What it is and what it does
The Siemens 3RH1140-1BN40-0AA6 is a SIRIUS auxiliary contactor in the S00 frame size — a compact, 45 mm wide switching block that mirrors the contactor's armature position to signal back to a PLC or safety relay. It carries four normally-open instantaneous contacts rated 10 A in AC-12 duty (resistive loads at 250 V), so it handles pilot-duty signalling, solenoid valves, and small contactor coils without derating. The 24 V DC coil draws 3.2 W sealed, which is the same as its inrush — no extra hold-in margin to budget for.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail. The S00 footprint — 45 mm wide, 57.5 mm tall, 72 mm deep — fits standard panel layouts and leaves room alongside the main contactor. Wiring accepts solid or ferruled stranded conductors: 2x 0.5–1.5 mm², 2x 0.75–2.5 mm², or 2x 4 mm² per terminal. IP20 on the front means it's protected against finger contact but lives inside an enclosure.
Ratings and what they mean for your panel
The headline number is 10 A at AC-12 (resistive) — that's the current the contacts can make and break reliably for pilot-duty loads like contactor coils, relays, and indicator lamps. For DC switching at 24 V it's also rated 10 A, but at 110 V DC that drops to 1 A and at 220 V DC to 0.27 A — the arc extinction limits DC current more sharply than AC. Rated impulse withstand voltage is 6 kV, which covers surge coordination for industrial control circuits in pollution degree 3 environments. Mechanical life is 30 million operations; contact reliability is one failure per 100 million at 17 V, 1 mA — fine for dry-circuit PLC inputs.