SIRIUS coupling contactor, size S0 — 24 VDC coil, spring terminals
The Siemens 3RT2025-2KG40 is a SIRIUS coupling contactor in size S0, designed for DC switching applications where a 24 VDC coil and spring-type terminals are specified. Its primary role is to isolate or couple control circuits, often used between a PLC output and a higher-power contactor or motor starter, providing a clean interface point. The spring-type terminals accept solid or stranded conductors from 1 to 10 mm², and the contactor mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715.
DC switching ratings — what the numbers mean for your circuit
The DC-13 rated switching currents are the key selection criteria here: 10 A at 24 V, 2 A at 48 V and 60 V, 1 A at 110 V, 0.9 A at 125 V, and 0.3 A at 220 V. These ratings define the maximum inductive DC load the contacts can break reliably. For a 24 VDC control circuit — typical for PLC outputs — the 10 A rating provides generous headroom for driving multiple contactor coils or solenoid valves in parallel. The arcing time is tight at 10 ms, and the mechanical life is rated at 10,000,000 operations, which suits high-duty-cycle applications like packaging or material handling lines.
Mounting and panel integration — S0 footprint
The S0 contactor measures 45 mm wide, 102 mm high, and 107 mm deep. Clearance requirements: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the side. The mounting position allows ±180° rotation on a vertical surface and ±22.5° tilt forward/backward. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C.
Wiring — spring terminals, conductor ranges
The magnet coil uses spring-type terminals. Main contacts accept solid or stranded conductors from 1 to 10 mm². For auxiliary wiring, two conductors of 0.5 to 2.5 mm² each are supported. The auxiliary switch is not fitted as standard. No special tooling is needed beyond a screwdriver for the spring-cage release.
Operating frequency — duty cycle limits
Maximum switching frequency at AC-1, AC-2, AC-3, and AC-3e duty is 1,000 operations per hour. At AC-4 duty (frequent plugging or inching), the limit drops to 300 operations per hour. These figures govern the thermal load on the contacts; exceeding them in a high-duty application will shorten contact life.