What it is and what the ratings mean
The Siemens 3RT2336-1AV00-4AA0 is a 4-pole power contactor from the SIRIUS family, rated AC-3 at 51 A and 22 kW at 400 V. The AC-3 rating is the motor-switching duty class per IEC 60947-4-1 — it governs inrush and breaking of squirrel-cage motors during starting and running. The 51 A figure means this contactor can handle a motor drawing 51 A under full load, not just the resistive AC-1 current. The 22 kW at 400 V is the practical motor power it can switch across a 400 V three-phase line. The coil is 400 V AC, 50 Hz. That's the control voltage — make sure your control circuit matches it. The auxiliary contacts are 1 NO + 1 NC, built into the contactor, so you don't need a separate aux block for basic status feedback or interlocking.
Where it goes in the panel
Frame size S2 is a standard DIN-rail mount, sized for the 51 A AC-3 rating. The screw terminals accept the power and control wiring directly — no crimp-on lugs needed for the main circuit if you're within the terminal capacity. The 122.5 x 82 x 142 mm footprint fits a typical motor starter lineup alongside a matching overload relay.