This European Standard applies to welded composite enclosures of cast and wrought aluminium alloy pressurized with dry air, inert gases (e.g. sulphur hexafluoride or nitrogen or a mixture of such gases), used in indoor and outdoor installations of high-voltage switchgear and controlgear with rated voltages above 1kV, where the gas is used principally for its dielectric and/or arc-quenching properties with rated voltages above 1 kV and up to and including 52 kV and with gas-filled compartments with design pressure higher than 300 kPa relative pressure (gauge); and with rated voltage above 52 kV. The enclosures comprise parts of electrical equipment not necessarily limited to the following examples: circuit-breakers; switch-disconnectors; disconnectors; earthing switches; current transformers; voltage transformers; surge arrestors; busbars and connections; etc. The scope also covers enclosures of pressurized components such as the centre chamber of live tank switchgear, gas-insulated current transformers, etc.