In certain areas which have frequent lightning strikes, it is worthwhile to outfit your home with a lightning protection system. This is not a job for the average do-it-yourselfer, and even a professional electrician needs to have specialized training to properly install a system. Manufacturers of lightning protection equipment will only sell to certified installers.
The basic idea of a residential lightning protection system is to give a path by which the high voltage electrical discharges accompanying lightning can pass from the atmosphere to the ground without traveling through parts of your house. The electricity that lightning generates is on the order of thirty million volts and twenty five thousand amps; needless to say it can cause quite a bit of damage to the non-conducting materials in a home such as concrete, brick, masonry and wood. It will also do a good job of ruining home electronic and electrical equipment, wiring, computers, appliances and lighting.
A lighting protection system is comprised of three components; air terminals, ground terminals and conductors between the two. Air terminals are also known as lightning rods. They consist of vertical rods of aluminum, copper or copper alloy, ten inches long or more, mounted on the highest portions of a building, normally the roof. There is usually one air terminal every twenty five feet or so on the roof, plus one on projecting areas like the chimney or dormers.
Each air terminal is connected to a conducting cable of braided copper or aluminum. The conductors pass the electrical energy from any lightning striking the air terminal to the ground terminals. There are specific rules for laying out the conductor run, such as minimum radius of bends in the cable and maximum angle of bends, to avoid having the electrical charge jump around sharp corners and into the house structure, which the installer must follow.
The conductors connect at the other end to the ground terminals, plates or rods of copper or aluminum, buried in the ground. It is standard practice to have at least one ground terminal at each end of the house, at opposing diagonal corners from each other. They should enter the ground at least two feet away from the house.
Depending on the soil type, and size and shape of the house, type and number of ground terminals, and how deep they are buried varies. A depth of ten feet down for a copper-sheathed steel ground terminal rod is common.
In addition to lightning protection for your house, you should also consider installing protection in any trees that are less than ten feet from it and higher than the house. Another lightning protection feature is to install a secondary surge protector.
This is a device that your utility company can install in your service breaker box or on the power lines leading to the house. It’s purpose is to isolate your home’s electrical system from power surges caused by lightning strikes on the power lines in the vicinity of your house.
To locate a certified installer in your area, you can consult the local fire department or fire marshal. For more information, contact the Lightning Protection Institute, or the Underwriters Laboratories Master Label Lightning Protection Program.