earthing Conductors on page 4 28 e Conductor bonding shall be made using exothermic welding listed irreversible high compression fittings or other fittings listed for use in lightning protection systems See Bonding to the External Grounding Earthing Electrode System on page 4 40
65. e 4 66 for an example of a grounding electrode grid system for an available area of 9 1 m x 9 1 m 30 ft x 30 ft with all ground rods separated by 3 m 10 ft ADJACENT BUILDINGS ROUND RODS 16 TOTAL COMMUNICATIONS GROUND RODS 16 TOTAL SITE BUILDING TOWER GROUNDING GRID 9 1 m 30 ft SQUARE FIGURE 4 66 TYPICAL GROUNDING GRID 68P81089E50 B 9 1 05 4 91 SPECIAL GROUNDING EARTHING SITUATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 11 3 4 11 4 4 92 NOTE See Interpreting Test Results on page B 10 to determine if the desired resistance to earth can be achieved using different rod lengths and or separation If the resistance to earth cannot be achieved using standard rods electrolytic rods should be considered Burying the grounding conductor in at least 152 mm 6 in of grounding electrode encasement material should also be considered as a method of improving the resistance to ground See Grounding Earthing Electrode Encasement Materials on page 4 27 In shallow topsoil conditions the above grounding electrode grid system can utilize ground plates instead of ground rods TOWERS WITH LIMITED SPACE FOR A GROUND RING Towers installed close to a building may not have adequate space for a complete tower ground ring or for ground rods spaced properly to achieve the resistance requirements of the site Depending on the available space the tower can be grounded earthed using multiple
66. e circuit will exist Current will flow from one metal to the other due to the electrical connection and return path through the soil This naturally occurring phenomenon is why current is obtained from a battery when its terminals are electrically connected to a load TIA EIA 222 F R2003 See Figure 4 26 for an example of installations with and without galvanic corrosion ROD WHEN BOTH RODS ARE OF THE SAME METAL ELECTRONS DO NOT FLOW FROM ONE ROD TO THE OTHER THEREFORE GALVANIC CORROSION DOES NOT OCCUR CONDUCTIVE SOIL CONDUCTIVE SOIL ROD ROD FIGURE 4 26 INSTALLATIONS WITH AND WITHOUT GALVANIC CORROSION 4 36 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES DISSIMILAR METALS AND CORROSION CONTROL Metals may be listed in order of their respective potentials such a list is called a galvanic series A galvanic series of commonly used grounding earthing electrode system metals and alloys is given in Table 4 6 from TIA EJA 222 F R2003 and MIL HDBK 419A When a complete circuit exists corrosion occurs on the metal listed higher in the galvanic series The metal listed higher in the galvanic series anode is where current exits and travels through the soil toward the metal listed lower on the galvanic series cathode The galvanic series of commonly used metals and alloys is as follows TABLE 4 6 GALVANIC SERIES OF COMMON METALS Anodic Active End Magnesium Zinc material used to galva
67. e ground rod s as described in Type A Site Grounding Earthing on page 4 48 and elsewhere throughout this chapter NOTE It is recommended to use two grounding electrodes as the minimum installation even if 25 ohms is achieved with a single grounding electrode 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 4 7 2 TYPE B SITE STANDARD DUTY e Using a site drawing determine where to install the minimum required ground rods while maintaining equal separation between rods See External Building and Tower Ground Ring on page 4 22 for additional information regarding ground rod placement requirements along ground rings e Determine if radial grounding earthing conductors should be installed at the site such as when the site is located in a high lightning prone geographic area or when the site is normally occupied such as a dispatch center See Radial Counterpoise Grounding Conductors on page 4 24 e Calculate the resistance of the grounding electrode system using Calculating Resistance of Complex Ground Rod Systems on page B 30 e Ifthe required resistance cannot be met recalculate using one or more of the follow techniques e Recalculate using longer ground rods e Recalculate using radial grounding conductors if not already included See Radial Counterpoise Grounding Conductors on page 4 24 e Recalculate using c
68. ed the grounding conductors shall be 50 mm csa 1 0 AWG or coarser bare copper The buried grounding conductors shall be installed in separate trenches and buried to a minimum depth of 457 mm 18 in below grade Access to the grounding conductor bonding points should include ground test wells See Figure 4 59 Ground Test Wells on page 4 27 and MIL HDBK 419A Volume II section 1 2 3 for additional information e BURIED BARE peng NEARBY STRUCTURE CONDUCTOR o 7 50 mm 1 0 AWG OR COARSER yy QD STRUCTURES SEPARATED 6 1 to 61 m 20 to 200 ft e MAIN STRUCTURE e e b FIGURE 4 59 TWO ELECTRICALLY INTERCONNECTED BUILDINGS LOCATED IN THE SAME AREA Structures or facilities having no interconnection cables and or separated by a distance greater than 61 m 200 ft generally do not require their grounding electrode systems to be interconnected MIL HDBK 419A Volume II section 1 2 3 Buildings sharing a common tower require bonding of their respective ground rings to the common tower ground ring 4 83 SPECIAL GROUNDING EARTHING APPLICATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING P p Z E M T N 4 10 3 4 84 4 10 3 1 4 10 3 2 BURIED BARE CONDUCTOR 35 mm 42 AWG OR COARSER N STRUCTURE 2 4 4 z N Te 7 lt TOWER TOWER GROUND RI
69. ed at a ground rod e Building ground rings and tower ground rings shall be bonded together in at least two points using 35 mm csa 2 AWG or coarser bare solid tinned or un tinned copper conductor ANSI J STD 607 A 2002 section C 4 7 ANSI T1 334 2002 figure 1 and MIL STD 188 124B The conductors should be physically separated as much as practical See Common Grounding Earthing on page 4 5 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS TOWER RING BONDED TO BUILDING RING IN AT LEAST 2 PLACES 68P81089E50 B 9 1 05 4 23 GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 4 1 7 4 24 RADIAL COUNTERPOISE GROUNDING CONDUCTORS For high lightning prone geographical areas sites normally occupied such as 911 dispatch centers sites with high soil resistivity or when bedrock prohibits the driving of ground rods radial counterpoise grounding earthing conductors should be employed to improve equalization of the grounding electrode system ANSI T1 334 2002 section 5 4 and to help meet the site s grounding electrode system resistance requirements see Grounding Earthing Electrode System Resistance Requirements on page 4 46 Radial grounding conductors are conductors installed horizontally in the ground and radiating away fr
70. ed on pads that incorporate a footing should consider the use of concrete encased electrodes in addition to the ground ring See Concrete Encased Electrodes on page 4 20 Depending on the location of the cabinet s internal ground point the grounding conductor installed between the grounding electrode system and the cabinet s internal ground point may need to be routed through the concrete footing pad in order to allow conductor routing in a direct manner This requires the grounding conductor to be installed before the concrete is poured 4 61 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING CONCRETE ENCASED ELECTRODE UFER GROUND 4 7 9 4 62 FIGURE 4 41 CABINET GROUNDING SYSTEM RF TRANSMISSION LINE AND PREAMPLIFIER GROUNDING EARTHING Tower mounted antenna preamplifiers shall be bonded to the tower using 16 mm csa 6 AWG or coarser solid or stranded tinned copper conductor Connection to the amplifier shall be made in accordance with the amplifier manufacturer requirements Connection to the tower shall be made using tower manufacturer approved methods typically a type of mechanical clamp Transmission lines shall be bonded to the tower in order to prevent lightning from creating a difference of potential between the tower and the transmission lines and to help drain lightning energy to earth A potential difference could cause arcing between the tower and the RF transmissi
71. electrode is directly proportional to soil resistivity and inversely proportional to the total area in contact with the soil Grounding electrode encasement materials also known as backfill or ground enhancing material may consist of the following bentonite or bentonite containing material concrete or conductive concrete or cement made with graded granular carbonaceous aggregate in place of the conventional sand or gravel Grounding electrode encasement materials can absorb water from surrounding soil and have hydration and water retention properties When placed around grounding electrodes and their interconnecting cable grounding electrode encasement materials greatly increase the effective area in contact with soil which in turn reduces the resistance of the grounding electrode system See MIL HDBK 419A Volume I section 2 9 and BS 7430 1998 section 8 5 for more details Grounding electrode encasement material may be used as needed to improve the grounding electrode system resistance and or to protect the grounding electrode system components from corrosive soil BS 7430 1998 section 19 6 1 Grounding electrode encasement material is generally used with electrolytic ground rods but may also be used on grounding conductors standard ground rods and ground plates as a way to improve the resistance to earth of a grounding electrode system Requirements for the use of grounding electrode encasement material are as follows 4 27 GROUNDING EA
72. encased in a grounding electrode encasement material See Grounding Earthing Electrode Encasement Materials on page 4 27 and Electrolytic Ground Rods on page 4 16 e When soil conditions are not favorable such as highly acidic or alkaline the useful life of a copper ground rod can be extended by using solid copper ground rods instead of copper clad rods if soil conditions allow driving of the solid copper rod When soil conditions are not favorable such as highly acidic or alkaline the useful life of buried grounding conductors can be extended by using larger conductors such as 70 mm csa 42 0 AWG instead of 35 mm 2 AWG e Use a listed conductive anti oxidant compound on all mechanical connections ANSI T1 334 2002 section 9 The anti oxidant compound shall be liberally installed between the two metals see Figure 4 27 on page 4 40 e See Guy Anchor Points on page 4 54 for information regarding proper grounding techniques to help minimize galvanic corrosion of the guy anchor 4 39 BONDING TO THE EXTERNAL GROUNDING EARTHING ELECTRODE SYSTEM CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 6 4 6 1 4 40 BONDING TO THE EXTERNAL GROUNDING EARTHING ELECTRODE SYSTEM REQUIREMENTS All below grade grounding earthing electrode system connections shall be joined using exothermic welding or listed irreversible high compression fittings compressed to a minimum of 13 3 tonnes 12 tons of pressure or as
