I was asked as well as challenged as pertaining to my comments and
suggestions as related to grounding for lightning protection as applied
to the station power supply and or power source. To further provide
information and studies, I offer the following with references for
followup consideration.
73
Bob, K4TAX
~ National Lightning Safety Institute ~
September 5, 2012
Section 5.3.1
Recommended Grounding Guidelines
Prominent lightning engineers and major technical codes and standards
agree as to proper grounding guidelines. We present summaries of those
generally accepted designs.
1. From Golde, Lightning, Academic Press, NY, 1977, vol. 2, chapter 19 by
H. Baatz, Stuttgart, Germany, p. 611:
"Equalization of potentials should be effected for all metallic
installations. For lightning protection of a structure it is of greater
importance than the earthing resistance...
The best way for equalization of potentials utilizes a suitable earthing
system in the form of a ring or foundation earth. The down conductors are
bonded to such a ring earth; additional earth electrodes may be
unnecessary?"
2. From Sunde, Earth Conduction Effects in Transmission Systems, Van
Nostrand, NY, 1949, p. 66:
"Adequate grounding generally requires that the resistance of the ground
, at the frequency in question, be small compared to the impedance of the
circuit in which it is connected. By this criterion, it may be
permissible in some instances to have a ground of high resistance,
several thousand ohms, as in the case of "electrostatic" apparatus
ground, the impedance to ground of insulated apparatus cases being
ordinarily quite high. In other [situations], however, a resistance of
only a few ohms may be required for effective grounding."
3. From Horvath, Computation of Lightning Protection, Research Studies
Press, London, 1991, p. 20:
"The earthing of the lightning protection system distributes the
lightning current in the soil without causing dangerous potential
differences. For this purpose the most effective earthing encloses the
object to be protected. The potential increases on the earthing and on
all earthed metal parts of the object relative to the zero potential at a
distant point. It may reach a very high value but it does not cause any
danger if the potential differences inside the object to be protected are
limited. Potential equalization is realized by the bonding of all
extended metal objects."
4. From Hasse, Over voltage Protection of Low Voltage Systems, Peter
Peregrinus Press, London, 1992, p. 56.
''Complete lightning protection potential equalization is the fundamental
basis for the realization of internal lightning protection; that is the
lightning over voltage protection for the electrical and also the
electronic data transmission facilities and devices in buildings. In the
event of a lightning stroke, the potential of all installations in the
affected building (including live conductors in the electrical systems
with arrestors) will be increased to a value equivalent to that arising
in the earthing system -- no dangerous over voltages will be generated in
the system?
Nowadays lightning protection potential equalization is considered
indispensable. It ensures the connection of all metal supply lines
entering a building, including power and communication cables, to the
lightning protection and earthing system by direct junctions across
disconnection spark gaps, or arrestors in the case of live conductors."
5. From IEEE Emerald Book, Powering and Grounding Sensitive Electronic
Equipment, IEEE Std 1100-1992, IEEE, NY, 1995, p. 216:
"It is important to ensure that low-impedance grounding and bonding
connections exist among the telephone and data equipment, the ac power
system's electrical safety-grounding system, and the building grounding
electrode system. This recommendation is in addition to any made
grounding electrodes, such as the lightning ground ring. Failure to
observe any part of this grounding requirement may result in hazardous
potential being developed between the telephone (data) equipment and
other grounded items that personnel may be near or might simultaneously
contact."
6. From International Standard IEC 1024-1, Protection of Structures
Against Lightning, International ElectroTechnical Commission, Geneva,
1991, p. 23:
"In order to disperse the lightning current into the earth without
causing dangerous over voltages, the shape and dimensions of the
earth-termination system are more important than a specific value of the
resistance of the earth electrode. However, in general, a low earth
resistance is recommended.
>From the viewpoint of lightning protection, a single integrated
structure earth termination is preferable and is suitable for all
purposes (i.e. lightning protection, low voltage power systems,
telecommunication systems).
Earth termination systems which must be separated for other reasons
should be connected to the integrated one by equipotential bonding?"
7. From FAA-STD-019b, Lightning Protection, Grounding, Bonding, and
Shielding Requirements for Facilities, Federal Aviation Administration,
Washington DC, 1990, p. 20:
"The protection of electronic equipment against potential differences and
static charge build up shall be provided by interconnecting all
non-current carrying metal objects to an electronic multi-point ground
system that is effectively connected to the earth electrode system."
8. From MIL-STD-188-124B, Grounding, Bonding and Shielding, Department of
Defense, Washington DC, 1992, p. 6 and p. 8:
"The facility ground system forms a direct path of known low voltage
impedance between earth and the various power and communications
equipments. This effectively minimizes voltage differentials on the
ground plane which exceed a value that will produce noise or interference
to communications circuits." (p.6)
"The resistance to earth of the earth electrode subsystem should not
exceed 10 ohms at fixed permanent facilities." (p. 8)
9. From MIL-STD-1542B (USAF), Electromagnetic Compatibility and Grounding
Requirements for Space Systems Facilities, Department of Defense,
Washington DC, 1991, p. 19:
"This Standard, MIL-HDBK-419, and MIL-STD-188-124 do not recommend the
use of deep wells for the achievement of lower impedance to earth. Deep
wells achieve low dc resistance, but have very small benefit in reducing
ac impedance. The objective of the earth electrode subsystem is to reduce
ac and dc potentials between and within equipment. If deep wells are
utilized as a part of the earth electrode subsystem grounding net, the
other portion of the facility ground network shall be connected to them."
10. From National Electrical Code, NEC-70-1996, National Fire Protection
Association, Quincy MA, 1996, Article 250 - Grounding, p. 120 & p. 144:
"Systems and circuit conductors are grounded to limit voltages due to
lightning, line surges, or unintentional contact with high voltage lines,
and to stabilize the voltage to ground during normal operation. Equipment
grounding conductors are bonded to the system grounded conductor to
provide a low impedance path for fault current that will facilitate the
operation of over current devices under ground-fault conditions." (p.
120)
"Metal Underground Water Pipe. A metal underground water pipe in direct
contact with the earth for 10 ft. (3.05 m) or more (including any metal
well casing effectively bonded to the pipe) and electrically continuous
(or made electrically continuous by bonding around insulating joints or
sections or insulating pipe) to the points of connection of the grounding
electrode conductor and the bonding conductors. Continuity of the
grounding path or the bonding connection to interior piping shall not
rely on water meters or filtering devices and similar equipment. A metal
underground water pipe shall be supplemented by an additional electrode
of a type specified in Section 250-81 or in Section 250-83. The
supplemental electrode shall be permitted to be bonded to the grounding
electrode conductor, the grounded service-entrance conductor, the
grounded service raceway, or any grounded service enclosure." (p. 145)
11. From MIL-HDBK-419A, Grounding, Bonding, and Shielding for Electronic
Equipments and Facilities, Department of Defense, Washington DC, 1987, p.
1-2, p. 1-6, p.1-102 and p. 1-173:
"The value of 10 ohms earth electrode resistance recommended in Section
1.2.3.1a represents a carefully considered compromise between overall
fault and lightning protection requirements and the estimated relative
cost of achieving the resistance in typical situations." (p. 1-2)
"At fixed C-E facilities, the earth electrode subsystem should exhibit a
resistance to earth of 10 ohms or less." (p.1-6)
"All metallic pipes and tubes (and conduits) and their supports should be
electrically continuous and are to be bonded to the facility ground
system at least at one point." (p. 1-102)
"Water pipes and conduit should be connected to the earth electrode
subsystem to prevent ground currents from entering the structure." (p.
1-173)
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