Applicable to welded composite enclosures of cast and wrought aluminium and aluminium alloy enclosures pressurized with dry air, inert gases, for example, sulphur hexafluoride, carbon tetrafluoride, or nitrogen or a mixture of such gases, used in indoor or outdoor installations of high-voltage switchgear and controlgear, where the gas is used principally for its dielectric and/or arc-quenching properties, with rated voltages: (a) 1 kV and up to and including 52 kV and with gas-filled compartments with design pressure greater than 3 bar (gauge); and (b) 72.5 kV and above. Also covers pressurized components such as the centre-chamber of live tank switchgear and controlgear, gas-insulated current transformers, etc.