What the 4000 A rating means for your main distribution board
The 66 kA Icu at 220…440 V AC (IEC 60947-2) tells you it can safely interrupt a fault up to that level and still be usable afterward; the 65 kA Ics service breaking capacity means it handles repeated faults without needing replacement, which matters for selectivity coordination downstream. At 690 V the Icu drops to 50 kA, so if your system runs at 690 V, the available fault current must stay under that ceiling.
Environmental and isolation capability
Rated insulation voltage 1000 V AC and impulse withstand voltage 12 kV — the breaker holds off transients common in industrial networks. Mechanical durability is 20000 cycles with maintenance, 10000 without; electrical durability is 5000 cycles at 440 V, 2500 at 690 V.