73. er electrodes named after Herbert G Ufer or foundation earth electrodes are not required by this standard they should be used in new construction as a method of supplementing the grounding earthing electrode system IEC 61024 1 2 section 3 3 5 Concrete encased electrodes Figure 4 17 enhance the effectiveness of the grounding electrode system in two ways the concrete absorbs and retains moisture from the surrounding soil and the concrete provides a much larger surface area in direct contact with the surrounding soil This is especially helpful at sites with high soil resistivity and or limited area for installing a grounding electrode system See IEEE STD 142 1991 section 4 2 3 and the International Association of Electrical Inspectors publication Soares Book on Grounding and Bonding 9th Edition Appendix A for additional information Requirements for a concrete encased electrode if used are listed below IEC 61024 1 2 NFPA 70 2005 Article 250 52 and NFPA 780 2004 section 4 13 3 e Concrete encased electrodes shall be encased by at least 51 mm 2 in of concrete located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth e Concrete encased electrodes shall be at least 6 1 m 20 ft of bare copper conductor not smaller than 25 mm csa 4 AWG or at least 6 1 m 20 ft of one or more bare or zinc galvanized or other conductive coated steel reinforcing bars or rods at least 12
74. et the application requirements and allow for future growth 305 mm 12 in is recommended as the minimum length Mounting brackets Stainless steel 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 IMPORTANT For improved lightning protection at the site the RF transmission line entry point and 4 32 4 4 3 1 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 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 minim
75. ete and asphalt are listed below e Cover the area with gravel e Landscape the area e Use electrolytic ground rods when the area must be covered with concrete or asphalt SPECIAL GROUNDING EARTHING SITUATIONS Site conditions such as limited area and high poor soil resistivity can sometimes require special consideration for effective grounding earthing Some methods for achieving an effective grounding electrode system in some common applications are described below in the following sections Consultation with Motorola Engineering or other engineering firm may be required in some situations 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING SITUATIONS 4 11 1 ROOFTOP AND INTEGRATED COMMUNICATIONS SITES Rooftop and integrated communications sites high rise buildings may require special techniques for achieving a suitable grounding earthing electrode system when effectively grounded structural steel is not available and when encircling the building with a ground ring would not be feasible such as in a downtown metropolitan location Some options may be e Consult with Motorola Engineering or other engineering firm e Installation of a small ground ring in an available location See Figure 4 64 e Installation of multiple parallel rods in a straight line See Figure 4 65 e Installation of electrolytic ground rod systems IMPORTANT If a supplemental grounding ele
76. follows e Each corner of the metal container shall bond directly to the grounding electrode system Conductors shall meet the requirements of Grounding Earthing Conductors on page 4 28 e Conductor bonding to the metal shipping container shall be exothermically welded whenever practical See Exothermic Welding on page 4 41 When exothermic welding is not practical other suitable mechanical connections may be used e Conductor bonding to the grounding electrode system shall be made using exothermic welding or listed irreversible high compression fittings See Bonding to the External Grounding Earthing Electrode System on page 4 40 4 87 SPECIAL GROUNDING EARTHING SITUATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 10 5 4 11 4 88 EXOTHERMICALLY WELD EACH CORNER TO GROUND RING pui LEE EN N I I I I I I L FIGURE 4 63 GROUNDING METAL SHIPPING CONTAINERS GROUNDING EARTHING ELECTRODE SYSTEMS COVERED BY CONCRETE OR ASPHALT When installing a grounding earthing electrode system every attempt should be made to ensure that the surface area above the grounding electrode system is not covered with concrete or asphalt Areas covered with concrete or asphalt will dry out over time therefore increasing the resistance to earth of the grounding electrode system See MIL HDBK 4194 for additional information Some alternatives to covering the area with concr
77. g earthing electrode system such as building or tower ground ring and radial grounding conductors or any metallic item grounded to the grounding electrode system shall be effectively bonded to the external grounding electrode system to help prevent shock hazard to personnel from lightning or other electrical anomalies ANSI T1 334 2002 section 5 3 3 In high lightning prone geographical areas or areas of high soil resistivity it is recommended to effectively bond fencing that is located within 3 m 10 ft of the external grounding electrode system or within 3 m 10 ft of a grounded metallic item ANSI T1 313 2003 section 10 3 2 When fences are located at an electrical power substation the fence grounding shall be made as required by local code and by the electric power utility company The fence grounding should comply with IEEE STD 80 2000 and is beyond the scope of this document A fencing grounding scheme is shown below in Figure 4 48 for a typical communications site with a nearby installed perimeter fence system GATE BONDED TO GATE POST 7 EGB Fr EX COMMUNICATION SITE TOWER GROUND RING he Sis GATE POST BONDED AT ALL EXTERNAL GROUND RING CORNER FENCE POSTS METALLIC FENCE FIGURE 4 48 FENCE BONDING EXAMPLE 1 The series or daisy chain method which refers to any method of connection whereby the conductors are connected from one peripheral device to a second and p
78. he Larger Surface Area Steel Steel Copper Copper Galvanized Steel Suitable Suitable Suitable Suitable Steel in Concrete Not Suitable Not Suitable Suitable Suitable Galvanized Steel in Concrete Suitable 2 Suitable Suitable Lead Suitable Suitable Suitable Key Suitable Materials suitable for bonding Not Suitable 2 Materials not suitable for bonding Materials suitable for bonding but the galvanizing on the smaller surface may suffer This table is based on Table 8 of BS 7430 1998 4 5 3 MISCELLANEOUS GENERAL INFORMATION e Galvanized steel is strongly electronegative to copper and steel encased in concrete therefore careful consideration must be give before galvanized ground rods are used at a site that contains a concreted encased electrode See BS 7430 1998 clause 11 2 for additional information See Concrete Encased Electrodes on page 4 20 e Steel encased in concrete has a potential similar to that of copper therefore may be bonded to copper or copper clad ground rods See BS 7430 1998 and IEEE STD 142 1991 for additional information 4 5 4 METHODS TO HELP REDUCE CORROSION Listed below are some general requirements and guidelines to help prevent corrosion of the grounding earthing electrode system and other metallic items at the communications site e same metal shall be used throughout the grounding electrode system whenever possible e Aluminum or copper clad aluminum grounding co
79. he external ground bus bar EGB if installed or directly to the grounding electrode system ensuring a continuous downward flow toward the grounding electrode system is maintained No TE Transmission lines installed on a wooden pole structure shall bond to the wooden pole vertical grounding conductor in the same manner as described above AN caution Braided grounding conductors shall not be used under any circumstances Braided conductors corrode easily and become a point for RF interference 68P81089E50 B 9 1 05 4 63 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING ANTENNA GROUND KIT GROUND KIT GROUND KIT BUILDING GROUND RING Required ground kit for towers taller than 61 m 200 ft optional ground kit for towers 61 m 200 ft or less FIGURE 4 42 LOCATION OF TRANSMISSION LINE GROUNDING KITS FIGURE 4 43 TRANSMISSION LINE GROUND KIT 4 64 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS TRANSMISSION LINE p GROUNDING CONDUCTOR FIGURE 4 44 GROUNDING TRANSMISSION LINE TOP AND MIDDLE TUBULAR TOWER TRANSMISSION LINE GROUNDING CONDUCTOR FIGURE 4 45 GROUNDING TRANSMISSION LINE TOP AND MIDDLE ANGULAR TOWER 68P81089E50 B 9 1 05 4 65 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING TGB GROUNDING CONDUCTOR ROU
80. he rebar electrically connected to the tower holding bolts ANSI T1 313 2003 section 10 3 1 e Install radial grounding conductors if needed See Radial Counterpoise Grounding Conductors on page 4 24 EXOTHERMIC WELD OR MECHANICAL CLAMP FLEXIBLE NONMETALLIC CONDUIT MIN 762 mm 30 in GROUND RODS FIGURE 4 33 EXAMPLE SELF SUPPORTING TOWER GROUNDING EXOTHERMIC WELD OR OTHER SUITABLE MEANS GROUND RING b a nm CONCRETE GROUND ROD EXOTHERMIC WELD OR IRREVERSIBLE HIGH COMPRESSION FITTING FIGURE 4 34 EXAMPLE OF MONOPOLE TOWER GROUNDING 4 52 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 4 7 6 2 GUYED TOWERS Guyed towers shall minimally be grounded earthed as follows e The tower shall be encircled by a ground ring ANSI T1 334 2002 section 5 and MIL HDBK 419A e The tower ground ring shall be installed at least 610 mm 2 ft from the tower structure base or footing ANSI T1 334 2002 section 5 3 1 e The tower ground ring shall be installed in accordance with External Building and Tower Ground Ring on page 4 22 e The tower ground ring shall be bonded to the building ground ring in at least two points using a35 mm csa 2 AWG or coarser bare solid tinned or un tinned copper conductor ANSI T1 334 2002 figure 1 and MIL STD 188 124B See External Building and Tower Ground Ring
81. hen used are listed below e EGB shall be constructed and minimally sized in accordance with Table 4 3 on page 4 32 ensuring the ground bus bar is large enough to accommodate all transmission lines and other grounding connections e EGB shall be designed for the purpose of grounding and should be UL listed e EGB shall be installed at the point where the antenna transmission lines and other communications cables enter the building or shelter e EGB shall be connected directly to the grounding electrode system using a downward run of 35 mm csa 2 AWG or coarser bare solid or stranded tinned or un tinned copper conductor it is recommended to use a larger conductor such as 120 mm 84 0 AWG United States National Weather Service Manual 30 4106 2004 Lightning Protection Grounding Bonding Shielding and Surge Protection Requirements See Figure 4 23 The grounding conductor shall be installed in a direct manner with no sharp bends or narrow loops See Bending And Routing Grounding Earthing Conductors on page 4 29 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS e Connection of the grounding electrode conductor to the EGB shall use exothermic weld or listed irreversible compression connections ANSI T1 313 2003 For reduced impedance to the grounding electrode system the EGB can be conne
