The Siemens 3RA2140-4FD45-0AK6 is a SIRIUS 3RA21 series combination motor starter — a non-reversing unit, frame-mounted, S3 size, rated 28-40 A. It packs a contactor and an overload relay into one assembly, so you land one part instead of two on the DIN rail. That saves panel space and cuts wiring time on motor control circuits up to 40 A.
The 28-40 A current range covers IEC frame-size S3 motor loads. The overload relay inside gives thermal protection, so this starter handles the start-and-run cycle without a separate overload block. For a line-down swap, the S3 footprint matches the standard SIRIUS 3RA21 mounting pattern; no re-drilling the backplate.
Frame-mounted design means the starter bolts directly to the mounting plate — no DIN-rail adapter needed, though it also accepts the standard 3RA21 snap-on foot if you prefer rail mounting. For a commissioning engineer: the overload relay's current-setting dial is accessible from the front, so you can dial in the motor FLA without pulling the unit.