The Siemens 3RV5901-1E is a SIRIUS transverse auxiliary switch designed to plug into the front of circuit breakers in sizes S00, S0, S2, and S3. It provides one normally open and one normally closed instantaneous contact, wired via screw-type terminals. The 45 mm width and 12 mm height match the breaker face; the 17 mm depth projects forward from the mounting plane — a dimension to check when the panel door or adjacent components are tight on clearance.
At 24 V the contacts handle 1 A; at 48 V that drops to 0.3 A; at 60 V it is 0.15 A; at 230 V it recovers to 0.5 A. These are the make-and-break ratings for the contact set — they govern whether the switch can reliably interrupt the connected PLC input, relay coil, or indicator lamp without welding or excessive arcing. For a 24 VDC control circuit drawing 0.5 A, this switch has margin; for a 48 VDC solenoid pulling 0.4 A, it is at the edge of the rating.
Mounting is by plug-in fixing — the switch snaps onto the front of the breaker without tools, occupying the transverse auxiliary switch position. The screw-type terminals accept two conductors per clamp: solid or stranded 0.5 to 1.5 mm² on one side, and 0.75 to 2.5 mm² on the other. For AWG, that translates to 2x (20 to 14) on the smaller side. No DIN-rail space is consumed — the switch rides on the breaker itself.