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68P81150E62
for Cellular Radio InstallationsGROUNDING GUIDELINE
COMPUTER SOFTWARE COPYRIGHTS
The Motorola products described in this instruction manual may include copyrighted Motorola computer programs stored in semiconductor memories or othermedia. Laws in the United States and other countries preserve for Motorola certain exclusive rights for copyrighted computer programs, including the exclusiveright to copy or reproduce in any form the copyrighted computer program. Accordingly, any copyrighted Motorola computer programs contained in the Motorolaproducts described in this instruction manual may not be copied or reproduced in any manner without the express written permission of Motorola. Furthermore,the purchase of Motorola products shall not be deemed to grant either directly or by implication, estoppel, or otherwise, any license under the copyrights, patents orpatent applications of Motorola, except for the normal non–exclusive, royalty free license to use that arises by operation of law in the sale of a product.
68P81050E85–O
USAGE AND DISCLOSURE RESTRICTIONS
The software described in this document is the property of Motorola, Inc. It is furnished under a license agreement and may be used and/or disclosed only inaccordance with the terms of the agreement.
Software and documentation are copyrighted materials. Making unauthorized copies is prohibited by law. No part of the software or documentation may be repro-duced, transmitted, transcribed, stored in a retrieval system, or translated into any language or computer language, in any form or by any means, without priorwritten permission of Motorola, Inc.
While reasonable efforts have been made to assure the accuracy of this document, Motorola, Inc. assumes no liability resulting from any omissions in thisdocument, or from use of the information obtained herein. The information in this document has been carefully checked and is believed to be entirelyreliable. However, no responsibility is assumed for inaccuracies. Motorola, Inc. reserves the right to make changes to any products described herein toimprove reliability, function, or design, and reserves the right to revise this document and to make changes from time to time in content hereof with noobligation to notify any person of revisions or changes. Motorola, Inc. does not assume any liability arising out of the application or use of any product orcircuit described herein; neither does it convey license under its patent rights or the rights of others.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
��Motorola, Inc. 1992All Rights ReservedPrinted in U.S.A.
68P81150E62–A 7/23//92–
Technical Education & Documentation1501 W. Shure Drive, Suite 3223B, Arlington Heights, Il 60004
GROUNDING GUIDELINE
FOR CELLULAR RADIO INSTALLATIONSGeneral Systems SectorCellular Infrastructure Group
CONTENTS
1. INTRODUCTION 2. . . . . . . . . . . . . . . . . . . . . . . . 1.1 Purpose 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Assumptions 2. . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Overview 2. . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. GENERAL TECHNIQUES 2. . . . . . . . . . . . . . . . 2.1 External Ground Sub–System 2. . . . . . . . . . . . 2.2 Internal Ground Sub–System 2. . . . . . . . . . . . 2.3 Surge Protection 2. . . . . . . . . . . . . . . . . . . . . .
3. DEFINITIONS 3. . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 CADWELD Process 3. . . . . . . . . . . . . . . . . . . . 3.2 External Ground Bar (EGB) 3. . . . . . . . . . . . . 3.3 External Ground Ring (EGR) 3. . . . . . . . . . . . 3.4 Ground Rods 3. . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Internal Ground Ring (IGR) 3. . . . . . . . . . . . . 3.6 Isolated Ground Bar (IGB) 3. . . . . . . . . . . . . . 3.7 Isolated Ground Zone (IGZ) 3. . . . . . . . . . . . . 3.8 Master Ground Bar (MGB) 3. . . . . . . . . . . . . . 3.9 Multi–grounded Neutral (MGN) 3. . . . . . . . . . 3.10 Tower Ground Ring 3. . . . . . . . . . . . . . . . . . . . 3.11 Ufer Grounds 3. . . . . . . . . . . . . . . . . . . . . . . . .
4. GENERAL PRACTICES 4. . . . . . . . . . . . . . . . . . 4.1 Conductors 4. . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Connections 4. . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Sharp Bends In Conductors 5. . . . . . . . . . . . . . 4.4 Cable Trays 5. . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Insulating Mats 5. . . . . . . . . . . . . . . . . . . . . . . 4.6 RS–232 Line Protection 5. . . . . . . . . . . . . . . .
5. UTILITY SERVICE ENTRANCES 6. . . . . . . . . 5.1 General 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Telephone Lines 6. . . . . . . . . . . . . . . . . . . . . . 5.3 AC Power System Protection 6. . . . . . . . . . . .
6. EXTERNAL GROUNDING SYSTEM 7. . . . . . . 6.1 Overview 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 External Building Ground Ring 7. . . . . . . . . . 6.3 Tower Grounding 8. . . . . . . . . . . . . . . . . . . . . . 6.4 Transmission Line Grounding 9. . . . . . . . . . . . 6.5 Miscellaneous External Ground
Connections 10. . . . . . . . . . . . . . . . . . . . . . . . . .
7. BUILDING INTERNAL GROUND SYSTEM 107.1 Single Point Ground System 10. . . . . . . . . . . . . 7.2 Surge Producing Equipment 11. . . . . . . . . . . . . 7.3 Surge Absorbing Equipment 11. . . . . . . . . . . . . 7.4 Internal Ground Ring (IGR) 12. . . . . . . . . . . . . 7.5 Other Non–surging Equipment 12. . . . . . . . . . . 7.6 Isolated Ground Zone (IGZ) 12. . . . . . . . . . . . .
8. INTERCONNECTIONS OF THE EXTERNALAND INTERNAL GROUND SYSTEMS 13. . . . .
8.1 General 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 IGR To EGR Connection 13. . . . . . . . . . . . . . . 8.3 MGB To EGR Connection 13. . . . . . . . . . . . . .
9. GROUND RESISTANCE MEASUREMENTS 13
10. MAINTENANCE AND INSPECTIONS 14. . . . .
APPENDIXES:A. Ground Testing Methods For Cellular Radio
Sites 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Document References 19. . . . . . . . . . . . . . . . . . C. Galvanic Corrosion 21. . . . . . . . . . . . . . . . . . . . D. Grounding Checklists 23. . . . . . . . . . . . . . . . . . E. Reference Diagrams 25. . . . . . . . . . . . . . . . . . .
, Motorola, and EMX are trademarks of Motorola, Inc.
CADWELD is a registered trademark of Erico Products, Inc.Megger is a registered trademark of Biddle Instruments.
2 68P81150E62–A 7/23/92
1. INTRODUCTION
1.1 PURPOSE
This document is intended to provide methods and practicalstandards for installing ground systems which will minimizethe hazards to personnel, protect the equipment from perma-nent damage, and where practical, prevent temporarydisruptions of the cellular system operation during lightningsurges and ground faults.
1.2 ASSUMPTIONS
It is assumed throughout this document that the soil in whicha ground system is to be established is of average resistivityand that subsurface formations do not prevent ground rodsfrom being driven to the depths specified. Should localconditions prevent the above assumptions from being met,contact Systems Engineering for the special engineering thatwill be required.
1.3 OVERVIEW
A cellular radio grounding system is made up of a number ofsub–systems, both interior and exterior. These consist ofcertain basic components arranged to achieve the goals ofthe ground system and adapted to the characteristics of eachindividual site. Although the exact configurations vary fromplace to place, the components which are included in aground system generally remain the same, and the generalguiding principles always do. While the specifics of thoseprinciples can fill volumes, and this document is notintended to be a theoretical teaching medium, the basicphilosophy of this type of ground system can be summed upquite briefly.
Local codes take precedence if they are moreconservative.
NOTE
2. GENERAL TECHNIQUES
The general techniques by which a ground system is imple-mented are described below. While these statements aresomewhat simplified, it can be fairly stated that most cellularradio grounding is based on these principles and techniques,and adapted when necessary to meet special requirements atparticular sites.
2.1 EXTERNAL GROUND SUB–SYSTEM
For sites with radio towers, the purpose of the ground systemis to provide the lowest impedance path possible (withinpractical limits) from the antennas and tower to ground,external to the building. Several sub–systems are used toachieve this goal. The tower ground consists of a buried ringof wire encircling the tower base. The external buildingground usually takes the form of a buried ring of wire aroundthe building, although it may be necessary to use otherdesigns. This external ground ring (EGR) provides theprimary connection to earth for the remainder of the site. TheEGR and the tower ring are connected together and supple-mented with ground rods. Finally, all rf transmission lineshields are grounded at several points.
2.2 INTERNAL GROUND SUB–SYSTEM
The internal system must have a low impedance path toground and also achieve a minimal potential differencebetween conductive structures within the site, while elimi-nating (or at least minimizing) any surge current flowthrough the site equipment. Safety of personnel and equip-ment is the overriding concern of this document, not signalgrounding. The construction of cellular fixed equipmentachieves good internal signal grounding through the inherentquality of the equipment design.
Internal ground connections are made to the Master GroundBar (MGB). The MGB is a large copper bar used as a lowresistance junction point for all internal grounds. All rfequipment is tied directly to this main bar. The MGB is tiedto the external ground system, the commercial ac ground,and other ground sources such as building steel. Otherground bars, tied back to the MGB, are used to tie clusters ofassociated equipment together. This isolates equipmentclusters from surges while minimizing inter–equipmentvoltage potentials within that local cluster. Equipment racksor bays must be isolated from any unplanned ground paths toavoid surge current flow. This can usually be achieved byplacing the racks or bays on insulating pads. Finally, anelevated wire ring (Internal Ground Ring, IGR) encirclingthe equipment area ties miscellaneous conductive items,such as door frames, to the ground bar. The elevated wirering is also tied to the outside ground system at severalpoints. This improves the effectiveness of the MGB.
2.3 SURGE PROTECTION
To prevent the above efforts from being circumvented bysurges entering “by the back door”, all conductors that enterthe building must be protected by devices such as gas tube orMOV protectors. These conductors include all power, tele-communications, and tower lighting lines. The protectorswill dissipate surges arriving on those conductors. There arevarious types of surge protection devices, and care must be
GROUNDING GUIDELINE
37/23/92 68P81150E62–A
taken to see that the type provided by utilities companies, thecustomer, or Motorola are of the correct type and rating forthe application.
3. DEFINITIONS
A summary of the various terms and component parts used inground systems, with their abbreviations and definitions, aregiven in the following paragraphs.
3.1 CADWELD� PROCESS
CADWELD (registered trademark of Erico Products, Inc.,Cleveland, Ohio) is a process for making exothermic welds.Instead of gas or arc welding apparatus, a unique powderedmetal mixture is used in conjunction with special graphitemolds. The powder reacts to produce molten copper, whichflows around and slightly melts the items being joined. Theresult is a permanent, high quality, strong, and low resistancejoint. Examples of various CADWELD products are given inAppendix E, Figure 13 through Figure 15.
3.2 EXTERNAL GROUND BAR (EGB)
The EGB is a large copper bar with pre–drilled holes formounting lugs. It may be equipped with a 2” copper strap,1/16 inch thick to serve as a connection to the EGR. It servesas a convenient, low resistance tie point for ground leadsfrom the transmission line ground kits at the point of entry tothe equipment room. It is located directly under the wave-guide entry window on the outside of the equipment room.Refer to Figure 2 (Appendix E).
3.3 EXTERNAL GROUND RING (EGR)
The EGR is a buried external bare wire that is usually in theform of a ring around the building. The EGR together withthe tower ring and associated ground rods form the mainground terminus for the site. The EGR may take the physicalform of a “C” or an “L” shape in cases where all sides of thebuilding are not accessible. Also see paragraph 3.11 UferGrounds on page 4of this document.
3.4 GROUND RODS
Ground rods are usually copper–clad steel and a minimum of8–feet long and 5/8–inch diameter. Longer and larger diam-eter rods are available. Also, stainless steel rods are requiredif objects of corrosion–prone metal are buried near the
copper of the ground system installation. (Refer to AppendixC to determine if stainless steel rods are required.)
3.5 INTERNAL GROUND RING (IGR)
This is a ring of bare wire (sometimes referred to as the“halo”) mounted on the equipment room walls. It serves toconnect the miscellaneous metal, non–surging equipment orobjects to a common ground at the master ground bar. TheIGR is grounded to the EGR at several points.
