The Nuts and Bolts of Lightning Protection
Lightning is perhaps the most spectacular display of the awesome force and raw power of nature. According to the National Severe Storm Laboratory, lightning is the most dangerous and frequently-encountered weather hazard that most people experience each year.
- A single bolt of lightning can carry over 30 million volts of electricity.
- A direct strike to a structure can rip through roofs and chimneys, explode brick and concrete and ignite fires.
- An indirect or secondary lightning strike to a nearby tree or power line can induce unwanted surges into a home.
- Lightning can also enter through phone, cable lines and computer modems, as well as roof projections such as weather vanes, antennas and satellite dishes.
- Home extras like irrigation systems, invisible fences and electric gates can provide a low-resistance pathway for lightning’s destructive energy.
Thunderstorms Result from a Ground/Air Attraction
Thunderstorms result from the powerful clash between cold and warm weather air masses. A cloud to ground lightning strike begins as an invisible channel of electrically charged ions moves from the cloud toward the ground. When one channel nears an object on the ground, a powerful surge of ions from the ground moves upward toward the cloud and produces the visible lightning strike. This interchange of oppositely charged ions from cloud to ground results in lightning striking buildings, chimneys, trees and even humans as these charges try to meet.
A lightning protection system is designed to control or force the discharge onto a specified path, thereby eliminating the chance of fire or explosion within non-conductive parts of the house such as those made of wood, brick, tile, etc. A lightning protection system is not intended to prevent a strike. Its purpose is to provide a safe path on which the current can be safely directed to the ground.
Each year thousands of home and other properties are destroyed or damaged by lightning strikes. Unprotected homes risk the possibility of damage by fire, explosion or electrical surges and pose a safety risk to occupants. The effects of a lightning strike can be both physically and emotionally devastating.
Protecting Your Home
Protecting your home is a matter of contacting a professional who is qualified to design and install a certified lightning protection system. Lightning protection is not a do-it-yourself project. Only experienced and reputable Underwriters Laboratories (UL) listed and Lightning Protection Institute (LPI) certified lightning protection contractors should install these systems. Qualified specialists use UL-listed materials and ensure that methods of installation comply with nationally recognized safety standards of LPI, UL and the National Fire Protection Association (NFPA).
A complete lightning protection system is typically made up of the following components:
- Air terminals – Also referred to as lightning rods, these inconspicuous copper or aluminum rods are vertically mounted on the roof at regular intervals. The air terminals serve as strike receptors, designed to intercept the lightning strike.
- Main conductors – Constructed of aluminum or copper, these braided cables connect the air terminals to the other system components and the grounds.
- Grounds – A minimum of two ground rods, driven at least 10 feet deep in the earth are required for all structures. The ground terminations direct the dangerous current into the ground, to eliminate the chance of injury or damage to the structure.
- Bonds – Bonding joins metallic bodies (roof components) and grounded building systems to the main conductor to ensure conductivity and prevent side flashing (lightning jumping between two objects).
- Surge Arresters and Suppressors – A surge is an increase in electrical current due to a lightning strike on or near a power line or utility service. Surge suppression is installed at the electrical panel(s) to prevent the entrance of overvoltages which can cause a fire. Arresters installed at electrical panels help protect heavy appliances and prevent fires at service panel entrances. Additional devices may be needed to protect other in-house electronics. Surge protection devices are typically installed in conjunction with a lightning protection system.
- Tree Protection – The Lightning Protection Institute recommends that any tree taller than a home or within 10 feet of the structure be equipped with a lightning protection system. Trees do not offer protection and many homeowners choose to have trees protected for their own value. An unprotected tree in close proximity to a structure can also create a side-flash hazard to the nearby home.