What it is and what it does
The Siemens 3RH1140-1BD40 is a SIRIUS auxiliary contactor in size S00, built to extend the contact count on a main contactor or to handle signal-level switching in a control circuit. Its 42 V DC coil pulls in at 0.8x rated voltage and holds at 3.2 W, so the control transformer or PLC output driving it needs to source that inrush and seal current. The four normally-open instantaneous contacts are rated for switching at various voltages: 10 A at 24 V, 1 A at 110 V, 0.27 A at 220 V, 6 A at 230 V, 3 A at 400 V, 2 A at 500 V, and 1 A at 690 V — meaning the same contact set handles both 24 VDC pilot-duty and 400 VAC motor-circuit interlocking, but the ampacity drops fast as voltage climbs.
Panel fit and mounting
This contactor snaps onto a 35 mm DIN rail or screws directly to a mounting plate — the fastening method supports both. At 45 mm wide, 57.5 mm tall, and 72 mm deep, it fits a standard 45 mm slot in a control panel layout. The mounting position allows +/-180° rotation on a vertical surface and +/-22.5° tilt forward/backward, so it can be oriented to match wire routing without derating. The IP20 front means it's protected against finger contact but not washdown — keep it inside an enclosure.
Wiring and termination
Terminals accept solid or stranded copper: 2x (0.5...1.5 mm²), 2x (0.75...2.5 mm²), or 2x 4 mm² per clamp, with AWG equivalents of 2x (20...16), 2x (18...14), or 1x 12. That's enough for daisy-chaining control wiring through the same terminal without a separate junction block. Pollution degree 3 (conductive pollution or dry non-conductive that becomes conductive) is the rated environment — typical for industrial control panels not hermetically sealed.
Environmental and endurance
Operating temperature spans -25 to +60 °C; storage and transport go from -55 to +80 °C. Shock resistance is 10g for 5 ms and 5g for 10 ms, so it survives shipping drops and moderate machine vibration. Contact reliability is rated at one incorrect switching operation per 100 million cycles at 17 V, 1 mA — that's dry-circuit capability for PLC-level signals, not just power contacts. The mechanical endurance is 30 million operating cycles typical.