Lightning Protection

Notes on lightening protection for GCSE double award science electricity

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Lightning Protection
The National Board of Fire Underwriters reports that lightning is the number one
cause of farm fires. Lightning is also responsible for more than 80% of all livestock
losses due to accidents and millions of dollars in damage to farm buildings and
equipment annually.
A system that protects your family, livestock and farm
property from lightning strikes prevents or significantly
reduces these dangers. Lightning protection systems should
be installed only by qualified individuals who have the
necessary credentials and equipment. However, a working
knowledge of the principles of lightning protection will help
you to communicate with these experts and oversee the
proper maintenance of your system once installed.
A Quick Primer
Lightning is an uncontrolled, massive electric spark with tremendous voltage
and amperage.
Lightning always tries to follow the shortest, easiest path to earth, and often
follows several paths simultaneously.
The basic principle of lightning protection is to provide a direct, easy path for
the lightning bolt to enter or leave the earth without passing through a
nonmetallic or nonconducting part of the structure or other object.
An effective lightning protection system includes many essential parts.
Generally, a protection system for buildings must include air terminals, down
conductors, secondary conductors, arresters and ground connections, with all
system components linked together.
The most reliable choice is a Master Label System that meets minimum
requirements established by Underwriter Laboratories Inc. (U.L).
How Lightning Behaves
Lightning is a visible discharge of static charges that can occur within a cloud,
between clouds or between a cloud and the earth. A buildup of opposite charges
(one negative and one positive) separated by an insulating air gap can cause the
charges to rush toward each other, producing a sudden release of energy. A lightning
discharge will have 10,000,000100,000,000 Volts and 1,000300,000 Amperage. A
bolt packs so much voltage that it may leap a mile or more through the air. Lightning
strikes buildings or other objects because the materials in them provide easier paths
to ground than the air. Lightning is more likely to strike on projecting objects such as
tress, poles, wires or building steeples than on larger, flatter surfaces projecting to the
same height or lower. Lone buildings are also primary targets.
When a lightning bolt uses a building or other object as an electrical conductor, it
generally follows a metallic path to the ground. "Sideflashes" may also occur when
current leaps from its main path to the plumbing, appliances, water lines, a person or
an animal. Sideflashes are dangerous because they can ignite a fire or cause
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Lightning can enter a building through a direct strike, by striking a metal
object attached to the building, by leaping over to the building after striking a nearby
tree, or by following a power line or ungrounded wire fence attached to a building.
Utility distribution systems use multiple groundings per mile and other protective
devices to help dissipate lightning strikes and send them to the earth.…read more

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