14 069 c 109 1

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EXHIBIT 19 DOCKET 14-069-C

IEEE Guide for the Protection of
IEEE Std 90003™-2008 Installations from
Communication
IEEE Std 90003™-2008
Lightning Effects

IEEE Power Engineering Society

Sponsored by the
Power Systems Communications Committee

IEEE
3 Park Avenue
New York, NY 10016-5997
USA
15 August 2011

IEEE Std 1692™-2011


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IEEE Std 1692 -2011

IEEE Guide for the Protection of
Communication Installations from
Lightning Effects
Sponsor

Power Systems Communications Committee
of the

IEEE Power Engineering Society
Approved 16 June 2011

IEEE-SA Standards Board


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Abstract: The document addresses methods and practices necessary to reduce the risk of
damages to communications equipment within structures arising from lightning surges causing
GPR (ground potential rise) and similar potential differences.
Keywords: IEEE 1692, lightning, protection, communications equipment, towers
Acknowledgments: Figures 1, 2, and 7 reprinted with permission from Expert Systems
Programs and Consulting, Inc., GPR-Expert—Ground Potential Rise Protection using a High
Voltage Interface. June 15, 1998. Original graphics of Figures 1, 2, and 7 copyrighted © by John
S. Duckworth, P.E., CEO, Expert Systems Programs and Consulting, Inc.

•

The Institute of Electrical and Electronics Engineers, Inc.
3 Park Avenue, New York, NY 10016-5997, USA

Copyright © 2011 by the Institute of Electrical and Electronics Engineers, Inc.
All rights reserved. Published 15 August 2011. Printed in the United States of America.
IEEE is a registered trademark in the U.S. Patent & Trademark Office, owned by the Institute of Electrical and Electronics
Engineers, Incorporated.
National Electrical Code, NEC, and NFPA 70 are registered trademarks in the U.S. Patent & Trademark Office, owned by the National Fire
Protection Association, Inc.
PDF:
Print:

ISBN 978-0-7381-6671-1
ISBN 978-0-7381-6672-8

STD97120
STDPD97120

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Introduction
This introduction is not part of IEEE Std 1692-2011, IEEE Guide for the Protection of Communication Installations
from Lightning Effects.

The document addresses methods and practices necessary to reduce the risk of damages to communications
equipment within structures arising from lightning surges causing GPR (ground potential rise) and similar
potential differences.
According to the National Lightning Safety Institute accurate information about lightning-caused damage is
elusive (see National Lightning Safety Institute [B31]).a The U.S. Insurance Institute estimates the annual
damages from lightning in the United States to be $5 billion with the lightning strike claims, not including
U.S. government property losses, paid per year being $820 million (see Brashear [B6]). Other sources
provide much higher values. Lightning damage to equipment results in losses exceeding $26 billion
annually in North America, and nearly three times that worldwide with more than 150 strikes per second

(see Duckworth [B9]). Insurance payout resulting from lightning damage, accounts for approximately 7.5%
of all U.S. insurance company distributions (see Brashear [B6]). Ironically, lightning damage to equipment
could be all but totally prevented.
Special protection methods to minimize lightning damage are simple, very reliable, and inexpensive,
particularly when compared to the cost of equipment repair and replacement, as well as the possible
consequences of harm to personnel. However, methods for lightning special protection cannot be found in
the code books, e.g., National Electrical Code® (NEC®) or the National Electrical Safety Code® (NESC®).b
Per the scopes of these two well-known codes, lightning protection is not covered, yet they are relied upon
for practically all general construction in the United States. The Lightning Protection Standard® (NFPA
780®) should not be expected to provide guidance for the prevention of lightning damage to equipment.
The scope of NFPA 780 covers the protection of structures only. NFPA 780 (4.18.3.2) does contain
requirements for the surge protection of all service entrance signal, data, and communication circuits as
well as surge protection for all service entrance power circuits. Common grounding requirement (4.14) for
electric service, communications, and antenna system grounds as well as underground metallic piping
systems is also included in NFPA 780.
Documented methods for the special protection of equipment from lightning cannot be found in the two
main codes, NEC or NESC, or the Lightning Protection Standard that are systematically referred to for
practically all general construction in the United States. This is in part the reason why there is so much
needless lightning damage. This guide is dedicated to providing special lightning protection methods for
equipment and filling the vacuum that currently exists today (see Duckworth [B9]).
Protection of the structure from lightning plays an important role in the protection of the equipment within
the structure. While the protection of the equipment is the main objective of this document, the protection
of the structure housing the equipment is also covered in this document. The equipment housed in the
structure is often worth many times the value of the structure.
This standard was prepared by the Wire-Line Subcommittee of the IEEE Power Systems Communications
Committee of the IEEE Power Engineering Society.

a

The numbers in brackets correspond to those of the bibliography in Annex A.

