The Surge Protective Device (SPD) is a part of the electrical installation protection system. It connects to the power supply circuit of the loads it is supposed to protect in parallel. SPD is also known as a device for lightning protection.

If a surge current or voltage is suddenly generated in an electrical circuit or communication circuit due to external interference, the surge protection device will conducts the shunt in the current in a very short time, thereby avoiding the damage of the surge to the other equipments in the circuit system.