OBO BETTERMANN :
SPD(Surge Protection Device )
SPD uses to protect our system from lightning surge and switching surge
Surge Protection Devices (SPD) are used for electric power supply networks, telephone networks, and communication and automatic control buses.
The Surge Protection Device (SPD) is a component of the electrical installation protection system.
This device is connected in parallel on the power supply circuit of the loads that it has to protect. It can also be used at all levels of the power supply network.
This is the most commonly used and most efficient type of overvoltage protection.
Types : Class B, Class B+C, Class C, Class D