... device (hereinafter called SPD) is suitably used in the IT, TT, TN-C, TN-S, TN-C ... . The visible window show white color in normal service, if to be separated from network, it will ... B surge protective device (SPD), used in the connection between equal potential electrodes while thunder occur. ... incoming distribution panel, overhead incoming.As required, the user can assemble single pole or three poles ...