Alightning arrester(alternative spellinglightning arrestor) (also calledlightning diverter) is a device used onelectric powersystems andtelecommunicationsystems to protect theinsulationand conductors of the system from the damaging effects oflightning. The typical lightning arrester has ahigh-voltageterminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrester, in most cases to earth.