A lightning arrester or lightning arrestor also known as a lightning diverter is a device that is used on many electrical and telecommunication systems to protect it against the damage caused by lightning strikes. Typically most lightning arrester setups feature both a high-voltage and a ground terminal. When a lightning surge occurs in the power line to the lightning arrester, the surge current is diverted through the arrester to the ground in most cases.
In telegraphy/telephony, a lightning arrester is installed where the wires enter a structure, this will prevent damage to electronic components on the inside and ensure the safety of the individuals in a close proximity to them. Surge protectors are the smaller versions of lightning arresters. These devices are connected between electrical conductors in the power, communications systems and the ground. They prevent the flow of the normal currents to ground, while providing a path for the high-voltage lightning current to flow, bypassing all of the connected equipment. The purpose of these devices are to limit the rise in voltage when a line is struck by lightning or is nearby a lightning strike.
If for whatever reason the protection fails or is absent, lightning strikes the electrical systems and introduces thousands of kilovolts that can damage the lines, and will most likely also cause severe damage to transformers and other electronic items. Lightning strikes produces extreme voltage spikes in power lines can damage electrical home appliances and in severe cases be the cause of death.
Lightning arresters are also used to protect electric fences and consist of a spark gap or sometimes a series inductor. Lightning arresters can also be a component in large electrical transformers which can be fragment during transformer ruptures or lightning strikes.