The Siemens SIRIUS 3RH1431-1BW40 is a size S00 auxiliary contactor with a 48 VDC coil, three normally-open and one normally-closed instantaneous contacts. It's built for control-circuit switching in motor starter assemblies, conveyor zone logic, or any panel where you need to multiply contact signals from a PLC or relay output. The 48 VDC coil draws 3.2 W closing and holding, so the power supply budget is straightforward — no inrush spike to derate against.
Ratings and what they mean for fit
The contact ratings are given per voltage: 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. These are thermal current values for the auxiliary contacts — they tell you the continuous current the contacts can carry at each voltage level. For a 24 VDC control circuit feeding multiple sensor inputs, the 10 A rating gives plenty of headroom. At 690 V, the 1 A limit means this contactor is not for power switching; it's strictly a signal-level auxiliary device. Pickup voltage is 0.8 x rated (38.4 VDC), drop-out is 1.1 x rated (52.8 VDC). That's a standard margin — the coil will reliably pull in at 38.4 V and drop out when voltage rises above 52.8 V. The 6 kV surge voltage resistance (rated impulse withstand) means it can handle transient spikes common on industrial control panels without flashover. Mechanical life is 5 million operations typical. Contact reliability is rated at one incorrect switching per 100 million operations at 17 V, 1 mA — that's the dry-circuit reliability spec for low-level signal switching. Pollution degree 3 (conductive pollution or dry non-conductive that becomes conductive) is typical for industrial control panels not in a sealed enclosure.
Mounting and integration
Mounts via screw or snap-on to DIN rail. The size S00 footprint is compact: 57.5 mm high, 90 mm wide, 72 mm deep. The mounting position is flexible — +/-180° rotation on a vertical surface, and can be tilted forward/backward by +/-22.5°. That's useful when you're squeezing it into a crowded panel alongside contactors and overload relays. IP20 on the front means it's protected against solid objects larger than 12.5 mm (fingers), but not against moisture — keep it inside an enclosure. Wire termination accepts solid conductors: 2x (0.5... 1.5 mm²), 2x (0.75... 2.5 mm²), or 2x 4 mm². AWG equivalents: 2x (20... 16), 2x (18... 14), or 1x 12. The auxiliary switch block is field-expandable (product extension auxiliary switch: Yes), so you can add more contacts if the built-in 3 NO + 1 NC isn't enough.