Lightning protection systems prevent the effects of lightning strikes, primarily by protecting the health and lives of people and electrical equipment from damage. Earth electrodes are installed in the ground, on the outside of the building, also in concealed locations. The condition of the earthing system should feature the lowest possible electrical resistance in order to efficiently discharge the input electricity to earth. In addition to earthing components (earth electrodes), the lightning protection system also includes surge arresters to protect domestic or office equipment from transient surges. Depending on the equipment to be protected, surge arresters are divided into classes A, B, C and D (sequentially from the highest surge values, like those emerging on overhead lines, to the lowest surge levels, for very sensitive equipment).