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 downconductors
are bonded to such a ring earth; additional earth electrodes may be
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
4. From Hasse, Overvoltage 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 overvoltage 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 overvoltages 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 overvoltages, 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
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
"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
10. From National Electrical Code, NEC-70-1996, National Fire Protection
Association, Quincy MA, 1996, Article 250 - Grounding, p. 120 & p.
"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 overcurrent devices under ground-fault conditions."
"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 22.214.171.124a represents a carefully considered compromise between
overall fault and lightning protection requirements and the estimated
relative cost of achieving the resistance in typical situations."
"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."