Lightning strikes can cause serious damage to structures as well as cause injury or even death. Strikes can be hotter than the surface of the sun and can cause fire with heat sensitive materials such as wood. In order to protect people and property, protection systems have been developed to guide high voltage strikes away from individuals and electrically sensitive structures and materials.
Lightning Rod or Air Terminal Systems
During a strike, the high voltage always takes the path of least resistance from the air to the ground. Damage results when persons or property are part of this low resistance path. The main piece of any type of lightning protection system is the lightning rod or air terminal. The purpose of the air terminal is to intercept lightning strikes and provide a path to ground. Typically, copper or aluminum air terminals are installed on the roof of the structure and connected to ground electrodes (ground rod) buried in the Earth with conductor cable (wire). Instead of a lightning strike hitting the structure and damaging the people and items inside, the air terminals are hit, and the high voltage travels along the conductor cable and into the earth. This kind of system, known as the Franklin System, can be implemented using one air terminal or several that are connected to form a protective mesh around the structure (Faraday Cage).
Structures are also vulnerable from strikes that happen away from the structure and travel along the electrical or telephone lines into the building. A surge protector is a special device placed at electrical connections between the structure and the grid. When high voltage is detected, a switch is tripped, and the electrical equipment is bypassed. The high voltage is instead diverted to the earth via a ground wire instead of traveling into the structure.
Care must continue to be given to these protection systems after the initial install, or their effectiveness will be drastically reduced. Air terminals and ground terminals are subject to corrosion which is electrically non-conductive. If either terminal becomes corroded and offers too much electrical resistance, strikes will take an easier path to earth potentially through building or through electrically sensitive equipment. The ground wire also must be periodically checked for breaks or obstructions. Current could arc over or around such a break and possibly find a new path to the earth that travels into the building.
Northeast Lightning Protection has been installing lightning protection systems, including lightning rods in Connecticut (CT), Massachusetts (MA), New York (NY), New Hampshire (NH), Vermont (VT) and Rhode Island (RI) since 1976.