What it is and where it lands
The Siemens 3RT1024-1AL20-1AA0 is a SIRIUS S0-frame power contactor rated for motor switching at 7.5 kW on 400 V AC-3 duty, 5.5 kW on AC-2. It snaps onto 35 mm DIN rail per EN 50022 or screws directly to a panel backplate — the 45 mm width and 85 mm height leave room for adjacent devices in a crowded enclosure.
Ratings that decide the fit
AC-3 rating at 400 V is 7.5 kW — that's the motor-switching number that governs the BOM line for a 3-phase induction load. AC-4 at 400 V is 12.5 A, covering reversing or inching duty where the contactor breaks full-load current. The auxiliary contact set handles 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V, so it can drive a PLC input or a smaller relay coil without an interposing device. Operating temperature range is -25 to +60 °C, which covers most indoor panel environments without derating. Pollution degree 3 means it's rated for industrial atmospheres with conductive dust or occasional condensation — no conformal coating required for a standard IP20 panel.
Panel integration and wiring
Main circuit terminals accept 2x (1 to 2.5 mm²) stranded or 2x (2.5 to 6 mm²) solid, max 2x 10 mm² — enough for the motor leads at this frame size. Auxiliary terminals take 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²). Side-by-side mounting is allowed with 6 mm clearance between units; no derating required at 100% duty. Type 2 coordination (fuse gL/gG: 25 A) limits let-through energy so the contactor survives a short circuit without welding. Type 1 coordination (63 A fuse) allows the contactor to be replaced after a fault — choose based on whether the line can tolerate a swap.