What it is and what it does
The Siemens 3RT2027-2EL20 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads and resistive loads in industrial control panels. It is fitted with a 24 VDC magnet coil terminated via spring-type terminals, which eliminates the need for periodic screw retorquing in high-vibration environments. The contactor includes an integrated auxiliary switch, providing a separate set of contacts for status feedback or interlocking without requiring a separate add-on block.
Key ratings and what they mean for fit
The auxiliary contact is rated at 10 A at 24 V, which is the typical control-circuit voltage in most modern panels. This rating is the current-carrying capacity for the auxiliary circuit, not the main power path — it governs the size of the load the auxiliary contacts can switch, such as a PLC input or a pilot light. Switching frequency is rated at 1,000 cycles per hour under AC-1 (resistive) load, 750 cycles per hour under AC-3 (motor) load, and 250 cycles per hour under AC-4 (inching/plugging) duty. The AC-3 rating is the one that governs most conveyor and pump applications — 750 cycles per hour translates to one start every 4.8 seconds, which is adequate for most standard duty cycles. The coil hold-in voltage is specified at 24 V rated value, with a drop-out threshold that typically falls below 18 V. The spring-type terminals on the coil accept solid or stranded wire from 1 to 10 mm², and also accept two conductors of 0.5 to 2.5 mm² each for daisy-chaining control wiring. Mechanical service life is rated at 10,000,000 operations typical, which is the expected life before mechanical wear (not electrical contact erosion) becomes a factor. Electrical life will be lower and depends on the switched load and duty cycle.
Where it fits in the panel
The contactor mounts via screw or snap-on onto a 35 mm DIN rail per DIN EN 60715. The S0 frame occupies 45 mm width on the rail, with a depth of 97 mm and height of 102 mm. 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, giving flexibility in tight enclosures. Operating temperature range is -25 to +60 °C, with storage range from -55 to +80 °C. The storage range is wider because the contactor is not switching current during storage — the limit that matters for installation is the operating range.