What this switch does on a contactor
The Siemens 3RH1921-2JE11 is a SIRIUS auxiliary switch block designed to snap onto S0-frame contactors (3RT1 series) and contactor relays. It adds one normally-open and one normally-closed instantaneous contact, wired via spring-loaded terminals. The 10 mm width means it tucks in alongside the contactor without widening the DIN-rail footprint beyond what the S0 frame already occupies. Rated for 6 kV surge voltage and 500 V insulation at pollution degree 3, it handles control-circuit isolation in standard industrial panels. The mirror-contact function per IEC 60947-4-1 (confirmed with 3RT1 contactors) means the NC position mechanically mirrors the main contact position — relevant for safety circuits where you need positive indication that the power contacts have opened.
Snaps directly onto the contactor body — no DIN rail needed for the switch itself, though the contactor mounts on the rail. The second can be mounted laterally, so you can stack multiple auxiliary blocks on one contactor if the control scheme demands more than one NO/NC pair. Spring-loaded terminals accept 2x (0.5... 2.5 mm²) solid or stranded, or 2x (20... 14 AWG). Finely stranded with core-end processing goes up to 1.5 mm². Strip and push; no screw torque to check. The IP20 front protection keeps fingers out but the block is inside the panel anyway.
Durability and contact reliability
Rated for 5 million mechanical operating cycles typical. The 0.3 A draw at 24 V, 48 V, or 60 V is the coil consumption of the contactor it rides on — the auxiliary contacts themselves carry the load of the control circuit they switch.