82. ial is generally considered to be ineffective and should not be used without additional grounding electrode system components Solid rock is no more conductive in a hole than on the surface Radial grounding conductors encased in a grounding electrode encasement material such as conductive concrete would be more effective and more economical SAND CORAL OR LIMESTONE ENVIRONMENTS Sites with very high soil resistivity such as sites with sand coral and limestone may require special grounding earthing techniques in order to achieve an effectively grounded site Some options to help achieve an effectively grounded site are as follows Consult with Motorola Engineering or other engineering firm Installation of concrete encased electrodes as part of new construction See Concrete Encased Electrodes on page 4 20 In addition to the building and tower ground rings installation of radial grounding conductors with vertical ground rods throughout the available property Install radial grounding conductors and rods as specified in this chapter Encasing all components in a grounding electrode encasement material can further increase the effectiveness of the grounding electrode system Installation of electrolytic ground rod systems instead of standard ground rods See Electrolytic Ground Rods on page 4 16 In addition to the building and tower ground rings installation of a grounding electrode grid system throughout the site See Sites Wi
83. ic Objects Requiring Bonding on page 4 67 e Above ground bonding conductors should be jacketed whenever practical ANSI T1 334 2002 section 5 1 e Solid straps or bars may be used as long as the cross sectional area equals or exceeds that of the specified grounding conductor spo WARNING The AC power system grounding conductors shall be sized appropriately for the electrical service and shall be approved by the authority having jurisdiction 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 e Sharp bends shall be avoided ANSI T1 334 2002 section 13 4 e 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 e 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
84. ic object may be a point for RF interference See Chapter 8 Minimizing Site Interference e Grounding down conductor shall be run in as straight a line as is practical NFPA 70 2005 Article 810 21 e See Bending And Routing Grounding Earthing Conductors on page 4 29 e Grounding down conductors shall have a minimum bend radius of 203 mm 8 in and the included angle shall not exceed 90 degrees as shown in Figure 4 22 on page 4 29 ANSI T1 313 2003 section 11 3 MIL STD 188 124B and NFPA 780 2004 section 4 9 5 See Bending And Routing Grounding Earthing Conductors on page 4 29 e Grounding down conductors shall be securely fastened at intervals not exceeding 914 mm 3 ft See NFPA 70 2005 Article 250 64 b 810 21 c and NFPA 780 2004 section 4 10 for additional information See Protecting and Securing Grounding Earthing Conductors on page 4 30 e Grounding down conductors run outside from the roof top to ground shall be protected for a minimum distance of 1 8 m 6 ft above grade level when located in areas susceptible to damage such areas may include but are not limited to runways driveways school playgrounds cattle yards public walks NFPA 780 2004 section 4 9 11 and section 4 9 11 2 See Protecting and Securing Grounding Earthing Conductors on page 4 30 If the building grounding electrode system resistance cannot be verified or cannot provide a low resistance to earth see Grou
85. ing on page 4 22 Bonding of all metallic objects as described in Metallic Objects Requiring Bonding on page 4 67 e Installation of radial grounding conductors as described in Radial Counterpoise Grounding Conductors on page 4 24 Radial grounding conductors should be installed regardless if the grounding electrode system resistance is 5 ohms or less without the radial grounding conductors A minimum of five radial grounding conductors should be installed TR AAA ZA ZA 9 1 m 30 ft MINIMUM BETWEEN TOWER AND BUILDING PREFERRED CABLE ENTRY PORT WITHIN 610 mm 2 ft OF FLOOR PREFERRED NOTE EGB AND COAX ICE BRIDGE GROUNDING NOT SHOWN SIDE VIEW OF BUILDING FIGURE 4 58 GROUNDING ELECTRODE SYSTEM FOR DISPATCH CENTER CO LOCATED WITH A TOWER 4 82 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING APPLICATIONS 4 10 2 68P81089E50 B Two OR MORE ELECTRICALLY INTERCONNECTED SEPARATE BUILDINGS LOCATED IN THE SAME GENERAL AREA When two or more structures or facilities are located in the same general area less than 61 m 200 ft apart and are electrically interconnected with the continuous metallic shield of signal control RF or monitor circuits it is recommended to either provide a common grounding earthing electrode subsystem or interconnect the separate grounding electrode systems with two buried grounding conductors When install
86. ing and or military installations larger conductors such as 50 mm 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 e 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 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 4 4 2 2 68P81089E50 B 9 1 05 e 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 e Above ground conductors used for bonding individual metallic objects shall be 16 mm 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 e Above ground conductors used for bonding multiple metallic objects used as a ground bus conductor shall be 35 mm csa 2 AWG or coarser tinned or un tinned copper conductors See Metall
87. ing electrical connections without an external heat source such as electricity or gas The process is based on the reaction of granular metals which when combined produce a molten metal This reaction which is completed in seconds takes place in a crucible The liquid metal flows from the crucible into a mold where it meets the ends of the conductors to be welded The temperature of the molten metal is sufficient to fuse the metal of the conductors resulting in a welded molecular bond Exothermic welding alloys are available for aluminum copper and copper to steel connections 4 41 BONDING TO THE EXTERNAL GROUNDING EARTHING ELECTRODE SYSTEM CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 42 WARNING To help prevent injury from molten metal or sparks and to reduce the risk of fire follow the exothermic welding manufacturer s safety warnings and requirements e Heavy clothing work shoes or boots gloves and safety glasses shall be worn when performing exothermic welding e Exothermic welding shall not be performed unless another person capable of rendering first aid is present A suitable fire extinguisher shall be close by with an attendant during the process e Observe the following prerequisites for exothermic welding Follow the manufacturer s recommendations Use the proper molds for the conductors being welded Use the proper weld material for the metals being welded Properly clean all metal parts prior to welding
88. l allow The ground rings should be encased in a grounding electrode encasement material A conductive concrete may be the best grounding electrode encasement material for use in shallow topsoil environments since the conductive concrete would not require a covering of topsoil for protection See External Building and Tower Ground Ring on page 4 22 and Grounding Earthing Electrode Encasement Materials on page 4 27 e Installation of horizontal ground rods or horizontal electrolytic ground rods along the length of the ground rings instead of vertical ground rods The ground rods shall be installed perpendicular to the building and tower Encasing the ground rings and horizontal ground rods in a grounding electrode encasement material can further increase the effectiveness of the grounding electrode system 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING SITUATIONS 68P81089E50 B 9 1 05 COMMUNICATION SITE XL UFER GROUND FIGURE 4 67 MOUNTAINTOP SYSTEMS INSTALLATION OF HORIZONTAL GROUND RODS e Installation of ground plates along the length of the ground rings instead of vertical ground rods Encasing the ground rings and ground plates in a grounding electrode encasement material can further increase the effectiveness of the grounding electrode system See Ground Plate Electrodes on page 4 19 COMMUNICATION SITE UFER GROUND VERTICAL GROUND PLATES FIGURE
89. lded joints on galvanized material shall be coated with a zinc enriched paint to prevent corrosion e Copper aluminum joints shall be avoided wherever possible In cases where they cannot be avoided the connections shall be exothermically welded or made using an AL CU listed bimetallic transition connector IEC 61024 1 2 section 5 2 Use a listed conductive anti oxidant compound on all mechanical connections ANSI T1 334 2002 section 9 e Solid bare tinned copper conductor should be used to minimize galvanic corrosion between tower legs and other parts of the grounding electrode system ANSI T1 313 2003 section 10 7 Grounding connections to galvanized towers shall be exothermally welded whenever possible When exothermic welding is not possible the tower grounding conductor shall be constructed of tinned copper IEC 61024 1 2 section 5 2 e Select appropriate grounding electrode system components using Table 4 5 When soil conditions are not favorable such as highly acidic or alkaline grounding electrode system component corrosion may be reduced by encasing the components in a grounding electrode encasement material See Grounding Earthing Electrode Encasement Materials on page 4 27 and BS 7430 1998 section 19 6 1 for additional information e When soil conditions are not favorable such as highly acidic or alkaline grounding electrode system component corrosion may be reduced by installing electrolytic ground rods
90. lic conduit to help prevent incidental contact with other metals allow for protection of the conductor and to help support the conductor In order to reduce the amount of lightning energy diverted towards the equipment building shelter and to provide seismic isolation between the building and tower it is recommended to secure the cable bridge ice bridge to the tower through a non conductive slip joint type device When a slip joint type device is used grounding of the cable bridge ice bridge at the building shall be completed as described above grounding at the tower end of the cable bridge ice bridge shall be completed as follows e Installing a 35 mm csa 2 AWG or coarser bare copper conductor bonded directly to the grounding electrode system Conductor bonding to the grounding electrode system shall be made using exothermic welding or listed irreversible high compression fittings Conductor bonding to the cable bridge ice bridge shall be made using exothermic welding or listed two hole lugs and stainless steel hardware The grounding conductor should be installed in a flexible non metallic conduit to help prevent incidental contact with other metals allow for protection of the conductor and to help support the conductor See Figure 4 52 INSULATING MATERIAL SUCH AS FIBERGLASS BONDING JUMPER ISOLATING BRACKET WITH SLOT ADJUSTMENT BUILDING TRANSMISSION LINE ENTRY PORTS LEXIBLE CONDUIT FIGURE 4 52