National Electrical Code, NEC, and NFPA 70 are registered trademarks in the U.S. Patent & Trademark Office, owned by the
National Fire Protection Association.
b

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Notice to users

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Patents
Attention is called to the possibility that implementation of this recommended practice may require use of
subject matter covered by patent rights. By publication of this recommended practice, no position is taken
with respect to the existence or validity of any patent rights in connection therewith. The IEEE is not
responsible for identifying Essential Patent Claims for which a license may be required, for conducting
inquiries into the legal validity or scope of Patents Claims or determining whether any licensing terms or
conditions provided in connection with submission of a Letter of Assurance, if any, or in any licensing
agreements are reasonable or non-discriminatory. Users of this recommended practice are expressly
advised that determination of the validity of any patent rights, and the risk of infringement of such rights, is
entirely their own responsibility. Further information may be obtained from the IEEE Standards

Association.

Participants
At the time this recommended practice was submitted to the IEEE-SA Standards Board for approval, the
PSCC Wire-Line Subcommittee (SC-6) had the following membership:
Percy E. Pool, Co-Chair and Technical Editor
Larry S. Young, Co-Chair and Secretary
Ron Baysden
Steve Blume
Joe Boyles
Claude Brisson
Timothy Conser

Jean DeSeve
Ernest M. Duckworth, Jr.
John Fuller
Ernie Gallo
Gaetano Grano
David P. Hartmann

Dan Jendek
Richard L. Knight
Randall Mears
Mark Simon
John Wruble

The following members of the individual balloting committee voted on this recommended practice.
Balloters may have voted for approval, disapproval, or abstention.
William J. Ackerman
S. Aggarwal

John Banting
R. Baysden
Joe Boyles
Chris Brooks
Gustavo Brunello
William Byrd
Suresh Channarasappa
Timothy Conser
Michael Dood
Ernest Duckworth
Donald Dunn
Gary Engmann
Gaetano Grano
Randall Groves
Edward Hare
John Hawkins
Lee Herron
Gary Hoffman

Ronald W. Hotchkiss
Piotr Karocki
Yuri Khersonsky
Stanley Klein
Richard Knight
Joseph Koepfinger
Robert Konnik
Jim Kulchisky
David Landry
Greg Luri
Michael Maytum

William McCoy
Daniel McMenamin
Joseph Mears
Jerry Murphy
Arthur Neubauer
Michael S. Newman
Gary Nissen
Chris Osterloh
Lorraine Padden

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Copyright © 2011 IEEE. All rights reserved.

Donald Parker
Percy Pool
R. Ray
Charles Rogers
Bartien Sayogo
Gil Shultz
Mark Simon
James Smith
Jeremy Smith
Jerry Smith
Gary Stoedter
David Tepen
James Tomaseski
Eric Udren
John Vergis
Karl Weber
James Wilson

Jan Wisniewski
John Wruble
Larry Young


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When the IEEE-SA Standards Board approved this standard on 16 June 2011, it had the following
membership:
Richard H. Hulett, Chair
John Kulick, Vice Chair
Robert M. Grow, Past Chair
Judith Gorman, Secretary
Masayuki Ariyoshi
William Bartley
Ted Burse
Clint Chaplin
Wael Diab
Jean-Philippe Faure
Alexander Gelman
Paul Houzé

Jim Hughes
Joseph L. Koepfinger*
David J. Law
Thomas Lee
Hung Ling
Oleg Logvinov
Ted Olsen

Gary Robinson
Jon Walter Rosdahl
Sam Sciacca
Mike Seavey
Curtis Siller
Phil Winston
Howard L. Wolfman
Don Wright

*Member Emeritus

Also included are the following nonvoting IEEE-SA Standards Board liaisons:
Satish K. Aggarwal, NRC Representative
Richard DeBlasio, DOE Representative
Michael Janezic, NIST Representative
Don Messina
IEEE Standards Program Manager, Document Development
Erin Spiewak
IEEE Standards Program Manager, Technical Program Development

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Contents
1. Overview .................................................................................................................................................... 1
1.1 Scope ................................................................................................................................................... 1
1.2 Purpose ................................................................................................................................................ 1

