What It Is and Where It Fits
The Siemens 3RH2140-2LB40 is a SIRIUS coupling relay sized S00, designed for switching auxiliary circuits in control panels. It carries 4 instantaneous N/O contacts and a 24 V DC coil rated at 2.8 W closing power, with a built-in varistor surge suppressor across the coil. The relay mounts on standard 35 mm DIN rail via screw or snap-on, and the mounting position is flexible: ±180° rotation on a vertical surface, plus ±22.5° tilt forward/backward. This makes it straightforward to fit into tight panel layouts or retrofit into existing SIRIUS contactor assemblies. Clearance distances are specified: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the side, so plan your DIN-rail spacing accordingly to maintain arc flash and creepage margins.
Switching Ratings — What They Mean for Your Circuit
The contact rating is 10 A at 24 V AC/DC and also 10 A at 230 V AC, so it handles both control-voltage loads and higher-voltage auxiliary circuits. At 400 V AC it's rated 3 A, and at 690 V AC it's 1 A — these numbers matter when switching contactor coils or signal lamps fed from different line voltages. Mechanical endurance is 30 million operations typical. Electrical life at AC is 10,000 operations per hour. Arcing time is 10 to 15 ms, and the minimum DC switching duration is 7 to 20 ms. For DC circuits, ensure the load time constant doesn't exceed these windows to avoid contact welding.
Environmental and Compliance
Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. Pollution degree 3 means it's suitable for industrial environments with conductive pollution or dry non-conductive pollution that becomes conductive due to condensation. RoHS compliance date is 2009-10-01, covering the EU RoHS directive. The varistor surge suppressor is integrated — no external snubber needed for most inductive loads.