What it is and where it fits
The Siemens SIRIUS 3RH2122-1BF40-0AA6 is an auxiliary contactor — a control-circuit switching device, not a main power contactor. It carries 2 NO instantaneous contacts and is driven by a 110 V DC coil that draws 4 W during both pick-up and hold. That constant-power coil design means the control transformer doesn't see a current surge on closure; sizing the DC supply is straightforward. It belongs to the SIRIUS family and is built in the S00 frame size. The S00 footprint is the smallest in the SIRIUS contactor range — 45 mm wide, 57.5 mm tall, 73 mm deep — which keeps the DIN-rail fill factor tight when you're stacking multiple auxiliaries next to a main contactor. Mounting is via screw or snap-on onto a standard 35 mm mounting rail. The mounting position is flexible: ±180° rotation on a vertical surface, plus ±22.5° tilt forward or backward. That's useful when the panel layout forces an unconventional orientation — the contactor's mechanical life of 30 million operations isn't derated by the angle within those limits.
Switching capability — what the DC ratings actually mean
The 110 V DC coil is the identity of this variant. The contact ratings are tabulated by voltage: at 24 V it switches 10 A, at 60 V it's 4.7 A, at 110 V it's 3 A, at 220 V it's 1.2 A, and at 600 V it drops to 0.26 A. These are DC-13 (solenoid/brake) load ratings — the current falls as voltage rises because DC arcs are harder to extinguish. If you're switching an inductive DC load like a brake coil or a solenoid valve, use the voltage row that matches your circuit; don't interpolate between rows. AC ratings are also present: 10 A at 230 V, 3 A at 400 V, 1 A at 690 V. The arcing time is 10–15 ms, and the maximum mechanical switching rate is 10,000 operations per hour. For a signal-level auxiliary contactor those numbers are typical — the contacts are silver-alloy, sized for control-circuit duty, not motor inrush.
Clearance and environment
Minimum clearances to adjacent devices: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the side. That's the spacing needed to avoid heat buildup and arc flashover between auxiliaries packed on the same rail. Pollution degree 3 means it's rated for industrial environments where conductive dust or occasional condensation is present — no additional conformal coating required for most panel builds. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. Relative humidity minimum is 10 % — the contactor is not damaged by dry conditions. The substance prohibition date of 10/01/2009 aligns with RoHS compliance; the part is RoHS-compliant and REACH-registered as standard for SIRIUS products.