What it is and where it fits
The Siemens SIRIUS 3RH2140-1MB40-0KT0 is a coupling relay for switching auxiliary circuits. It carries 4 normally-open instantaneous contacts, each rated 10 A at 24 V, and is sized for the S00 contactor footprint. The coil pulls 1.6 W to close and holds at 1.6 W. Mounting is screw-fix or snap-on onto a standard 35 mm DIN rail, and the mounting position is flexible — you can rotate it ±180° on a vertical surface or tilt it ±22.5° forward or backward. That matters when you're squeezing it into a crowded panel on a retrofit. Dimensions are 45 mm wide, 57.5 mm tall, 73 mm deep — it's a compact block that fits alongside S00 contactors in a common rail layout.
Contact ratings and what they mean for your circuit
The contacts are rated for AC switching at 10 000 operations per hour, with an arcing time of 10 to 15 ms. That's fast enough for most relay-logic and PLC-interposing duties, but if you're switching inductive loads, plan for the arc duration in your timing budget. DC switching is specified by pulse duration of 5 to 20 ms — a reminder that DC arcs don't self-extinguish like AC, so the relay is designed to clear quickly. Current ratings drop as voltage rises — a common derating curve for air-break contacts. At 24 V you get the full 10 A; at 230 V it's still 10 A; at 400 V it's 3 A; at 690 V it's 1 A. If you're using this relay to switch a control transformer primary at 400 V, the 3 A limit is the one to watch, not the headline 10 A number. The relay is rated for pollution degree 3, meaning it's suitable for industrial environments where conductive dust or condensation may be present. Operating temperature range is -25 to +50 °C, storage is -55 to +80 °C. Relative humidity minimum is 10 % — no upper limit stated, but the pollution degree 3 rating implies it can handle typical factory floor humidity without creepage issues.
Panel integration notes
Wire termination accepts 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or 2x 4 mm² solid or stranded. That's flexible enough for most control wiring — you can daisy-chain two conductors per terminal for commoning. The 4 mm² option lets you run a heavier feed wire if the relay is some distance from the power supply. Clearance distances: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the side. These are the minimum air gaps to maintain for safe operation at rated voltage. In a dense panel, you'll want to respect the 6 mm side clearance to adjacent devices, especially if they generate heat or arc. The 3RH2140-1MB40-0KT0 does not have a built-in auxiliary switch extension — it's a bare 4-pole relay. If you need additional signaling contacts, you'll add a separate auxiliary switch block from the SIRIUS range. The product extension auxiliary switch field is marked 'No', so plan your feedback wiring accordingly.