What this auxiliary switch does on a contactor
The 3RH1921-1EA02-ZX90 is a SIRIUS auxiliary switch block that snaps onto the side of an S0-size contactor or contactor relay — it adds extra signal contacts without widening the main power path. The block is 10 mm wide — it adds minimal DIN-rail footprint when side-mounted, and the IP20 front protection means it's safe for open-panel use behind a cabinet door.
Snap-on mounting to the contactor side — no DIN-rail slot consumed, but the block adds 10 mm to the assembly width. The mirror contact feature per IEC 60947-4-1 is present when paired with a 3RT1 contactor — this matters for safety circuits where the N/C contact must positively indicate the main contact position.
Environmental and compliance envelope
RoHS compliance date is July 1, 2006 — the part meets the original RoHS directive; verify REACH and UKCA status against the current Siemens declaration pack for your jurisdiction.