SIRIUS S0 power contactor — 24 V DC coil, varistor suppressed
The Siemens SIRIUS 3RT1025-3KB44-1LA0 is a size S0 power contactor with a 24 V DC magnet coil, internally suppressed by a varistor. It mounts on a 35 mm DIN rail per EN 50022, screw or snap-on, and supports side-by-side mounting for dense panel layouts. Rated for AC-2 duty at 400 V at 7.5 kW and AC-4 at 400 V at 15.5 A, this contactor handles motor switching with moderate inrush and reversing loads. The main circuit uses screw-type terminals; the auxiliary and control circuit uses spring-loaded terminals for faster wiring. Coil draw is 23 W closing, 7 W holding — a standard DC coil curve that keeps the control transformer sized for the inrush. The varistor clamps the turn-off spike, protecting downstream PLC outputs.
Coordination and protection
For Type 2 coordination (no damage after a fault) the manufacturer specifies a gL/gG fuse of 25 A; for Type 1 coordination (equipment may be damaged but no fire risk) it is 63 A. This lets the panel builder size the branch protection to match the required coordination class without guesswork. Degree of pollution 3 means the contactor is rated for conductive environments — typical in industrial panels without climate control. The IP20 front enclosure protects against finger contact; the terminal area is IP00, so the panel enclosure must provide the final touch protection.
Environmental and mechanical ratings
Operating temperature range is -40 to +70 °C, covering most unheated plant floors and outdoor cabinet installations. Mechanical endurance is 10 million operations typical — the contactor itself is not the life-limiting component in a normal cycling application. Dimensions: 88 mm height, 70 mm width, 153 mm depth. The 153 mm depth is the dimension that matters most in shallow enclosures — verify the gland plate clearance before committing the layout.
Sourcing and lifecycle
RoHS compliance is documented with a substance prohibitance date of 01.07.2006, covering the EU RoHS directive. The reference code per IEC 81346-2 is Q — useful for panel documentation and labelling standards.