Are lightning rods adequate protection?
Our old barn has three lightning rods with glass balls, but our house has none. The barn is taller, so would this attract lightning away from the house?
Although your barn may be closer to the sky than your house, lightning strikes are known to be unpredictable. While taller objects have a higher possibility of receiving strikes, there have been countless times when lightning has chosen a less likely path. Before cloud-to-ground lightning occurs, paths of ionized air called "leaders" stretch toward the earth from the cloud. As the leaders near grounded objects, the objects release ions called "streamers".
When the streamers reach up and meet the leaders, the conductive path is complete for the cloud to discharge electricity directly to ground. Lightning rods don't really attract lightning--but properly installed--they provide a path to ground with less resistance than other nearby objects. This can prevent the massive, harmful electrical current from damaging buildings.
Components of a lighting protection system
There is more to a proper lightning protection system than sticking a few pointy rods on a roof.
Air Terminals. "Air terminals" are the official name for lightning rods. Each terminal is considered to be providing a zone of protection to a portion of a building. How many terminals and how far apart is determined by the type and slope of the roof.
Main Conductors. "Main conductors" are the cables that interconnect all air terminals and form the path to the grounding rod. They are usually braided copper and sometimes aluminum
Grounding Electrodes. "Grounding Electrodes" are the rods driven into the ground, that deliver the surge of electrical current safely into the earth. Typically two separate grounding electrodes are required for one system. In areas where soil conditions don't provide a good ground, the spacing between electrodes might be reduced, the conductor size increased or supplemental electrodes using large rings or plates can be used.
Bonding. "Bonding" is the joining of the lightening protection system with other conductive systems in a building with additional conductors. This helps prevent "side flashing" of electricity from the lightning system to other components.
Surge Protectors. "Surge protectors" or "surge suppressors" are installed to protect against surges of excess voltage that might enter the electrical system from the utility power lines. Although not visible on the exterior, and not intended to redirect a lightning strike's damage to the structure, it is still a part of a complete lightning protection system. It's more important now then ever with all the appliances and electronics we've installed in our homes.
Getting lightning protection correct
Older systems are often not installed to today's well-researched standards. It is not unusual to find that remodeling or additions to an older home have altered the original lightning protection design, resulting in an ineffective system. Buying properties with existing systems does not mean they are adequate or installed by trained professionals and pre-purchase general home inspection usually excludes ancillary systems, like lightning protection systems. Very few electricians are trained and certified to install or inspect entire lightning protection systems.
Since the early 1970s, the Lightning Protection Institute has had a certification program for installers, designers and inspectors. Underwriters Laboratories® (UL), known for testing and approving electrical system components and devices, also has a program for certifying lightning protection system installations.
William Kibbel III is a home inspector and restoration consultant specializing in historic residential and commercial buildings. He is vice president of Tri-County Inspection Company serving Southeastern Pennsylvania and Central New Jersey.