This clause of IEC 60364-4-44 deals with protection of electrical installations against transient overvoltages of atmospheric origin transmitted by the supply distribution system including direct strikes to the supply system and against switching overvoltages. This clause does not apply in case of transient overvoltages due to direct or nearby lightning stroke to structure, where IEC 62305 series apply. If protection against transient overvoltage in accordance with IEC 62305 is provided, the requirements of clause 443 for protection against transient overvoltage of atmospheric origin are considered covered. The requirements of 443 do not apply in case of transient overvoltages due to direct or nearby lightning stroke to structure, where IEC 62305 series apply. In general, switching overvoltages are lower than transient overvoltages of atmospheric origin and therefore the requirements regarding protection against transient overvoltages of atmospheric origin normally cover protection against switching overvoltages. If no transient overvoltage protection against disturbances of atmospheric origin is installed protection against switching overvoltages may need to be provided. NOTE 1 Overvoltages due to switching can be longer in duration and can contain more energy than the transient overvoltages of atmospheric origin. See 443.2 The characteristics of transient overvoltages of atmospheric origin depend on factors such as: the nature of the supply distribution system (underground or overhead); the possible existence of at least one surge protective device upstream of the origin of the 21 installation; the voltage level of the supply system. NOTE 2 As regards transient and overvoltage of atmospheric origin, no distinction is made between earthed and unearthed systems. Requirements for protection against transient overvoltages transmitted by data-transmission systems are not covered by clause 443. See IEC 61643-22. NOTE 3 If there is a need for SPDs on the power supply lines, additional SPDs on other Iines such as telecom lines are also recommended. Selection and installation of surge protective device (SPD) shall be in compliance with clause 534 of IEC 60364-5-53.