3.6 ISOLATED GROUND BAR (IGB)
IGB is similar to, but usually smaller than the MGB. IGBserves as a single grounding point for all equipment withinthe Isolated Ground Zone (IGZ). The IGB references the IGZequipment to the same potential, and is only connected toground through the MGB.
3.7 ISOLATED GROUND ZONE (IGZ)
The IGB is an association of non–surging, switch–relatedequipment (i.e., equipment that is not likely to be exposed tolightning surges). This equipment is directly connected to alocal common ground point called the “Isolated GroundBar”, which in turn is connected to the MGB. The ac outletsin the IGZ must be grounded to the IGB in order to preventanother connection to ground.
3.8 MASTER GROUND BAR (MGB)
This is a large copper bar with pre–drilled holes for mountinglugs. The MGB serves as a convenient, low resistance tiepoint for ground leads either directly from the equipment orindirectly through the IGR or IGB. An example of MGBusage is shown in Figure 5 (Appendix E); different types areillustrated in Figure 10 (Appendix E).
3.9 MULTI–GROUNDED NEUTRAL (MGN)
This is the ground lead that is the third wire of a single phaseac service drop, or the fourth wire of a three phase ac servicedrop. It is labeled multi–grounded because of the typical(though not always required) power industry practice ofgrounding this lead at several points along the utility trans-mission path.
3.10 TOWER GROUND RING
This is a ring of bare, buried wire surrounding the tower base,connecting the several tower ground rods together. It isconnected to the tower by one or more conductors. It mustalso be connected to the EGR.
4 68P81150E62–A 7/23/92
3.11 UFER GROUNDS
Named after the engineer who first developed this groundingtechnique, this term refers to the use of concrete as an inter-face medium between a ground conductor (in the form of awire in a concrete–filled trench, or a wire mesh embedded ina concrete slab) and the surrounding earth. Ufer grounds areusually used at sites where the local soil exhibits poorconductivity or on rocky sites covered with little or no soilcover. The concrete, being highly hygroscopic, absorbs andretains moisture from the surrounding soil, thus enhancingits conductivity. Because the concrete makes direct contactwith the imbedded conductor, and has a large surface area incontact with the soil or rock, the effectiveness of thegrounding system is greatly improved. In more normal sites,a significant benefit results from connecting the groundsystem to the site foundation if it is made of reinforcedconcrete because this type of foundation is basically a Uferground.
4. GENERAL PRACTICES
4.1 CONDUCTORS
These are the wires, straps, and rods which form ground ringsand allow connection of objects to be grounded to the groundsystem. Conductor type and size are determined by imped-ance, and ability to withstand fusing and corrosion (particu-larly underground).
Conductors which are only partially under-ground (e.g. connections from the tower ring)are to be treated as below ground conductors.
NOTE
4.1.1 Conductor Types
Above Ground: Either solid or stranded copper wire ispermitted. Internal ground ring (IGR) and all externalconductors must be bare. Equipment ground leads in cabletrays must be insulated. (Green color insulation is desirablefor ready identification.) Miscellaneous interior groundsfrom the IGR to door frames, etc., may be insulated ifdesired.
Below Ground: Rings or wires connecting to rings are to betinned, solid copper wire.
Ground rods are to consist of copper clad steel, exceptincases where nearby steel or galvanized steel could
contribute to galvanic corrosion. In this case, stainless steelrods are required.
It is imperative that tinned copper wire beutilized for tower guy ground leads to preventcorrosion of galvanized guys. Refer to para-graph 6.3 Tower Grounding on page 8of thisdocument.
NOTE
4.1.2 Conductor Sizes
Above Ground: For ground rings and the interconnection ofinternal and external ground rings, #2 AWG or larger isrequired. For grounding of equipment and miscellaneousmetallic objects, #6 AWG minimum is required.
Exceptions: Connection from the isolated ground bar (IGB)to master ground bar (MGB) shall be #2 AWG, minimum.
The EGB shall be grounded through a minimum 2–inchwide, 16–gauge copper strap, or alternately with two #2AWG wires. The wires are to be connected at opposite endsof the EGB, with a minimum of 12 inches separationbetween them
Below Ground: All wire must be #2 AWG, minimum. Ground rods are to be a minimum of 8 feet in length and 5/8inch in diameter. In the case of a deep basement adjacent tothe rod, the rod must be long enough to extend a minimum ofthree feet below the basement floor.
4.2 CONNECTIONS
4.2.1 Below Ground
All below ground connections should be of an exothermicweld construction or equivalent.
Exceptions: Bolted clamps are recommended for thefollowing:
� connections between tower and building groundsystems
� connections between EGR and any other exteriorground system, such as a utility ground.
The purpose of these mechanical connections is to facilitatethe testing and maintenance of the site ground system. Asthese connections can easily be removed and reconnected,each major component of the ground system can be testedseparately to aid in isolating high impedance components ofthe system.
GROUNDING GUIDELINE
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A mechanical, below ground connection such as this must beprotected by locating it inside a covered test well (the side ofthis well must be constructed of non–metallic material).Materials utilized for the connection must not corrode, dete-riorate, or loosen.
4.2.2 Above Ground
When two or more grounding conductors are to be joinedabove ground, either exothermic weld or split–bolt joint(copper alloy or pressure type crimp connectors) are accept-able, except that crimp connections shall not be used on solidconductors.
Exceptions: For connections which may be exposed toextreme stress such as weathering and/or surging,exothermic welds must be used at both ends. These includethe following:
� connections between lightning arrestor bracket andEGR
� connections between EGB and EGR
� connections between tower leg and ground rod
4.2.3 Connection to Equipment
Connection of conductors to equipment should be by the useof lugs or clamps appropriate to the size and type of wire andprovisions of the equipment being grounded.
4.2.4 Connection Joint Preparation
The surfaces of each conductor to be connected are to be wellcleaned, removing all paint, dirt, and corrosion in the area ofconnection before each joint is made, whether it be amechanical or welded joint. After mechanical joints arecompleted, application of an anti–oxidant compound, suchas “NO–OX” or equivalent is recommended. When usingnon–welded mechanical connections, such as bolt–on lugs,the following practices should be followed:
� To ensure good electrical contact, the mating surfacesshould be clean and flat.
� Two–holed lugs are required on all #2 AWG or largerground leads mechanically attached to the MGB, IGB,and EGB, and are preferred for other grounding leadswhere the size of the wire (#6 AWG or larger) mightexert sufficient stress on the lug to loosen a singlemounting bolt.
� Stainless steel mounting hardware (nuts, bolts, etc.) isrequired on all outside connections as well as on theMGB and IGB, and is preferred for all other groundleads. Lugs may be tinned rather than stainless.
� The lug holes and stainless bolt sizes are to be chosento match the mounting hole sizes, so that there isminimal play in the mechanical assembly prior totightening the nuts. Split ring type lock–washersshould be used to prevent the nuts from loosening.Refer to Figure 5, Detail A for proper hardwareassembly.
Exothermic connections may be made betweensome dissimilar metals (those which wouldcorrode if mechanically connected together) asthe discrete interface (which instigates thecorrosion) between the two metals no longerexists in an exothermic weld. An exception tothis is a weld between aluminum and copper. Anexothermic weld using these two metals willcorrode in a very short period of time. Seeappendix C for more information regardingcorrosion from dissimilar metals.
NOTE
4.3 SHARP BENDS IN CONDUCTORS
These are to be avoided as they add inductance and are proneto damage from lightning derived magnetic flux. A bendingradius of 8 inches or more is required.
4.4 CABLE TRAYS
All cable tray sections are to be jumpered together using #6wire. All paint around the connection area is to be removed,and a split–ring lock–washer is to be used to ensure goodsurface contact.
Exception: The cable tray in the IGZ is not to be connectedto the non–IGZ cable tray.
4.5 INSULATING MATS
It is required that all EMX and surge producing racks beprotected from any casual ground contacts. This can beimplemented through the use of insulating mats and hard-ware in the rack floor mounting, as well as insulating hard-ware between the racks and the cable tray, should bracing tothe cable tray be required.
4.6 RS–232 LINE PROTECTION
The RS–232 interfaces in the base station and the cellularswitch are easily damaged by lightning surges if proper
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system design and/or installation procedures are notfollowed. Those interfaces include data modem ports on thebase station and the switch, the base station maintenancemodem port, and the TTY interfaces on the switch. If theseRS–232 ports are connected through cables to other RS–232devices, such as modems, DSUs, TTYs, etc., and the logicreferences at the opposite ends of the cable differ by morethan 20–25 volts, the RS–232 device drivers at one or bothends of the RS–232 link may be destroyed during a lightningsurge. For this reason, the base station data modems arenormally dc powered off the same voltage buses that feed theBSC RS–232 circuitry. The cellular switch data modems arepowered from the same dc circuitry as the switch itself. Withthis arrangement, the logic ground references at both ends ofthe RS–232 links are the same. In addition, frame groundingprocedures at the cell and switch sites must be carefullyfollowed. The maintenance modems normally supplied areonly powered from the telco lines feeding them, and theRS–232 link is internally isolated to avoid destructiveground reference differences.
Special consideration must be given to the maintenanceterminal (TTY) interface. The TTY RS–232 link is suscep-tible to surge damage if the TTY is not powered by ac sourcefrom within the IGZ (i.e. an isolated orange outlet). For thisreason, if the TTY is powered from outside the IGZ, it isrequired that an isolation technique, as described in thefollowing paragraph, be used.
If the RS–232 interfaces are not installed according to theabove guidelines, specific surge protection devices must beadded to the RS–232 links to protect the device drivers fromdamage by lightning induced surges. The best approach tosurge protection is the use of back–to–back fiber opticRS–232 serial modems. The fiber optic link between themodems provides the ultimate in isolation between the twoends of the link. Another isolation approach is the use ofback–to–back transformer isolated short haul modems.There must be no metallic ground connections between thetwo modems, so that the transformer isolation (with 1500volt or higher isolation rating) will protect the RS–232 fromdamage.
Clamping type RS–232 surge protectors are not recom-mended. Although these devices may protect the RS–232device drivers from damage during a surge, they will passlarge surge currents into the equipment ground structurewhich may disrupt the operation of microprocessors, etc.Using the proper modems discussed earlier, will provide theproper RS–232 line protection.
5. UTILITY SER VICE ENTRANCES
5.1 GENERAL
Utility service entrances deserve discussion in themselvesbecause, not only do surges tend to enter the site via theservice entrances, but if properly installed, they have theirown grounding systems. It is important that these separatesystems be integrated into the cellular ground system. Notethat the cellular grounding system does not constitute asubstitute for the utility ground system, only a separate,complementary system. It is critical that all separategrounding systems at a site be electrically tied together inorder to eliminate potential differences between the systems.For this reason, it is required that any ac neutral and the tele-phone grounding systems be connected to the MGB. In addi-tion, the exterior grounding electrodes of these utilities are tobe tied into the external cellular ground system. It is recom-mended that a mechanical connection be used (as describedin section 4. General Practices paragraphs beginning onpage 4of this document). This allows for testing of the EGRsystem by temporarily opening the cross connection withoutremoving the ground on the utility, which would create asafety hazard.
5.2 TELEPHONE LINES
Each telephone line pair (this includes telephone circuits forthe cellular voice channels, data circuits, dial–up modems,alarm reporting auto–dial lines, and any other switchednetwork or leased telephone lines) entering or leaving a siteshould be equipped with a three–electrode gas tube protectorsuch as the Cook Electric 9A or equivalent.
If possible, negotiate with the local telephone utility toprovide the type of protectors described above. Normally,telephone companies will provide carbon protectors whichdo no meet the above requirements. The ground for theseprotectors should then be connected to the cellular groundsystem as previously described in paragraph 5.1.
