What It Is and Where It Fits
The Siemens 3RT2026-1BW40 is a SIRIUS power contactor in the S0 frame size, built for switching motor loads and resistive circuits in control panels. It's an active-production part, so you're not hunting for NOS or surplus — it's a current catalog line. The coil is rated at 48 V DC, with screw-type terminals. That 48 V coil makes it a fit for control systems running a 48 VDC bus — common in some industrial and rail-adjacent applications — rather than the more typical 24 VDC or 110 VAC coils you see on the shelf.
Mounting and Clearance
It snaps onto 35 mm DIN rail per DIN EN 60715, or you can screw-mount it. The S0 footprint is compact at 45 mm wide, 85 mm tall, and 107 mm deep — that depth is the dimension to watch if you're shoehorning it into a shallow enclosure or a tight backpanel layout. Clearance requirements are straightforward: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the sides. That's tight enough to stack contactors side-by-side in a multi-pump starter section without wasting rail space. Mounting position is flexible — it can be rotated ±180° on a vertical surface and tilted forward/backward ±22.5°. That helps when you're retrofitting into an existing panel where the rail is already welded in at an odd angle.
Ratings and What They Mean for the Line
For motor starting duty (AC-3), the contactor is rated for 750 operating cycles per hour. That's about one start every 4.8 seconds — plenty for a conveyor or pump cycling on a level control, but if you're doing rapid reversing on a positioning axis (AC-4), the rate drops to 250 cycles per hour, so plan accordingly. The auxiliary switch is built in, which saves you bolting on a separate side-mount block for basic status feedback to the PLC or indicator light. Mechanical service life is rated at 10 million operations typical — that's well into 'fit-and-forget' territory for most MRO routes. Operating temperature range is -25 to +60 °C, with storage from -55 to +80 °C. That covers most indoor panel environments and unheated warehouses; if this contactor lives near a hot motor or a drying oven, keep it below 60 °C ambient.
Wiring and Termination
Main power terminals accept solid or stranded wire from 1 to 10 mm². For the coil and auxiliary circuit, you can land 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) — handy for daisy-chaining control wiring without a separate terminal block. The contactor's dropout time on DC is 15 to 18 ms, and arcing time is 10 ms. That's fast enough for most emergency-stop circuits, but if you're coordinating with a safety relay that expects a faster break, verify the timing against your safety PLC's input filter settings.
Sourcing Reality
If you're comparing it to the 3RT2026-1KB40 (which carries a 24 VDC coil), the mechanical footprint and wiring are identical — same S0 frame, same DIN rail clip, same wire ranges. The only decision is your control voltage: 48 VDC vs 24 VDC. No rewiring required to swap between them on the power side, just the coil supply.