LV Breakers, Switches, Fuses and Contactors: IEC 60947 Coordination
How to select ACB/MCCB, switch-disconnectors, fuses and contactors without confusing utilization category, breaking capacity, withstand duty and short-circuit c
1. Separate the Device Standards
IEC 60947-2:2024 covers low-voltage circuit-breakers up to 1,000 V AC or 1,500 V DC. IEC 60947-3 covers switches, disconnectors and switch-disconnectors. IEC 60947-4-1:2023 covers electromechanical contactors and motor-starters; IEC 60269 covers the relevant low-voltage fuse system.
A contactor controls a motor but is not normally the device that interrupts a short circuit. The fuse, breaker, starter coordination and motor protection must be selected as a declared combination.
2. Selection Data
| Device | Key data to compare |
|---|---|
| ACB / MCCB | Ue, Ui, Uimp, In, Icu, Ics, Icw, Ipk, trip functions, neutral pole and isolation suitability |
| Switch-disconnector | Utilization category, operational current, isolation, short-circuit withstand and interlock |
| Fuse | Voltage, class, rated current, breaking capacity, time-current curve and let-through I²t |
| Contactor / starter | Utilization category, motor current, coil/control, starts per hour, overload and declared coordination type |
3. Coordination Workflow
Start with the maximum and minimum prospective fault at the installation point, the transformer impedance, conductor lengths, motor infeed and the actual source operating modes. Check that the protective device can interrupt the fault and that the busbar, cable, contactor and motor withstand the let-through duty.
Then evaluate selectivity, backup or cascading claims, energy limitation, trip curves, motor starting, inrush, neutral currents, harmonics and emergency operation. A manufacturer coordination table is valid only for the exact device references, settings and upstream/downstream arrangement stated in that table.
4. Commissioning Controls
- Lock the exact order code, trip unit, sensor rating, fuse link and accessory set.
- Record settings for long-time, short-time, instantaneous, earth-fault and motor overload functions.
- Test mechanical interlocks, undervoltage release, shunt trip, auxiliary contacts and remote control.
- Preserve the time-current and coordination evidence with the panel revision; never replace a fuse or breaker with a “similar” rating without repeating the study.
*Reference: IEC 60947-2:2024; IEC 60947-3:2020+A1:2025; IEC 60947-4-1:2023; IEC 60269 series.*
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