5.3 AC POWER SYSTEM PROTECTION
5.3.1 Commercial Power
It is critical that the ac power system be properly grounded,as this is a common “back–door” method for surges to enterthe site. It is the commercial power authority’s responsibilityto ensure proper external grounding of the Multi–GroundedNeutral (MGN). This consists of a connection from the MGNto a ground rod, usually at the last power pole before thepower is brought into the customer’s power service entry.The customer is responsible for installing a separate
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grounding system at the ac power service entry to his facili-ties. This is at the first point of entry, usually at the main acpower disconnect. The requirement consists of a connectionfrom the MGN to a ground rod connection. This groundingelectrode system is to comply with applicable electricalcodes, such as the NEC (Section 250–81). Refer to Figure 11in Appendix E for further illustration.
In addition, surge protection is to be installed on the ac powersystem. Recommended are the Joslyn protectors, availablefor a variety of service entry configurations. Other equiva-lent ac surge protectors, when correctly sized for the applica-tion and potential energy levels, are also available. CellularSystem Engineering can assist in the selection of anappropriate model for particular installations.
The protector must connect to and protect each under groundservice conductor. These protectors are to be connected onthe load side of the main disconnect.
5.3.2 Generators
If an outdoor generator exists on site, it is also recommendedthat a surge protector be installed on the load side of thegenerator transfer switch. This will ensure protection to theac power distribution system when the commercial power isoff–line.
If the generator is a separately derived source of power (i.e.its neutral is separate from the neutral of the commercial acpower source), the neutral of the generator must have its owngrounding electrode system which is then tied into thecellular external ground system. A convenient way to deter-mine if the generator is separately derived source is throughinspection of the generator transfer panel. If the neutral onthe load side of the transfer panel is switched between thecommercial neutral and that of the generator, the generator isconsidered a separately derived source. If the neutral isunswitched (i.e. the commercial power neutral is at all timescontinuous with the generator neutral and the neutral to theloads), then the generator neutral must not have a separategrounding electrode system.
6. EXTERNAL GROUNDING SYSTEM
Consult with the local utility (electric, gas, tele-phone, and water) companies to determine thelocation of any underground facilities prior todigging. Failure to do so can result in expensivedamage to those systems, as well as injury ordeath to personnel.
WARNING
6.1 OVERVIEW
The external ground system consists of the building ground,the tower and transmission ground (if radio equipment existsat the site), and any miscellaneous metal objects which are inproximity to any of the above. The objective of a goodgrounding system is two–fold:
� to connect all components together with the leastimpedance between components. This will minimizethe potential difference between components shouldsurge occur, which in turn will minimize damage.
� to provide the path of least impedance from the groundsystem components to earth ground. Any surge thatdoes occur will then be dissipated quickly. In general,ground system resistances of less than 10–ohms mustbe achieved, with 5–ohms or less being the goal.
Exceptions may be permitted in unusualcircumstances if the impedance goal cannot bemet. System Engineering must review suchsites.
NOTE
The following list is a summary of the drawings found inAppendix E that are applicable to the external groundsystem:
� Figure 2, External Ground Window Detail
� Figure 4, Typical Monopole Grounding
� Figure 6, Typical Cell Site Ground Plan
� Figure 7, Tower Base and Guy Wire GroundingDetails
� Figure 8, Example of Ufer Ground Plan.
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6.2 EXTERNAL BUILDING GROUND RING
6.2.1 Stand–alone Building
The building external ground system begins with a groundrod beneath the cable entry ground window, rods at eachcorner of the building, and additional rods as necessary, toreduce the distance between the rods to 16 feet. (If, forexample, a building side is longer than 16 feet but shorterthan 32 feet, one rod must be placed near the center.) Therods should be driven, using the proper tool to prevent roddeformation and thread damage to threaded coupling rods, ifused. (The use of non–threaded rods joined by exothermicconnections are recommended.) Ground rods are not to beplaced in drilled holes, unless specifically approved bySystems Engineering. The rods are to be sunk until the rodtops are at a minimum depth of 18 inches below finishedgrade. The majority (more than 2/3) of the rod length must bebelow the local frost line. The rods should be placed in a lineapproximately two feet from, and parallel to, the buildingfoundation.
Rods will be connected in a ring (the external ground ring, orEGR) buried to the same depth as the tops of the ground rods.This wire interconnecting ring must be exothermicallywelded to each of the rods.
6.2.2 Inaccessible Building Sides
If all sides of a building are not accessible, constructing astraight or “L” shaped ground bus on each accessible side,supplemented by Ufer grounding, connections to thebuilding steel, etc., will be acceptable. Refer to Figure 8.
An example of an inaccessible building would be a cell sitein a shopping center, in which only the front and rear areas ofthe building are accessible to the customer. In this situation,ground wires and rods would be installed at the front andback in a manner similar to stand–alone building. These twosections would be interconnected by a #2 AWG wire laid in,or under, the building concrete, and supplemented by Ufergrounds if possible. The above information is for planningpurposes only; consult with Systems Engineering forspecific guidance.
6.2.3 Sites Located in Existing Buildings
Existing buildings can present a particularly difficultgrounding situation. Usually the most difficult problem is tofind a usable ground. Every effort should be made to deter-mine what grounding provisions already exist in thebuilding.
Particularly important is finding the building ground if itexists. Other alternatives are metallic water pipes (if they canbe verified as completely metal runs) which are always
accessible with some effort (the building’s maintenancedepartment will know where), and the building’s structuralsteel, whether girders, elevator shaft vertical support beamsor reinforcement rods. These can be effective when used tosupplement one another.
While none of these will provide a very low impedance pathto earth if the site is several stories up, the important goal is tokeep everything within the site at nearly the same (albeithigh) potential.
The foregoing assumes an older, reinforced concrete or brickbuilding; in the case of a smaller, one story structure in whichthe site rests upon concrete slab in contact with the earth, acombination of external ground and an Ufer ground(obtained by cutting into the slab to find the reinforcing bar)may be the solution.
Finally, common sense plus a bit of creativity, guided by theunderlying principles of the foregoing problems should atleast allow initial planning to take place. However, beforefinal grounding plans for an unusual site are completed, it isstrongly suggested that System Engineering be sought forguidance and specific recommendations.
6.3 TOWER GROUNDING
In general, the tower base is surrounded by a ring installedaccording to the guidelines for buried conductors. The towerring is to have a minimum of three ground rods (four in caseof monopole tower). If the spacing between these rods isgreater than 16 feet, additional rods are to be added to ensurea spacing of no more than 16 feet between the rods. It isrecommended that two connections be made between thetower ring and the building external ground ring.
6.3.1 Lattice (Self–supporting) Towers
Lattice towers are to be grounded with at least one groundrod adjacent to each tower leg. Rods are to be connected tothe tower leg with #2 AWG solid, tinned, copper wire, and toone another with a ring of #2 AWG solid, tinned, copperwire. The vertical wire from the tower leg to the ring shouldbe insulated from earth contact for the first 12 inches or moreby passing it through a PVC pipe. This is to reduce the stepvoltage in the immediate vicinity of the tower. (Refer toAppendix E, Figure 6, Inset A.) Exothermic weld joints areto be used for both the above and below ground connections.Again, if the distance between ground rods is more than 16feet, additional rods will be driven midway between the twotower leg rods.
It is recommended that the base ground ring of unguyedtowers be supplemented by at least two radial wires. If thediameter of the tower ground ring is less then 16 feet, thenthese radials are required if the size of the site permits (any
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exceptions should be reviewed by System Engineering).These should be approximately 20 feet, or as long as it ispractical for the site, and extend away from the building.Ground rods should be placed at the middle and at the end.Refer to Appendix E, Figure 6 for more information.
6.3.2 Monopole Masts
These antenna supports typically exhibit much greatercurrent surges when struck by lightning, as compared toguyed towers which have additional paths to ground. Theymust therefore be grounded with a minimum of four groundrods, connected together as specified in paragraph 6.3.1above, and as shown in Figure 4 (Appendix E). The additionof two short radials (20 feet each is adequate) extendedoutward from the monopole base and away from the sitebuilding is required, if the size of the site permits. Anyexceptions should be reviewed by System Engineering. Thiswill serve to reduce the share of current on the rf transmissionlines by lowering the base impedance of the tower. Theseground radials should have a ground rod at the middle and atthe end, and will otherwise follow the construction guide-lines for external buried conductors. Any large metal objectssuch as fences encountered along their path will be jumperedto the radial, to reduce shock hazards.
6.3.3 Guyed Towers
Although the tower base is to be surrounded by a ring withthree (minimum) ground rods, only one connection from thebase to one of the ground rods is required. Guy wires added toan antenna tower not only add stability to the tower installa-tion, but can also reduce the current share of the tower (andthus the surge voltage level of the MGB), since the towerguys become part of the overall ground circuit of the antennainstallation. Another benefit of guyed towers is the widerarea over which current can be dispersed, allowing morerapid dissipation and reduced step voltage. It is very impor-tant, however, that the guys be well grounded.
Each guy wire will be grounded at the anchor point. Aground rod will be installed at each guy anchor andconnected to #2 AWG solid, tinned, copper wire, using anexothermic connection. This wire will pass through an insu-lating pipe such as PVC, or similar, extending from severalinches above the ground to at least 12 inches below ground.This will greatly reduce the step voltage hazard. The connec-tion from the tinned copper wire to the guy wires must bemade with bronze, stainless steel, or galvanized steel clampsto avoid corrosion of the guys. Care must be exercised at thetime of installation to maintain the integrity of the tincoating. Under no circumstance is bare copper wirepermitted to be in contact with galvanized steel, as a seriouscorrosion potential will exist. After tightening, the clamps
should be well protected by an anti–oxidant compound suchas “No–Ox”, as bare or taped joints will soon deteriorate.Refer to appendix E, Figure 7 for more information.
6.3.4 Roof Mounted Antennas
Antennas mounted on the roof of an existing building poseparticular problems. If the roof is open to provide directconnection to the steel structure, the opportunity for a goodground is present, and the ground leads are to be attached toat that time. Other possibilities include elevator shaft steelsupport girders and pre–existing lightning protectionsystem. Any of these alternate possibilities must beinspected or tested to confirm their electrical continuity toground.
The antenna supporting structure should be grounded by aminimum of #2 AWG conductor to the building ground ifpossible. If multiple grounds or connection points are avail-able, a ground ring around the base of the tower or group ofantennas and transmission lines should be formed, much asat the ground level site. Connections, analogous to groundrods at a normal site, will be made from this ring to whatevergood grounds are to be found.
6.4 TRANSMISSION LINE GROUNDING
6.4.1 Overview
The transmission line system is probably the most likely pathfor surges to enter the site. It is critical, therefore that thissystem be thoroughly grounded. All transmission lines,cellular and non–cellular must be properly grounded.
6.4.2 Outer Conductor Grounding
Where To Ground: The transmission line outer conductorsshall be grounded at the following places:
� top of the vertical run on the tower.
� bottom of the vertical run on the tower.
� point of entrance to the radio equipment building.
� If the tower is greater than 200 feet, additionalgrounding kits must be installed. These additional kitsare positioned such that there is no more than 200 feetof transmission line between ground kits.
How To Ground: Grounding of transmission lines is to beaccomplished by use of an appropriate grounding kitsupplied by the transmission line manufacturer. These kitsare to be installed as follows:
� On top of the tower, each ground kit is to run from thetransmission line to the tower or a steel bar attached to
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the tower (thereby establishing a good electricalconnection with the tower). The tower then becomesthe main conductor of any surges to ground. The sametype connection is used at any mid–tower groundingpoints.
� At the bottom of the vertical run, the ground kits arerun either to the tower or a steel bar attached to thetower. The tower again becomes the main conductorof any surges through the transmission line. It is notrequired to run a separate lead from the steel bar toground, as the tower is a good conductor.
� At the point of entrance to the building, the ground kitsare connected to the External Ground Bar (EGB). TheEGB should be equipped with either a 2–inch copperstrap or two #2 AWG tinned, solid, copper wires, posi-tioned at opposite ends of the EGB. The strap (orwires) is to be exothermically bonded to the EGB andthe EGR. All connections from the EGB to the EGRwill pass through an insulating pipe such as PVC,extending from several inches above the ground to atleast 12 inches below ground. This will greatly reducethe step voltage hazard.
