Surge

A lightning surge is a type of external surge caused by lightning. When electric charge accumulates within a thundercloud to a level that exceeds the limit of adiabatic compression by the atmosphere, a discharge occurs between the cloud and the ground, or between clouds. The electric current is said to reach 20-150kA. An extremely high voltage generated by a direct lightning discharge that applies to power lines or communication cables is called a "direct lightning surge." In contrast, a voltage induced by electrostatic or electromagnetic induction in cables near the lightning strike point is called an "induced lightning surge." Additionally, if lightning strikes a lightning rod and raises the ground potential, the grounding potential of equipment also increases. This may result in an abnormally large difference between the cable and the ground, which is referred to as a "lightning surge due to ground potential rise." The energy of a direct lightning surge is extraordinarily large, and a surge protector alone cannot protect equipment. Some devices adopt a countermeasure by absorbing most of the energy through both a lightning rod and an overhead ground wire, and absorbing the remaining energy with a surge protector.