The Siemens 3RV6901-1D is a transverse auxiliary switch from the SIRIUS family, designed to snap onto the front of a circuit breaker. It adds one CO (changeover) contact — one normally-open and one normally-closed in a single contact block — to the breaker's auxiliary circuit. The part fits breaker frame sizes S00, S0, S2, and S3, which covers the common motor-protective and system-protective breaker range in a 45 mm wide footprint. Rated at 10 A at 690 V AC, this switch handles the signal-level loads typical of control circuits — PLC inputs, contactor coils, indicator lamps — not main power.
Mounting is plug-in fixing: the switch clips onto the front of the breaker without tools. Depth is 17 mm, height 12 mm, width 45 mm — it adds minimal projection beyond the breaker face, which matters when the panel door clearance is tight. Terminals are screw-type, accepting solid or stranded wire from 0.5 to 2.5 mm² (AWG 20 to 14). For fine-stranded wire with ferrule, the same range applies. Two wires per terminal are allowed — useful for daisy-chaining the common to multiple switches.
RoHS compliance date is 05/01/2012, meaning the part has been RoHS-compliant since that date. No separate UL or CSA listing appears in the spec record, but the SIRIUS series typically carries IEC 60947 approvals for industrial control equipment.