The Siemens 3RH1140-1HB40 is a SIRIUS coupling relay designed for switching auxiliary circuits — think interposing between a PLC output and a larger contactor coil, or isolating control signals across voltage domains. It's built into the S00 contactor footprint, so it shares the same 45 mm width and snap-on DIN rail mounting as the SIRIUS contactor line. The coil pulls 2.3 W DC both on pick-up and hold, and the rated operating current hits 10 A at AC-12 duty (resistive loads at 24 V).
Terminal wiring accepts solid conductors: two per clamp in 0.5–1.5 mm², 0.75–2.5 mm², or a single 4 mm². That's enough for most control-circuit runs without needing bootlace ferrules, though ferruled stranded is fine. Side clearance is zero — you can butt it against the next device. The IP20 front rating is standard for enclosed panels; keep it behind a gland plate or cabinet door.
The relay has 4 normally-open instantaneous contacts and no auxiliary switch block. Pick-up voltage is 0.7 x rated (about 16.8 V DC); drop-out is 1.25 x rated (30 V DC) — meaning it releases reliably when the coil voltage rises above that threshold, not below. Mechanical endurance is 30 million operations, which outlasts most panel designs. Shock resistance is 10g at 5 ms and 5g at 10 ms, so it holds up in machine-mounted enclosures near presses or conveyors.