What it is and what it does
The Siemens 3RH1140-2JB40 is a SIRIUS coupling relay designed to switch auxiliary circuits in control panels — think PLC output isolation, interposing between a controller and a motor contactor coil, or extending contact density in a safety circuit. It's a size S00 device, meaning it shares the same compact 45 mm wide footprint as the SIRIUS contactor family, and mounts via screw or snap-on onto a DIN rail. The 24 VDC coil draws a constant 2.3 W whether picking or holding, so there's no inrush spike to stress a PLC output card.
Contact ratings — what they mean for your circuit
This relay carries four instantaneous normally-open contacts (no delayed, lagging, or make-before-break variants). The headline number is 10 A at AC-12 (resistive loads) and 10 A at 24 V rated value — that's the current it can switch when controlling incandescent lamps, resistive heaters, or solenoid valves within the same control voltage. For higher-voltage auxiliary circuits, the current drops off: 6 A at 230 V, 3 A at 400 V, 2 A at 500 V, and 1 A at 690 V. That derating curve tells you this part is at home in 24 VDC or 230 VAC control schemes, not for switching 690 V motor loads directly.
Mounting and environment
The relay mounts on a DIN rail via the integrated snap-on latch or with screws through the base. It can be rotated ±180° on a vertical surface and tilted ±22.5° forward or backward — useful when you're squeezing it into a crowded backpanel. The front face is IP20, so it's protected against finger contact but not washdown; keep it inside a closed enclosure. Pollution degree 3 means it's rated for industrial environments with conductive or dry non-conductive pollution. Operating temperature range is -25 to +60 °C; storage and transport go from -55 to +80 °C. The coil includes a built-in diode surge suppressor, so you don't need an external flyback diode across the coil terminals — one less part to install and one less thing to verify polarity on.
Mechanical endurance
Rated at 30,000,000 mechanical operating cycles — that's the life of the mechanism before wear, not the electrical life under load. For a relay that mostly sits energized in a control cabinet, that number is effectively infinite for the panel's service life. Shock resistance is 10g for 5 ms and 5g for 10 ms, which covers most industrial vibration from contactors and drives in the same enclosure.