91. loser spaced ground rods resulting in more ground rods at the site do not install ground rods closer than one ground rod length apart from other ground rods e Ifthe resistance requirement still cannot be met see Special Grounding Earthing Situations on page 4 88 e Develop a detailed site grounding electrode system drawing based on the previous steps e Install the grounding electrode system using components and techniques as specified throughout this chapter e Test the grounding electrode system resistance to earth as described in Appendix D e Bond all external metal objects to the grounding electrode system as required throughout this chapter 4 7 3 SPECIAL GROUNDING EARTHING SITUATIONS e See Calculating Multiple Grounding Electrode System Resistance Electrodes In Straight Line on page B 19 for the information required to calculate the resistance to earth of multiple ground rods installed in a straight line e See Multiple Grounding Electrode System Resistance Calculation Electrodes In Ring Configuration on page B 24 for the information required to calculate the resistance to earth of multiple ground rods installed in a ring configuration e See Calculating Multiple Grounding Electrode System Resistance Ground Rod Grid Configuration on page B 24 for the information required to calculate the resistance to earth of multiple ground rods installed in a ground rod grid configuration 68P81089E50 B 9 1 0
92. m 3 m 10 ft to 6 1 m 20 ft or longer as a special order Electrolytic ground rods are generally constructed of 54 mm 2 125 in diameter hollow copper pipe This copper pipe is filled with a mixture of non hazardous natural earth salts Holes at various locations on the pipe allow moisture to be hygroscopically extracted from the air into the salt within the pipe therefore forming conductive electrolytes These electrolytes then leach out of the pipe into the soil improving soil conductivity Electrolytic ground rods are inserted into a pre drilled hole or in the case of L shaped rods placed into a trench at least 762 mm 30 in deep and encased in a grounding electrode encasement material See Grounding Earthing Electrode Encasement Materials on page 4 27 Electrolytic ground rods should be considered for use in grounding electrode systems covered by concrete or pavement such as parking lots By allowing moisture to enter the design of the electrolytic ground rod improves the resistance of the grounding electrode system 4 16 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 68P81089E50 B NOTE Unless prohibited by local environmental authorities condensation from the site s HVAC system may be routed to the ground rod area to keep the soil moist improving conductivity 9 1 05 Electrolytic ground rods may provide sig
93. mately 40 e Installation of a parallel ground rod The ground rods shall maintain a minimum separation of 1 8 m 6 ft from one another NFPA 70 2005 Article 250 56 For maximum parallel efficiency the ground rods should be separated by the sum of their respective lengths See Grounding Barthing Electrode Resistance Characteristics and Sphere of Influence on page 4 9 and Figure 4 31 for additional information 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 68P81089E50 B NOTE NOTE 9 1 05 EXOTHERMIC WELDS OR IRREVERSIBLE HIGH COMPRESSION FITTINGS NOT LESS THAN 1 8 m 6 FT FIGURE 4 31 PARALLEL GROUND ROD INSTALLATION It is recommended to use two grounding electrodes as the minimum installation even if 25 ohms is achieved with a single grounding electrode e Installation of a small ground ring Figure 4 64 on page 4 89 e Installation of an electrolytic ground rod At an existing building the AC power system grounding electrode system will typically serve adequately as the communications Type A grounding electrode system A supplemental Type A grounding electrode system may need to be installed if the site has an RF transmission line or other communications cables entry point at a different location than the AC power utilities entrance If a supplemental Type A grounding electrode system is installed it shall be bonded t
94. nding Earthing Electrode System Testing Verification on page D 1 a supplemental grounding electrode system should be installed to ensure the resistance requirement of the site is met The supplemental grounding electrode system shall be bonded to the existing grounding electrode system NFPA 70 2005 See Common Grounding Earthing on page 4 5 See Figure 4 54 for an example of a supplemental grounding electrode system Consult the building engineer or manager to determine information about any existing building grounding electrode systems The building engineer should also be informed before attempting to weld or drill on the building rooftop Depending on the available locations for grounding down conductors and the entry point of the RF transmission lines into the building it may be necessary to install a supplemental grounding electrode system 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ROOF MOUNTED ANTENNA MASTS AND METAL SUPPORT STRUCTURES ANTENNA TRANSMISSION LINE GROUND KIT ANTENNA SUPPORT STRUCTURE 35 mm csa m i 42 AWG CONDUCTORS ELECTRICAL SERVICE GROUND RODS GROUND RODS FIGURE 4 54 ROOF MOUNTED ANTENNA MAST GROUNDING WITH SUPPLEMENTAL GROUNDING ELECTRODE SYSTEM IMPORTANT When installed supplemental grounding electrode systems shall be effectively bonded to the building grounding electrode system See Common Groun
95. nductors shall not be used NFPA 70 2005 Article 250 64 e Copper shall not come into incidental contact with galvanized steel e Copper shall not come into incidental contact with aluminum Precipitation run off from copper and copper alloys can attack galvanized parts BS 6651 1999 and IEC 61024 1 2 section 5 2 therefore bare copper conductors or copper bus bars shall not be installed above galvanized steel such as a tower unless the steel is protected against the precipitation run off IEC 61024 1 2 section 5 2 4 38 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES DISSIMILAR METALS AND CORROSION CONTROL 68P81089E50 B 9 1 05 caution Extremely fine particles are shed by copper parts which result in severe corrosive damage to galvanized parts even where the copper and galvanized parts are not in direct contact IEC 61024 1 2 section 5 2 e 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 or other suitable material Where tinned conductors or galvanized ground rods are used care shall be exercised during installation so that surfaces are not damaged If surfaces of these ground elements are damaged the potential for deterioration from galvanic action increases ANSI T1 313 2003 section 11 5 and ANSI T1 334 2002 section 13 6 e Exothermically we
96. ng energy can be controlled and diverted to earth ANSI T1 313 2003 and ANSI T1 334 2002 Antenna masts and metal support structures shall be grounded NFPA 70 2005 Article 810 15 IMPORTANT For towers installed at high lightning prone geographical areas or sites normally occupied such as 911 dispatch centers radial grounding conductors should be employed to improve equalization of the grounding electrode system ANSI T1 334 2002 section 5 4 See Radial Counterpoise Grounding Conductors on page 4 24 This is recommended even if the grounding electrode system resistance requirement is met without the use of radial grounding conductors Towers can be classified into three basic categories ANSI T1 334 2002 section 6 3 e Self Supporting Towers including monopoles e Guyed Towers e Wooden Structures poles 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 4 7 6 1 68P81089E50 B 9 1 05 Some antenna structures such water storage tanks require special grounding and bonding techniques due to the possibility of corrosion and should be designed by a licensed engineer IMPORTANT When only the minimum number of tower ground rods are used the ground rods shall be separated from other ground rods by the sum of their respective lengths whenever practical When the tower ground ring is large enough additional ground rods
97. ng prone geographical areas and sites normally occupied such as dispatch centers should also include enhancements to the grounding electrode system regardless if the resistance requirements are met Some techniques for enhancing the grounding electrode system are described below e Installation of radial grounding conductors e Installation of concrete encased electrodes in new construction e Installation of longer ground rods Doubling the length of a ground rod will reduce its resistance value by approximately 4096 assuming homogeneous soil e Installation of electrolytic ground rods e Use of grounding electrode encasement materials e Specific design by Motorola Engineering or other engineering firm TYPE A SITE GROUNDING EARTHING In sites defined as Type a single ground rod may be sufficient if it can achieve 25 ohms or less throughout the year If a single ground rod cannot achieve 25 ohms or less throughout the year then the grounding earthing electrode shall be augmented by an additional grounding electrode NFPA 70 2005 Article 250 56 and MIL HDBK 419A section 2 2 2 1 or alternate methods shall be used Such alternate methods may include the following e Installation of concrete encased electrodes as part of new construction e Installation of a longer rod that can achieve 25 ohms or less throughout the year In general doubling the length of a ground rod will reduce its resistance value by approxi
98. nificant improvement over standard ground rods of the same length and may last several years longer than standard ground rods The resistance to earth of electrolytic ground rods is generally more stable in environments with variations in temperature and moisture Requirements for the use of electrolytic ground rods are listed below Electrolytic rods shall be UL listed or equivalent Electrolytic rods shall be installed per the manufacturers recommendation Electrolytic rods shall be free of paint or other nonconductive coatings NFPA 70 2005 Article 250 53 and NFPA 780 2004 section 4 13 2 2 Electrolytes within the rod shall be environmentally safe and approved by the environmental authority having jurisdiction L shaped electrolytic rods shall be installed perpendicular to the building or shelter L shaped electrolytic rods horizontal portion shall be installed at least 762 mm 30 in below the earth s surface Grounding electrode encasement materials also known as backfill shall be environmentally safe and approved by the environmental authority having jurisdiction See Grounding Earthing Electrode Encasement Materials on page 4 27 Electrolytic rods should be maintenance free GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING COVERED TEST WELL GRADE BREATHER HOLES 35 mm csa EXOTHERMIC WELD 2 AWG OR COARSER COPPER CON
99. nize steel Aluminum Steel Iron Lead Tin Brass Copper Bronze Silver Graphite Cathodic Most Noble End The rate of corrosion mainly depends on the conductivity of the soil and the relative position of the metals in the galvanic series The higher the soil conductivity low resistivity and the further apart the metals are in the galvanic series the faster the rate of corrosion TIA EIA 222 F R2003 To some extent the rate of corrosion also depends on the relative surface areas of the metals BS 7430 1998 and STD 142 1991 A small anode such as a galvanized steel guy anchor point and large cathode such as a copper grounding electrode system should not be installed in this case the total current is confined to a small space and the current density is large therefore corroding the galvanized steel IEEE STD 142 1991 General guidance on the suitability of metals for bonding together with neighboring metals is given below in Table 4 7 BS 7430 1998 both metals are assumed to be located in the earth The bond between the neighboring metals could be located above or below ground 68P81089E50 B 9 1 05 4 37 DISSIMILAR METALS AND CORROSION CONTROL CHAPTER 4 EXTERNAL GROUNDING EARTHING TABLE 4 7 SUITABILITY OF METALS FOR BONDING Electrode metal or item assumed to have the Smaller Surface Area Galvanized Tinned Metal assumed to have t