1.3 Application .......................................................................................................................................... 1
2. Normative references.................................................................................................................................. 2
3. Definitions acronyms, and abbreviations ................................................................................................... 2
3.1 Definitions ........................................................................................................................................... 2
3.2 Acronyms and abbreviations ............................................................................................................... 3
4. Overview and background .......................................................................................................................... 3
5. Lightning effects......................................................................................................................................... 4
5.1 Surge protective devices (SPD) and wire-line ..................................................................................... 5
5.2 Isolation techniques ............................................................................................................................. 6
5.3 Lightning—a major source of ground potential rise .......................................................................... 10
6. Handling lightning strike current .............................................................................................................. 10
7. Locating (siting) towers ............................................................................................................................ 11
8. Grounding (earthing) considerations ........................................................................................................ 11
8.1 Grounding impedance........................................................................................................................ 12
8.2 Grounding requirements .................................................................................................................... 13
8.3 Radial counterpoises .......................................................................................................................... 13
8.4 Grounding conductor requirements in equipment buildings ......................................................... 14
8.5 Interior equipment ground ring (IEGR) ............................................................................................. 15
8.6 AC power grounding electrode .......................................................................................................... 15
8.7 Coaxial cable, waveguide, and building entrance panel (BEP) ......................................................... 15
8.8 Communication facility isolation from a lightning induced ground potential rise ............................ 16
8.9 Single point ground ........................................................................................................................... 16
8.10 Installation of ground rods and bonding requirements .................................................................... 16
9. Grounding (earthing) tower and equipment.............................................................................................. 17
9.1 Single point grounding ...................................................................................................................... 17
9.2 Ice bridge ........................................................................................................................................... 17
9.3 Building entrance panel ..................................................................................................................... 17
10. Entrance cables ....................................................................................................................................... 18
11. AC power surge protection ..................................................................................................................... 18
11.1 Protecting ac services entering and exiting the building .................................................................. 19

11.2 Surge protective devices (transient voltage surge suppression) ....................................................... 19
12. Personnel safety considerations .............................................................................................................. 20
13. Equipment building lightning protection system .................................................................................... 20
Annex A (informative) Bibliography ........................................................................................................... 21

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Annex B (informative) Lightning protection guide checklist for risk management ..................................... 23
B.1 Key considerations for the application of this Guide ........................................................................ 23
B.2 How to use this Guide ....................................................................................................................... 23
Annex C (informative) Basic concepts for lightning protection of structures .............................................. 25
Annex D (informative) Power-line isolation: theory and application........................................................... 26
D.1 LGPR and equipotential planes ........................................................................................................ 26
D.2 LGPR detection and isolation activation .......................................................................................... 26
D.3 Back-up power and rectifier implications ......................................................................................... 26
D.4 Power line transient protection ......................................................................................................... 27

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.

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IEEE Guide for the Protection of
Communication Installations from
Lightning Effects
IMPORTANT NOTICE: This standard is not intended to ensure safety, security, health, or
environmental protection. Implementers of the standard are responsible for determining appropriate
safety, security, environmental, and health practices or regulatory requirements.
This IEEE document is made available for use subject to important notices and legal disclaimers.
These notices and disclaimers appear in all publications containing this document and may
be found under the heading “Important Notice” or “Important Notices and Disclaimers
Concerning IEEE Documents.” They can also be obtained on request from IEEE or viewed at
/>
1. Overview

1.1 Scope
This document presents engineering design guidelines for the prevention of lightning damage to
communications equipment within structures.

1.2 Purpose
The purpose of this guide is to provide reliable engineering methods and practices to minimize damages to
communications equipment located within a structure.

1.3 Application
The protection of the structure plays an important role in the protection of the equipment within the
structure. While the protection of the equipment is the main objective of this document, the protection of
the structure housing the equipment is also covered in this document.

1
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IEEE Std
-2011
IEEE Guide for the Protection of Communication Installations from Lightning Effects

2. Normative references
The following referenced documents are indispensable for the application of this document (i.e., they must
be understood and used, so each referenced document is cited in text and its relationship to this document is
explained). For dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments or corrigenda) applies.
Accredited Standards Committee C2-2007, National Electrical Safety Code (NESC). 1
IEEE Std 487™-2007, IEEE Recommended Practice for the Protection of Wire-Line Communication
Facilities Serving Electric Supply Locations..2, 3
IEEE Std 1590™-2009, IEEE Recommended Practice for the Electrical Protection of Communication
Facilities Serving Electric Supply Locations Using Optical Fiber Systems.
NFPA 70, 2008 Edition, National Electrical Code (NEC). 4
NFPA 780, 2000 Edition, Standard for the Installation of Lightning Protection Systems.

