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ÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇ

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.

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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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28 68P81150E62–A 7/23/92

Figure 3. Example of Typical Collocated Cell/MTSO Site Ground Plan

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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

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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

O

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

O

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

O

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