100. o any other grounding electrode system at the site See Common Grounding Earthing on page 4 5 For an example of bonding a supplemental grounding electrode system to an existing AC power service grounding electrode system see Figure 4 54 on page 4 77 and Figure 4 64 on page 4 89 A single 2 4 m x 15 9 mm 8 ft x 0 625 in ground rod requires a soil resistivity of approximately 6 250 ohm cm or less throughout the year in order to achieve a resistance value of 25 ohms a 3 m x 15 9 mm 10 ft x 0 625 in ground rod would require 7 500 ohm cm a 4 9 m x 15 9 mm 16 ft x 0 625 in ground rod would require 11 200 ohm cm and a 6 1 m x 15 9 mm 20 ft x 0 625 in ground rod would require 13 600 ohm cm See Chapter Soil Resistivity Measurements for additional information 4 49 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 7 6 4 50 GROUNDING CONDUCTOR GROUNDING CONDUCTOR TOP OF ROD JUST BELOW SOIL SURFACE RECOMMENDED DEPTH MINIMUM DEPTH FIGURE 4 32 TYPICAL SINGLE GROUNDING ELECTRODE INSTALLATION TOWER GROUNDING EARTHING An external grounding earthing electrode system for a communications tower is required to disperse lightning energy to earth before it is able to enter the associated communications structure or enclosure Although is impossible to prevent all lightning energy from entering the communications structure or enclosure the majority of the lightni
101. om the tower and building In typical soil resistivity conditions of 10 000 ohm cm the addition of five radial conductors 7 6 m 25 ft in length may reduce the tower grounding electrode system resistance by a factor of two or three More importantly adding radial conductors divides lightning strike current into segments that allow for more effective dissipation of energy into the earth and away from the equipment building When used radial conductors shall meet the following specifications e The conductors shall radiate away from the building and tower ANSI T1 334 2002 section 5 4 e The conductors shall be installed at the tower or tower ground ring whenever possible If the conductors cannot be installed at the tower installation at the building is acceptable but should be installed near the RF transmission line entry point 4 AVI ARAMA AAA AAA CN ANIA AT MN NNN NNN 7 25 N 2 FIGURE 4 19 INSTALLATION RADIAL CONDUCTORS When radial conductors are used a minimum of three to five conductors should be used e The conductors shall be installed equally spaced from one another as much as practical 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 68P81089E50 B NOTE NOTE 9 1 05 conductors shall be bonded directly to the tower and tower ground ring ANSI T1 334
102. on due to the possibility of galvanic corrosion damage to the anchor points Although various methods for grounding guy anchor points are possible any variation from the requirements and guidelines in this section shall be designed by a licensed professional engineer Guy wire anchors shall minimally be grounded as outlined in the following sections New Construction e The guy anchor shall not be permitted to make direct contact with soil by being encased in reinforced concrete over the entire embedded length of the anchor The concrete encasement shall extend a minimum of 152 mm 6 in above grade NOTE Encasing the anchor in reinforced concrete over the entire embedded length of the anchor helps prevent galvanic corrosion from the guy anchor to copper components of the grounding electrode system Galvanized steel encased in concrete has a similar potential to that of copper see Miscellaneous General Information on page 4 38 Additionally encasing the anchor in reinforced concrete over the entire embedded length of the anchor will help prevent the galvanic corrosion that would otherwise exist from the portion of the anchor in direct contact with soil to the portion encased in concrete GUY WIRE 7 CLAMPS 35 mm CSA 42 AWG OR COARSER TINNED COPPER GROUNDING CONDUCTOR 152 mm 6 IN MINIMUM 25 COPPER GROUND ROD 2 4 M 8 FT MINIMUM CONCRETE ANCHOR CONCRETE ANCHOR SIZED ACCORDING TO PROFESSIONAL ENG
103. on line cable resulting in damage to the transmission lines See Figure 4 43 through Figure 4 46 for examples of transmission line grounding earthing conductor attachment methods All transmission lines shall be bonded to the tower using ground kits as follows e Transmission line ground kits shall be installed per manufacturer specifications e Transmission line ground kits shall be sealed from the weather to prevent water and corrosion damage to the transmission line ANSI T1 313 2003 section 10 5 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS e Transmission line ground kits shall be attached to an effectively grounded vertical member of the tower using tower manufacturer approved methods typically a type of mechanical clamp Transmission line ground kits may attach to a tower bus bar in lieu of directly attaching to the tower structure see Tower Ground Bus Bar on page 4 32 See Figure 4 42 through Figure 4 46 for examples of methods used to attach to the tower ANSI T1 313 2003 section 10 5 e Transmission line ground kit grounding conductors shall be installed without drip loops parallel to the transmission line and pointed down towards the ground to provide a direct discharge path for lightning ANSI T1 313 2003 section 10 5 1 e Transmission line ground kits shall be installed at the first point of contact near the antenna ANSI T1 334 2002 se
104. one of the following techniques Installing a 16 mm csa 6 AWG or coarser copper conductor bonding jumper between the cable bridge ice bridge and the tower Conductor bonding to the cable bridge ice bridge shall be made using exothermic welding or listed two hole lugs and stainless steel hardware Conductor bonding to the tower shall be made using exothermic welding or other suitable hardware See Bonding to the External Grounding Earthing Electrode System on page 4 40 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS e Installing a 16 mm csa 6 AWG or coarser copper conductor bonding jumper between the cable bridge ice bridge and the tower ground bus bar TGB Conductor bonding to the cable bridge ice bridge and TGB shall be made using exothermic welding or listed two hole lugs and stainless steel hardware See Bonding to the External Grounding Earthing Electrode System on page 4 40 e Installing a 35 mm csa 2 AWG or coarser bare copper conductor bonded directly to the grounding electrode system Conductor bonding to the grounding electrode system shall be made using exothermic welding or listed irreversible high compression fittings Conductor bonding to the cable bridge ice bridge shall be made using exothermic welding or listed two hole lugs and stainless steel hardware The grounding conductor should be installed in a flexible non metal
105. or size in AWG MCM 6 10 10 8 16 6 25 4 35 2 50 1 0 75 2 0 95 3 0 120 4 0 150 300 MCM 185 350 MCM 240 500 MCM 300 600 MCM 400 800 MCM NOTE Down conductors alone should not be relied on for an effective grounding electrode system Other methods listed in this section such as building and tower ground rings should also be used to help achieve an effective grounding electrode system e Installation of copper strap radial grounding conductors on the surface of the rocks in all directions from the tower The copper straps may be covered with top soil and or ground enhancing material such as conductive concrete Each copper strap radial should be a different length to help prevent ringing of the tower during a lightning strike IMPORTANT At sites such as stone mountain tops where it is difficult to achieve an effective grounding electrode system the need for single point grounding and transient voltage surge suppression TVSS on all input outputs is of paramount importance 68P81089E50 B 9 1 05 4 95 SPECIAL GROUNDING EARTHING SITUATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 11 5 4 96 NOTE See Table 4 8 on page 4 94 for proper _ conductor sizing based on length COMMUNICATION SITE LM UFER GROUND AREAS OF AVAILABLE SOIL FIGURE 4 69 EXAMPLE OF SOILLESS GROUND SYSTEM The concept of drilling holes in solid rock to insert a ground rod surrounded by a grounding electrode encasement mater
106. ossibly on to a third device in a series arrangement whereby the removal of the second connection point interrupts the ground path from the first device shall not be used 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 68P81089E50 B 9 1 05 The fencing system for a nearby installed fence at a communications site shall be grounded bonded as follows e Each corner fence post shall be bonded to the nearest location of the building ground ring using 35 mm csa 2 AWG or coarser bare solid or stranded tinned copper conductors The grounding conductors shall be buried to the same depth as the building ground ring wherever practical See ANSI T1 313 2003 figure 3 a e fence fabric near each corner bonding point shall also be bonded to the building ground ring This bond may be made using the same grounding conductor used for the corner fence post or by bonding directly to the fence post using approved methods described within this chapter The fence fabric bond should be made in at least three points down the fence fabric as shown in Figure 4 49 MIL HDBK 419A Volume II section 1 12 DETERRENT WIRE GROUNDING CLAMP EXOTHERMIC WELD CONNECTION FENCE FABRIC GROUNDING CLAMP 1 OF 3 SOFT DRAWN TINNED SOLID COPPER CONDUCTOR BONDING FENCE FABRIC TO GROUND CONDUCTOR GATE JUMPER WITH EXOTHERMIC WELD GROUND CONDUCTOR WITH EXOTHERMIC WELD
107. otherwise required by the specific component manufacturer ANSI T1 313 2003 figure 3 a Manufacturer requirements shall be followed for all connections Connectors and fitting used shall be listed for the purpose for the type of conductor and for the size and number of conductors used All above grade grounding electrode system connections such as grounding electrode conductor connection to ground bus bars and tower legs shall be joined using exothermic welding or listed irreversible high compression fittings compressed to a minimum of 13 3 tonnes 12 tons of pressure or as otherwise required by the specific component manufacturer ANSI T1 313 2003 figure 3 a All above grade bonding connections such as bonding to ancillary equipment or bonding coaxial ground kits to bus bars shall be joined using exothermic welding listed lugs listed pressure connectors listed clamps or other listed means required by the specific component manufacturer Connecting hardware shall be designed for the purpose for the type of conductor and for the size and number of conductors used All mechanical connections shall be coated with a listed conductive anti oxidant compound The anti oxidant compound shall be liberally applied between the two metals see Figure 4 27 NFPA 70 2005 Article 250 70 METALLIC BONDING REMOVE PAINT IF PRESENT SURFACE AND APPLY ANTIOXIDANT COMPOUND BOT GROUND LOCKWASHER LUG GROUND BUS BAR OR EQUIPMENT SURFACE