3. Definitions acronyms, and abbreviations
For the purposes of this document, the following terms and definitions apply. The IEEE Standards
Dictionary: Glossary of Terms & Definitions should be consulted for terms not defined in this clause. 5

3.1 Definitions
all-dielectric optical fiber cable: An optical fiber cable containing no metallic or conductive components.

ground ring: A buried grounding electrode, in the form of a conductor in direct contact with the earth,
encircling the structure being grounded.
ground potential rise (GPR): The product of a ground electrode impedance, referenced to remote earth,
and the current that flows through that electrode impedance.
halo ground: An internal closed loop metallic ground. Usually a 6 AWG sized conductor that is routed
around the room approximately 2 to 2.4 m (6 to 8 feet) above the floor. This ground is used to dissipate
unwanted energy off of metallic surfaces. This ground is used to bond and ground metal objects such as
metal doors, door frames or casings, window frames or casings, air handling ducts, and air conditioning
housings (except fire suppression equipment). It is not to be used to ground communication equipment or
equipment supporting hardware.
high-voltage interface (HVI): Protective apparatus that provides electrical isolation of wire-line
communications conductive paths.
1
National Electrical Code, NEC, and NFPA 70 are registered trademarks in the U.S. Patent & Trademark Office, owned by the
National Fire Protection Association.
2
IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331,
Piscataway, NJ 08855-1331, USA ( />3
The IEEE standards or products referred to in this clause are trademarks of the Institute of Electrical and Electronics Engineers, Inc.
4
NFPA publications are published by the National Fire Protection Association, Batterymarch Park, Quincy, MA 02269, USA
( Copies are also available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box
1331, Piscataway, NJ 08855-1331, USA ( />5
The IEEE Standards Dictionary: Glossary of Terms & Definitions is available at />
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IEEE Guide for the Protection of Communication Installations from Lightning Effects

lightning ground potential rise (LGPR): A ground potential rise condition caused by a lightning strike to
the earth or object attached to the earth. Characteristics include rise times in the μs and sub-μs time frame,
current flow nominally radial from the strike point, and high differential ground potentials created over
extended distances (subject to local soil resistivity).
primary (or extrinsic) communication SPD: An surge protective device capable of diverting or arresting
a considerable portion of the surge current away from the system it is protecting. They are generally
installed at the cable entrance to a building, on the main distributing frame, or at the equipment/cable
interface.
radial counterpoise: A conductor or system of conductors located on, above, or most frequently below the
surface of the earth; and connected to the grounding system of towers or poles.

3.2 Acronyms and abbreviations
ABD
ac
AWG
BEP
dc
EMP
GDT
GPR
HVI
IEGR
LGPR

MCOV
MDF
MGB
MGN
MOV
MTBF
NEC
NESC
NFPA
PSAP
PVC
SAD
SAS
SBTC
SCR
SPD
SPG
TVSS
UPS

avalanche breakdown diode
alternating current
American wire gauge
building entrance panel
direct current
electro magnetic pulse
gas discharge tube
ground potential rise
high-voltage interface
interior equipment ground ring

lightning ground potential rise
maximum continuous operating voltage
main distributing frame
master ground bar
multigrounded neutral
metal oxide varistor
mean time between failures
National Electrical Code
National Electrical Safety Code
National Fire Protection Association
public safety answering point
polyvinyl chloride
silicon avalanche diode
silicon avalanche suppressor
solid bare tinned copper
silicon controlled rectifier
surge protective device
single point ground
transient voltage surge suppression (see SPD)
uninterruptible power system

4. Overview and background
This Guide presents recommended engineering design practices to reduce the risk of lightning damages to
communications equipment within structures. If equipment is protected from damage by lightning, then
personnel using, or associated with, the equipment may also be protected. Specific measures for the
protection of personnel are not covered in this Guide.
3
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This Guide includes discussion on the following topics:
 Lightning effects on grounded towers, buildings, and equipment (Clause 5)
 Lightning—a major source of ground potential rise (Clause 5)
 Divide and control lightning strike current (Clause 6)
 Tower location with respect to equipment building, electromagnetic radiation, need for Faraday cage
(Clause 7)
 Grounding (earthing) considerations (Clause 8)
 Voltage divider circuit from lightning traveling down a tower (Clause 9)
 Single point ground location (Clause 9)
 Coordinate the coaxial cable entry with building equipment grounding (Clause 10)
 Entrance panel, bulkhead, or wave guide hatch (Clause 10)
 Isolate wire-line communications from remote earth (Clause 10)
 AC power surge protection and uninterruptible power system at the power entrance facility (Clause
11)
 AC disconnect isolation