� On monopole antennas, transmission line groundingarrangements must be specified when the monopole ispurchased, to be sure top and bottom groundingconnection points are provided.
� A very significant reduction in surge potential will berealized as the departure point of the transmissionlines from the tower is lowered. Whenever sitecircumstances permit, the lines should be run to withinseven feet of the ground or less before leaving thetower, to keep the shield potential (and the relatedcurrent) as low as possible. The ideal situation is to runthe transmission line to ground level before leavingthe tower. This allows the ground kits to be attached tothe tower at its base, thereby bringing the surge poten-tial on the outer conductors closer to true groundpotential.
6.4.3 Inner Conductor Grounding
Lightning protector equipment is to be installed on all trans-mission lines entering the building. This equipment is to beinstalled within 3 feet inside the waveguide entry window.The ground plane of this equipment is to be connected to theEGR via a #2 solid tinned wire (since it is partially buried)which will pass through the wall via non–conductiveconduit.
6.4.4 Unused transmission Lines
Any unused transmission line should have its centerconductor shorted to the outer conductor, or have a lightningarrestor installed.
6.5 MISCELLANEOUS EXTERNAL GROUNDCONNECTIONS
Objects which should be connected to the external groundnetwork include, but are not limited to, the following:
� Any metal fence within seven feet of the externalground network or any other grounded object.
� The transmission line entrance hatch (if metallic).
� Metal building parts not otherwise grounded by theinternal ground ring, such as downspouts, siding,security grates over windows, metal ground mats, etc.
� Fuel storage tanks, whether above or below ground.
If fuel storage tanks are steel or galvanized (notstainless) and unprotected by an anti–corrosioncoating, care must be taken to avoid a galvanicreaction source. Hardware of the same metal, orstainless steel hardware should be used to makeany ground connections. Refer to Appendix Cfor further information on corrosion. As copperwill react with steel (or galvanized steel), allcopper grounding hardware must be kept aminimum of 5 feet from any source of thesemetals. If this is not feasible, then stainless steelgrounding hardware must be used.
NOTE
� A ground rod or rods provided by the power or tele-phone utility for grounding of ac ground or protectors.
� Any significant metal object (more than 2 sq. ft. inarea) within seven feet of the external ground systemor any other grounded object.
� Reinforcing bar in concrete floors, if accessible. (Thisis actually a type of “Ufer” ground—a very effectivesupplemental ground.) For sites on concrete slabs incontact with earth, the considerable ground systemimprovement which may be realized by including this
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ground will nearly always justify the effort required.However, because of the very high current density atthe tower base, placing ground rods in tower founda-tions is not advised, to avoid possible heating effectdamage to the concrete.
� Building skids or pier foundation anchors of pre–fab-ricated buildings.
� Exterior cable tray and ice shields, which are to begrounded at the tower end also.
� If the generator is a separately derived power source,its grounding electrode must be cross–tied to theexternal grounding system.
7. BUILDING INTERNAL GROUNDSYSTEM
7.1 SINGLE POINT GROUND SYSTEM
7.1.1 Overview
The internal ground system consists of several majorelements:
� surge producing equipment
� surge absorbing equipment
� internal ground ring (IGR), to which non–surgingequipment is connected
� at the MTSO sites, the isolated ground zone (IGZ) inthe EMX area.
The single point ground philosophy is one which dictatesthat all major elements of the system be grounded to a singlepoint. The connections to this point are made in such a waythat any surges which are produced will be taken to groundalong the path of least impedance, inflicting as little damageas possible. Implementing this philosophy entails insulatingsurge producers from any casual connections to ground (suchas through rack floor bolts connecting with re–bar andconcrete in the floor), and installing a single low impedanceconnection from each surge producer to the single pointground. The single point ground is then methodicallyconnected to various surge absorbers in order to dissipate anysurges of energy.
Other major non–surging components of the internal groundsystem, such as the IGR and the IGZ, are also connected tothe single point ground in order to minimize potential differ-ences between various types of equipment. This in turn mini-mizes personnel safety hazards, as well as noise currents
which may affect the operation of sensitive switching andcomputer equipment.
7.1.2 Location and Mounting
The single point ground consists of a heavy, rectangular,copper bar that has been drilled to accept a number ofconnecting lugs and exothermically welded straps andcables. The bar is referred to as the Master Ground Bar(MGB). The bar is to be insulated from its supporting struc-ture. Appropriate types of bars are shown in Appendix E,Figure 10. The bar should ideally be mounted in a locationcentral to all connecting equipment in order to make theshortest connections possible.
7.1.3 Connections to Single Point Ground
The MGB forms the central, key ground node of the internalgrounding system. Its connections are arranged in fourgroups: surge producers, surge absorbers, non–surgingequipment, and the Isolated Ground Zone. Appropriategrouping of the connections is illustrated in Appendix E,Figure 5. Figure 3 illustrates the internal grounding systemat a collocated site.
7.2 SURGE PRODUCING EQUIPMENT
There are several sources of surge energy, whether from alocal lightning strike or power surge, or from one moredistant, coupled into the site via telephone or ac power lines.As these surges can be significant, it is critically importantthat surge producers, including ac power and telephoneentrance panels be located as close to the MGB as possible.Connections from the surge producing equipment to thesingle point ground are to be made via #6 AWG minimumwire with green insulation for easy identification.
The following surge producers are to be directly connectedto the MGB:
� Radio racks – Connection is to be made to the top ofeach rack, to the lug specifically designated for thispurpose. Each rack is to be insulated from the buildingfloor by installing insulating mats and mounting hard-ware. Adjoining racks may have casual contact witheach other providing the adjoining rack is also directlyconnected to the MGB. Otherwise, insulating hard-ware must be used between adjoining racks.
� Waveguide entry window (if metallic)
� Receiver Multicoupler (RMC) – Each RMC is to haveits own connection to the MGB. However, additionalMGB connections to the RMC rack and RMCextenders (mounted in the same rack) are not neces-
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sary if the RMC and RMC extenders have been rackmounted with threaded hardware. The RMC rack is tobe insulated from the building floor in the samemanner described for the radio racks.
� Telephone protector grounding terminal
� Emergency generator chassis
A separate internal ground system in generatorroom may be used, but it must be connected tothe site ground system at either the external ringor the MGB to equalize potentials.
NOTE
� Channel banks
7.3 SURGE ABSORBING EQUIPMENT
Surge absorbers are those equipments or systems which canreadily absorb an energy surge and quickly dissipate it intoearth ground. The following surge absorbers are to beconnected directly to the MGB:
� External ground ring using #2 AWG solid, tinnedcopper wire (minimum); a 2–inch copper strap mayalso be used. Either lead must pass through an insu-lating channel to the EGR by the most direct route.Sharp bends are not permitted.
� Metal water utility pipes on the street side of the meter(when permitted by local codes).
Do not use gas pipe for grounding.
NOTE
� The ac multi–grounded neutral. (The ac entry panelshould be close to the MGB.)
The multi–grounded neutral and the maindisconnect panel are also to be connected to itsown separate ground system as described in 5.Utility Service Entrances paragraphs on page6 of this document. The connections to theutility ground and the MGB must both takeplace within the main disconnect panel. Themulti–grounded neutral must not be connectedto ground at any other point within the facility.
NOTE
4. Building steel (i.e., girders and/or reinforcementbar) if accessible.
7.4 INTERNAL GROUND RING (IGR)
7.4.1 General
The IGR (sometimes called the “halo”) allows short lengthsof wire from non–surge producing metal objects (doorframes, air ducts, etc.) to be connected to the internal groundsystem for safety purposes.
The IGR is to be connected to the master ground bar (MGB)as well as to the external ground at several points. This prac-tice improves the effectiveness of the MGB grounding byreducing its inductance to the EGR and therefore to trueground. Refer to Figure 6 in Appendix E. The IGR is toconsist of #2 AWG minimum, solid or stranded wire. It shallnot be concealed or painted. This is to facilitate inspectionand future add–ons of equipment.
7.4.2 IGR Location and Mounting
The IGR should encircle the radio equipment at cell sites, theEMX and related equipment at MTSO sites, and both radioand EMX equipment at collocated sites. The radio and EMXequipment is not to be directly connected to the IGR. Theseequipments are connected to the MGB or IGB as explainedin later paragraphs. The ends of the IGR are to be connectedto the MGB.
The IGR should be the lower of a level about six inches fromthe ceiling or 8 to 10 feet above the floor. It should bemounted on stand–offs or be suspended to permit easyconnections.
7.4.3 Connections to the IGR
The following connections to the IGR are to be made with #6AWG insulated stranded copper wire (green insulation ispreferred):
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� Ventilation louvers or sheet metal ductwork
� The non–IGZ cable tray system (at multiple pointsbest)
� Metal door and window frames
� Metal battery racks
� Halon fire suppression system
� Generator transfer switch enclosure
� Any other permanent, significant, metal object withinseven feet of any other grounded object
Do not connect the main ac disconnect panel tothe IGR as this is connected to the ac groundingsystem.
NOTE
7.5 OTHER NON–SURGING EQUIPMENT
In addition to the IGR, the +24 V dc power plant ground barand the –48 V dc power plant ground bar are to be connectedto the non–surge producing section of the MGB.
7.6 ISOLATED GROUND ZONE (IGZ)
7.6.1 General
The EMX location uses an isolated ground windowapproach. This means all grounds are tied together at a singlepoint, the isolated ground bar, which becomes a “window” tothe actual ground. Examples are illustrated in Figure 10 inAppendix E. Conductors to the IGB shall be green insulated,minimum #6 AWG stranded copper wire.
7.6.2 Isolated electrical Outlets
All electrical outlets in the EMX isolated ground zone are tobe of the isolated orange–coded type. The third or “green”wire grounds from these outlets are to be connected to theIGB. The purpose of this isolated ground wire system is twofold:
� It reduces noise currents in the IGZ.
� Should test equipment or TTYs be connected to theEMX during a surge, any potential difference acrossthe equipment will be minimized, as all groundswithin the IGZ are connected at the same point.
One of the most straightforward methods of implementingthe isolated electrical outlets is to utilize a separate distribu-tion panel which is powered from an appropriately sizedcircuit on the main distribution panel. Refer to Appendix E,Figure 12 for details.
7.6.3 Isolated Cable Trays
These trays are those which are carrying any switch–relatedcabling and may not carry any rf cabling. They are to beisolated from any non–IGZ trays.
7.6.4 Items to be Grounded to IGB
� MGB via #2 AWG wire
� The EMX (500, 250, and 100+) via a lug at the top ofany of the bays (It is assumed the EMX frames have allbeen electrically connected together via the groundbraid located at the bottoms of the racks.) For the EMX2500, the PDF bay ground bus will be used.
� Third wire grounds from the isolated ac outlets in theIGZ
� Cable tray within the IGZ (connected at one pointonly)
� IGZ distribution frame, if no outside metallic lines orprotector grounds are present.
� Modem frames, if not electrically connected to theEMX frames.
� Other EMX associated, non–surging equipmentframes
7.6.5 Additional RS–232 Protection
Equipment which is connected both to ac outlets and cellularequipment is particularly susceptible to potential differencesduring surge conditions. It is therefore recommended that allRS–232 connections be further protected through the use offiber–optic protectors. For more information, refer to theparagraphs of 4.6 RS–232 Line Protection on page 5.
14 68P81150E62–A 7/23/92
8. INTERCONNECTIONS OF THEEXTERNAL AND INTERNAL GROUNDSYSTEMS
8.1 GENERAL
The interconnection is accomplished by connecting theMGB and the IGR to the EGR.
8.2 IGR TO EGR CONNECTION
The IGR to EGR connections are to be made with #2 AWGsolid tinned bare wire routed through non–conductingconduit in the walls. These connections shall be made at eachcorner of the equipment room, and as needed betweencorners to keep all connections at a minimum of 16 feetapart.
