The AC-3 16 A rating at ≤440 V governs motor switching: it is the current the contactor can make and break under full-load motor start conditions. For a 400 V three-phase motor, that translates to roughly 7.5 kW (10 HP) — enough for a small conveyor or pump. The AC-4 rating, while not quantified here, tells you the contactor is designed for the higher arc erosion of reversing and jogging, not just steady running. The 400 V AC coil is a specific control voltage — not 230 V, not 24 VDC. If your control circuit runs 400 V line-to-line, this coil matches directly. If your panel uses a lower control voltage, you need a different coil variant in the TeSys K family. Mechanical shock and vibration ratings (10 Gn on Y/Z axis closed, 4 Gn vibration closed per IEC 60068-2-27/6) mean it holds in on rail or mobile equipment without dropping out.
The preassembled reversing busbar saves panel wiring time but fixes the pole arrangement; you cannot reconfigure it in the field.