“Packing up to 100 million volts of electricity, a bolt of lightning
has the power to tear through buildings, explode walls made of
brick and concrete, disturb steel and ignite deadly fires. The cost
of this damage can be enormous.”
Purposes for Grounding
Personnel Safety: Proper grounding of power sources should prevent system
source voltages from permanently appearing on metallic frames that
personnel physically come in contact with.
Equipment Circuit Protection: To prevent electrical fires and limit damage to
equipment and associated circuit conductors, the Building Safety Protection
System shall provide a low resistance/impedance path for lightning currents
to flow to earth when lightning strikes.
Electrostatic Discharges (ESD): ESD should be reduced by maintaining low
resistance/impedance paths between grounded points throughout any
Where Lightning Strikes
• System Description –
– The entire lightning protection system shall be designed and
installed in accordance with:
• A) National Fire Protection Assoc. (NFPA) Document # 780
• B) Underwriters’ Laboratories, Inc. (UL) Standard # 96A
• C) Lightning Protection Institute (LPI) Standard # 175
• Submittals –
– A complete shop drawing shall be submitted to the architect and
engineer for approval prior to commencement of the installation.
The shop drawing will show the extent of the system layout
designed for the structure along with details of the products to be
used in the installation.
A grounding system neither attracts, repels or prevents a lightning strike. The
lightning protection system simply provides a safe path for the lightning current to
follow - allowing the harmful current to be guided safely into the ground and away
from your home.
• A true earth ground, is a rod driven into the earth to a minimum depth of 8
Type Advantages Disadvantages
Vertical rods Simple design. Easy to install in good High impedance. Hard to install
soils. Hardware readily available. Can be in rocky soil. Step voltage on
extended to reach the water table. earth surface can be high under
large fault currents or during a
direct lightning strike.
Plates Can achieve low resistance contact in Most difficult to install. Should
limited area. be installed vertically.
Horizontal bare wires Low impulse impedance. Good RF Subject to resistance fluctuations
(radials) counterpoise when laid in star pattern. with soils drying. Not
recommended with unstable
Incidental electrodes Can achieve very low resistance in certain Little or no control over future
(water pipes, applications. alternations. Must be employed
buried tanks) with other electrodes, not as sole
Ring ground Straightforward design. Easy to install Problems with asphalt and
around existing facility. Hardware readily concrete around the facility? Not
available. Very efficient due to volume. desirable where large rocks are
How to Ground a Building Effectively
• Gather Accurate Soil Resistivity Data
Soil resistivity is a physical property unique to every soil. Prior to designing a
grounding system, soil resistivity testing must be completed to determine the
electrical properties of the soil at and around the site.
• Inside Grounding Should Be Configured As Single Point
Inside grounding involves the electrical bonding of all internal metallic's in a building
to the outside grounding system. Each facility should have a master ground bar
(MGB) that serves as a hub with all grounding for the building being either directly or
indirectly bonded to it.
• Outside Grounding Should Address Lightning
Lightning storms can produce peak currents up to 400,000 amps. It is important that
the grounding system is configured properly and is sufficiently robust to handle the
intense energy contained in a lightning strike. Outside grounding must provide a low
impedance path to allow lightning energy to dissipate into the earth without causing
any damage to the protected structure and its contents.
• Surge Protection Is Crucial
Surge protection should be installed at the main AC service entrance and on any
service panel feeding critical equipment. Surge protection should also be installed on
incoming twisted pair telephone lines, data lines and co-axial cables entering your
facility. The majority of surges are not caused by direct lightning strikes to the facility
but are either carried in on utility lines, or generated internally.
Components of a Grounding System
Minimum Equipment Ground Conductor
Under table 250.122 In the NEC2005 Book, you can find minimum size
requirement for up to 6000 Amp. (Pg#70-112)
A "GFCI" is a ground fault circuit
The GFCI is designed to protect people from severe or fatal electric
shocks. Because a GFCI detects ground faults, it can also prevent
some electrical fires and reduce the severity of others by interrupting
the flow of electric current.
In the home's wiring system, the GFCI constantly monitors electricity
flowing in a circuit, to sense any loss of current. If the current flowing
through the circuit differs by a small amount from that returning, the
GFCI quickly switches off power to that circuit. The GFCI interrupts
power faster than a blink of an eye to prevent a lethal dose of
electricity. You may receive a painful shock, but you should not be
electrocuted or receive a serious shock injury.
Three common types: Receptacle Type, Circuit Breaker Type,