MT 51 - TC 17/SC 17A/MT 51

IEC 62271-105:2021 is available as IEC 62271-105:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 62271-105:2021 applies to three-pole units for public and industrial distribution systems which are functional assemblies of switches composed of switches or switch-disconnectors and current-limiting fuses designed so as to be capable of
- breaking, at the rated voltage, any 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 third edition cancels and replaces the second edition published in 2012. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
- the document has been updated to be in alignment with the second edition of IEC 62271-1:2017;
- rated TRV has been removed (TRV is only a test parameter), as in the latest revision of IEC 62271-100;
- differentiation has been introduced between requirements expressed for fulfilling the function expected from a switch-fuse combination, from requirements only relevant when the function is performed by a stand-alone device. The goal is to avoid duplication or conflicts of requirements with a standard dealing with assemblies, when the function is implemented within such an assembly.

IEC 62271-105:2012 applies to three-pole units for public and industrial distribution systems which are functional assemblies of switches including switch-disconnectors and current-limiting fuses designed so as to be capable of
- breaking, at the rated recovery voltage, any 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.
It does not apply to fuse-circuit-breakers, fuse-contactors, combinations for motor-circuits or to combinations incorporating single capacitor bank switches. This second edition cancels and replaces the first edition of IEC 62271-105, published in 2002, and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- implementation of figures at the place where they are cited first;
- renumbering of tables;
- addition of some of the proposals from IEC paper 17A/852/INF;
- addition of missing subclauses of IEC 62271-1;
- implementation of 6.105 "Extension of validity of type tests" and consequently removing of the relevant parts in the different existing clauses;
- change of 7th paragraph of 6.101.4 as there is now a definition of NSDD given in 3.7.4 of IEC 62271-1:2007. Harmonization with IEC 62271-107;
- some referenced clauses in other standards like IEC 60282-1 were changed and therefore changed the editions under 1.2 to the ones referred to;
- addition of a new Annex C defining tolerances.
This publication is to be read in conjunction with IEC 62271-1:2007.