108. ound resistance requirements of the site See NFPA 780 2004 section 4 13 8 1 for additional information 68P81089E50 B 9 1 05 Consult with Motorola Engineering or other engineering firm Installation of concrete encased electrodes as part of new construction See Concrete Encased Electrodes on page 4 20 Installation of ground rings around the building and tower with the ground rings buried as deep as the soil will allow The ground rings should be encased in a grounding electrode encasement material A conductive concrete may be the best grounding electrode encasement material for use in shallow topsoil environments since the conductive concrete would not require a covering of topsoil for protection See External Building and Tower Ground Ring on page 4 22 Installation of ground plates along the length of the ground rings instead of vertical ground rods The ground plates should be encased in a grounding electrode encasement material See Grounding Earthing Electrode Encasement Materials on page 4 27 and Ground Plate Electrodes on page 4 19 Installation of a grounding electrode grid system using ground plates instead of vertical ground rods The grounding conductors and ground plates shall be buried as deep as the soil will allow The grounding conductors should be encased in a grounding electrode encasement material A conductive concrete may be the best grounding electrode encasement material for use in shallo
109. r For example five 3 m 10 ft ground rods installed 6 1 m 20 ft apart in an 24 4 m 80 ft straight line will achieve a resistance to earth of 7 8 ohms assuming 10 000 ohm cm soil Nine 3 m 10 ft ground rods installed 3 m 10 ft apart in the same 24 4 m 80 ft straight line will achieve a resistance to earth of 5 7 ohms 4 4 1 2 68P81089E50 B 9 1 05 GROUND RODS Typical ground rods are shown in Figure 4 7 Requirements for ground rods are listed below See IEEE STD 142 1991 section 4 3 1 and UL 467 2004 for additional information i FIGURE 4 7 TYPICAL GROUND RODS 4 4 1 2 1 GROUND ROD SPECIFICATIONS Ground rods shall be UL listed or equivalent Ground rods shall be constructed of copper clad steel solid copper hot dipped galvanized steel or stainless steel ANSI J STD 607 A 2002 section C 4 3 and ANSI T1 334 2002 section 5 3 2 See NFPA 70 2005 Article 250 52 and UL 467 2004 section 9 2 1 for additional information GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING NOTE Stainless steel ground rods shall be formed of an austenitic stainless steel of the 18 percent chromium 8 percent nickel type UL 467 2004 section 9 2 6 Ground rods shall have a minimum length of 2 4 m 8 ft ANSI T1 313 2003 section 10 3 1 ANSI T1 334 2002 section 5 3 2 NFPA 70 2005 Article 250 52 and UL 467 2004 For areas highly prone to lightning
110. r Ground Ring on page 4 22 The ground ring shall be installed at least 610 mm 2 ft from the cabinet foundation pad The cabinet ground ring shall have a ground rod installed at each corner and as needed to limit the distance between rods from 3 m to 4 6 m 10 to 15 ft Ground rods shall have a minimum separation from other ground rods equal to its length ANSI T1 313 2003 The cabinet ground ring shall bond to the tower ground ring as detailed in External Building and Tower Ground Ring on page 4 22 Towers associated with outdoor cabinets shall be grounded as detailed in Tower Grounding Earthing on page 4 50 RF transmission lines shall be grounded bonded as detailed in RF Transmission Line and Preamplifier Grounding Earthing on page 4 62 Metallic objects near the cabinet shall be bonded to the cabinet grounding electrode system as detailed in Metallic Objects Requiring Bonding on page 4 67 The cabinet grounding electrode system shall bond to the cabinet s internal ground point and cabinet housing using a 35 mm csa 2 AWG or coarser tinned or un tinned copper conductor The conductor 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 See Bending And Routing Grounding Earthing Conductors on page 4 29 In addition to the above requirements the follow recommendations should be considered Cabinets install
111. rge protection devices SPD shall be incorporated at a communications site in order to provide an adequate level of protection See Chapter 7 Surge Protective Devices for details and requirements A grounding electrode system shall have low electrical impedance with conductors large enough to withstand high fault currents The lower the grounding electrode system impedance the more effectively the grounding electrode system can dissipate high energy impulses into the earth WARNING The AC power system ground shall be sized appropriately for the electrical service and shall be approved by the local authority having jurisdiction 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 Special Grounding Earthing Situations on page 4 88 in these instances Consultation with Motorola Engineering or an engineering firm specializing in grounding electrode system design is recommended Some of the benefits of a properly designed and installed low impe
112. s are used the conductors should be of different lengths to help prevent resonant ringing of the tower from a lightning strike Low resistance in radial counterpoise grounding configurations is desirable but not critical Low resistance in the dissipating path of strike currents into the earth is of secondary importance when compared to the primary objective of controlling voltage gradients and voltage differences between structures and equipment close to the tower ANSI T1 334 2002 section 5 4 e When soil conditions allow the effectiveness of the radial grounding conductor may be increased by including a ground rod every 4 9 m 16 ft or twice the length of the ground rods installed as described in Ground Rods on page 4 11 See Figure 4 19 on page 4 24 for an example of ground radials Figure 4 20 on page 4 26 shows the resistance characteristics of a radial grounding conductor The resistance to earth of a straight horizontal electrode radial grounding conductor may be calculated as follows 1 E Pur TL 2aD Where D L R The resistance of the electrode in ohms p The soil resistivity in meter ohms L The length of the electrode in metres a The electrode radius in meters D The electrode depth in meters 4 25 GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING Radial Grounding Conductor Resistance AWG
113. s not alleviate the requirement to remove nonconductive coatings from attachment surfaces See Figure 4 27 for proper star lock washer location Star washers should only be used as a lock washer e After bonding to a painted or galvanized structure the area shall be painted with a zinc enriched paint e Exothermic welding is the preferred method for bonding connections to the external grounding electrode system e Two hole lugs secured with fasteners in both holes are preferred over single hole lugs Two hole lugs prevent movement of the lug e When connecting ground lugs or compression terminals to ancillary equipment such as air conditioners and vent hoods a lock washer shall be placed on the nut side See Figure 4 27 Sheet metal screws and or self tapping screws shall not be used e All mechanical connections shall be coated with a listed conductive anti oxidant compound NFPA 70 2005 Article 250 70 ANSI T1 334 2002 section 9 The anti oxidant compound shall be liberally installed between the two metals see Figure 4 27 on page 4 40 BoNDING METHODS The following paragraphs describe acceptable methods for bonding to the external grounding earthing electrode system Exothermic welding and the use of listed irreversible high compression fittings are the only acceptable methods for below grade bonding Other mechanical connection methods shall not be used below grade EXOTHERMIC WELDING Exothermic welding is a method of weld
114. soils Where frozen high resistivity soils are encountered optimum grounding can only be accomplished by special attention to both surface and subsurface terrain The resistivity of frozen soils can be 10 to 100 times greater than in the unfrozen state therefore seasonal changes in temperature and moisture greatly affect the resistance to earth of the grounding electrode system See Appendix B for additional information regarding soil resistivity changes as a function of temperature and moisture See MIL HDBK 419 A Volume I section 2 11 1 for additional information Seasonal freezing accounts for an increase in grounding electrode system resistance If frozen soil has a high resistivity then providing larger electrodes reduces the resistance to earth In arctic areas that generally have very shallow surface thaw layers horizontal rods or conductors may be easier to install than driven rods and provide an equivalent resistance to earth Whether to install multiple electrodes or a single deep driven rod or horizontal conductors is usually dependent on soil conditions at the site and the economics of installation See MIL HDBK 419 A Volume I section 2 11 1 for additional information An option for an effective grounding electrode system may be to install electrolytic ground rods that are encased in a grounding electrode encasement material See Electrolytic Ground Rods on page 4 16 and Grounding Earthing Electrode Encasement Materials
115. ssion sleeve or exothermic weld Threaded rods or compression sleeves shall be UL listed IEEE STD 142 1991 section 4 3 1 See Figure 4 10 for an example of splicing ground rods together L 129 1L FIGURE 4 10 SPLICING TWO GROUND RODS 4 14 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 68P81089E50 B 9 1 05 4 4 1 2 3 EFFECT OF GROUND ROD SIZE ON RESISTANCE TO EARTH Increasing the diameter of a ground rod does not significantly reduce its resistance to earth Doubling the diameter of a rod reduces its resistance to earth by approximately 10 See Figure 4 11 50 4 45 40 35 30 25 20 Approximate Resistance to Earth in Ohms 0 0 50 0 75 1 00 1 25 1 50 1 75 2 0 Ground Rod Diameter Inches 3 m 10 ft Ground Rod in 10 000 ohm cm soil FIGURE 4 11 RESISTANCE TO EARTH DUE TO GROUND ROD DIAMETER As the length of a ground rod is increased its resistance to earth is substantially reduced In general doubling the length of a ground rod reduces the resistance to earth by 40 See Figure 4 12 140 120 4 o o B o Approximate Resistance to Earth in Ohms 20 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Ground Rod Length Feet 15 9 mm 0 625 in Diameter Ground Rod in 10 000 ohm cm soil
116. t each corner of the shelter and as follows e If2 4m 8 ft ground rods are used additional ground rods shall be installed as needed to reduce the distance between rods from 3 m to 4 6 m 10 to 15 ft ANSI T1 334 2002 e If longer ground rods are used a larger separation proportional to the increase in rod length may be used e Ground rods shall be placed a minimum of one rod length apart along the ground rings ANSI T1 313 2003 figure 3 a e Ground rods shall not be separated from an adjacent ground rod along the ground ring by more than the sum of their respective lengths MIL HDBK 419A ground rods shall be installed in accordance with Ground Rods on page 4 11 ground rods shall be exothermically welded to the ground ring or as otherwise allowed in Bonding to the External Grounding Earthing Electrode System on page 4 40 e building ground ring shall be bonded to the tower ground ring using a minimum of two 35 mm csa 2 AWG or coarser bare solid tinned or un tinned copper conductors See External Building and Tower Ground Ring on page 4 22 and Figure 4 4 on page 4 8 e tower shall be grounded in accordance with Tower Grounding Earthing on page 4 50 Determine if radial grounding conductors should be installed at the site see Radial Counterpoise Grounding Conductors on page 4 24 GENERATORS EXTERNAL TO THE BUILDING Generators installed outside
