This standard applies to welded composite enclosures of cast and wrought aluminium and aluminium alloy enclosures pressurized with dry air, inert gases, for example sulphur hexafluoride or nitrogen or a mixture of such gases, used in indoor or outdoor installations of high-voltage switchgear and controlgear with rated voltages of 72,5 kV and above, where the gas is used principally for its dielectric and/or arc-quenching properties. 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- Sur