8.3 MGB TO EGR CONNECTION
This connection is to be made either via a 2–inch wide by1/16–inch thick copper strap or a #2 AWG solid, tinned,copper wire. It is recommended that the connection at theMGB be mechanical so that it may be temporarily discon-nected during testing and maintenance of the ground system.The conductor is to be routed through the wall through anon–conductive conduit. All sharp bends are to be elimi-nated.
9. GROUND RESISTANCEMEASUREMENTS
The maximum ac resistance between any point on theground system and a non–trivial reference ground should be5 ohms or less. Exceptions may be permitted in unusualcircumstances, with a slightly higher resistance beingallowed in the case of very rocky sites. Such sites andcircumstances shall always require review and evaluation bySystems Engineering; safety and certain warranty relatedissues being involved. An instrument designed specificallyfor this type of measurement (such as the Biddle Instru-ments’ Megger Earth Testers) must be used and the instruc-tions provided with the instrument should be followed forproper measurement method.
The “fall of potential” method is recommended for smallsites with an overall ground system diameter of less than 100feet. A Megger Earth Tester, or equivalent, is recommendedfor this test. Note that an accurate measurement requires adistant probe placed at a distance of at least five times thediameter of the overall ground system of the site; for largesites, this may not be practical. Should this situation beencountered, an alternative method may be used. Briefly,this consists of taking a series of closer–in readings whichgive false results, but which trend toward more accurateones. By using a graph of these results, and extrapolating thetrend, one may closely estimate true ground values. Refer toAppendix A for a detailed, step–by–step procedure.
All connections should be checked if this specificationcannot be met, and after a thorough inspection, System Engi-neering should be consulted for a special evaluation of thegrounding system.
10. MAINTENANCE AND INSPECTIONS
A ground system by its very nature is exposed to weatheringcorrosion. This coupled with the importance of the groundsystem to the safety of personnel and equipment makes itmandatory that periodic inspections be made of all groundsystem components. A suggested schedule is immediatelyafter the ground installation has been installed or modified,six months afterward, and then annually. The security of allbolted or clamped connections and the condition of the wirejumpers exposed to physical damage are two key checks tobe made. No–Ox is to be reapplied to all mechanical connec-tions. The tower must also be inspected for corrosion, loos-ening bolts, etc.
A ground resistivity test is also recommended, as anyincrease in resistivity from previous readings indicates dete-rioration of the ground system. If an increase is measured,the problem may be isolated by measuring the various sub–systems of the ground system. This may be easily done ifmechanical connections (in test wells if underground) havebeen implemented between the subsystems. These connec-tions may then be used to disconnect the various sub–sys-tems from each other, in order to measure each oneindependently of others. These sub–systems include thetower ground ring (and radials), the external ground ringaround the building, the internal ground system, and anyutility ground systems.
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APPENDIX A — Ground Testing Methods For Cellular Radio Sites
1. “FALL OF POTENTIAL” METHOD
1.1 EQUIPMENT AND MATERIALS REQUIRED
� Megger Null Balance Earth Tester (Biddle Instru-ments, Blue Bell, PA).
� Extra test lead wire (2 spools; 500 ft., #12 or #14 AWGinsulated wire).
� Test stakes (included with Earth Tester).
� Long tape measure (100 ft. or more).
� Compass (to ensure a straight path along which the P2probe of the Earth Tester will be placed).
� Two small ( 1/2 in. diameter) metal hose clamps, orsimilar device, to fasten extension lead to C2 and P2probes.
1.2 PROCEDURE
Figure 1 (Appendix E) illustrates the followingprocedure, with a sample graph of the resultsexpected. For sites with very large groundsystems or obstructions, please read the para-graphs of 2. The “Asymptote Variation” OfThe Fall Of Potential Method on page16.
NOTE
Step 1. If a 4–terminal tester is utilized, jumper the C1and P1 terminals of the Earth Tester together.(These are internally jumpered on the 3–terminaltester.)
Step 2. Connect the short test lead from terminal C1 onthe Earth Tester to the approximate electricalcenter of Ground system Under Test (GUT).
The electrical center of the ground system willprobably be the vertical lead to the site externalground bar, where the rf transmission lineshields will be grounded just prior to enteringthe building. This is also near the point wherethe tower ground ring is tied to the building’sexternal ground system. Other site configura-tions will require local evaluation.
NOTE
Step 3. Connect a long test lead, extended by a length (seefollowing note) of #12 or #14 AWG insulatedwire, to the C2 terminal of the Earth Tester.
The C2 probe will be driven 1.5 to 2 feet into theground at a point that is at least 5 times the diam-eter of the site ground system (including thetower ground and grounded fences, guy wireanchors, etc.) from the site. Choose a conve-nient direction that has no obstacles to the wireor to the insertion of the P2 and C2 probes.
NOTE
Step 4. Firmly clamp the opposite end of the C2 test leadto the side and near the top of the C2 probe. Leaveenough clearance between the top of the probeand the test lead connection to avoid hammercontact and damage to the clamp.
16 68P81150E62–A 7/23/92
Step 5. With the tape measure, mark a number of pointsalong a straight line (use compass) correspondingto the following percentages of the overall C1 toC2 distance (600 ft. is used in this example):
Point % Feet to P2 Ohms
1 20 120 _________
2 30 180 _________
3 40 240 _________
4 50 300 _________
5 55 330 _________
6 62 372 _________
7 70 420 _________
8 80 480 _________
P2length of wire added
C2length of wire added
Step 6. At each indicated P2 distance (determined inStep 5), insert the P2 probe, its lead extended by afixed amount of wire as required. (NOTE: do notchange length of wire during test.) Recordamount and size of the wire used so its resistancecan be subtracted.
Step 7. Using the Earth Tester, measure and recordapparent ground system resistance at each of the 8test points.
As mentioned in the Megger Earth Testermanual, a slightly slower or faster crankingspeed of the generator will be required if themeter exhibits instability at a particular speed.This is due to stray, interfering 60 Hz powercurrents in the ground. Resistances should bemeasured only to the nearest tenth of an ohm.This precaution does not apply to battery oper-ated versions of the Earth Tester.
NOTE
Step 8. Plot the accumulated data on linear graph paper.The 62% point will show the true resistance of theground system when the resistance of the extrawire is subtracted (approximately 1/2 to 1 ohm,depending on exact wire type).
If the data point for the 62% measurement is offthe general line of the curve, it may have beencorrupted by buried pipes, etc. or inaccuratemeasurements. The curve as plotted will show agood estimate of the true ground system resis-tance in that case.
NOTE
2. THE “ASYMPTOTE VARIATION” OFTHE FALL OF POTENTIAL METHOD
2.1 INTRODUCTION
Ground tests of cellular infrastructure sites may at timesseem to indicate a poor or insufficient ground. While it iscertainly possible that the ground plan was inadequate for aparticular site, it is important to be aware of the possibility ofmeasurement errors that can result from the choice of anincorrect ground testing method, as opposed to thoseresulting from mistakes made in the actual reading of themeter itself. A fairly common error is caused by the use of the“Fall of Potential” method (described in paragraphs1 of thisappendix) when the C1 to C2 distance is too small ascompared to the overall dimensions of the site groundsystem.
2.2 BACKGROUND
If the site ground system is of large size, the required C1 toC2 distance of 5 times the overall diameter of the groundsystem can become impractical, particularly as this is actu-ally the minimum distance for reasonable accuracy (adistance of up to 10 times the diameter is preferable). In sucha case, a variation of the “Fall of Potential” method, used byNASA and other government departments, can obtain veryaccurate results at much shorter (and practical) distances.
This technique results in several incorrect ground resistancereadings, obtained from a set of three normal “Fall of Poten-tial” tests done as usual, except for the use of C2 positionswhich are too close to the site. These positions vary fromvery close to somewhat close. The resultant false groundvalues (they will be erroneously high) are then plotted onlinear graph paper, and a best–fit, falling exponential curve,connecting each series’ 62% reading, is extrapolated out toits asymptote, or nearly flat value. This very closely approxi-mates the true value of ground resistance.
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The principle involved is that these false readings will tendtowards an accurate value as the C1 to C2 distance increases,even though the proper distance is never achieved. The pointat which the curve becomes flat (or nearly so) is a closeapproximation of that true value. An actual example of theresults of both methods, performed on the same site andsuperimposed on the same graph is shown in Figure 9(Appendix E). It can be seen that the two results closelyagree. The method is explained in further detail in thefollowing step–by–step procedure.
2.3 EQUIPMENT AND MATERIALS REQUIRED
Equipment and material requirements are identical to thosedescribed in paragraph 1. “Fall Of Potential” Method (ofthis appendix).
2.4 DETAILED STEPS FOR USING THE“ASYMPTOTE VARIATION”
Step 1. Choose three C2 points at convenient (but non–trivial) distances, such as 100, 200, and 300 feetfrom the site center.
Step 2. Choose a direction that is free of obstructions(underground pipes, etc.). All measurementsmust lie along the same line.
Step 3. Select one of the C1 to C2 distances determined inStep 1 and take a series of readings with the P2probe, at eight measured intervals representing30, 40, 50, 55, 62, 65, 70, and 80 percent of each
C2 distance. The procedure used for each series ofmeasurements at a given C2 distance is the sameas described in paragraph 1. “Fall Of Potential”Method (of this appendix). Again, all of thesemeasurement points (both within a series, andeach C2 point) must be in a straight line. Recordthe data.
Step 4. Move the C2 rod to the next point, as determinedin Step 1, and repeat the test of Step 3. Record thedata. Repeat for each of the remaining points.
Should additional wire be needed for thefurthest measurement, it must be insulated #14AWG or heavier. Make a clean, solid clampedconnection to the C2/P2 test leads on the EarthTester.
NOTE
Step 5. The length and gauge of any extension wireshould be recorded. The resistance of this wire isthen calculated and subtracted from the results.
Step 6. Plot the accumulated data (three curves) in themanner explained previously. Then plot the(curve–fitted) 62% points (the “false groundvalues”) from each series in an exponential curve.The asymptote, or tangential value toward whichthis fourth curve tends, is easily seen. This repre-sents the true ground system resistance.
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APPENDIX B — Document References
The following references were used in preparing this document, and provide further information on the subject of grounding.
AC Service Grounding Engineering Application, GTE Practices section 795–805–072
Controlling Lightning Damage at Radio Sites, by Richard Little, Principle Staff Engineer, Motorola Radio TelephoneSystems Group
Electrical Protection Engineering Fundamentals, GTE Practices section 887–000–050
Electrical Protection Guide for Land–Based Radio Facilities, Josyln Electronic Systems manual by David Boethe
Electrical Protection of Radio Stations, Bell System Practices section 886–030–085
Electrical Considerations Radio Station Protection, GTE Practices section 887–030–085
Fundamental Considerations of Lightning Protection and Grounding, NASA/FAA publication # N79–76935. U.S. Govern-ment Printing Office
Getting Down to Earth, Biddle Instruments
Grounding and Bonding, Volume 2–1988 P/O “A Handbook Series on Electromagnetic Interference and Compatibility”, byInterference Control Technologies, Inc.
The “Grounds” for Lightning and EMP Protection, by Roger Block, Polyphasor Corporation
Grounding Cellular Installations, by Richard Little, Principal Staff Engineer, Motorola Radio Telephone Systems Group
Grounding Guidelines for Cellular Radio, by Randy Thompson, Motorola Radio Telephone Systems Group
Grounding Principles and Corrosion Protection, National Marine Electronics Association Technical Papers; Tinton Falls,NJ. Chapters “Planning Marine HF–SSB Systems” and “ Selection and Installation of Marine Antenna Systems”, byKarl M. Schulte, Motorola Radio–Telephone Systems Group
Lightning Protection Code, National Fire Protection Association (ANSI/NFPA 78–1989)
National Electrical Code, National Fire Protection Association (ANSI/NFPA 70–1990)
Protective Grounding Systems General Equipment Ground Requirements for Microwave Radio and Auxiliary Stations, BellSystem Practices section 802–001–197
Radio and Microwave Towers Bonding and Grounding Network Installation, GTE Practices section 621–800–200
Structural Standards for Steel Antenna Towers and Antenna Supporting Structures, Electronic Industries Association stan-dard number RS222
Telecommunications Engineering and Construction Manual, Section 825 (Situations Requiring Special Protection), andSection 810 (Electrical Protection of Electronic Analog and Digital Central Office Equipment), Rural ElectrificationAdministration.
