The Siemens 3RV1936-2C is a SIRIUS door-coupling rotary operating mechanism designed for EMERGENCY-OFF applications on circuit-breakers size S2. It's the heavy-duty operator that lets you mount the breaker inside the enclosure while the red/yellow actuator sits on the door — a standard safety layout for panel builders who need a single, visible emergency-stop point without running the breaker handle through the panel face.
This part is in product phase-out. The description explicitly flags the phase-out and names the preferred successor: the 3RV2936-2C. The drilling pattern changes between the two, so a panel designed around the 3RV1936-2C will need rework to accept the replacement. If you're holding a BOM line with this code, you have two paths: source the 3RV1936-2C through independent distribution against an RFQ (we can quote it), or plan the panel modification to adopt the 3RV2936-2C. There is no functional substitute from a different series that drops in without changes.
The 78 mm depth, 75 mm width, and 75 mm height define the operator's through-panel footprint — critical for door cutout planning and clearance behind the door. The 300 mm length is the shaft or cable length that reaches from the operator to the breaker mechanism; verify this matches your enclosure depth from door to breaker mounting plane. Screw fixing means you need a screwdriver and access to the back of the door for installation — no snap-on or tool-less mount. Rated for a maximum of 151 operating cycles per hour. That's about one cycle every 24 seconds — fine for occasional emergency-stop use, but not for a continuously cycled disconnect.
The actuator color is red / yellow, which is the standard international scheme for emergency-stop devices — red pad on yellow background. This is a regulatory expectation, not a cosmetic choice; EN ISO 13850 and IEC 60947-5-5 both mandate that emergency-stop actuators be red on yellow. If your panel is being certified, this part meets that requirement out of the box.