What this SIRIUS contactor is and what it does
The Siemens SIRIUS 3RT1025-3XB40-0LA2 is a size S0 power contactor with a 24 V DC coil, designed for switching motor loads in industrial control panels. It mounts on a 35 mm DIN rail per EN 50022 and uses screw-type terminals for the main circuit. The DC coil draws 10 A at 24 V inrush, holding at 0.7 A (the initial vs. full-scale values), so your 24 VDC power supply needs to handle that peak pull-in current. Drop-out is typically below 18 V — a standard curve for DC-operated contactors. AC motor ratings tell you what this contactor can handle: 3 hp at 230 V, 10 hp at 460/480 V, and 15 hp at 575/600 V. For IEC duty, it's rated 11 kW at 690 V. The AC-4 switching current at 400 V is 15.5 A — that's the reversing/plugging duty cycle, which is more demanding than AC-3. DC switching ratings are given at several voltages: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, and 0.3 A at 220 V. These are resistive load values — inductive DC loads will need derating or arc suppression.
Physical fit and panel integration
At 45 mm wide, 119 mm tall, and 100 mm deep, this S0 contactor occupies standard DIN-rail space. The 45 mm width is the same as many motor starters and overload relays in the SIRIUS family, so it aligns neatly in a multi-row panel. Clearance requirements: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 10 mm at the side. That's enough for airflow and wiring access in a typical enclosure. Side-by-side mounting is permitted, so you can gang multiple contactors without spacing. Screw terminals accept 2x (0.25–2.5 mm²) solid or stranded, and up to 2x 10 mm² for the main circuit. The IP20 rating on the front protects against finger contact; the terminal area is IP00, so live parts are exposed — standard for panel-mounted contactors.
What the ratings mean for your application
The rated impulse withstand voltage of 6 kV means this contactor is suitable for installation in circuits with overvoltage category III up to 400 V — typical for industrial motor branch circuits. The maximum operating altitude of 2,000 m limits installation to most standard industrial sites without derating. Mechanical life of 10 million cycles is typical for a contactor of this class. Electrical life will be lower depending on the switching load — AC-4 duty at 15.5 A will reduce it significantly compared to AC-1 resistive switching.