What the ratings mean for fit
The AC-3 4 kW/400 V rating is the key selection parameter: it tells you this relay can handle a 4 kW motor load under IEC 60947-4-1 utilization category AC-3, which covers starting and plugging/plug-stop of cage motors. If your motor is larger than 4 kW, you need a larger frame (S0, S2, etc.) or a higher-rated variant. The DC 24 V coil with 0.7...1.25×US means the relay picks up reliably even when the control voltage sags to 16.8 VDC and stays pulled in up to 30 VDC — useful on long cable runs or shared power supplies. Size S00 is the smallest SIRIUS contactor frame (45 mm width), so it fits in tight panel layouts and on standard DIN rails. The single NC contact is factory-fitted; if your application needs more auxiliary contacts, you'll add a side-mount auxiliary contact block from the same SIRIUS family.