Western Electric Installation Engineering Handbook 261
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APPENDIX C — Galvanic Corrosion
The bonding of two metals may result in Galvanic corrosion. This reaction occurs at the junction of dissimilar metals whenexposed to moisture. The degree and rate of corrosion depends on the relative position of the metals in the electromechanicalseries. Following is a chart depicting this series. The metals at the top of the chart will corrode more easily than those at thebottom. To determine the likelihood of two metals reacting, determine the difference between their listed EMFs. If it is greaterthan 0.6 volts, the metals are too dissimilar to be bonded. If the difference is 0.6 volts or less, the metals may be safely bonded.
METAL EMF (Volts)
Magnesium +2.37Magnesium Alloys +0.95Beryllium +1.85Aluminum +1.66Zinc +0.76Chromium +0.74Iron or Steel +0.44Cast Iron *Cadmium +0.40Nickel +0.25Tin +0.14Stainless Steel *Lead +0.13Brass *Copper –0.34Bronze *Copper–Nickel Alloys –0.35Monel *Silver Solder –0.45Silver –0.80Graphite –0.50Platinum –1.20Gold –1.50
* Reliable values N/A
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APPENDIX D – Grounding Checklists
The following is contains checklists to be used to facilitate the inspection of site grounding. For additional details, refer to themain body of this document. For unique grounding situations, contact Systems Engineering for consultation.
KEY: EGB External Ground Bar IGR Isolated Ground RingEGR External Ground Ring IGZ Isolated Ground ZoneIGB Isolated Ground Bar MGB Master Ground Bar
GENERAL: All bends in ground wires are to have a minimal 8–inch bending radius.AC surge protector to be installed on the load side of the main ac disconnect.AC to tower lighting to be surge protected.IGZ cable tray to be isolated from all other cable trays.IGZ cable tray to be isolated from all casual contacts with ground.No ground wires in metal conduit unless conduit is bonded to ground at both ends.
Table 1. External Site Grounding ChecklistITEM � DESCRIPTION CONDUCTOR CONNECTION
All Sites (MTSO And Cell) Require:
Connections to the EGR (External Ground Ring):
1 EGB Note 2 CADWELD
2 IGR (each corner and every 16 feet between) #2 solid CADWELD
3 ground rods (every 16 feet) and under EGB #2 solid CADWELD
4 MGB #2 solid CADWELD
All Cell Sites Require:
Connections to the EGR (External Ground Ring):
1 tower ground ring (2 connections recommended) #2 solid mechanical
2 lightning arrestor bracket #2 solid CADWELD
Connections to the tower:
1 from tower ground ring #2 solid CADWELD
2 top of rf lines ground kit mechanical
3 rf lines at exit from tower ground kit mechanical
4 guy wire to ground rods (guyed towers only) #2 stranded mechanical
Connections to the tower ring:
1 from tower leg(s) #2 solid CADWELD
2 from EGR (2 connections recommended) #2 solid CADWELD
Miscellaneous external grounding connections(connect to nearest point of external system):
1 metal fencing within 7 feet #2 solid Note 1
2 metal building parts #2 solid Note 1
3 fuel storage tanks #2 solid Note 1
4 utility grounding electrode systems #2 solid Note 1
5 metal objects more than 2 ft. sq. and within 7 ft. #2 solid Note 1
6 reinforcing bar in concrete floor (if accessible) #2 solid Note 1
7 building skids or anchors (if accessible) #2 solid Note 1
8 exterior cable tray, ice bridge #2 solid Note 1
9 generator grounding system (if applicable) #2 solid Note 1
10 generator chassis (if not otherwise grounded) #2 solid Note 1
Connections to the EGB (External Ground Bar):
1 waveguide entry window #2 stranded mechanical
2 rf line ground kits at building entry #2 stranded mechanical
3 EGR #2 solid CADWELD
NOTES: 1. All below ground connections must be exothermic. Above ground connections may be mechanical.2. Either two #2 AWG solid wires or one 2–inch x 1/16–inch copper strap must be used.
24 68P81150E62–A 7/23/92
Table 2. Internal Site Grounding Checklist
ITEM � DESCRIPTION CONDUCTOR CONNECTION
Connections to the MGB (Master Ground Bar):
1 racks containing rf equipment #6 stranded mechanical
2 waveguide entry window #6 stranded mechanical
3 RMC (receiver multicoupler) #6 stranded mechanical
4 telephone protector grounding terminal #6 stranded mechanical
5 generator chassis (if not otherwise grounded) #6 stranded mechanical
6 channel bank racks #6 stranded mechanical
7 EGR #2 solid mechanical
8 metal water utility pipe #6 stranded mechanical
9 multi–grounded neutral #6 stranded mechanical
10 building steel (if accessible) #6 stranded mechanical
11 IGR #2 stranded mechanical
12 IGB #2 stranded mechanical
13 ground bar of +24 Vdc power system #6 stranded mechanical
14 ground bar of –48 Vdc power system #6 stranded mechanical
Connections to the IGR (Internal Ground Ring):
1 all racks not grounded to MGB or IGB #6 stranded mechanical
2 ventilation louvers and ducts #6 stranded mechanical
3 cell site cable tray (multiple points) #6 stranded mechanical
4 metal door and window frames #6 stranded mechanical
5 metal battery racks #6 stranded mechanical
6 Halon system #6 stranded mechanical
7 transfer switch enclosure #6 stranded mechanical
8 miscellaneous significant metal objects #6 stranded mechanical
9 EGR (every 16 ft.) #2 solid mechanical
10 MGB #2 stranded mechanical
Connections to the IGB (Internal Ground Bar):
1 MGB #2 stranded mechanical
2 cellular switch frame #6 stranded mechanical
3 grounds from ac outlets in the IGZ #6 stranded mechanical
4 IGZ cable tray (one point only) #6 stranded mechanical
5 IGZ distribution frame #6 stranded mechanical
6 modem frame #6 stranded mechanical
7 other EMX associated frames #6 stranded mechanical
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APPENDIX E — Reference Diagrams
The following is a table of contents for Appendix E.
DIAGRAM PAGE
Figure 1. Ground System Testing — “Fall of Potential” Method 26
Figure 2. External Ground Window Detail 27
Figure 3. Example of Typical Collocated Cell/MTSO Site Ground Plan 28
Figure 4. Typical Monopole Grounding 29
Figure 5. Typical Master Ground Bar Connections (for Smaller Sites) 30
Figure 6. Typical Cell Site Ground Plan 31
Figure 7. Tower Base and Guy Wire Grounding Details 32
Figure 8. Example of Ufer Grounding Plan 33
Figure 9. Ground System Testing; Fall of Potential — Asymptote Method 34
Figure 10. Representative Ground Bars 35
Figure 11. AC Power Utility Grounding 36
Figure 12. AC Outlet Grounding in the Isolated Ground Zone 37
Figure 13. Making CADWELD Connections 38
Figure 14. CADWELD Connection Styles: Cable–to–Cable/Cable–to–Rod 39
Figure 15. CADWELD Connection Styles: Cable–to–Surface 40
26 68P81150E62–A 7/23/92
Figure 1. Ground System Testing — “Fall of Potential” Method
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Figure 2. External Ground Window Detail
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28 68P81150E62–A 7/23/92
Figure 3. Example of Typical Collocated Cell/MTSO Site Ground Plan
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DIN
G S
TE
EL
TE
LCO
MD
F(N
OT
E 5
)T
O M
GB
MA
IN A
C P
OW
ER
PA
NE
L(N
OT
E 5
)
TO
IGB
IDF
TO
MG
B
TO
IGR
IGR
TO
TO
IGR
–
(SE
E N
OT
E 1
)
... . . ... . . . . . .... . . ... . . . . . . ............
. ...
. ....
.. . .
..
. . ..
.
. ... . . . . . . ......... ..... . ....... . .... . .
. ... . . . . . . ......... ..... . ....... . .... . .
..
..
....
. ..... .
... .
..
. ... . . ... . . . . . . ..... . ..
... . . ... . . . . . .... . . ... . . . . . . ........ . ..
.... .
.. ..
. ...
. . ..
..
. . .... . ....... . ..... ......... . . . . . . . . . ..
.... .
... ...
.. ....
..
.
. . .... . ....... . ..... ......... . . . . . . . . . ..
... ...
.. ..
....
.... .
.
......
......... .............
......
...
...
.............. .............
......
...
...
BS
BS
BS
BS
RE
CT
MO
DE
MB
AY
MO
DE
MB
AY
CC
BS
WB
NU
MTA
PE
CE
BA
SB
PB
MG
BT
O
–48V BATTERY
NO
TE
S:
1. A
N ID
F O
R C
HA
NN
EL
BA
NK
MA
Y B
E P
AR
T O
F IG
Z O
NLY
IF IT
C
ON
TAIN
S N
O C
ON
NE
CT
ION
S T
O O
UT
SID
E M
ETA
LLIC
2. O
RA
NG
E–C
OD
ED
, IS
OLA
TE
D A
.C. P
OW
ER
OU
TLE
TS
FO
R IG
Z:
T
HE
SE
WIL
L H
AV
E T
HE
IR ”
GR
EE
N W
IRE
” G
RO
UN
D C
ON
NE
CT
ED
T
O IG
B O
NLY
.
3. A
LL IG
Z E
QU
IPM
EN
T. T
TY
’S S
CO
PE
S, E
TC
. MU
ST
US
E T
HE
IGZ
O
RA
NG
E IS
OLA
TE
D A
C O
UT
LET
S.
4. L
OC
AL
AC
DIS
CO
NN
EC
T B
RE
AK
ER
PA
NE
L F
OR
IGZ
: TH
IRD
WIR
E
GR
OU
ND
FR
OM
ISO
LAT
ED
OU
TLE
TS
TE
RM
INA
TE
S O
N IS
OLA
TE
D
GR
OU
ND
BU
S W
HIC
H T
HE
N C
ON
NE
CT
S T
O IG
B. T
HE
TH
IRD
GR
OU
ND
FR
OM
TH
E M
AIN
BR
EA
KE
R P
AN
EL
TE
RM
INA
TE
S
TO
TH
E L
OC
AL
BR
EA
KE
R P
AN
EL
EN
CLO
SU
RE
.
5. IT
IS S
TR
ON
GLY
RE
CO
MM
EN
DE
D T
HA
T T
HE
AC
MA
IN E
NT
RY
T
HE
RF
EN
TR
Y W
IND
OW
, AN
D T
HE
TE
LCO
MD
F/E
NT
RY
C
LOS
E T
O T
HE
MG
B.
CO
ND
UC
TO
RS
.
WIR
EO
NLY
PA
NE
L,B
E L
OC
AT
ED
DA
L.00
1.29
09.IL
O
GROUNDING GUIDELINE
297/23/92 68P81150E62–A
Figure 4. Typical Monopole Grounding
MO
NO
PO
LE
NO
TE
1
NO
TE
2
3. G
RO
UN
DIN
G C
ON
DU
CT
OR
S F
RO
M W
ITH
IN T
HE
S
ITE
BU
ILD
ING
AR
E T
O B
E P
AS
SE
D T
HR
OU
GH
LO
CA
LLY
PU
RC
HA
SE
D P
VC
OF
AP
PR
OP
RIA
TE
SIZ
E
A
ND
SE
ALE
D.
4. W
ITH
IN R
F C
AB
LE L
OS
S P
AR
AM
ET
ER
S, A
ND
WH
EN
C
HO
ICE
EX
IST
S, M
ON
OP
OLE
SH
OU
LD B
E F
UR
TH
ER
T
HA
N 1
0’0”
FR
OM
BU
ILD
ING
.
