The Siemens 3RH2911-4HA01 is a SIRIUS auxiliary switch designed for snapping onto the front of contactor relays and power contactors in sizes S00, S0, S2, and S3. Contact reliability is 1 faulty switching per 100 million at 17 V and 1 mA. The ring terminal lug connection means wiring is done with crimped ring terminals, not spring-cage or screw-clamp — factor that into your panel wiring method and terminal strip planning.
Rated operational current at AC-12 (resistive load) is 10 A maximum, and at AC-15 (inductive load typical of contactor coils) it's 1 A at 690 V — so this switch handles control-circuit isolation for the contactor itself, not motor power. The AC-15 current ratings across common control voltages are: 6 A at 24 V, 2 A at 48 V and 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V and 250 V, and 3 A at 400 V — these are the values that govern whether the auxiliary contacts can reliably switch the connected pilot devices or PLC inputs without welding. The mirror contact feature per IEC 60947-4-1 is critical for safety circuits: when used with 3RT2 contactors, the normally-closed mirror contact cannot remain closed if the main contacts weld, providing a reliable feedback path for the safety relay or PLC. Surge voltage resistance rated at 6 kV means the auxiliary switch withstands transient overvoltages typical of industrial control panels without flashover — important for maintaining isolation integrity in mixed-voltage cabinets.
Specify the order code, confirm the contactor frame size (S00 through S3), and the snap-on front mount plus ring terminal connection are fixed.
Snap-on mounting onto the front of the contactor means no DIN rail space is consumed — the auxiliary switch rides on the contactor itself, keeping the panel layout compact. Dimensions are 36 mm wide, 43.7 mm deep, 37.5 mm high — verify clearance in front of the contactor for the ring terminal wiring access, especially in dense panels. Operating temperature range is -25 to +60 °C, storage -55 to +80 °C — adequate for most indoor industrial control panels, but check if your enclosure ambient exceeds 60 °C near heat sources like drives or transformers.