IEC 61148:2011 is applicable to the terminal markings for the main circuits of valve device stacks and assemblies, and of integrated conversion equipment. The terminal markings refer to stacks, assemblies and equipment comprising semiconductor valve devices. The object of this standard is to specify a logical alphanumeric marking system for the identification of the external main terminals of the main power circuits in a stack, valve device assembly or integrated conversion equipment, which is applicable for the purpose of reference in circuit diagrams, catalogues, descriptions, and information exchange and storage. In the case of stacks and assemblies, alphanumeric terminal marking systems are indicated for those converter connections which are the most important and most commonly used ones. Terminal marking systems making use of graphic symbols or identifying colours are not considered in this standard. This second edition includes the following significant technical changes with respect to the previous edition: - the whole document has been rewritten according to the current Directives; - the identification codes were deleted according to the withdrawal of IEC 60971; - examples of terminal marking were added, especially for self-commutated converters.