Why You Need Lightning
Protection:
Lightning protection systems have changed drastically since Benjamin Franklin
first invented lighting rods in 1752. Today's systems must protect modern
appliances, electrical systems and building constructions - they have to keep up
with tile changing requirements of modern technology.
Computers, high-end home theater systems and DVRs, either received as part of
special
Comcast promotions or
purchased outright, are expensive equipment that need to be protected with
quality surge suppressors from the dangerous effects of lightning.
Underwriters Laboratories Inc. (UL) keeps up with these changes. Our
experience in the safety testing field has earned UL worldwide recognition and
respect jurisdictional authorities, government agencies, insurance
representatives and
consumers
alike have looked for the UL Mark on products and systems for almost100 years.
When you see the Mark, it means that the product or system on which it appears
compares with UL's internationally recognized Standards for Safety.
In the lighting protection field, UL has been serving home and building
owners since 1908. Today, UL has a large number of trained lighting protection
field representatives located throughout tile United States. UL inspects sites
ranging from cow barns to missile silos, front golf Course shelters to high-rise
building systems. In fact, some of the most famous buildings in the world are
protected by UL Master Labeled lightning protection systems, including the White
House, the Sears Tower and the Washington Monument.
The Need for Lightning
Protection:
Lightning can strike anywhere on earth - event the North and South Poles! In
any U.S. geographical location, lightning storms occur as few as five times or
as many as 100 times per year (see Fig. 1). The Northeast United States has the
most violent thunderstorms in the country because of the area's extremely high
earth resistivity. High earth resistivity (the earth's resistance to conduct
current) increases the potential of a lightning strike. (See fig. 2)If struck,
structures in these areas will generally sustain more damage when there is no
lightning protection system present.
Each year, thousands of
homes and other properties
are damaged or destroyed by lightning. It accounts for more than a quarter
billion dollars in property damage annually in the United States. Lightning is
responsible for more deaths and property loss than tornadoes, hurricanes and
floods combined, but of these violent forces of nature, lightning is the only
one we call economically afford to protect ourselves against.
Some properties have a higher risk of lightning damage. When considering
installation of a lightning protection system, you may want to assess this risk.
A risk assessment guide for determining lightning loss for all types of
structures can be found in Appendix I of the National Fire Protection
Association's Lightning Protection Code, NFPA 780. This guide takes into
consideration the type of structure, type of construction, structure location,
topography, occupancy, contents and lightning frequency. Information may be
obtained from tile NFPA, I Batterymarch Park, Quincy, MA, 02269, (800)
344-3555.
How a Lightning Protection System
Works:
Lightning is the visible discharge of static electricity within a cloud,
between clouds, or between tile earth and a cloud. Scientists still do not fully
understand what causes lightning, but most experts believe that different kinds
of ice interact in a cloud. Updrafts in the clouds separate charges so that
positive charges moves end up at the top of the cloud while negative flow to the
bottom. When the negative charge moves down, a "pilot leader" forms. 'This
leader rushes toward the earth in 150-foot discrete steps, ionizing a path in
the air. 'The final breakdown generally occurs to a high object the major part
of the lightning discharge current is then carried in the return stroke which
flows along the ionized path.
A lighting protection system provides a means by which this discharge may
enter or leave earth without passing through and damaging non-conducting parts
of a structure, such as those made of wood, brick, tile of- concrete. A
lightning protection system does not prevent lightning from striking; it
provides a means for controlling it and preventing damage by providing a low
resistance path for the discharge of lightning energy.
FIG. 3 Lightning protection system for a dwelling: 1) air
terminals spaced 20 feet apart along ridges and within two feet of ridge ends;
2) down conductors; 3) minimum of two groundings at least 10-feet
deep; 4) roof projections such as weather vanes connected to system;
5) air terminal located within two feet of outside corners of chimney;
6) dormers protected; 7) antenna mast connected to roof
conductor:- 8) connect gutters or other grounded metals as required;
9) surge arrester installed at service panel to protect appliances;
10) transient voltage surge suppressors installed in receptacles to which
computers and other electronic equipment are connected.
FIG. 4
Lightning protection system commercial/industrial installation 1) air
terminals spaced 20 feet apart around the perimeter of the building; 2)
down conductors; 3) ground rods at least 10-feet deep; 4) art
handling units bonded to system (may be in need of air terminals mounted on
unit); 5) air terminals mounted within two feet of outside corner;
6) mid-roof conductor and air terminals at maximum 50-foot spacing;
7) grounded metal bodies bonded into system; 8) surge arresters
installed at main electrical panels; 9) transient voltage surge suppressors
installed in receptacles to protect computers and other office
equipment.