The Siemens 3RV2742-5FD10 is a SIRIUS circuit breaker in the S3 frame, rated 35 A operational current at 50/60 Hz. It is designed for system protection and carries UL 489 / CSA C22.2 No. 5 listing — meaning it is certified for branch-circuit protection in North American panels, not just motor-circuit protection. The magnetic short-circuit trip and thermal overload release are both internal, so it combines two functions in one DIN-rail footprint.
Breaking capacity at 240 VAC is 100 kA; at 400 VAC it is also 100 kA. That full-rated interrupting capacity at 400 V matters for panels where the fault current at the board is high — common in industrial distribution upstream of motor control centers. The 35 A frame still clears 100 kA at 400 V, which gives selectivity headroom downstream.
Mounting position any. Clearances: 70 mm above and below, 10 mm at the sides. The S3 frame is physically larger than the S0 or S00 frames — verify the panel cutout and door cutout before swapping from a smaller frame breaker.
Main contacts use M8 screw-type terminals. Accepts solid or stranded: 2x (2.5 … 16 mm²) or 1x (10 … 70 mm²). AWG 8 for the main contacts. The screwdriver shaft is hex socket, 4 mm tip size. The auxiliary switch option is available as a product extension (not included).
Relative humidity 10 to 95 % during operation. Substance prohibitance date 03/01/2017 — the part is RoHS-compliant (REACH and RoHS documentation available from the manufacturer).