IEC 62271-203:2011 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. This second edition of IEC 62271-203 cancels and replaces the first edition of IEC 62271-203, published in 2003, and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: – adopting the structure and the content to IEC 62271-1, – harmonisation with IEEE C37.122, – addition of the new Annex F and the new Annex G. This publication is to be read in conjunction with <a href='http://webstore.iec.ch/webstore/webstore.nsf/ArtNum_PK/45395'>IEC 62271-1:2007</a>.