117. t use of two hole lugs Method of attachment of grounding electrode conductor Exothermic welding Irreversible crimp connection 4 5 DISSIMILAR METALS AND CORROSION CONTROL Although the type of metals used in a grounding earthing electrode system do not affect the resistance to earth of the grounding electrode system consideration should be given to select a metal that is resistance to corrosion in the type of soil in which it will be installed The two areas that should be considered regarding the corrosion resistance of a metal are the compatibility with the soil itself and possible galvanic corrosion effects when it is electrically connected to neighboring metals at the site BS 7430 1998 4 5 1 CORROSION RELATED TO SOIL TYPE The compatibility of a metal with soil is determined by the chemical composition of the soil The chemical composition factors associated with the corrosion of metals in contact with the soil are as follows acidity or alkalinity pH salt content soil porosity aeration and the presence of anaerobic bacteria BS 7430 1998 and TIA EIA 222 F R2003 The following list gives a general representation of the aggressiveness of soils listed in order of increasing aggressiveness BS 7430 1998 e Gravelly soils Least Aggressive Sandy soils e Silty soils loam e Clays e Peat and other organic soils e Made up soils containing cinders Most Aggressive 4 34 68P81089
118. table grounding electrode system that meets the resistance requirements defined in this chapter may be to install a grounding electrode grid system using all available space on the property A grounding electrode grid system consists of grounding electrodes typically rods installed in a grid pattern The grounding electrodes are all equally spaced and connected together underground with a grounding conductor See MIL HDBK 419A for additional information Requirements for a grounding electrode grid system are as follows e grounding electrodes shall meet the specifications and installation requirements of Grounding Earthing Electrodes on page 4 9 4 90 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING SITUATIONS e Grounding conductors used to connect the grounding electrode shall meet the specifications and installation requirements of Grounding Earthing Conductors on page 4 28 Whenever possible the grounding conductors shall be buried at least 762 mm 30 in deep or below the frost line whichever is deeper e Grounding conductors shall be bonded together wherever they intersect this is typically completed at a ground rod or other grounding electrode e Bonding of all components shall be made using exothermic welding or listed irreversible high compression fittings See Bonding to the External Grounding Earthing Electrode System on page 4 40 See Figur
119. tem components are but not limited to the following Building ground ring See External Building and Tower Ground Ring on page 4 22 Tower ground ring See External Building and Tower Ground Ring on page 4 22 e Ground rods properly installed and spaced around the building and tower ground rings See Ground Rods on page 4 11 e Radial grounding conductors for high lightning prone geographical areas sites that are normally occupied such as 911 dispatch centers sites with high soil resistivity or when bedrock prohibits the driving of ground rods See Radial Counterpoise Grounding Conductors on page 4 24 e Proper bonding of all grounding electrode system components See Bonding to the External Grounding Earthing Electrode System on page 4 40 Proper bonding of all ancillary equipment See Bonding to the External Grounding Earthing Electrode System on page 4 40 The grounding electrode system resistance requirement is determined based on the classification of the site Communications sites are classified by this standard into two categories Type A See Type A Sites Light Duty on page 4 46 e B See Sites Standard Duty on page 4 47 TYPE A SITES LIGHT DUTY Type A sites shall have a grounding earthing electrode system resistance design goal of 25 ohms or less for a single grounding electrode NFPA 70 2005 Article 250 56 MIL HDBK 419A
120. th Limited Space for the Grounding Earthing Electrode System on page 4 90 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING SITUATIONS Using multiple large copper plates 0 88 to 1 8 m 10 to 20 ft buried to an optimal depth of 1 5 m to 2 4 m 5 to 8 ft The plates are placed vertically on edge and bonded to the grounding electrode system using exothermically welded 35 mm csa 2 AWG solid copper wire Placing the plates on vertical edge allows the plates to be buried with a minimum of excavation and may make it possible to obtain more surface area contact with the soil when backfilling The use of a number of well placed ground plates in parallel is preferred to placing longer rows of ground plates IEEE STD 142 1991 section 4 2 4 Encasing the ground plates in a grounding electrode encasement material can further increase the effectiveness of the grounding electrode system 4 11 6 SHALLOW TOPSOIL ENVIRONMENTS Some sites are located in areas where bedrock is near the surface or where the top soil is less than 305 mm 1 ft deep These areas require installation of specialized grounding earthing electrode systems and may require the support of an engineering firm Requirements and recommendations for grounding electrode systems in areas with shallow topsoil are provided below Reasonable attempts should be made to use as many options as possible and as needed to meet the gr
121. th the device manufacturer requirements Grounding conductors shall meet the specifications and installation requirements of Grounding Earthing Conductors on page 4 28 Bonding to the vertical grounding conductor shall be made using listed irreversible compression fittings or exothermic welding as described in Bonding Methods on page 4 41 2 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING EARTHING APPLICATIONS 4 10 4 68P81089E50 B BOND FROM EXTERNAL GROUNDING STUD ON ACCESS POINT TO GROUNDING ELECTRODE SYSTEM FIGURE 4 62 GROUNDING ACCESS POINT MOUNTED ON NON METALLIC POLE METAL SHIPPING CONTAINERS USED AS COMMUNICATIONS BUILDINGS Grounding earthing electrode systems for metal shipping containers used as communications buildings shall conform to the requirements specified in this chapter for a dedicated communications building see Dedicated Communications Building Grounding Earthing on page 4 59 All equipment inside the shipping container shall conform to the grounding requirements of Chapter 5 Internal Grounding Earthing In addition to the requirements listed above the outside of the shipping container shall be bonded to the grounding electrode system in at least all four corners using 35 mm csa 2 AWG or coarser bare solid copper conductors Requirements for bonding the metal shipping container to the grounding electrode system are as
122. the following e The additional ground rod shall meet the requirements of Ground Rods on page 4 11 e The additional ground rod shall be installed using methods described in Ground Rods on page 4 11 e The grounding conductor between the ground rod and generator shall be 35 mm csa 2 AWG or coarser bare solid tinned or un tinned copper conductor The grounding conductor shall meet the requirements of Grounding Earthing Conductors on page 4 28 e Bonding to the ground rod shall be made using exothermic welding or listed irreversible high compression fittings See Bonding to the External Grounding Earthing Electrode System on page 4 40 GENERATOR MORE THAN 1 8 M 6 FT ADDITIONAL GROUND ROD FROM BUILDING GENERATOR LESS THAN 1 8 M 6 FT FROM BUILDING FIGURE 4 40 GENERATOR GROUNDING 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING EARTHING REQUIREMENTS 4 7 8 68P81089E50 B 9 1 05 OUTDOOR CABINET GROUNDING EARTHING Outdoor cabinets are grounded earthed in a very similar manner as a dedicated communications building ANSI T1 313 2003 section 1 1 See Dedicated Communications Building Grounding Earthing on page 4 59 for details Outdoor cabinets shall be grounded as follows The cabinet shall be encircled with a ground ring The ground ring shall meet the requirements defined in External Building and Towe
123. tively grounded If the utility pole must be made effectively grounded it shall minimally be grounded as described for a Type A site in Type A Site Grounding Earthing on page 4 48 4 85 SPECIAL GROUNDING EARTHING APPLICATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING 1 4 86 BOND FROM EXTERNAL GROUNDING STUD ON ACCESS POINT TO METALLIC SUPPORT ARM USING APPROPRIATE HARDWARE BOND FROM EXTERNAL GROUNDING STUD ON ACCESS POINT TO METALLIC POLE USING APPROPRIATE HARDWARE ite METAL POLE METAL ARM METAL POLE NONMETALLIC ARM NOTE FIGURE 4 61 GROUNDING ACCESS POINT MOUNTED ON METAL POLE If the access point or wireless router is mounted to a non metallic arm on the metallic utility pole the access point or wireless router shall be grounded as described above by bonding to the metallic portion of the pole as shown in Figure 4 61 4 10 3 3 2 NON METALLIC POLE MOUNTED Non metallic utility poles used for supporting access points and wireless routers shall be grounded earthed in the same manner as described in Wooden Structures Poles on page 4 58 The access points and wireless routers shall be bonded to the pole s vertical grounding conductor using a 16 mm csa 6 AWG or coarser solid or stranded copper conductor as shown in Figure 4 62 Connection to access points and wireless routers shall be made to an adequately sized dedicated grounding point in accordance wi
124. tning protection system is not available roof mounted antenna masts and metal support structure shall be grounded by directly bonding to the building s grounding electrode system or to a supplemental grounding electrode system FAA STD 019d 2002 section 3 7 9 4 Bonding to the grounding electrode system shall use effectively grounded structural building steel when available When effectively grounded structural building steel is not available bonding to the grounding electrode system shall use at least two down conductors whenever practical ANSI T1 334 2002 section 8 2 When effectively grounded structural building steel is not available and the use of two down conductors is not practical the use of a single down conductor should be approved by an engineer Available water piping systems may also be used as a grounding down conductor but should only be used under the advice of an engineer Bonding to the structural building steel shall be made using exothermic welding listed irreversible high compression fittings or other fittings listed for use in lightning protection systems See NFPA 780 2004 section 4 16 for additional information regarding the use of structural building steel as a main grounding conductor Figure 4 53 shows examples of acceptable building steel bonding connections FIGURE 4 53 ACCEPTABLE STRUCTURAL BUILDING STEEL BONDING CONNECTIONS Down conductors shall be routed to the grounding electrode
