Specifies requirements for gas-insulated, metal-enclosed switchgear in which the insulation is obtained, at least partly, by an insulating gas other than air at atmospheric pressure, for alternating current of rated voltages above 52 kV, for indoor and outdoor installation, and for service frequencies up to and including 60 Hz. For the purpose of this standard, the terms \'GIS\' and \'switchgear\' are used for \'gas-insulated metal-enclosed switchgear\'. The gas-insulated metal-enclosed switchgear covered by this standard consists of individual components intended to be directly connected together and able to operate only in this manner. This standard completes and amends, if necessary, the various relevant standards applying to the individual components constituting GIS. This first edition of IEC 62271-203 cancels and replaces the third edition of IEC 60517, published in 1990, and constitutes a technical revision. With the revision, significant changes from the previous edition have been made. The most important changes are deleting not used technologies, like 3-phase PD measurements, adopting the content to IEC 62271-1 \'Common Clauses\' and harmonisation with IEEE C37.122. This standard is now more up to date to today\'s products on the world market. This International Standard should be read in conjunction with IEC 60694, second edition, published in 1996, its Amendment 1 (2000) and its Amendment 2 (2001), to which it refers and which is applicable unless otherwise specified.