The Siemens 3RH2911-2HA20 is a SIRIUS auxiliary switch block that snaps onto the front of contactor relays and power contactors in frame sizes S00, S0, S2, and S3. It carries two instantaneous normally-open contacts — no leading or lagging delay built in. This is the part you add when the main contactor needs to signal its position back to a PLC, light a panel indicator, or interlock another device in the circuit.
Snap-on mounting means it clips directly onto the front of the contactor — no tools, no DIN rail. Dimensions are 36 mm wide, 47.7 mm deep, 41.5 mm tall. The IP20 protection on the front is standard for enclosed panels; keep the panel door closed during operation. Wiring accepts 2x (0.5 to 2.5 mm²) solid or stranded, or 2x (20 to 14 AWG). Finely stranded with ferrule goes up to 1.5 mm². Strip length and screw torque follow the standard SIRIUS practice — the spring-cage terminal is the same as the 3RT2 contactor family.
Compliance and reliability
The auxiliary contacts are mirror contacts per IEC 60947-4-1 when used with 3RT2 contactors — meaning if a welded contact is detected, the mirror contact's state is guaranteed to reflect the main contact position, a safety requirement for certain isolation circuits. RoHS compliance date is noted as October 1, 2009.