Overview

An electrical surge is a sudden strong rise in voltage that can appear on power and communications lines entering homes, offices, and other facilities. Surges caused by natural or manmade actions can easily destroy or disable any unprotected electronic equipment connected to the power or communication lines. Electronic products that are especially vulnerable to surges include microprocessors or microcontrollers, such as computers, TV sets, stereo systems, cordless telephones, and fax machines.

A succession of weak surges, powerful enough to stress but not destroy or disable electronic components or circuitry in a single event, can cause the performance of electronic equipment to deteriorate over time. Repeated overvoltages reduce the working lives of both active and passive circuit components by as much as 50 percent. They can also cause the insulation of wires to become brittle because of repeated abnormal heating cycles. Even robust electrical and electromechanical components such as lamps and motors can be degraded from the cumulative effects of surges, so the problem is not confined to electronic circuits.

The highest-magnitude surges are caused by lightning strikes on or near power lines, but destructive surges can also be caused by the on/off line switching of an electric utility's generators, a failure in a transformer, or some malfunction in other distribution equipment. Electrical surges can also be caused by the showers of charged particles from solar flares that enter the atmosphere. They have disabled extensive electric power distribution networks in the recent past.

Electric utilities install surge protective devices on...