SPDs shall at least be installed as close as possible to the origin of the installation.
*For protection against effects of lightning and against switching overvoltages, class II tested SPDs shall be used.
*Where the structure is equipped with an external lightning protection system or protection against effects of direct lightning is otherwise specified, class I tested SPDs shall be used.
*Where the structure is not equipped with an external lightning protection system and where the occurrence of direct lightning strike to the overhead lines between the last pole and the entrance of the installation is to be taken into consideration, class I tested SPDs at or near the origin of the electrical installation may be also selected。
Additional class II tested or class III tested SPDs may be needed to sufficiently protect the installation and shall be located downstream in the fixed electrical installation, for example in the sub-distribution boards or at the socket outlets.
These SPDs shall not be used without SPDs being installed at the origin of the installation and shall be coordinated with SPDs located upstream. If a class | tested SPD is not able to provide protection, it shall be accompanied by a coordinated class II tested or class III tested SPD to ensure the required voltage protection level.
Additional class II tested SPDs or class III tested SPDs may be needed close to sensitive equipment to sufficiently protect the equipment according to Rated impulse withstand voltage (Uw) (see 2.6) and shall be coordinated with SPDs located upstream.
