When lightning strikes, large-power equipment starts or stops, or when static discharge occurs, instantaneous overvoltage (surge) will be generated, causing damage to the equipment. SPD (Surge Protective Device) is the abbreviation of surge protector. SPD is installed at the front end of the equipment to be protected. When surge occurs, SPD can conduct quickly and discharge the surge to the ground, limiting the voltage to a safe level, thereby protecting the equipment at the rear end.