Modern electrical design relies on selectivity (keeping a fault isolated to the smallest possible section of the network). IEC 60947-2 provides the rules for verifying that upstream breakers don't trip unnecessarily.
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Title: Low-voltage switchgear and controlgear – Part 2: Circuit-breakers Modern electrical design relies on selectivity (keeping a
| Standard | Scope | |----------|-------| | IEC 60898-1 | Circuit-breakers for household (domestic) installations – typical use in homes, not industrial. | | IEC 60947-1 | General rules for all low-voltage switchgear – must be used together with part 2. | | IEC 60947-4-1 | Contactors and motor-starters. | | IEC 60947-6-2 | Transfer switching equipment (e.g., automatic transfer switches). | | IEC 61439 | Low-voltage switchgear assemblies (panels, boards) – references 60947-2 for component selection. | Visit the IEC website, search for "60947-2", and
The standard breaks down breakers into two main categories:
For selective breakers (Type B), Icw defines how long the breaker can withstand a fault current without tripping—typically 0.05 to 1 second. This allows coordination with downstream devices.