The Siemens SIRIUS 3RT1024-1KB40-1AA0 is a power contactor in the S0 frame size, designed for switching motor loads in control panels. It mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022, occupying 45 mm of panel width. The 24 V DC coil includes an integrated varistor surge suppressor, which suppresses back-EMF during de-energization — a detail that matters when the coil is driven by a PLC output or solid-state relay that cannot absorb inductive kickback. For motor duty, the AC-3 rating at 400 V is 7.5 kW, meaning it switches a 3-phase induction motor up to that load under full running current. The AC-4 rating at 400 V is 12.5 A, governing the contactor's life under reversing or inching duty where the contacts make and break locked-rotor current.
Key ratings and what they mean for fit
The coil draws 4.2 W both at pickup and hold — a constant-holding-power design that simplifies the control transformer sizing. The 24 V DC coil holds above 18 V typical dropout; the integrated varistor means no external free-wheel diode is needed, but verify polarity: the suppressor is polarity-sensitive. Short-circuit coordination: with Type 2 coordination (no damage to the contactor), the required upstream fuse is gL/gG 25 A. For Type 1 coordination (contactor may need replacement after fault), the fuse can be gL/gG 63 A. This governs the branch circuit protection design. The main contacts accept screw-type terminals rated for 2x (0.5...1.5 mm²) solid, 2x (0.75...2.5 mm²) stranded, or up to 2x 4 mm² max. For AWG: 2x (16...12) solid, 2x (14...10) stranded, or 1x 8. The front face carries IP20; the terminal area is IP00 — the panel builder must ensure finger-safe shrouding or enclosure clearance. Operating temperature range is -25 to +60 °C, with a maximum operating altitude of 2,000 m. Pollution degree 3 means it tolerates conductive pollution in industrial environments — no additional conformal coating required for typical panel conditions. Side-by-side mounting is permitted without derating, saving panel width when multiple contactors are ganged. The 6 mm clearance to adjacent components on the side is the minimum for heat dissipation.
Auxiliary contact ratings and mechanical life
The auxiliary contact block (integrated or add-on) carries rated operational currents: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, and 0.3 A at 220 V DC. These ratings are for the control circuit; the DC switching capability at 220 V (0.3 A) is notably limited — verify the inductive load current if switching DC contactors or relays. Mechanical life is rated at 10 million operations typical — a figure that assumes no load on the contacts. Electrical life depends on the switched current and duty cycle; for AC-3 motor switching at full rating, expect roughly 1–2 million operations before contact replacement.