|The image is from Lightning Prevention Systems, Inc. in New Jersey a state that has only about 45,000 lightning strikes a year|
Though summer is the peak season for lightning, it does strike year round. According to the National Oceanic and Atmospheric Administration (NOAA) 25 million cloud-to-ground lightning strikes occur in the United States each year. Generally speaking lightning strikes are geographically concentrated in the southeast, south and mid-west. Until we moved to Virginia (with an annual average of 344,702 lightning strikes a year) from California, I had not thought much about lightning. Texas is that state with the most lightning strikes a year averaging almost 3 million a year and much smaller Florida 1.4 million strikes a year! The creation of lightning is a complicated process. According to NOAA we know what conditions are needed to produce lightning, but there is still debate about exactly how lightning forms. The exact way a cloud builds up the electrical charges that lead to lightning is not completely understood. A channel of negative charge, called a step leader, shoots to the ground in a zigzag of roughly 50-yard segments in a forked pattern. As it nears the ground, the negatively charged step leader is attracted to a channel of positive charge from the earth reaching up, a streamer, normally through something tall, such as a tree, house, or telephone pole. When the oppositely-charged leader and streamer connect, a powerful electrical current begins flowing. A flash can consist of one or as many as 20 return strokes.
Cloud to ground (CG) discharges, are the most common, but there are other known types of lightning that have no channel to ground. These cloud discharges are classified as in-cloud (IC), cloud to air (CA), or cloud to cloud (CC). There is also lightning that originates at the top of the thunderstorm. This area carries a large positive charge. Lightning from this area is called positive lightning that frequently strikes away from the rain core, either ahead or behind the thunderstorm. It can strike as far as 5 or 10 miles from the storm, and is it typically has a longer duration, so fires are more easily ignited. Positive lightning usually carries a high peak electrical current, which is more likely to kill.
The air within a lightning strike can reach 50,000 degrees Fahrenheit, and one ground lightning stroke can generate between 100 million and 1 billion volts of electricity. Lightning is a major cause of building fires, even though highly effective (though not perfect) protection has long been available. In the 1700s Benjamin Franklin (remember the kite and key story) proposed a method of protecting structures from the effects of lightning using elevated rods and down-conductors. His ideas were furthered by the work of Nikola Tesla, Michael Faraday and other scientists to develop and document successful designs. In 1904, The National Fire Protection Association, NFPA, established the American standard for installation of lightning protection systems now known as NFPA 780- the Standard for the Installation of Lightning Protection Systems. Historical documentation shows that fire losses to protected buildings were between 1.3%-7% of the damage to unprotected buildings during the first two decades of the twentieth century as the standard developed and our knowledge increased. Experience of the fire-insurance companies showed that if buildings were properly "rodded", they would be practically safe from damage by lightning. Remember this is based on statistics lightning is most likely to hit the highest object, and is also more likely to strike something with a good path to ground, such as a lightning protection system.
Installation of such a system in conformance with NFPA 780 is not a simple matter and can cost thousands of dollars depending on the size and shape of the house. Whether it makes economic sense for you depends on many factors such as location, value of the property in dollars and sentiment, insurance and the amount of the deductible, what you can afford and how you feel about lightning. My husband and his brother who grew up in the same house that was struck by lightning came to different decisions. To provide effective protection for structures, a lightning protection system must include a sufficient number of rods with tips exposed and extending above the structure. These lightning rods, now called air terminals become the preferred strike receptor for a descending step leader from the thundercloud. That rapidly-varying lightning current must then be carried away from the building into the earth through a down conductor system, that will provide the path of least resistance and impedance to the flow of current must be so low that "side flashes" to other objects in the vicinity of the system do not occur. It is essential that the system is designed to prevent it from heating or dislodging from the structure by the force of the power surge. All nearby metal components of the structure (solar panels, generator, roof vents, water and sewer pipes etc.) must be properly connected to the down-conductor system to minimize the probability of side flashes and ensure the flow of current to the earth. The connections from the down conductors to the earth must allow the lightning current to flow into the ground without the development of large electrical potential differences on the earth's surface and without creating other hazards.
