What it is and what it does
The Siemens SIRIUS 3RT1025-1AG24 is a Size S0 power contactor designed for switching motor loads and resistive loads in industrial control panels. It mounts on a 35 mm DIN rail per EN 50022 via screw or snap-on fixing, with a 45 mm width that fits standard panel layouts. Rated for AC-4 duty at 15.5 A at 400 V, this contactor handles the high inrush of reversing or plugging motor applications where the contacts break under full load. For AC-2 at 400 V it carries 7.5 kW, covering slip-ring motor switching. The 24 VDC coil draws 10 A at rated value, with a dropout below 18 V typical for this class. Side-by-side mounting is permitted with 6 mm clearance at the side, and the front face carries IP20 protection while the terminals are IP00.
Sourcing and lifecycle
For a BOM freeze or a replacement for a failed unit, the 3RT1025-1AG24 is a straightforward line-item. The screw terminals accept 2x (0.5 to 1.5 mm²) solid or 2x (0.75 to 2.5 mm²) stranded, with a maximum of 2x 4 mm², matching typical control wiring practices.
What the ratings mean for fit
The AC-4 rating of 15.5 A at 400 V is the key number for motor reversing or jogging duty — it tells you the contactor can break the stalled-rotor current without welding contacts. For standard AC-3 motor starts, the 500 V rating of 10 kW and 690 V rating of 11 kW cover most European 3-phase motor sizes up to 11 kW. Type 2 coordination requires a 25 A gL/gG fuse upstream (type 1 allows 63 A). This matters for selectivity studies — if your panel demands Type 2 coordination to minimize downtime after a fault, the 25 A fuse limit is the binding constraint. Operating temperature range of -25 to +60 °C covers most indoor panel environments, including non-conditioned enclosures in warm climates. The 2000 m maximum altitude limit is standard for low-voltage gear; derate above that.
Panel integration notes
At 85 mm height and 140 mm depth, the S0 frame fits shallow enclosures. The screw terminals for the main circuit accept AWG 16 to 8, with two conductors per terminal allowed — useful for daisy-chaining power feeds. The 2 instantaneous auxiliary contacts (standard configuration) can be wired for status feedback or interlocking without an add-on block. Pollution degree 3 rating suits industrial environments with conductive dust or condensation.