What it is and what it does
The Siemens 3RT6026-1KB40 is a SIRIUS coupling contactor in size S0, designed for switching auxiliary and control circuits where galvanic isolation or signal routing is needed rather than main motor loads. It's a 45 mm wide unit with screw-type terminals on both main and auxiliary/control circuits, and it carries an integrated varistor surge suppressor across the coil. The 24 VDC coil draws 6 A at rated value, so check your control transformer sizing — that's a healthy inrush for a 24 VDC bus.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022. The mounting position is flexible — ±180° rotation on a vertical surface, and can be tilted forward/backward ±22.5° on a vertical surface. Side-by-side mounting is allowed, so you can pack multiple units on a rail without forced spacing gaps. Depth is 151 mm, which is standard for the S0 frame; verify gland plate clearance if your enclosure is shallow.