What it is and what it does
The Siemens 3RH1140-2JC40 is a SIRIUS coupling relay — a compact auxiliary contactor block designed to switch control circuits, signal lamps, PLC inputs, and small solenoid loads in a panel. It carries 4 NO instantaneous contacts rated 10 A at 24 V in AC-12 duty (resistive load at rated voltage), with a built-in diode surge suppressor across the coil.
Mounting and panel fit
Mounts via screw or snap-on to DIN rail. The 45 mm width and 60 mm height fit a standard S00 contactor footprint. Clearance at the side is 0 mm — it can butt directly against adjacent devices. Mounting position allows +/-180° rotation on a vertical surface and +/-22.5° tilt forward/backward, so it fits tight enclosures or angled subpanels.
Ratings and what they mean for the buyer
The 10 A AC-12 rating at 24 V is the headline figure for resistive switching — it tells you the relay can handle the inrush of a contactor coil or a bank of indicator lamps without welding contacts. For inductive loads at higher voltages, the current capability drops: 6 A at 230 V, 3 A at 400 V, 1 A at 690 V. The 4 NO contacts are all instantaneous (no delayed or make-before-break), so timing-critical circuits need external delay modules. IP20 on the front means it's protected against finger contact but not moisture — keep it inside a sealed enclosure. Shock resistance of 10g / 5 ms and 5g / 10 ms covers most industrial vibration environments. Pollution degree 3 means it's rated for conductive pollution typical in control panels.