Lightning rod: Encyclopedia II - Lightning rod - Arrestors

Lightning rod - Arrestors

A lightning arrestor is a device that shunts or diverts the massive voltage and electrical current of a lightning strike to an earthed ground. Electrical equipment can be protected from lightning by an arrester, a device that contains one or more gas-filled spark gaps between the equipment's cables and earth. An arrester is designed to handle much higher jolts of electricity than a surge protector, which cannot handle a direct strike at all.

Should lightning strike a building, the current will travel through the conductor rather than through the fabric of the building, causing less damage. Should lightning strike one of the cables, the high voltage will cause the gas in the spark gap to break down and become a conductor, providing a path for the lightning to reach the ground without passing through the equipment. It typically involves a spark gap, across which a normal voltage cannot arc.

When lightning exceeds the arrestor's breakdown voltage, the currents arcs to the ground and prevents arcing around inside sensitive electronic equipment connected further downline. The spark gap may be filled with a noble gas, or with air. Other types may work by blocking normal alternating current (AC), but allowing the direct current (DC) from a lightning discharge.

Lightning arrestors are typically installed on electric power transmission lines, and on radio tower feedlines between the radio antenna and transmitter. Smaller ones can also be installed on the mains electricity service coming into a building (even a home), just before the circuit breaker panel. Telephone wires also have fusible links sometimes where they enter a building, connected by carbon which will vaporize with very high current.

Adapted from the Wikipedia article "Arrestors", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki