What it is and where it lands
The Siemens 3RT1023-1AM20 is a SIRIUS power contactor in the S0 frame size, rated for motor switching at 4 kW under AC-2 duty at 400 V and 8.5 A under AC-4 at 400 V. It mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022, making it a direct fit for standard control panels. The front face carries IP20 protection; the terminal area is IP00, so panel builders should account for clearance around the wiring zone.
Ratings that decide the fit
AC-2 duty at 4 kW / 400 V covers wound-rotor motor switching where the contactor makes and breaks at reduced current. AC-4 duty at 8.5 A / 400 V handles plugging and inching — the high-stress cycles that wear contacts faster. For resistive loads, the AC-12 maximum operating current is 10 A. The auxiliary contact block supports 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V, so it can drive small relays or PLC inputs directly without an interposing relay.
Coordination and wiring
Type 2 coordination requires a gL/gG fuse rated 25 A; Type 1 coordination allows a 63 A fuse. Main circuit terminals accept solid or stranded conductors up to 2x 10 mm² (AWG 8). The auxiliary terminals take 0.5 to 4 mm². Pollution degree 3 means the contactor is rated for industrial environments with conductive pollution — no extra conformal coating needed for typical panel conditions.