The Square D / Schneider Electric A9-40-00-84 is a 4-pole IEC contactor from the A-Line series, A9 frame. It carries a 21 A rated current with a 120V AC coil and is rated for 600V. The contact configuration is four normally-open (N.O.) power poles.
The 21 A rating is the continuous thermal current (Ith) per IEC 60947-4-1, so it governs the maximum load current the main poles can carry in a panel environment without derating. For motor switching, the AC-3 utilization category derates that figure — a 21 A contactor typically handles a 5.5 kW (7.5 HP) motor at 400V three-phase, but verify the specific motor FLA against the contactor's AC-3 rating in the datasheet. The 120V AC coil draws its holding current from the control transformer; confirm the coil's inrush VA does not exceed the control circuit's fuse rating.