Lightning arresters are important transmission and distribution system protective devices, especially in geographic areas prone to large amounts of lightning. Arresters channel the high voltage and current from lightning that strikes the electrical system into the earth before it can cause major damage to the distribution system and equipment.
Lightning arresters can be made from a variety of components and function similar to a switch, either preventing or allowing electrical flow through them. To do this, a lightning arrester uses semi-conductor materials that act like conductors under some conditions and insulators under other conditions. At normal line voltage the device acts like a high resistance open switch so that electricity cannot flow through it and must stay in the distribution conductors where it normally belongs.
Once a lightning strike hits the distribution system, however, the higher than normal voltage causes the lightning arrestor material to become a conductor and provides an easy, purpose-designed path for the lightning to flow from the distribution system conductors into the earth. Once the energy from the lightning strike leaves the system and the voltage returns to normal levels, the components inside the arrester again act like an open switch thus removing the temporary path to the earth.