The protection of electrical devices, elements of electrical installations and even the entire electrical power system is a very important branch of electrical engineering. The most common cause of electronic system failures are overvoltages that are superimposed on the operating signal, and reach the device and can cause its damage. The most common cause of overvoltage in electrical installations is atmospheric discharge, i.e. lightning strikes. Overvoltage protection used in electrical installations is a three-stage protection. The role of overvoltage protection devices is to protect electrical and electronic equipment and installations. Properly installed and coordinated external and internal lightning protection will successfully protect electrical installations and devices from overvoltages. In facilities connected to the low-voltage network, it is not necessary to install class I overvoltage protection devices, but a class II device installed behind the fuse and before the meter is sufficient. Class III overvoltage protection devices in overvoltage protection are installed by the owner of the facility himself. The diploma thesis explains the basic concepts and examines the issues of overvoltage protection at low voltage. The results of this thesis show how protection works in the event of overvoltage.