To verify that an existing system is designed and installed correctly you could have it certified. Certification of a lightning protections system assures that the system meets the standards set forth by NFPA 780 and the Underwriter's Laboratories (UL 96A). If like me you are going to install a lightning protection system make sure your designer and installer has at least his Journeyman Installers certification from the Lightning Protection Institute, LPI and/or certified by Underwriters Laboratories. Journeyman Installers must pass two levels of tests for LPI Certification. Master Installers must pass a series of four tests, and carry a brass card issued by LPI. Annual re-testing is required for continued certification. There is also a Master Installer and Designer designation- that might be the best choice. You can go the LPI web site to obtain a list of certified installers in your area. Likewise you can go to the Underwriters Laboratories website for a list of certified installers. Many counties do not require a building permit to install a lightning protection system. Without the help of the county building department staff you will have to make sure that your system is designed and installed in conformance with NFPA 780 or UL96A there are differences between the standards, but they are similar in many ways. The American Society for Agricultural Engineers (ASAE) Standards also has specification for lightning protection though they are geared to farms, the principals are the same. ASAE develops and publishes consensus standards for agricultural tractors and machinery, agricultural structures, turf and landscape equipment, irrigation and drainage equipment and systems, environmental aspects of food production and resources management. In addition, you might want to take a look at other installation jobs and make sure that they are as unobtrusive as possible. Aluminum cables are likely going to be run across your roof and down the sides of your house in addition to installing a rod on every gable and at least every 20 feet along a roof span. Check for a valid contractor’s license, references and the Better Business Bureau.
Though copper with 98% conductivity when annealed, is the preferred material for lightning protection on farm structures. Alloyed metals are typically used today. Aluminum while having only 59% the conductivity of copper is acceptable as a substitute for copper in lightning protection when electrical grade aluminum is used. Aluminum is subject to corrosion by ocean air or soil, but resistance in other environments can be excellent due to a thin surface layer of aluminum oxide that forms when the metal is exposed to air, effectively preventing further oxidation. Aluminum is preferred on structures with aluminum trim to prevent corrosion from the reaction of the aluminum coming in contact with copper wires- add rain to copper and aluminum and you are making a battery.
The lightning protection system must terminate into the earth to dissipate the charge using a copper clad steel cable. The slightly acidic nature of the soil will corrode the aluminum and impede system performance. The choice of material used on the structure is based on cost, and the other materials of construction- copper has less resistance than aluminum, but can have other problems other than cost. The down conductors should be as widely separated as possible and each building must have at least two, but there should be at least one down conductor for each 100 feet of perimeter. Usually aluminum is used against the house because copper gutters are not as common these days, aluminum is much cheaper and so bi-metal connectors must be used to make the transitions into the copper clad steel cable in the earth to assure proper grounding and dissipation of the lightning. Also bi-metal transition connectors must be used if the air terminals are copper. Underground metallic piping, including water piping, well casings, sewer and septic lines must be considered in the design or they are potential points of failure. Lightning arresters should also be installed on the lead-in wire or cable for the electrical supply and bonded to the lightning protection system directly or through a common ground. NOVEC, my power company, offers to install and maintain a “collar” system at the electrical meter for $10 per month or you can purchase separate surge protectors.
In summary, all the science and experience of century prove that properly designed and installed lightning protection systems work, though there is still some dispute about the most effective design theory. Each year, lightning is the cause of an estimated 17,400 fires 55% of which occur outdoors, and 41% occur inside structures. According to Federal Emergency Management Agency, FEMA, dollar loss per fire is nearly twice that from all U.S. fires and in 1998 that was around $10,000 and probably close to double that now. Roofs, sidewalls, framing, and electrical wires are the areas most ignited by lightning fires. Though a lightning protection system will have little or no effect on how likely it is that lightning will strike in the immediate area, the energy will be conducted directly to ground, without having to go through your house, its internal wiring and electrical equipment and appliances. Whether it makes sense to install one is an economic decision based on where you live, your insurance deductible and other factors. Our very high insurance deductible combined with the irreplaceable paper book collection that is the centerpiece of our lives would not survive a fire caused by a lightning strike or the water and mold associated with fire response. So, even with a cost of thousands of dollars, we will install one here in Virginia.