SIRIUS S3 circuit breaker, 50 A — UL 489 system protection
The Siemens 3RV2742-5JD10 is a SIRIUS S3 frame circuit breaker rated at 50 A operational current, designed for system protection per UL 489 and CSA C22.2 No. 5. It delivers 100 kA breaking capacity at both 240 V and 400 V AC — that's the same interrupting rating across the common industrial voltage band, so you don't lose headroom stepping from 240 to 400 V. The thermal overload release handles the long-time protection curve; the magnetic short-circuit trip handles the instantaneous fault clearing. That's a clean two-element trip curve for motor branch circuits and feeder protection.
Mounting and wiring — DIN rail, screw terminals, 70 mm²
Main circuit terminals are screw-type, M8, accepting solid or stranded up to 2x 50 mm² or 1x 70 mm². That's a heavy lug for an S3 frame — enough for parallel feeds or a single large conductor. Auxiliary switch option is available (product extension auxiliary switch: Yes). The screwdriver shaft takes a 4 mm hex socket. Clearance: 70 mm above and below, 10 mm at the sides.