MT 9 - TC 121/SC 121A/MT 9

IEC 60947-2:2024 applies to circuit-breakers, intended to be installed and operated by instructed or skilled persons, the main contacts of which are intended to be connected to circuits, the rated voltage of which does not exceed 1 000 V AC or 1 500 V DC; it also contains additional requirements for integrally fused circuit-breakers.
This document also applies to circuit-breakers with ratings at or below 1 000 V AC, additionally having one or more ratings above 1 000 V AC but not exceeding 1 500 V AC.
This sixth edition cancels and replaces the fifth edition published in 2016 and its Amendment 1: 2019. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) suitability for isolation (see Clause 1);
b) removal of the classification according to the interrupting medium, according to the design, according to the suitability for isolation (see Clause 4);
c) adjustment of current settings with an external device connectable to the release (see 5.7.3);
d) requirements for circuits with protective separation (see 8.2.3.8);
e) additional tests for ground-fault overcurrent releases (see 9.3.4.2.5);
f) additional tests concerning dielectric properties in tripped position (see 9.3.4.3);
g) use of DC voltage for dielectric tests (see 9.3.4.6.2 and 9.4.6);
h) tests of individual pole breaking capacity under phase-to-neutral AC voltage (see 9.3.11);
i) improvement of measurement of power loss in Annex G;
j) changes in EMC tests (see Annex J);
k) introduction of CBI class W in Annex L.

IEC 60947-2:2016 applies to circuit-breakers, the main contacts of which are intended to be connected to circuits, the rated voltage of which does not exceed 1 000 V a.c. or 1 500 V d.c.; it also contains additional requirements for integrally fused circuit-breakers. This fifth edition cancels and replaces the fourth edition published in 2006, Amendment 1:2009 and Amendment 2:2013. This edition constitutes a technical revision. This edition includes the following significant additions with respect to the previous edition:
- tests for verification of selectivity in Annex A (see A.5.3);
- critical load current tests for d.c. circuit-breakers (see 8.3.9);
- new Annex P for circuit-breakers for use in photovoltaic applications;
- new Annex R for residual-current circuit-breakers with automatic reclosing functions. The contents of the corrigendum of November 2016 have been included in this copy.

This standard applies to circuit-breakers, the main contacts of which are intended to be connected to circuits, the rated voltage of which does not exceed 1 000 V a.c. or 1 500 V d.c.; it also contains additional requirements for integrally fused circuit-breakers. It applies whatever the rated currents, the method of construction or the proposed applications of the circuit-breakers may be.

IEC 61912-2:2009(E), which serves as an application guide for the determination of selectivity between over-current protective devices of low-voltage switchgear and controlgear, summarises the definitions of the terminology and provides examples of application.

This technical report, which serves as an application guide for the short-circuit ratings given in IEC standards for low-voltage switchgear and controlgear and assemblies, summarises the definitions of the ratings and provides examples of their application. This edition cancels and replaces the first edition of IEC 61912, published in 2006, and corrigendum 1 (May 2006). The changes are only editorial.