125. tower and building structures regardless of earth resistivity by insuring that a low impedance current path exists throughout the area ANSI T1 334 2002 section 5 3 Requirement for external ground rings are listed below see Figure 4 18 e Unless otherwise stated ground ring conductors shall be 35 mm csa 2 AWG or coarser bare solid tinned or un tinned copper ANSI T1 313 2003 and ANSI T1 334 2002 section 5 3 1 See Grounding Earthing Conductors on page 4 28 for grounding conductor specifications e Solid bare tinned copper conductor should be used to minimize galvanic corrosion between tower legs and other parts of the grounding electrode system ANSI T1 313 2003 section 10 7 e For areas highly prone to lightning and or military installations larger conductors such as 50 mm csa 1 0 AWG or coarser should be considered MIL HDBK 419A and MIL STD 188 124B stranded conductors may be used in this application e Building ground rings shall encircle the building or shelter whenever possible ANSI T1 313 2003 ANSI T1 334 2002 MIL HDBK 419A and MIL STD 188 124B e Tower ground rings shall encircle the tower structure whenever possible ANSI T1 334 2002 section 5 3 and MIL HDBK 419A e The ends of the conductor shall be joined together to form a ring using an exothermic weld or listed irreversible high compression connector ANSI T1 334 2002 section 5 3 1 and MIL STD 188 124B This may be easily complet
126. trical Inspectors publication Soares Book on Grounding and Bonding 9th Edition Appendix B and the United States National Weather Service Manual 30 4106 2004 Lightning Protection Grounding Bonding Shielding and Surge Protection Requirements If the design goal of 10 ohms or recommended 5 ohms cannot be achieved with the minimum accepted grounding electrode system reasonable efforts shall be made to achieve the design goal using supplemental grounding techniques The supplemental grounding techniques are described in Supplemental Grounding Earthing on page 4 48 Type B sites typically have the following characteristics e Atower is associated with the site e 911 dispatch center Communications dispatch center e Base station and or repeater site e Telecommunication repeater equipment is installed such as cellular PCS or wide area repeater site e Large installation or multiple systems such as telephone or electronic switches LANs WANSs and Mobile Switching Offices MSO are installed e Critical public safety or military installation 68P81089E50 B 9 1 05 4 47 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 7 5 4 48 4 7 4 3 NOTE SUPPLEMENTAL GROUNDING EARTHING Sites with high poor soil resistivity shall require enhancements to the grounding earthing electrode system if the resistance requirement of the site cannot be met Sites in high lightni
127. unding Earthing Electrode System on page 4 40 e To help insure effective bonding connections the cable bridge ice bridge should bond to each support post using a using a 16 mm csa 6 AWG or coarser jacketed ANSI T1 334 2002 section 5 1 copper conductor bonding jumper Conductor bonding to the support post shall be made using exothermic welding Conductor bonding to the cable bridge ice bridge shall be made using exothermic welding or listed two hole lugs and stainless steel hardware e f more than one span of cable bridge ice bridge is used between the tower and building bonding jumpers should be installed between the sections to help ensure effective bonding The bonding jumpers shall be a 16 mm csa 6 AWG or coarser copper conductor The bonding jumpers should use listed two hole lugs and stainless steel hardware 4 71 MINIMUM SITE GROUNDING EARTHING REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 72 ICE BRIDGE SEGMENTS LEGS BONDED TOGETHER BELOW GRADE THEN BONDED TO GROUND RINGS USING 35 mm csa 2 AWG OR COARSER WIRE BUILDING GROUND RING TOWER GROUND RING FIGURE 4 51 PROPER GROUNDING OF SELF SUPPORTING ICE BRIDGE Grounding of tower and or building supported cable bridges ice bridges shall be completed as follows At the building The cable bridge ice bridge shall bond to the grounding electrode system Bonding to the grounding electrode system may be accomplished using a 16 mm
128. ute ANSI Australian Standards AS British Standards Institution BS International Association of Electrical Inspectors IAEI International Electrotechnical Commission IEC Institute of Electrical and Electronics Engineers IEEE National Fire Protection Association NFPA Telecommunications Industry Association TIA Underwriters Laboratories UL United States Department of Defence DoD United States Federal Aviation Administration FAA United States National Weather Service 4 1 INTRODUCTION CHAPTER 4 EXTERNAL GROUNDING EARTHING References to the specific industry codes and standards on which this chapter is based are provided throughout The requirements and guidelines in this chapter are provided to enhance personnel safety and equipment reliability Safety of personnel and protection of sensitive electronic 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 electrode systems that may help minimize damage caused by these events AN Grounding earthing and bonding alone are not enough to adequately protect a communications site Transient voltage surge suppression TVSS techniques using appropriate su
129. very 6 1 m 20 ft TRANSMISSION LINE GROUND ANTENNA MOUNT ANTENNA 35 csa 2 CONDUCTORS ELECTRICAL SERVICE GROUND RODS FIGURE 4 56 GROUNDING OF MULTIPLE SIDE MOUNTED ANTENNAS 4 78 68P81089E50 B 9 1 05 STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING EARTHING ROOFTOP MOUNTED TOWER STRUCTURES 4 9 68P81089E50 B GROUNDING EARTHING ROOFTOP MOUNTED TOWER STRUCTURES NOTE NOTE 9 1 05 Rooftop mounted towers may increase the lightning risk index for the buildings they are installed upon Due to their increased height and lightning risk probability all exposed buildings with rooftop towers shall be equipped with a lightning protection system as outlined in NFPA 780 2004 ANSI T1 313 2003 section 10 3 3 See Lightning Activity and Exposure on page 4 3 for information regarding lightning exposure to buildings and towers Consult the building engineer or manager to determine information about any existing building grounding earthing electrode systems The building engineer should also be informed before attempting to weld or drill on the building rooftop An engineering firm specializing in the design and installation of lightning protection systems should be consulted for proper design and installation of the building lightning protection system A licensed contractor specializing in the installation of lightning protection systems should be used The lightning protection
130. w topsoil environments since the conductive concrete would not require a covering of topsoil for protection See Sites With Limited Space for the Grounding Earthing Electrode System on page 4 90 and Figure 4 66 on page 4 91 for additional information on grounding electrode grid systems Installation of electrolytic ground rod systems See Electrolytic Ground Rods on page 4 16 4 97 SPECIAL GROUNDING EARTHING SITUATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING 4 98 NOTE Extend radial grounding conductors as allowed by available soil See Radial Counterpoise Grounding Conductors on page 4 24 FIGURE 4 70 GROUNDING ELECTRODE SYSTEM WITH GROUND PLATES e Installation of building radial grounding conductors in a trench extending away from the building at each corner The radial grounding conductors shall be buried as deep as the soil will allow The radial grounding conductors shall bond to the building ground ring using exothermic welding or listed irreversible high compression fittings The radial grounding conductors should be encased in a grounding electrode encasement material A conductive concrete may be the best grounding electrode encasement material for use in shallow topsoil environments since the conductive concrete would not require a covering of topsoil for protection Each radial grounding conductor may have ground plates installed every 1 8 to 4 9 m 6 to 16 ft along its length See Figure 4 7
131. with Motorola Engineering or other engineering firm may be required in some situations 4 10 1 EXTERNAL GROUNDING EARTHING FOR DISPATCH CENTERS CO LOCATED WiTH COMMUNICATIONS TOWERS Dispatch centers co located with communications towers require special protection considerations due to the critical nature of their operation and due to the inherent risk to personnel from lightning For optimum protection of a dispatch center the following shall be considered e Site design recommendations given in Design Considerations to Help Reduce Effects of Lightning on page 2 19 e Internal grounding and bonding as defined in Grounding Earthing for Dispatch Centers and Network Operator Positions on page 5 62 e Transient voltage surge suppression TVSS As defined in Surge Protection Considerations for Dispatch Centers and Operator Positions on page 7 43 68P81089E50 B 9 1 05 4 81 SPECIAL GROUNDING EARTHING APPLICATIONS CHAPTER 4 EXTERNAL GROUNDING EARTHING e Electrostatic discharge ESD precautions as defined in Protecting Against Electrostatic Discharge in Equipment Rooms and Dispatch Centers on page C 1 e External grounding earthing as follows e Grounding electrode system resistance design goal of 5 ohms or less See Site Standard Duty on page 4 45 e Installation of all minimum required grounding electrode system components as described in External Building and Tower Ground R
132. wn due to contact with rock formations may be driven at an oblique angle of not greater than 45 degrees from the vertical or may be buried horizontally and perpendicular to the building in a trench at least 762 mm 30 in deep as shown in Figure 4 9 NFPA 70 2005 Article 250 53 68P81089E50 B 9 1 05 4 13 GROUNDING EARTHING ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4 EXTERNAL GROUNDING EARTHING BURIED GROUNDING ELECTRODE CONDUCTORS 45 2 4m maximum 8 ft FIGURE 4 9 ANGLED GROUND ROD INSTALLATION spo WARNING When operating any kind of power tool always wear appropriate safety glasses and other protective gear to prevent injury e Hammer drills or electric jackhammers may be used to drive in the ground rods Do not deform the head of the ground rod See IEEE STD 142 1991 section 4 3 2 for additional information e frock formations prevent ground rods from being driven to the specified depth an alternate method of achieving an acceptable grounding electrode system shall be engineered and implemented See Special Grounding Earthing Situations on page 4 88 for additional information e When the grounding electrode system design requires deeper ground rods in order to lower the grounding electrode system resistance penetrate down to permanent moisture level or to penetrate below the frost line two or more ground rods may be joined together by use of a coupling threaded compre

Bonding to the External Grounding (Earthing)

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