5. Lightning effects
Lightning is an electrical discharge. The cloud-to-cloud or cloud-to-ground discharge generates electric,
magnetic, and electromagnetic fields. The most significant field is the magnetic one. The magnetic field
induces voltages in conductors and, if a loop is formed, currents in conductive loops. Cloud-to-ground or
grounded structure discharges will cause a localized ground potential rise (GPR). Currents flowing in

structures will cause localized differences in structure grounding voltage and the currents will create
localized magnetic fields.
Electrical equipment damage from lightning may be placed into three major categories:
 Improper or insufficient grounding
 Lack of protection from GPR
 Lack of protection from lightning transients
Improper or insufficient grounding will result in the equipment being stressed and/or damaged (potential
difference) from nearby equipment, metal objects, misdirected current flow, etc.
Lack of protection from GPR will result in the equipment being stressed from its connection to remote
earth at some distant location through communication wire-lines or power supply wiring and/or from
intrabuilding GPR arising from the voltage drop between power and telecommunication grounds references
(see IEEE Std C62.43 [B23], and Ma and Dawalabi [B29]).
Lightning GPR (LGPR) can result from strikes to objects or direct strikes to earth. Strikes to towers may
have higher probability when towers or metallic structures are present, but sites without towers or metallic
structures can suffer damage from nearby earth strikes.

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High differential ground potentials between local equipment and remote power grounds make the power

service conductors a favored discharge path for LGPR currents. Soil conditions have a significant effect on
differential ground potentials. Higher soil resistivity will result in higher differential ground potentials from
lightning strikes to earth. With cloud to ground electric potentials in the magnitude of tens of millions of
volts, an earth strike can be characterized as a current source. When the stroke discharge occurs the current
traveling in the earth will flow regardless of the soil impedance. General application of ohm’s law will
indicate the higher soil resistivity will result in a higher differential ground potential for a given discharge
current.
Sites without towers may experience LGPR effects as much, if not more, than sites with towers as they are
less likely to have extensive grounding infrastructure. Sites at most risk are areas with a higher occurrence
of lightning and high soil resistivity.

5.1 Surge protective devices (SPD) and wire-line
The standard surge protective devices (SPD) in the telecommunications industry, for the termination of
communication wire-line services is the gas discharge tube (GDT). GDTs are also called gas tubes. GDTs
can be found on virtually every telephone pair terminated in homes, buildings, and similar locations. GDTs
are designed to shunt most current to ground. If the magnitude shunted does not exceed a certain threshold
the SPD will help protect equipment, and personnel, from harm.
Most shunting devices, however, do not fully protect network electronic equipment from a GPR or
“outgoing current,” whether induced from lightning or from a faulted power line. When shunting devices
are connected to an elevated ground (outgoing current) during a GPR event, they merely offer an additional
current path off the site to remote earth (the other end).
When SPDs (GDTs, MOVs, ABDs, SCRs, SADs, SASs, etc.) are used as ground shunting devices, they
will not protect equipment from GPR. These devices merely offer an additional path to remote earth
through the communication pairs for any and all outgoing currents.
When there is a GPR event the SPD provides a connection of the communication path in the reverse
direction from which they were intended to operate and increases the possibility of equipment damage to
telephone and power installations.
The most susceptible locations are those where the equipment is located near, or under, towers and/or are
located at a higher altitude than the surrounding area.
Some of the susceptible locations to equipment damages include the Public Safety Answering Point

locations (also called 911 PSAP). The typical 911 PSAP center is a relatively small building under, or near,
a radio tower. This tower is a likely target for lightning. Personnel taking emergency calls coming into the
PSAP may be at a higher risk since they must be at the phones at all times and cannot be off the phones
during lightning storms, as recommended in virtually every telephone book in the United States. For
additional information see ATIS 0600321 [B2].
Whether the site is a 911 PSAP center or a cellular telephone (radio) antenna on top of a mountain, special
protection methods are available and must be used to reduce the risk of lightning damage to equipment and
associated working personnel. Methods will be presented in this Guide to enable engineers to incorporate
them into the general construction design.
Effective protection of sensitive equipment with SPD shunting devices is complex. A well-designed
installation requires coordination of the protection for low-voltage power feeds (ac and dc) with the
protection for telecommunications facilities in order to minimize the effect of intrabuilding GPR. The use
of secondary SPD is recommended to supplement the primary SPD (see ITU-T K.11 [B26]). Surge
resistibility and impedance of the terminal equipment must be compatible with the selected primary SPD.
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Finally, secondary and primary SPD must be coordinated to optimize adequate operation (see IEEE Std
C62.43 [B23], ATIS 0600338 [B4], ITU-T K.36 [B27], and ITU-T K.11 [B26]).
Even with a well-designed installation, part of the lightning current will reach the equipment and, in some

cases, can affect service quality and/or cause equipment damage.

