The 3RA2145-4HD45-1NB3: The 36-50 A range governs the motor full-load current it can switch and protect. For a 36 A motor, the starter runs near the bottom of its band; for a 50 A motor, it's at the top. That headroom matters for thermal overload coordination — the overload relay's adjustment range must match the motor nameplate FLA. The S3 frame size dictates the mounting footprint and busbar connections; it's the physical envelope for this current class.
Deployment context
It's wired between the motor branch circuit and the motor itself, combining the switching and protection functions. The non-reversing configuration means it drives the motor in one direction only — no reversing contactor pair inside.