What this auxiliary switch does in a panel
The 3RH1921-1EA11 is a SIRIUS auxiliary switch block designed to clip onto S0-size Siemens contactors — specifically the 3RT1 series — to signal contactor position back to a PLC or status lamp. It carries a single normally-open (NO) instantaneous contact, so it closes the instant the main contactor picks up, with no delay for mirror-contact compliance per IEC 60947-4-1 when paired with a 3RT1. The AC-12 maximum is also 10 A, meaning it handles resistive and light inductive loads in control circuits without derating at low voltage.
Snap-on footprint and wiring
This block measures 10 mm wide, 80 mm tall, and 71 mm deep — a single-module width that clips directly onto the contactor without taking extra DIN rail space. The snap-on mounting means it attaches laterally to the 3RT1, not to the rail itself. Finely stranded wire with ferrule is also supported in the same range. The IP20 front protection keeps fingers out inside the enclosure.
RoHS compliance date is July 1, 2006, so it meets the EU directive for new installations.