What it is and where it fits
The Siemens 3RH1921-1MA11 is a SIRIUS auxiliary switch block that adds one normally-open and one normally-closed contact to a 3RT1 power contactor. It snaps onto the contactor's front side — no tools, no wiring changes to the main circuit. The screw-type terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) conductors with core-end processing, or the AWG equivalents.
Switching capacity across voltages
Rated for AC-15 duty (solenoid and electromagnetic loads), the block carries 10 A at 24 V, 6 A at 125/230/250 V, 3 A at 400 V, and 0.26 A at 600 V. These are the switching currents at the respective control voltages — match your circuit's voltage to the row that governs the contactor coil or small solenoid you're piloting.
Reliability and environmental limits
Mechanical service life is 10 million switching cycles typical. Contact reliability is rated at one faulty switching per 100 million operations at 17 V, 1 mA — a dry-circuit spec that matters for PLC-level signal switching where oxide films on silver contacts can cause intermittents. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. Front-side protection is IP20, so the block belongs inside an enclosure, not exposed to washdown.
Panel integration notes
Snap-on mounting onto the 3RT1 contactor body. Dimensions: 44 mm wide, 38 mm tall, 51 mm deep. The cable entry is at the bottom — plan your wire routing accordingly; the block does not accept top-entry wiring. Rated impulse withstand voltage is 6 kV, and insulation voltage is 690 V AC at pollution degree 3.