What this contactor is and where it fits
The Siemens 3RT2027-1BF44 is a SIRIUS power contactor in the Size S0 frame, designed for switching motor loads and resistive circuits in industrial control panels. The 110 V AC coil uses screw-type terminals and mounts via screw fixing or snap-on onto 35 mm DIN rail per DIN EN 60715. The 45 mm width and 151 mm depth fit standard panel layouts; the S0 frame size is the mid-range footprint in the SIRIUS contactor family, balancing current capacity with panel density.
Ratings that decide the fit
Operating temperature range of -25 to +60 °C covers most indoor panel environments; storage from -55 to +80 °C. Mechanical life is typical 10,000,000 operations — this is the no-load endurance figure, not the electrical life under load. Switching rates vary by duty: up to 1,000 cycles/hour at AC-1 (resistive), 750/h at AC-2 and AC-3 (motor starting/running), and 250/h at AC-4 (plugging/inching) (–,). The AC-3e rating also caps at 750/h. For a motor starter application, the AC-3 rate is the one that governs — plan for 750 operations per hour maximum under full-load switching.
Wiring and clearances
Main contacts accept solid or stranded conductors from 1 to 10 mm². Auxiliary contact wiring uses 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²). Minimum clearance distances: 10 mm upwards, forwards, and downwards; 6 mm at the sides. Mounting position allows ±180° rotation on a vertical surface and ±22.5° tilt forward/backward — useful when fitting into tight or angled enclosures.