What it is and what it does
The Siemens 3RH1140-2BM40 is a SIRIUS auxiliary contactor in size S00, built to switch control circuits rather than motor loads directly. It carries four normally-open instantaneous contacts, rated for 10 A at 24 V and derated to 1 A at 690 V — so the same block handles 24 VDC PLC outputs and 400 VAC interposing relays without a separate contactor for each voltage level. The 220 VDC coil pulls 3.2 W closing and holding, which means the coil driver sees a steady resistive load, not an inductive spike on dropout.
Mounting and integration
Mounts via screw or snap-on onto a DIN rail, and the mounting position allows ±180° rotation on a vertical surface plus ±22.5° tilt forward/backward — useful when the panel layout forces a non-standard orientation. The 45 mm width and 60 mm height keep it within the S00 footprint, so it slots next to a 3RT2 contactor in a standard motor starter lineup without extra spacing. IP20 on the front means it's protected against finger contact but not washdown; keep it inside the enclosure.
Contact ratings and switching reliability
The four NO contacts are rated for conventional free-air thermal current (Ith) across several voltage bands: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, 2 A at 500 V, and 1 A at 690 V. For the 110 V and 220 V DC control circuits, the ratings drop to 1 A and 0.27 A respectively — a reminder that DC arc extinction is harder than AC, so if you're switching a 220 VDC solenoid, stay under 0.27 A or add a flyback diode. The contact reliability spec calls out one incorrect switching operation per 100 million at 17 V, 1 mA, which is the dry-circuit threshold for PLC input signals; below that, gold-plated contacts would be safer.