What it is and what it does
The Siemens 3RT2026-2BF40 is a SIRIUS power contactor in the S0 frame size, built for switching motor and resistive loads in industrial control panels. It carries a 110 V AC coil and uses spring-type terminals for the main and auxiliary circuits — no screwdriver needed, which speeds up panel wiring and cuts down on loose connections out here in the grease. Rated for a coil pickup at 0.8 x rated voltage and a dropout at 1.1 x full-scale, it holds in across the -25 to +60 °C operating range — wide enough for most cabinet environments without forced cooling.
Key ratings and what they mean for fit
The 110 V AC coil draws its rated value at 110 V; the contactor handles 10 A at 24 V DC, 2 A at 48 V and 60 V DC, 1 A at 110 V DC, 0.9 A at 125 V DC, 0.3 A at 220 V DC, and 3 A at 400 V AC — so it's sized for moderate motor loads and control circuits, not high-current feeders. Mechanical life is rated at 10 million operations typical, with switching frequencies up to 1000 cycles per hour at AC-1 (resistive) and 750 per hour at AC-3 (motor). That's enough for frequent cycling on a conveyor or pump station, but if you're hammering it at AC-4 (plugging/reversing) you're limited to 250 per hour — plan the duty cycle accordingly.
Mounting and integration
Mounts on a 35 mm DIN rail per EN 60715, using either screw or snap-on fastening. The S0 footprint is 45 mm wide, 102 mm tall, 107 mm deep — fits standard panel spacing, but watch the 107 mm depth when the gland plate or door is tight. Clearance requirements: 10 mm upwards and forwards, 10 mm downwards, 6 mm at the sides. That's lean enough for dense rail packing, but don't crowd the arc chute side — arcing time runs 10 to 10 ms, and the magnetic blowout needs room to stretch the arc. Mounting position is flexible — +/-180° rotation on a vertical surface, plus +/-22.5° tilt forward or backward. That helps when the panel layout forces an odd angle.
Wiring and terminals
Spring-type terminals accept solid or stranded wire from 1 to 10 mm², and you can land two conductors of 0.5 to 2.5 mm² each in the same clamp — handy for daisy-chaining control power or looping through an auxiliary contact. The auxiliary switch is built in (yes/no field says yes), and the main contact sequence is 18 to 8 — that's the standard NO/NC arrangement for SIRIUS contactors.