What this part is and what it does
The Siemens 3RT2027-2KA40 is a SIRIUS coupling contactor in size S0 — a compact, DIN-rail-mountable switching device designed for isolating and switching DC control circuits, typically between a PLC output module and a downstream load or as an interface between different voltage domains in a panel. It is rated for 10 A at 24 V DC and 2 A at 48 V DC, with a DC switching capacity that drops to 0.3 A at 220 V DC — so the buyer needs to match the contactor's DC-13 or resistive rating to the actual load voltage and current, not just the coil voltage. The coil is 24 V DC, and the contactor is fitted with spring-type terminals — cage-clamp style — which speeds wiring and eliminates screw-torque checks on the line.
Mounting and integration
Fastens via screw or snap-on onto 35 mm DIN rail per DIN EN 60715. The mounting position allows ±180° rotation on a vertical surface and ±22.5° tilt forward/backward — useful when the panel layout forces an unconventional orientation. Clearance requirements: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the side. At 45 mm wide, 102 mm high, and 107 mm deep, it fits a standard S0 footprint and leaves room for adjacent devices on the same DIN rail. Wire range: solid or stranded 1 … 10 mm², with dual-wire capability 2x (0.5 … 2.5 mm²). Spring terminals accept ferruled or solid conductors — strip length follows the manufacturer's recommendation for the terminal type.
Switching performance and lifecycle
Mechanical endurance is rated at 10 million operations typical. Electrical switching frequency depends on the duty category: up to 1,000 operations per hour at AC-1 (resistive), 750/h at AC-2 and AC-3 (motor starting/running), and 250/h at AC-4 (plugging/inching). Arcing time is 10 … 10 ms, and the DC make/break time is 19 … 21 ms — consistent with a standard DC contactor response.
Environmental and compliance
Operates in ambient temperatures from -25 °C to +60 °C; storage range is -55 °C to +80 °C. The contactor has no built-in auxiliary switch — if feedback or status signaling is needed, a separate auxiliary contact block must be added.