What it is and what it does
The Siemens SIRIUS 3RT1024-3KF40-1AA0 is a size S0 power contactor in the SIRIUS family, designed for switching motor loads in industrial control panels. It mounts on a 35 mm DIN rail per EN 50022, using either screw or snap-on fixing, and takes up 45 mm of panel width. The coil is rated 110 V AC and includes an integrated varistor surge suppressor, so you don't need to add a separate suppression module across the coil — one less part to wire and one less failure point to chase. Main power connections are screw-type terminals, accepting up to 2x 10 mm² or 1x 8 AWG stranded. The auxiliary and coil terminals take 2x (0.25...2.5 mm²) solid or 2x (1...2.5 mm²) stranded.
What the ratings mean for fit
The motor power ratings tell the real story: 7.5 kW at both 500 V and 690 V AC-3 duty. That means it switches a standard three-phase induction motor up to 7.5 kW on a 400 V or 690 V line — the AC-3 rating governs the load-break capability for starting and stopping a running motor, not just holding it closed. For heavy plugging or inching duty (AC-4), the contactor is rated 12.5 A at 400 V. That is the current it can break under those severe switching conditions — if your application involves frequent reversing or jogging, this is the number to size against, not the AC-3 power rating. The resistive-load rating (AC-12) maxes out at 10 A operating current — useful for switching heater banks or other non-inductive loads where the contactor sees no motor inrush. Short-circuit coordination matters for panel protection: with Type 2 coordination (limited damage to the contactor after a fault), the maximum fuse is gL/gG 25 A. With Type 1 coordination (contactor may need replacement after a fault), it can take up to gL/gG 63 A. Pick your fuse size based on which coordination level your panel design requires. Mechanical life is rated at 10 million operations typical — that is the mechanism's endurance under no-load cycling. Electrical life will be lower and depends on the switched current and duty cycle.
Where it goes and what it tolerates
The contactor is rated for operating ambient temperatures from -25 °C to +60 °C, with a pollution degree of 3 (conductive pollution or dry non-conductive pollution that becomes conductive due to condensation). That means it is suited for industrial control panels in factory environments, not for clean-room or sealed-cabinet use without derating. The front face carries IP20 finger protection — safe for panel installation where the front is accessible. The terminal area itself is IP00, meaning the wiring compartment is not touch-safe; that is normal for a panel-mounted contactor where the enclosure provides the overall protection. Side-by-side mounting is allowed without derating, which saves panel width when ganging multiple contactors. The 45 mm width per unit and 101 mm depth fit standard 200 mm deep enclosures with room for wiring. Maximum operating altitude is 2 000 m — above that, the air insulation and cooling derate, so factor that in for high-altitude installations.
Lifecycle and sourcing reality
Because it is an active Siemens SIRIUS part, the compliance documentation you would expect is available: the manufacturer provides RoHS, REACH, and CE declarations, plus UL/CSA recognition through the SIRIUS product family certification. The varistor surge suppressor is built in, so the contactor meets the relevant IEC 60947-4-1 standards for motor starters. Sourcing posture: this is a quoted-to-order item through standard industrial distribution. Submit an RFQ with your quantity and target delivery window, and we will confirm lead time against the current factory backlog.