5.2 Isolation techniques
To minimize the risk of equipment damage due to energy exchange between grounds, special protection
devices based on isolation techniques are very effective.
The isolation protection techniques are particularly recommended for:
1)

The protection of non-interruptible (class A) service (see IEEE Std 487-2007 or IEEE Std 15902009)

2)

The protection of sensitive equipment not designed for operation with standard primary SPD

3)

Sites exhibiting excessive trouble reports due to lightning activity

5.2.1 Wire-line isolation
Figure 1 and Figure 2 show the value of isolation in communication circuits. 6

NOTE 7 —Reprinted with permission from Duckworth et al. [B10]

Figure 1 —Communications without isolation protection

6

For simplification, power feeding of the isolation device is not shown. Grounding arrangement of a telecommunication room is
much more complex. Grounding standards for telecommunication rooms must be strictly followed to minimize equipment damage.
7

Notes in text, tables, and figures of a standard are given for information only and do not contain requirements needed to implement
this standard.

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Figure 2 —Communications with isolation protection
In some situations, economic considerations based on the cost of the telecommunication equipment to be
protected may be sufficient to justify the cost of the special protection devices. However, isolation does not
solve grounding deficiencies inside the telecommunications room. Isolation devices can be damaged on the
service and/or power supply side due to improper grounding design.
For critical services and sensitive equipment protection through isolation, using optical isolators or
isolation transformers is recommended. Isolators provide a path for a signal, using either optical or electromagnetic coupling, but do not provide a dc current path. If there is no path for incoming or outgoing
currents to flow, there will be no current flow. The risk of harm to equipment, cable, or associated working
personnel will be greatly reduced.
In the design of the isolation installation, intrabuilding GPR problems must be addressed (see Cohen [B7],
and Ma and Dawalabi [B29]). The “station” ground of the isolation device must be at the same ground
reference with the protected equipment and ac power neutral and dc ground reference. Without proper

grounding arrangement in the telecommunication room, equipment can be damaged no matter the kind of
protection used (SPD, optical fiber, isolation).
Figure 3 and Figure 4 show very simplified 8 installation examples depicting intrabuilding GPR and the
impact of the ground installation.

8

Grounding installations of the telecommunication room must be investigated in such a case.

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Figure 3 —Example of an acceptable and proper installation. Power, equipment,
and protection device grounds are at the same reference.

Figure 4 —Example of an improper installation. The equipment can be subjected to highvoltage difference (delta V). The wire inductance and time delay propagation of high
frequency lightning current can create large GPR difference (delta GPR).
5.2.2 AC service isolation
Additional protection for the conditions listed at the beginning of 5.2 can also be offered through complete
ac isolation where the ac utility is temporarily disconnected via automatic methods. Note that ac disconnect

isolation requires protected equipment to have reliable power back-up systems such as battery or generator
equipment for uninterrupted operation during ac isolation.
AC isolation preemptively open-circuits the secondary fault current paths of GPR (see Figure 5 and Figure
6). These secondary fault paths go through the equipment and are a result of momentary GPR events
creating high differential ground potentials and severe ground fault currents. Surge protection devices are
bi-directional and will conduct in the reverse direction when the grounding system is sufficiently elevated
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in potential. When this elevation (rise in potential) occurs on the communication lines it will directly
connect the system electronics to the energized grounding system.
The reactive nature of typical electronic communication system behaves differently at higher lightning
frequencies compared to 60 Hz. Batteries look inductive, wires look inductive, transformers behave more
capacitive, etc. The complexity of performing circuit analysis for a lightning fault condition becomes very
daunting. Therefore lightning fault current paths are created that do not always follow the intentional circuit
paths and are difficult to predict.
The utility power circuits provide a highly conductive path for lightning discharge currents to remote
grounds. When the terminal ground is elevated and the communication line surge protectors conduct, this
condition will put the electronic systems directly in a secondary fault current path. Disconnecting the
electronics from utility power removes this fault current path.

AC disconnect isolation also provides additional protection from power line fault conditions that are caused
by lightning activity. (See further discussion of LGPR in Clause 6). Figure 5 and Figure 6 present
simplified application circuits and LGPR discharge paths.

Figure 5 —Secondary LGPR discharge paths without ac isolation

Figure 6 —Secondary discharge current paths blocked with ac disconnect isolation
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5.2.3 Direct ac isolation method for protection of communication sites from lightning
induced ground potential rise
Consider the following when the use of ac isolation methods is necessary.