NO
TE
3S
TR
AP
2. A
LL E
XT
ER
IOR
GR
OU
ND
WIR
E IS
#2
AW
G B
AR
E,
TIN
NE
D S
OLI
D C
OP
PE
R A
ND
IS T
O B
E B
UR
IED
18’
0” T
O 2
4’0”
BE
LOW
SU
RFA
CE
, E
XC
EP
T
JUM
PE
RS
TO
FE
NC
E, W
HIC
H M
AY
BE
#6
AW
G.
NO
TE
3 NO
TE
2
INT
ER
NA
L
GR
OU
ND
RIN
G
(#2
AW
G B
AR
E)
(CE
LL S
ITE
AR
EA
)
MG
B
INT
ER
NA
L
GR
OU
ND
RIN
G
(#2
AW
G B
AR
E)
RF
CA
BLE
S
NO
TE
S:
EG
B
EX
TE
RN
AL
GR
OU
ND
SY
ST
EM
: MO
NO
PO
LE G
RO
UN
DIN
G
1. IN
NO
RM
AL
SO
IL, G
RO
UN
D R
OD
S A
RE
8’ (
5/8”
)
CO
PP
ER
CLA
D A
S I
ND
ICA
TE
D.
DA
L.00
1.29
10.IL
O
30 68P81150E62–A 7/23/92
Figure 5. Typical Master Ground Bar Connections (for Smaller Sites)
”P”
SE
CT
ION
SU
RG
E P
RO
DU
CE
RS
”A”
SE
CT
ION
”N”
SE
CT
ION
”I”
SE
CT
ION
SU
RG
E A
BS
OR
BE
RS
IGZ
EQ
UIP
ME
NT
MG
B
SP
EC
IFIC
LE
AD
S T
O B
E L
OC
AT
ED
IN E
AC
H S
EC
TIO
N O
F M
GB
1. L
EA
DS
TO
EA
CH
RF
R
AC
K, I
NC
LUD
ING
C
ELL
ULA
R B
AS
E
S
TAT
ION
S, M
ULT
I–
2. T
O M
DF
PR
OT
EC
TO
R
GR
OU
ND
(IF
AP
P–
L
ICA
BLE
).
1. T
O E
GR
3. T
O B
UIL
DIN
G S
TE
EL
(I
F A
PP
LIC
AB
LE).
4. T
O W
AT
ER
PIP
E
(IF
AP
PLI
CA
BLE
).
1. L
EA
DS
TO
IGR
.
2. T
O +
24V
PO
WE
R
PLA
NT
GR
OU
ND
BA
R.
3. T
O –
48V
PO
WE
R
PLA
NT
GR
OU
ND
BA
R.
1. T
O IG
B–1
.
2. T
O IG
B–2
(IF
A
PP
LIC
AB
LE).
NO
TE
S:
1. U
SE
2–H
OLE
LU
GS
ON
ALL
LE
AD
S T
O M
GB
.2.
US
E O
NLY
STA
INLE
SS
ST
EE
L H
AR
DW
AR
E W
ITH
SU
ITA
BLE
LO
CK
WA
SH
ER
S.
SE
E D
ETA
IL ”
A”.
3. M
GB
SE
CT
ION
S S
IZE
D A
CC
OR
DIN
G T
O T
HE
TO
TAL
NU
MB
ER
OF
LE
AD
S
RE
QU
IRE
D T
HE
RE
(i.e
., “P
” S
EC
TIO
N IS
US
UA
LLY
TH
E L
AR
GE
ST
SE
CT
ION
).4.
DO
NO
T M
OU
NT
TW
O O
R M
OR
E L
UG
S W
ITH
TH
E S
AM
E T
WO
BO
LTS
.
SE
E N
OT
E 3
2 H
OLE
LU
G
MG
B
LOC
KW
AS
HE
R
LOC
KW
AS
HE
R
DE
TAIL
”A
”
EG
R
EX
TE
RN
AL
GR
OU
ND
RIN
GIG
B I
NT
ER
NA
L G
RO
UN
D B
AR
IGZ
IS
OLA
TE
D G
RO
UN
D Z
ON
EM
DF
MA
IN D
IST
RIB
UT
ION
FR
AM
EM
GB
MA
ST
ER
GR
OU
ND
BA
RM
GN
MU
LTI–
GR
OU
ND
ED
NE
UT
RA
L
LEG
EN
D
5. R
EF
ER
TO
FIG
UR
E 1
0 (D
AL.
001.
2916
.ILO
) F
OR
EX
AM
PLE
S O
F V
AR
IOU
S M
GB
’S.
3. W
AV
EG
UID
E E
NT
RY
W
IND
OW
.4.
EM
ER
GE
NC
Y G
EN
ER
AT
OR
C
HA
SS
IS.
5. C
HA
NN
EL
BA
NK
S.
NO
N –
SU
RG
ING
EQ
UIP
ME
NT
2. T
O M
GN
(A
T A
C E
NT
RY
PA
NE
L)
CO
UP
LER
S,
MIC
RO
WA
VE
RA
CK
S.
DA
L.00
1.29
11.IL
O
GROUNDING GUIDELINE
317/23/92 68P81150E62–A
Figure 6. Typical Cell Site Ground Plan
ALL
GR
OU
ND
RIN
GS
MA
DE
OF
#2
AW
G B
AR
E, T
INN
ED
, SO
LID
CO
PP
ER
WIR
E.
TO
WE
R A
ND
BU
ILD
ING
GR
OU
ND
RIN
GS
AR
E T
O B
E B
UR
IED
MIN
IMU
M 1
8”.
2.1.NO
TE
S:
IGR
, #2
AW
G B
AR
E C
OP
PE
R W
IRE
CO
NN
EC
TIO
N T
OB
UIL
DIN
G/F
OU
ND
ATIO
N R
EB
AR
NO
TE
3
EX
TE
RN
AL
GR
OU
ND
RIN
G (
EG
R)(
NO
TE
1,2
)
MG
B
MIN
. 8”
RA
DIU
SA
LL C
OR
NE
RS
EG
R (
SE
E N
OT
E 1
,2)
GE
NE
RA
TO
R
CO
NN
EC
T T
O R
EB
AR
TO
WE
R
RF
CA
BLE
EN
TR
Y G
RO
UN
DB
AR
TO
WE
R G
RO
UN
D R
ING
NO
TE
1,2
OP
TIO
NA
L, B
UR
IED
15’ R
AD
IALS
FLA
SH
OV
ER
PR
EV
EN
TIO
NS
AF
ET
Y J
UM
PE
R
BU
RIE
D #
2 A
WG
MIN
.24
”
SE
CU
RIT
Y F
EN
CE
3.M
INIM
UM
8’ G
RO
UN
D R
OD
S, S
PAC
ED
MIN
IMU
M 1
5’ A
ND
AT
EA
CH
CO
RN
ER
PLU
S B
EN
EA
TH
RF
CA
BLE
EN
TR
Y A
RE
A.
ALL
GR
OU
ND
RO
DS
AR
E C
OP
PE
R C
LAD
ST
EE
L;T
OP
OF
RO
D T
O B
E D
RIV
EN
TO
MIN
IMU
M 1
8” B
EN
EA
TH
SU
RFA
CE
.4.
NO
TE
5
NO
TE
5
5.A
LL L
EA
DS
GO
ING
FR
OM
TO
WE
R L
EG
S T
O G
RO
UN
D R
OD
S T
O B
E IN
SU
LAT
ED
TO
TO
P G
RO
UN
D R
OD
BY
PLA
ST
IC P
IPE
, SE
E IN
SE
T “
A” A
ND
FIG
UR
E 7
(D
AL.
001.
2913
.ILO
).
TO
WE
R L
EG
PV
C O
RE
QU
IVA
LEN
T
GR
OU
ND
RO
D
MIN
. D
EP
TH
=18
”
INS
ET
”A
”
LEG
EN
D
EG
RE
XT
ER
NA
L G
RO
UN
D R
ING
IGR
INT
ER
NA
L G
RO
UN
D R
ING
MG
BM
AS
TE
R G
RO
UN
D B
AR
INS
ULA
TIN
G (
PV
C, E
TC
.) F
EE
D T
HR
U
DA
L.00
1.29
12.IL
O
32 68P81150E62–A 7/23/92
Figure 7. Tower Base and Guy Wire Grounding Detail
TIN
NE
D, S
OLI
DM
IN. #
2 A
WG
CO
PP
ER
WIR
E;
PO
RT
ION
NE
AR
GU
YS
SH
OU
LD B
E G
RE
AS
ED
OR
PA
INT
ED
TO
PR
EV
EN
T C
OR
RO
SIO
NO
F G
UY
WIR
E
GA
LVA
NIZ
ED
CLA
MP
GU
YS
#6 G
ALV
. JU
MP
ER
S8’
GR
OU
ND
RO
D
PV
C P
IPE
12’’
DE
EP
GU
Y A
NC
HO
R G
RO
UN
DIN
G
NO
TE
3N
OT
E 1
,2
CA
DW
ELD
(TM
)
NO
TE
1
PV
C M
IN.
12”
DE
EP
MIN
.18
”
NO
TE
S:
1.#2
AW
G B
AR
E, T
INN
ED
, SO
LID
CO
PP
ER
WIR
E.
2.G
RO
UN
D R
ING
TO
BE
BU
RIE
D18
”–24
”, A
ND
24”
FR
OM
CO
NC
RE
TE
.BA
SE
3.M
IN.
8’ C
OP
PE
R–C
LAD
5/8
” S
TE
EL
GR
OU
ND
RO
D.
CO
NC
RE
TE
PV
C,
MIN
12’
’ DE
EP
GR
OU
ND
RIN
G; N
OT
E 1
,2
NO
TE
3
TO
WE
R L
EG
CA
DW
ELD
(TM
)
CA
DW
ELD
(TM
)
SE
E A
LSO
NO
TE
3
4.”C
AD
WE
LD”
IS A
TR
AD
EM
AR
K O
F E
RIC
O IN
C.
SE
LF–S
UP
PO
RT
TO
WE
R G
RO
UN
DIN
G
GU
YE
D T
OW
ER
GR
OU
ND
ING
DA
L.00
1.29
13.IL
O
GROUNDING GUIDELINE
337/23/92 68P81150E62–A
Figure 8. Example of Ufer Grounding Plan
ME
SH
FO
UN
DAT
ION
WIR
E
NO
TE
4
NO
TE
3
TO
WE
R
MIN
. 8”
RA
DIU
SA
LL C
OR
NE
RS
BU
ILD
ING
GR
OU
ND
GR
OU
ND
EX
TE
RN
AL
WIN
DO
W B
AR
BA
R
INT
ER
NA
L M
AIN
WIR
E, #
2 A
WG
.G
RO
UN
DC
OP
PE
R
AP
PR
OX
2’
(AP
PR
X 8
’ HIG
H)
TR
EN
CH
(D
AS
HE
S)
/MA
ST
ER
T
HIS
GR
OU
ND
ING
SY
ST
EM
.
(RO
CK
/DIR
T)
”UF
ER
’ GR
OU
ND
RA
DIA
LS
20
’A
PP
RO
X.
NO
TE
4
INT
ER
NA
L G
RO
UN
D R
ING
(H
ALO
)
B
EIN
G T
HE
MO
ST
IMP
OR
TAN
T S
ITE
S.
C
LIM
AT
ES
TO
ALL
EV
IAT
E E
FF
EC
TS
OF
GR
OU
ND
FR
OS
T.
S
HO
ULD
BE
SU
NK
AS
WE
LL,
PA
RT
ICU
LAR
LY IN
NO
RT
HE
RN
R
EC
OM
ME
ND
ED
PO
INT
S A
RE
IN
DIC
AT
ED
BY
5. IF
CO
ND
ITIO
NS
PE
RM
IT,
SU
PP
LEM
EN
TAL
GR
OU
ND
RO
DS
T
OW
ER
BA
SE
AN
D T
HE
PO
INT
BE
NE
AT
H T
HE
GR
OU
ND
BA
RS
6. “
UF
ER
” IS
TH
E N
AM
E O
F T
HE
EN
GIN
EE
R W
HO
DE
VE
LOP
ED
WIR
E
6”18”
2. U
FE
R R
AD
IAL
WIR
ES
TO
BE
SU
PP
OR
TE
D 4
”–6”
AB
OV
E
B
OT
TO
M O
F T
RE
NC
H T
O A
SS
UR
E A
DE
QU
AT
E T
HIC
KN
ES
S O
F
C
ON
CR
ET
E O
N A
LL S
IDE
S.
