Any device designed to carry to the ground (to “ground”) the short-duration surge currents that appear on power lines and telephone lines during severe thunderstorms. Early forms of arresters consisted merely of spark gaps to ground, but in cases where the circuit power maintained the spark after termination of the surge, service could only be restored by momentarily shutting off circuit power. Hence, more elaborate arresters have been developed, especially for high-voltage lines, with features to ensure that the circuit power will not maintain the ground circuit after the surge dies out. Compare lightning rod.