Selection of Surge Protection device & Backup fuse

Protection against Surge protection device’s short circuits is provided by the overcurrent protective devices F2 (which are to be selected according to the maximum recommended rating for the overcurrent protective device given in the manufacturer’s SPD instructions. If the overcurrent protective has a rating smaller than or equal to the maximum recommended rating for the overcurrent protective devices F2, then F2 can be omitted. The cross-sectional area of conductors connecting the overcurrent protective devices to the line conductors shall be rated according to the maximum possible short circuit current. Depending on the location of protective devices used to disconnect the SPD in case of SPD failure, priority may be given either to the continuity of supply or to the continuity of protection.

When Priority is given to continuity of supply, Protective Device PD shall be installed just before the SPD as shown in Figure 56. In this case, once the SPD reaches the end of its life this disconnector device will blow and hence disconnects the faulty SPD from the System and supply to the equipment continues.