Use best protection practices for lightning protection as described in this document including the
use of single point ground, ac surge protection, and surge protection on wire-line communication
lines.



Follow NFPA 70 requirements, specifically maintaining a single N-G bond point in the service
disconnect cabinet.



Keep ground wires as straight as possible and minimize bends.



Placing the ac isolator between the ac service disconnect switch and the power transfer switch is
recommended.



Primary ac surge protection is to be located on the line side of the ac isolation unit. Use secondary
surge protection, in L-L and L-N modes, on the load side of the isolation unit. N-G surge
protection mode is not to be installed at the secondary location.

Note that ac disconnect isolation requires protected equipment to have reliable power back-up systems such
as battery or generator equipment for uninterrupted operation during ac isolation.

5.3 Lightning—a major source of ground potential rise
There is a 50% probability that a lightning strike will be approximately 30 kA (see Anderson and Eriksson
0). If the self-inductance of the earth is estimated very conservatively to be 0.5x10-6 H, and considering that
lightning takes the form of a pulse which has a typical rise time of 2x10-7 s, then using V = Ldi/dt yields the
estimated GPR of a 30 kA strike to be 7.5 kV. Higher current lightning strikes or strikes passing through
higher inductance will yield higher values of GPR.
If the inductance of a grounding system is estimated to be 1x10-6 H, then the GPR resulting from a 30 kA
lightning strike will be around 15 kV. Any grounded equipment that is connected to wire-line

communication pairs will then be in jeopardy from outgoing currents seeking a path to remote earth.
In large structures having a large number (1000+) of communication pairs, such as a telecommunications
central office, the GPR effect will be greatly reduced due to the current division in the many multiple paths
(the communication pairs) to remote earth. However, for small structures with relatively few
communication pairs, all the available grounding paths must be considered including wire-line,
multigrounded neutral (MGN), water pipes, building steel, etc. Structures connected to large metallic
infrastructure may have lower GPR values. For smaller structures, the isolation decision depends on many
considerations including equipment characteristics, type of services, and location.

6. Handling lightning strike current
Controlling the dissipation path for lightning strike current requires current redirection through a
combination of current division and current blocking techniques. This approach is an absolute must for
success, because of the magnitude of the current, the resulting surge impedance of any single dissipation
path and the availability of secondary fault current paths through the electronics equipment. Multiple
connections (minimum 4 but 10 preferred) between the tower and a grounding ring will divide lightning
current into smaller segments. This division will ensure that the lightning surges will follow the designated

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paths for dissipation into the earth and thus lower the resulting GPR to the adjacent equipment building
grounding system.
Fault current blocking through automatic ac disconnect isolation requires protected equipment to have
power back-up systems such as battery, uninterruptible power supply, or battery/generator equipment for
uninterrupted operation during ac isolation. AC service is automatically reconnected after the threat has
subsided below an acceptable threshold.
AC isolation periods for LGPR will nominally be several minutes but are automatically extended if the
LGPR threat condition persists. Isolation periods for power line fault conditions will be several seconds,
but also extend if power line conditions do not return to acceptable levels. AC isolation will respond to
power line sags, swells, and short term transients exceeding threshold levels.
Effective ac disconnect isolation requires preemptive detection of impending LGPR events. Detection of
LGPR from approaching storms and of rapidly changing local surface electric fields provides the
indications of imminent threat.
There is no means to predict power-related fault conditions. AC isolation will minimize the stress caused
by extended poor ac power quality. AC power is reconnected to the protected equipment after it stabilizes
within selected thresholds. As a result, the site is not exposed to power recovery transients following a
power service failure.

7. Locating (siting) towers
Design engineers attempting to keep transmission losses low, along with the real estate considerations,
usually dictate that the equipment building be as close to the antenna tower as possible. This practice goes
against the design of a reliable and robust equipment system to lightning.
The recommended minimum distance between the equipment buildings associated with nearby antenna
towers is (9 m [30 feet]) in order to minimize the effects of the electromagnetic field associated with
lightning and to reduce the risk of damage to equipment circuits. In general, electromagnetic field strength
drops off as the square of the distance. If real estate considerations prevent the building from being more
than 9 m (30 feet) from its antenna tower, then a Faraday cage (wire mesh) around the interior of the
building should be established. Without a Faraday cage, equipment damage cannot be prevented no matter
how well the equipment is grounded or isolated from remote earth.
The recommended minimum distance between the equipment buildings and the towers also contributes to

keep the LGPR at the tower base from saturating the building grounding system, before a majority of it can
be dissipated.
The two grounding electrode systems (for the tower and for the equipment building) must be bonded
together at one single point. However, a bond of 9 m (30 feet) or more will significantly reduce the
resulting GPR at the equipment building due to the impedance of this lengthy bond. This is one of those
rare exceptions in which a lengthy bond is an advantage in supporting a robust grounding system to
lightning.

