What it is and where it fits
The Siemens 3RH2140-1KF40 is a SIRIUS coupling relay designed for switching auxiliary circuits in control panels. It carries 4 normally open instantaneous contacts and is rated for a 110 V DC coil supply. The relay mounts via screw fixing or snaps onto a standard 35 mm DIN rail, making it a direct fit for most industrial enclosures. The S00 contactor size footprint — 45 mm wide, 57.5 mm tall, 73 mm deep — keeps panel space tight. The 4 NO contacts are rated for 10 A at 24 V, 3 A at 110 V, and 1.2 A at 220 V, covering typical auxiliary loads like PLC inputs, signal lamps, and small solenoid valves.
Mounting and clearances
Mounting position is flexible: the relay can be rotated ±180° on a vertical surface and tilted forward or backward by ±22.5°. Minimum clearances to adjacent devices are 10 mm upward, 10 mm forward, 10 mm downward, and 6 mm to the side — enough for airflow and wiring access in a dense panel. Terminals accept 2 x (0.5 to 1.5 mm²), 2 x (0.75 to 2.5 mm²), or 2 x 4 mm² solid or stranded wire. The built-in suppressor diode across the coil simplifies wiring: no external flyback diode needed for DC switching.
Switching performance and environment
Mechanical life is rated at 30 million operations typical. Electrical switching frequency reaches 10,000 cycles per hour at AC; DC switching arcs last 7 to 20 ms. Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C. Pollution degree 3 suits industrial environments with conductive dust or humidity. The relay complies with RoHS substance prohibitions dated October 1, 2009, and carries the SIRIUS brand approvals for UL, CSA, and CE — check the specific certification markings on the nameplate for your jurisdiction.