3. A
LL E
GR
/IGR
JU
MP
ER
S T
O B
E P
AS
SE
D T
HR
OU
GH
NO
N–
C
ON
DU
CT
IVE
PIP
E S
UC
H A
S P
VC
.
4. T
HE
SE
TW
O U
FE
R R
AD
IALS
AR
E O
PT
ION
AL;
US
E O
NLY
IF
G
RO
UN
D S
YS
TE
M R
ES
ISTA
NC
E IS
OV
ER
10
OH
MS
W/O
TH
EM
.
CO
NC
RE
TE
SU
RFA
CE
STA
KE
S
NO
TE
S:
A
PP
RO
XIM
AT
ED
BE
CA
US
E O
F T
HE
UN
KO
WN
1. L
EN
GT
H A
ND
NU
MB
ER
OF
UF
ER
GR
OU
ND
RA
DIA
LS A
RE
S
OIL
.
C
ON
DU
CT
ION
/RE
SIS
TAN
CE
OF
TH
E S
UR
RO
UN
DIN
G R
OC
K/
NO
TE
2
4–6”
, WIT
H T
HE
“UF
ER
” G
RO
UN
D
DA
L.00
1.29
14.IL
O
TR
EN
CH
34 68P81150E62–A 7/23/92
Figure 9. Ground System Testing; Fall of Potential — Asymptote Method
50 40 30 20 10
0
050
100
150
200
250
300
350
400
450
500
(P2
DIS
TAN
CE
IN F
EE
T)
O H M S
GR
OU
ND
SY
ST
EM
TE
ST
ING
FALL
OF
PO
TE
NT
IAL–
AS
YM
PT
OT
E V
AR
IAT
ION
(SA
MP
LE G
RA
PH
OF
ME
TH
OD
, W/ C
ON
TR
OL
CU
RV
E)
XX
XX
XX
XX
X
DE
SIR
ED
GR
OU
ND
RE
SIS
TAN
CE
NO
TE
:W
ITH
C2
PR
OB
E T
OO
CLO
SE
TO
SIT
E, T
HE
SE
62%
PO
INT
S S
HO
WIN
CO
RR
EC
T G
RO
UN
D R
ES
ISTA
NC
E A
S T
HE
Y A
RE
IN
FLU
EN
CE
D B
YT
HE
GR
OU
ND
TE
RM
INA
LS’ L
OC
AL
EF
FE
CT
S. H
OW
EV
ER
TH
E T
RE
ND
T
OW
AR
DS
”T
RU
TH
” C
AN
BE
EX
TR
AP
OLA
TE
D W
ITH
AN
AS
YM
PT
OT
IC C
UR
VE
.
TH
IS R
ES
ULT
OB
TAIN
ED
BY
US
ING
TH
E S
TAN
DA
RD
”FA
LL O
F P
OT
EN
TIA
L” M
ET
HO
D. T
HIS
SE
RIE
S S
HO
WS
TR
UE
SY
ST
EM
GR
OU
ND
AS
2.5
OH
MS
+/–
10%
. IT
WA
S D
ON
E A
S
A C
ON
TR
OL
AN
D T
O D
EM
ON
ST
RA
TE
TH
E A
CC
UR
AC
Y O
F T
HE
”AS
YM
PT
OT
E V
AR
IAT
ION
” O
F T
HE
”FA
LL O
F P
OT
EN
TIA
L”M
ET
HO
D. O
N A
LA
RG
ER
SIT
E, T
HE
RE
QU
IRE
D D
ISTA
NC
E
SH
OR
TE
R D
ISTA
NC
E M
EA
SU
RE
ME
NT
S T
O S
HO
W T
HE
TR
EN
D.
DIS
TAN
CE
, SIT
E C
EN
TE
R T
O C
2 P
RO
BE
IND
ICA
TE
D A
S S
HO
WN
BE
LOW
:
X
80’
5 O
HM
S
160’
240’
320’
WO
ULD
BE
IM
PR
AC
TIC
ALL
Y L
AR
GE
, TH
US
TH
E U
SE
OF
3
~ =A
SY
MP
TO
TE
DA
L.00
1.29
15.IL
O
3 O
HM
S
GROUNDING GUIDELINE
357/23/92 68P81150E62–A
Figure 10. Representative Ground Bars
1/4”
TY
PE
C1” 20
”
1–1/
8”T
YP
TY
PE
B
2–1/
2”
1/4”
x 4
” x
20”
CO
PP
ER
4”
1–5/
8”7/
16” 2”
4”3/
4”
2–1/
2”
1–3/
4”
TY
PE
A
6”1.
LU
GS
AR
E N
OT
INC
LUD
ED
.2.
SE
E A
LSO
FIG
UR
E 2
(D
AL.
001.
2908
.ILO
)
3/8”
1–1/
8”
TY
P
1/4”
x 8
” x
24”
CO
PP
ER
NO
TE
S:
(“E
XT
ER
NA
L G
RO
UN
D W
IND
OW
DE
TAIL
“).
DA
L.00
1.29
16.IL
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36 68P81150E62–A 7/23/92
Figure 11. AC Power Utility Grounding
GR
OU
ND
NE
UT
RA
L
1. IN
STA
LLE
D B
Y L
OC
AL
PO
WE
R A
UT
HO
RIT
Y.2.
INS
TALL
ED
BY
FA
CIL
ITY
OW
NE
R.
3. T
HE
NE
UT
RA
L IS
TO
BE
GR
OU
ND
ED
AT
TH
E S
ER
VIC
E
EN
TR
AN
CE
ON
LY. A
T A
LL O
TH
ER
PO
INT
S IN
TH
E
DIS
TR
IBU
TIO
N S
YS
TE
M, I
T IS
TO
RE
MA
IN IN
SU
LAT
ED
F
RO
M A
LL O
TH
ER
GR
OU
ND
S.
AC
SU
RG
EP
RO
TE
CT
OR
CO
NN
EC
TIO
NT
O E
GR
TO
MG
B
NO
TE
2
NO
TE
1
MA
IN A
CD
ISC
ON
NE
CT
PA
NE
L
L1 L2
GE
NE
RA
TO
RT
RA
NS
FE
R S
WIT
CH
L2L1
FR
OM
EM
ER
GE
NC
Y G
EN
ER
AT
OR
TO
AC
DIS
TR
IBU
TIO
NP
AN
EL
MG
NL1
L2
NO
TE
3
UN
SW
ITC
HE
DN
EU
TR
AL
NO
TE
4
4. IF
NE
UT
RA
L IS
SW
ITC
HE
D IN
TH
E G
EN
ER
AT
OR
TR
AN
SF
ER
PA
NE
L, T
HE
GE
NE
RA
TO
R M
US
T H
AVE
ITS
OW
N G
RO
UN
DIN
GE
LEC
TR
OD
E S
YS
TE
M.
DA
L.00
1.29
17.IL
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GROUNDING GUIDELINE
377/23/92 68P81150E62–A
Figure 12. AC Outlet Grounding in the Isolated Ground Zone
GR
OU
ND
NE
UT
RA
LN E U T R A L
GR
OU
ND
MG
BIG
B
NE
UT
RA
L
MA
IN A
CD
IST
RIB
UT
ION
PA
NE
L
ISO
LAT
ED
GR
OU
ND
ZO
NE
DIS
TR
IBU
TIO
N P
AN
EL
NO
TE
1
NO
TE
2
NO
TE
S:
1. T
HIS
GR
OU
ND
BA
R IS
TO
BE
ISO
LAT
ED
FR
OM
TH
E
PA
NE
L E
NC
LOS
UR
E. I
TS
ON
LY C
ON
NE
CT
ION
TO
GR
OU
ND
IS
TH
RO
UG
H T
HE
IGB
AS
ILL
US
TR
AT
ED
.2.
ALL
OU
TLE
TS
IN T
HE
ISO
LAT
ED
GR
OU
ND
ZO
NE
AR
E
TO
BE
OF
TH
E O
RA
NG
E C
OLO
R–C
OD
ED
TY
PE
, WIT
H
GR
OU
ND
S IS
OLA
TE
D F
RO
M T
HE
OU
TLE
T E
NC
LOS
UR
E.
GR
OU
ND
NE
UT
RA
L
CO
NN
EC
TIO
NT
O E
GR
MA
IN A
CD
ISC
ON
NE
CT
PA
NE
L
L1 L2
GR
OU
ND
DA
L.00
1.29
18.IL
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38 68P81150E62–A 7/23/92
Figure 13. Making CADWELD Connections
PR
OD
UC
TS
, IN
C.
TR
AD
E M
AR
K O
F E
RIC
OC
AD
WE
LD
IS A
RE
GIS
TE
RE
DN
OT
E:
mol
dgr
aphi
te
CA
DW
ELD
wel
dm
etal
mat
eria
lst
arte
r
disk
hold
ing
stee
l
cabl
e
rod
grou
nd
slag
bre
aks
off
slag
CA
DW
ELD
joi
ntco
olin
g
by C
AD
WE
LDca
ble
slee
ved
mol
ecul
arbo
ndin
g
cuta
way
vie
wC
onne
ctio
nC
AD
WE
LDT
he
met
al
now
for
m o
ne p
iece
mel
ted
copp
er a
nd w
ires
CA
DW
ELD
Con
nect
ion
A c
ompl
eted
mol
d cl
amp
to b
e jo
ined
clea
ned
cabl
esm
old
grap
hite
ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ
DA
L.00
1.29
19.IL
O
GROUNDING GUIDELINE
397/23/92 68P81150E62–A
Figure 14. CADWELD Connection Styles: Cable–to–Cable/Cable–to–Rod
TY
PE
TA
and
tap
cabl
es.
Tee
of h
oriz
onta
l run
TY
PE
SS
Spl
ice
of h
oriz
onta
l cab
les.
TY
PE
GR
of g
roun
d ro
d.
Cab
le ta
p to
top
TY
PE
GB
splic
e.
Gro
und
rod
T
RA
DE
MA
RK
OF
ER
ICO
PR
OD
UC
TS
, IN
C.
1. ”
CA
DW
ELD
” IS
A R
EG
IST
ER
ED
NO
TE
:
& N
X
TY
PE
GR
,GT,
NT
”One
Sho
t” M
old.
TY
PE
PC
Par
alle
l ta
p co
nnec
tion
of h
oriz
onta
l cab
les.
TY
PE
NC
to g
roun
d ro
d.
Thr
ough
and
tap
cab
les,
of g
roun
d ro
d.
Thr
ough
cab
le to
top
TY
PE
GT
DA
L.00
1.29
20.IL
O
40 68P81150E62–A 7/23/92
Figure 15. CADWELD Connection Styles: Cable–to–Surface
TY
PE
VS C
able
tap
dow
n at
45
degr
ees
to v
ertic
al s
teel
sur
face
or s
ide
of h
oriz
onta
l
or v
ertic
al p
ipe.
TY
PE
VB
or p
ipe.
vert
ical
ste
el s
urfa
ce
Cab
le ta
p do
wn
to
TY
PE
HA
Hor
izon
tal c
able
tap
to
horiz
onta
l st
eel
surf
ace
or p
ipe.
Cab
le
on s
urfa
ce.
TY
PE
LA
LU
G
TY
PE
GL
LUG
Cop
per
lug
to c
able
.
T
RA
DE
MA
RK
OF
ER
ICO
PR
OD
UC
TS
, IN
C.
1. ”
CA
DW
ELD
” IS
A R
EG
IST
ER
ED
NO
TE
:
DA
L.00
1.29
21.IL
O
Recommended