The effects of overcurrent or ground faults that may occur after degradation or end of life on the operation of the information system equipment must be considered. Therefore, overcurrent protection devices (such as fuses or air circuit breakers) and over surge protectors should be installed on the power supply side of the SPD. (Setted internally or externally) with the SPD to assume an expected maximum short-circuit current equal to or greater than the installation. When selecting, the maximum over-surge protector for the product specified by the SPD manufacturer should be considered. In addition, the manufacturer's specified SPD rated blocking current value should not be less than the expected short-circuit current at the installation. The residual surge protector device should also be installed in the TT system and should have a degraded display function. SPDs used in explosive hazardous locations should be explosion proof.
When considering the overvoltage protection level between devices, if the line is unshielded, the inductive voltage of the line should be taken into consideration. When considering the impact overvoltage level of the protected equipment, it should be considered at 80% of its value.