Siemens SIRIUS 3RT1025-1XF40-0LA2 — 110 V DC Power Contactor, Size S0
The Siemens SIRIUS 3RT1025-1XF40-0LA2 is a size S0 power contactor with a 110 V DC coil, rated for switching motor loads up to 11 kW at 690 V or 15 hp at 575/600 V. The DC coil includes a built-in varistor surge suppressor, which clips the inductive kickback on dropout — no external free-wheel diode needed for this variant. The contactor measures 45 mm wide by 116 mm high by 101 mm deep, fitting a standard 35 mm DIN rail per EN 50022. Side-by-side mounting is allowed, so you can pack multiple units without derating for heat buildup in the panel. Main circuit connections are screw-type terminals accepting solid or stranded wire: 2x (0.5...1.5 mm²), 2x (0.75...2.5 mm²), max. 2x (0.75...4 mm²) for the coil/auxiliary, and 2x (1...2.5 mm²), 2x (2.5...6 mm²), max. 2x 10 mm² for the main power circuit. AWG equivalents: 2x (16...12), 2x (14...10), 1x 8 for the main contacts.
Switching Ratings and Duty
The DC coil picks up at 70% of rated voltage (77 V minimum) and holds across the full 110 V DC nominal. Switching capacity varies by load voltage: 10 A at 24 V DC, 1 A at 110 V DC, 0.3 A at 220 V DC. For AC motor loads, the contactor is rated 15.5 A at AC-4 (400 V) for reversing or inching duty, and the AC-3 motor ratings are 3 A at 400 V, 10 kW at 500 V, 11 kW at 690 V. Motor horsepower ratings per NEMA: 1 hp at 110/120 V, 5 hp at 200/208 V and 220/230 V, 10 hp at 460/480 V, 15 hp at 575/600 V. The rated impulse withstand voltage of the main circuit is 6 kV, suitable for industrial environments with moderate surge exposure.
Mounting and Clearance
Fastening is by screw or snap-on onto a 35 mm standard mounting rail per DIN EN 50022. Required clearances around the contactor: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 10 mm at the side. These are the minimum air gaps for arc containment and heat dissipation — panel builders should respect them, especially when grouping multiple contactors side by side.