Detailed Information About Lightning Rod Systems
Some experts state that lightning strikes the earth fifty times every second, others say
one hundred strikes per second. Some U.S. insurance industry representatives say one
billion dollars in damage is caused by lightning each year, while others claim several billions
of dollars in damage annually from lightning. A typical lightning bolt contains 25,000 amps of
current, but some have been measured to contain 400,000 amps of explosive energy. While
"facts" and figures vary from source to source, they all support the truth that lightning is an
awesome force that is more widespread than one would generally think, but is the only natural
destructive force that we can protect ourselves from at reasonable cost.
As for who needs lightning protection, there is no simple answer. Tall structures, buildings with
a large footprint, and buildings located on hills, near water, or in open fields are well known to be
at high risk for a direct lightning strike. On the other hand, many buildings in low-lying areas
get struck, and nearly every building will receive damage from surges produced by nearby strikes.
Many buildings have survived decades of thunderstorms, only to burn to the ground after being
struck the first time. A properly installed lightning rod system will provide many years of peace-of-mind
and prevention of damage to electronic equipment, while being always ready for a potentially
devastating direct strike.
Only about one third of lightning is from cloud to ground, with two thirds being
from cloud to cloud. Cloud to cloud lightning is a hazard for planes, which is why planes have
lightning rods. Since heavy storm clouds hang relatively low, buildings located at high altitudes
can have lightning from all directions. Lightning begins in the clouds when winds churn ice crystals,
producing static electricity. The electricity in the clouds attracts an opposite charge from the
earth. This charge in the ground sends "leaders" toward the cloud charge. These leaders are
what cause your hair to stand up (the last warning you'll get) and are the reason that lightning
is considered to go from earth to sky. The lightning bolt you see is the "return stroke". A lightning
rod system provides a safe path for the upward leaders, and then the return strokes.
The grounding system
provides a low resistance connection to the earth. Northeastern U.S. soils are some of the most
difficult to work with. Granite bedrock, shale, gravel backfill (where most electrical system ground
rods are driven), and most sand is of very high resistance. High current lightning on a ground
rod in sand can cause the rod to be coated with glass, creating even more resistance. Wet clay
is ideal for grounding, but is not a material you want near the foundation of your building. Soils can
be tested for the design of a grounding system and the completed system can be tested to assure
that it will be effective. Foundations in holes blasted from rock can be grounded with a cable that
encircles the foundation (counterpoise), providing a cost-effective solution if planned before construction,
or added later with narrow trenching machines and hand trenching. Copper plates, deep sectional rods,
chemical grounds, conductive concrete, and other methods can also be used for various conditions.
Keep in mind that surge suppressors connected to a poor grounding system are of little, if any, value.
One of several conductive concrete grounding electrodes for a communication tower.
can be neatly attached to less noticeable exterior areas of finished buildings, in attics, under shingles, or
completely concealed during construction. Chimney cables can be concealed in the exterior
portions of chimneys during construction. Flat strip or solid rod conductors are sometimes used.
Copper cables can be tinned or lead coated for certain applications, and other circumstances require
aluminum materials. Codes and installation standards dictate how conductors must be installed, allowable
bends, and other restrictions. Acid rain can exacerbate galvanic reactions between dissimilar metals and
must be considered to prevent corrosion.
Counterpoise grounding cables encircle this foundation built in hole blasted from ledge.
of metal building components, water and gas piping systems, and other grounding systems
within and near a protected building prevents "sideflash" and allows control of the lightning
energy until it is safely dissipated in the earth.
(also called air terminals) must be mounted in locations determined by codes and
architectural considerations. A typical rod is only ten inches high, but decorative finials, and
the older style tripods and glass balls are also available. Protection for lower areas can often
be accomplished by placing rods at higher, less noticeable locations. Rods needed in areas
with traffic can be disguised as architectural elements, such as the lighthouse lightning rods shown
here. Weathervanes can be adapted for use as lightning rods, and Priestley has made many custom
lightning rods and weathervanes for customers from copper, brass, bronze, and stainless steel.
Some are shown below.
Here, replicas of the Lake Sunapee lighthouse are used as lightning rods on the 2nd-floor deck of a Lake Sunapee home.
are a critical component of lightning protection systems, but are often overlooked by many installers
who protect only the main power service. All wires that enter a building can provide paths for lightning.
Wires between buildings can create additional problems by creating "ground loops". Some examples of
cables that require protection include those which connect to power, telephone, cable TV, satellite
dishes, antennas, irrigation controls, electric gates, wells, fire pumps, surveilance cameras, landscape
lighting, remote outdoor receptacles, swimming pools, and generators. Automatic transfer switches often
require additional protection as they won't be protected by a suppressor on the main panel. The need
for Plug-in suppressors and uninterruptible power supplies should also be considered.
are considered by some as offering protection from lightning, but this theory is poorly thought out.
Softwood trees often explode into piles of splinters, while hardwoods often split. If the
tree is near a building, the lightning often "sideflashes" to the building, the tree could
fall on the building, or at the very least, a beautiful tree that required many years to
grow will die, requiring expensive removal. Valuable trees can be protected, and in fact,
the NFPA-780 Lightning Protection Standard recommends protecting any tree within
ten feet of a protected building. Valuable trees located anywhere on the property should
be considered as candidates for protection. Also consider that trees make dangerous
supports for metal clothesline cables and dog runs that connect to the house.
A direct strike to the tree will follow the cable to the house, and even nearby strikes will
induce a charge into the cable that will be immediately felt by any dog that happens to be
connected to the run.
of all Priestley Lightning Protection systems is provided by Underwriters Laboratories(UL), with a
Master Label Certificate. Beware of installers that say all of their materials are UL Listed (big deal)
or installers that are UL Listed, but then don't provide the inspection and certification. In recent
years UL has been issuing relatively meaningless certificates with "Surge Exemptions", which was a
sad, inept, temporary "solution" to a problem created by UL, with no end in sight. Priestley recommends
that you insist on a UL Master Label certification without surge exemption. Priestley considers the
many national and international installation standards to be minimum requirements that are applied
as a starting point when designing each particular system. Priestley often starts a system on a new
building during the excavation/foundation stage, coordinates with all other subcontractors during
construction, and doesn't finalize the system until people move in and all other systems are completed.
for lightning protection systems can vary widely depending on building size and complexity, soil around
the building, volatile metal prices, and other factors. A rough cost can be obtained by multiplying the
finished square foot area of a building by $2-$3. Firm quotes can be supplied if you send drawings and
or photos, or with a site visit.
are available to assess vulnerability to lightning damage for a particular building, solve existing
lightning related problems, and propose options to prevent future problems. Cost would be determined
by size of building/campus, electrical/electronic systems within the building(s), location, etc. Please
contact Priestley by using the information available on the Contact page.
Custom copper light fixture made by Priestley - Apx. 24" diameter.