What it is and where it fits
The Siemens 3RH1131-2BD40 is a SIRIUS auxiliary contactor in frame size S00 — the smallest footprint in the family, built for control-circuit switching in motor starter and contactor assemblies. Its 42 V DC coil draws 3.2 W during both pick-up and hold, so the coil-supply transformer or PLC output must be sized for that continuous load. Three normally-open instantaneous contacts handle the switching; there are no delayed, leading, lagging, or make-before-break contacts on this variant.
Switching capacity by voltage — what the ratings mean
The contact ratings are given at specific operating voltages, not as a single blanket current. At 24 V it carries 10 A; at 110 V it drops to 1 A; at 230 V it handles 6 A; at 400 V it is rated 3 A; at 500 V it is 2 A; and at 690 V it is 1 A. The 230 V and 400 V figures are the ones most often checked in European panel designs — 6 A at 230 V covers most pilot-duty and signal-lamp loads, while 3 A at 400 V is enough for small contactor coils or indicator circuits in a 400 V line. The 690 V rating (1 A) confirms it can be used in 690 V control circuits, but the current is low enough that you should verify the inrush of the downstream device.
Mounting and wiring details
Mounting is by screw or snap-on onto a DIN rail. The mounting position is flexible: it can be rotated ±180° on a vertical surface and tilted forward/backward ±22.5°, which helps when fitting into a crowded panel where the rail is not perfectly vertical. The screw terminals accept 2x (0.25 … 2.5 mm²) solid or 2x (24 … 14 AWG) stranded — strip length and ferrule size should follow the standard 8 mm practice for this terminal class. Pollution degree 3 means it is rated for industrial environments with conductive pollution or dry non-conductive pollution that becomes conductive due to condensation.
Environmental and mechanical endurance
Operating temperature range is -25 to +60 °C; storage and transport extend from -55 to +80 °C. Shock resistance is 10g / 5 ms and 5g / 10 ms — adequate for most industrial machinery but not for high-g mobile or marine applications without additional damping. The typical mechanical life is 30 million operations, and contact reliability is specified as one incorrect switching per 100 million operations at 17 V, 1 mA — a good figure for low-level signal switching where oxide film on contacts can cause intermittent faults. Surge voltage resistance is rated at 6 kV, which aligns with basic insulation coordination for 400 V systems.