What it is and what it does
The Siemens 3RT1026-3KF80 is a SIRIUS S0-frame power contactor — a switching workhorse for motor loads in control panels. It carries a 15.5 A AC-4 rating at 400 V, which is the duty cycle for reversing or inching a motor where the contacts make and break under full load. That number, not the AC-3 figure, is the one that governs real wear in frequent-start applications. The built-in varistor surge suppressor clamps the coil flyback spike, so you don't need an external snubber on the control wiring. Saves a DIN-rail slot and a wiring step.
Mounting and wiring fit
Snaps onto 35 mm DIN rail per EN 50022 — standard panel integration. The S0 footprint is 45 mm wide, 88 mm tall, 100 mm deep, so it fits a compact row alongside other SIRIUS gear. Side-by-side mounting is allowed, with a 6 mm gap to adjacent devices for cooling. Main circuit terminals are screw-type, accepting 2x (0.25...2.5 mm²) solid or 2x (1...2.5 mm²) stranded, up to 2x 10 mm² max. That's enough for the 15.5 A AC-4 path without piggyback lugs.