What it is and what it does
The Siemens SIRIUS 3RT2027-1DB40 is a Size S0 power contactor with a 24 VDC magnet coil, designed for switching motor loads in control panels. It mounts via screw or snap-on onto a 35 mm DIN rail per DIN EN 60715, fitting into the standard enclosure footprint for this frame class. The coil picks up at 0.8x rated voltage and holds in at 1.1x, with a DC dropout delay of 15 to 18 ms — a tight window that matters when coordinating undervoltage releases or safety circuits downstream. Mechanical life is rated at 10,000,000 cycles typical, and the contactor is approved for operating frequencies up to 1,000 1/h in AC-1 duty, 750 1/h in AC-2, AC-3, and AC-3e, and 250 1/h in AC-4 — so it handles high-rep applications like conveyor cycling without derating the mechanism.
Mounting and wiring
The 3RT2027-1DB40 accepts solid or stranded conductors from 1 to 10 mm² on the main circuit, and 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) fine-stranded on the coil and auxiliary terminals. Main contact screws are sized for an 8 to 16 mm spanner, typical for S0 frame terminations. Mounting position is flexible: +/-180° rotation on a vertical surface, plus +/-22.5° tilt forward or backward. Clearance requirements are 10 mm upwards, downwards, and forwards, and 6 mm at the sides — tight enough for dense DIN-rail layouts. The coil uses screw-type terminals, and the built-in auxiliary switch is wired separately — no shared termination block, so the control circuit stays isolated from the load side.
Auxiliary contact ratings
The integrated auxiliary switch is rated for 6 A at 24 V, 2 A at 48 V and 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V, and 3 A at 400 V. At 230 V it carries a 5 hp rating — useful for pilot-duty control of smaller motor starters.