What it is and where it fits
The Siemens 3RT2027-1BG40 is a SIRIUS-brand power contactor in Size S0, designed for switching motor loads in control panels. It mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715, with a width of 45 mm and depth of 107 mm — slotting into standard panel layouts without extra adapters. The contactor carries a full-scale factor of 1.1, meaning it can handle continuous current up to 110% of its rated value without tripping — useful for motor starting inrush. Rated operating time at DC is 15 to 18 ms, and arcing time is 10 ms, both typical for this class of IEC contactor.
Key ratings and what they mean for your BOM
At 24 V DC the contactor is rated 10 A — that's the auxiliary contact current capacity, not the main pole rating. For main contact switching, the 230 V AC rating is 5 hp (approx 3.7 kW motor), and at 400 V AC it's rated 3 A. The auxiliary switch is present (yes), wired with 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded. Mechanical life is typical 10 million operations, and maximum operating frequency varies by duty: AC-1 resistive loads up to 1000 cycles/hour, AC-2 and AC-3 motor switching up to 750 cycles/hour, and AC-4 plugging/reversing up to 250 cycles/hour. The AC-3e rating also caps at 750 cycles/hour — that's the energy-efficient motor switching variant.
Mounting and wiring constraints
Mounting position allows +/-180° rotation on a vertical surface, plus +/-22.5° tilt forward/backward — flexible for tight enclosures. Clearances: 10 mm upwards, 10 mm forwards, 10 mm downwards, 6 mm at the side. Main contact wire range is 1 to 10 mm² solid or stranded; auxiliary contacts accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²). Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. The coil terminal type is screw-type, so expect standard screwdriver termination — no spring-cage on this variant.