IEC 62271-107:2012 applies to three-pole operated units for distribution systems that are functional assemblies of a circuit-switcher and current-limiting fuses designed so as to be capable of: - breaking, at the rated recovery voltage, any load or fault current up to and including the rated short-circuit breaking current; - making, at the rated voltage, circuits to which the rated short-circuit breaking current applies. This second edition cancels and replaces the first edition, published in 2005. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition. - the reference to IEC 60694 has been changed to IEC 62271-1; - the new clauses and subclauses from IEC 62271-1 have been added and where necessary new wording has been provided; - the normative references have been updated: IEC 60265-1 to IEC 62271-103, IEC 60787 to IEC/TR 60787, IEC 60466 to IEC 62271-201, and IEC/TR 60787 was moved to the bibliography; - the figures and tables have been placed in the document where they are first cited; - the numbering of figures and tables has been changed to obtain the correct order; - the definition of NSDD was deleted. This definition is included in IEC 62271-1; - the acceptance criteria have been aligned with 6.101.4 of IEC 62271-103:2011; - the various provisions expressed about "extension of the validity of type tests" have been grouped under 6.103: some of the rules were duplicated in Clauses 6 and 8, and it seems better fitted to deal within each type test sub-clause only with the type test to be performed. Conditions have not been changed, but the wording is clearer; - new numbering of subclauses in Clauses 8 and 9 to avoid conflict with clauses from IEC 62271-1. This publication is to be read in conjunction with IEC 62271-1:2007.