8. Grounding (earthing) considerations
Take the following grounding considerations into account to reduce the risk of damages from lightning. An
example of a grounding system is depicted in Figure 7.

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NOTE—Reprinted with permission from Duckworth et al.[B10]

Figure 7 —Example of a grounding system

8.1 Grounding impedance

Use the following steps to design a grounding electrode system.
1)

Conduct a four (4) probe soil resistivity test, per IEEE Std 81 [B19], at each proposed tower and
equipment building location to obtain data for an engineering study to design a grounding system
that will meet specified grounding objectives. See items 2) and 3).

2)

Hardening against lightning GPR damage requires specially designed tower radial counterpoise
grounding system with a grounding impedance not exceeding two (2) ohms.
NOTE 1— If the objective is not economically achievable, provide the lowest possible ground impedance
value, using radial counterpoises, to minimize the grounding impedance (and thus GPR) as much as possible.

3)

Hardening against lightning GPR damage requires an associated tower equipment building
grounding system with a grounding impedance not exceeding two (2) ohms.
NOTE 2— If the objective is not economically achievable, provide the lowest possible ground impedance
value, using radial counterpoises, to minimize the grounding impedance (and thus GPR) as much as possible.

4)

The total overall site ground impedance (tower and building) should not exceed one (1) ohm.
NOTE 3— This may require significant real estate space if the site soil resistivity is greater than 500 meterohms at the anticipated grounding electrode depth.
NOTE 4— If the objective is not economically achievable, provide the lowest possible ground impedance
value, using radial counterpoises, to minimize the grounding impedance (and thus GPR) as much as possible.

As tested 5 ohms
5)

Measure the final total site grounding impedance, per IEEE Std 81 [B19] using the three (3) probe
method, at the single point ground (SPG) bar, to verify that the site grounding system meets the
specified objectives prior to the electrical connection of the power multi grounded neutral (MGN)
to site system ground.

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8.2 Grounding requirements
Consider the following items when designing and constructing the grounding system.
1)

All conductors for the grounding system are to be 2 AWG solid bare tinned copper (SBTC).

2)

Use low impedance conductive cement placed around all grounding conductor radial
counterpoises at locations where the soil resistivity is greater than 500 meter-ohms at the
grounding electrode depth.

Follow the items below for the installation procedure:
a)

The trench for the radial counterpoise is to be opened to a depth of a minimum of 457 mm
(18 inches) to a maximum of 610 mm (24 inches) or below the frost line.

b)

Place the conductor centered in the trench.

c)

Then use a 50 mm (2 inches) covering of dry, low impedance conductive cement on top of
the radial conductor. (Moisture from the earth will harden the low impedance conductive
cement within one week).

d)

Then, backfill the trench with removed earth, this will then cover the low impedance
conductive cement and radial wire and will level the earth thereby closing the trench.

NOTE 1— Low impedance conductive cement will not corrode, or crack, and is extremely low in resistivity.
Other materials might change resistivity depending on moisture content.

3)

All ground rods for the grounding system are to be stainless steel, copper, or galvanized steel and
a minimum of 2.4 m (8 feet) in length and 15.87 mm (5/8 inch) in diameter.

4)

All bonds to the grounding system in contact with the earth are to be done by exothermic welding
or irreversible compression connectors listed for the purpose.

5)

Provide an external ring ground, which should include ground rods, for the tower and the
equipment building. The ring ground is to be composed of 2 AWG SBTC conductors placed
below the frost line. Also provide a minimum of 4 radial counterpoises each 7.6 m (25 feet) in
length (see Figure 7). This combination of ring grounds and radial counterpoises provides
capacitive coupling of the lightning high frequency current to earth.
NOTE 2— The scheme described above needs a minimum of 30 m (100 feet) for the total combined length
of the radial counterpoises for best results.

6)

In corrosive environments, consideration should be given to the use of sacrificial magnesium
anodes against the effects of corrosion (to protect grounding system).

8.3 Radial counterpoises
Place the radial counterpoise conductor in a trench (500–600 mm [18–24 inches] in width) and low
resistivity cement, conductive cement, bentonite, or similar material, around the conductor.
The recommended minimum length of each radial counterpoise conductor is 7.6 m (25 feet). If the desired
resistance to earth is not achieved at this length then use longer radial counterpoise conductors in order to
obtain the desired resistance objective. Bond the radial counterpoise conductor to the tower base and to the

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