MT 18 - TC 121/SC 121A/MT 18

IEC 60947-6-1:2026 is available as IEC 60947-6-1:2026 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 60947-6-1:2026 applies to transfer switching equipment (TSE), to be used in power systems for ensuring the continuity of the supply and allowing the energy management of the installation, by transferring a load between power supply sources, the rated voltage of which does not exceed 1 000 V AC or 1 500 V DC. Specific requirements for bypass/isolation transfer switch equipment are given in Annex C, ATSE having closed transition capability are given in Annex D, stand-alone ATS controllers are given in Annex E, and TSE for electric driven fire pump controllers are given in Annex F.
It covers:
- manually operated transfer switching equipment (MTSE);
- remotely operated transfer switching equipment (RTSE);
- automatic transfer switching equipment (ATSE), including the controller;
- stand-alone ATS controllers;
- bypass/isolation transfer switch equipment (BTSE);
- ATSE having closed transition capability;
- fire pump TSE.
It does not cover:
- TSE configurations that are not fully manufacturer type tested or marked according to this document as a complete transfer switch;
- auxiliary contacts (for guidance, see IEC 60947-5-1);
- transfer switches used in explosive atmospheres (for guidance, see IEC 60079 (all parts));
- embedded software design (for guidance, see IEC TR 63201);
- cybersecurity aspects (for guidance, see IEC 63208);
- TSE rated for direct-on-line starting asynchronous motor of design NE and HE, according to IEC 60034-12. (for guidance, see AC-3e utilisation category according to IEC 60947 4 1);
- other types of TSE under consideration including overlapping neutral TSE, multi-source TSE (i.e. TSE with more than two sources of supply), TSE with load-shedding functions, bus-tie TSE, and hybrid TSE;
- static transfer switches covered by IEC 62310 series.
This fourth edition cancels and replaces the third edition published in 2021. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
- clarification of scope;
- clarification of terms and definitions;
- Annex C for Bypass/Isolation Transfer Switch Equipment;
- Annex D for ATSE having closed transition capability;
- Annex E for Stand-alone ATS controller;
- Annex F for TSE used with electric driven fire pump control equipment.

IEC 60947-6-1:2021 applies to transfer switching equipment (TSE), to be used in power systems for ensuring the continuity of the supply and allowing the energy management of the installation, by transferring a load between power supply sources, the rated voltage of which does not exceed 1 000 V AC or 1 500 V DC.
This third edition cancels and replaces the second edition published in 2005, and its Amendment 1:2013. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
– clarification of scope and object;
– clarification of terms and definitions;
– removal of unnecessary definitions;
– modification of characteristics;
– modification of utilization categories definitions;
– introduction of new markings requirements;
– addition of new requirements for clearances and creepage distances;
– addition of new requirements and tests for mechanical and electrical interlocks;
– clarification of transfer sequences;
– modification of requirements for rated short-time withstand currents;
– modification of new requirements for electromagnetic compatibility;
– clarification of performance requirements for CB type TSE, in alignment with requirements stated in IEC 60947-2;
– addition of new test sequence V: Critical load current performance of equipment with DC ratings.