The Siemens 3RH2911-4FA40 is a SIRIUS auxiliary switch block that snaps onto the front of contactor relays and power contactors in sizes S00, S0, S2, and S3. It provides 4 normally-open instantaneous contacts and no normally-closed or lagging contacts, making it a straightforward add-on for signaling or interlock circuits on a contactor. The connection type is ring terminal lug, which is a secure, vibration-resistant termination common in panel builds where screw terminals are standard.
Rated operational current at AC-15 at 24 V is 10 A, and at 230 V it carries 6 A — these are the contact ratings for inductive loads like contactor coils. The AC-12 maximum rating is also 10 A, covering resistive loads. For DC switching, the ratings drop with voltage: 6 A at 24 V, 2 A at 48/60 V, 1 A at 110 V, 0.9 A at 125 V, and 0.3 A at 220/250 V. This derating curve is typical for DC arcs — expect to size for the actual DC voltage in your circuit. The mirror contact feature per IEC 60947-4-1 is present when used with 3RT2 contactors, meaning the N/O contacts cannot weld closed if a power contactor welds — a critical safety function for fail-safe circuits.
Because it snaps onto the front of S00 through S3 contactors, it is a direct spare for any panel using those frame sizes. No rewiring is needed if replacing a failed unit of the same type.
Dimensions: 36 mm wide, 37.5 mm tall, 43.7 mm deep. The snap-on mounting means it clips directly onto the contactor front without DIN rail space. IP00 on the front — no water or dust ingress protection, so this switch lives inside a closed panel or enclosure, not on the machine exterior. RoHS compliance date is 2009-10-01, covering EU substance restrictions.