Why does electricity surge?
Alan Mantooth, professor of electrical engineering in the College of Engineering, replies:
Electricity surges for one of a couple of reasons. The first reason a surge may occur is when an electrical cable or line is struck by lightning. This electrical discharge causes a surge to travel down the line until it finds a ground connection. A second cause of an electrical surge is when a large device, say an industrial motor, suddenly turns on or off. This sudden demand for additional power -- when turned on -- may cause the voltage on the line to sag or droop. Conversely, when the motor is shut off the voltage or current may surge or rise on the line. These sags or surges can damage other equipment. Another reason for a surge would be due to a sudden outage in an area that causes the surrounding areas still with power to experience a surge.