The Siemens SIRIUS 3RT1016-2AX21-0AA3 is a size S00 power contactor rated for 4 kW at AC-2 duty on 400 V, meaning it handles moderate motor loads like conveyors and pumps where starting current is controlled. For inching or plugging duty (AC-4), it carries 8.5 A at 400 V — a real constraint if your application cycles the motor under load. Spring-loaded terminals accept 2x (0.25... 2.5 mm²) solid or stranded wire, or 2x (24... 14) AWG.
For type 2 coordination (contactor remains operational after a fault), step down to a gL/gG 20 A fuse. This distinction matters when you're specifying a panel that must survive a short circuit without a service call.
Integration notes
The contactor measures 45 mm wide, 60 mm tall, and 73 mm deep — a compact S00 footprint that fits tightly packed DIN-rail enclosures. The IP20 finger-safe front and terminal covers protect against accidental contact in open panels.