Description
Surge arresters are an important addition to the protection of an electrical installation. They protect electrical equipment against serious damage caused by overvoltages of atmospheric origin (lightning).
Surge arresters are devices that limit the effects of atmospheric overvoltages with frequencies of the order of several MHz whose peak value exceeds the maximum operating voltage of the installation. Such overvoltages result from a lightning discharge in a direct or indirect lightning strike. The arresters divert the impulse current to earth, limiting the overvoltage to a level that is safe for the electrical installation and the devices connected to it.
Surge arresters do not protect against power-frequency (temporary) overvoltages caused by poor regulation of the supply voltage.
Classes of surge arresters
- Class I (B)
- A surge arrester capable of discharging lightning current or partial lightning current in direct lightning strikes. Voltage protection level Up < 4 kV.
- Class II (C)
- A surge arrester capable of discharging surges caused by a nearby or distant lightning strike, as well as switching overvoltages. Voltage protection level Up < 2.5 kV.
- Class III (D)
- A surge arrester that protects a single appliance or a group of appliances against overvoltage and is installed as close as possible to the protected appliance. Voltage protection level Up < 1.5 kV.