The Siemens 3RA1145-4FB44-1BP4 is a SIRIUS non-fused motor starter — a direct-starter assembly that combines a contactor and a thermal bimetallic overload relay in one S3-size package, rated for AC-3 switching up to 690 V. The thermal bimetallic design provides a true RMS current sensing that handles the starting inrush without nuisance trips, unlike electronic overloads that can be more sensitive to harmonics. Snap-on mounting on a 35 mm standard rail in a vertical position keeps panel integration straightforward — no screws or brackets needed for the rail itself. The S3 size is a common footprint in Siemens SIRIUS load feeders, meaning it slots into existing S3 busbar systems and link modules without adapters.
Rated 40 A at both 480 V and 600 V, this starter handles motor loads up to 40 hp at 575/600 V and 30 hp at 460/480 V. At 400 V it delivers 18,500 W. These are the AC-3 motor-switching ratings — the values that govern real-world motor starting, not the resistive AC-1 numbers. The 690 V maximum gives headroom for 600 V class systems without derating. The supplied contactor is a 3RT1044-1BP40 and the link module is 3RA1941-1BA00 — both standard SIRIUS S3 components. If you already have an S3 busbar system, this starter mates directly; no special adapter needed. The main terminal accepts stranded wire from 2.5 to 70 mm², or 2x (10 to 50 mm²), which covers most motor feeds up to 40 A without needing a separate terminal block.
The enclosure measures 220 mm deep, 70 mm wide, and 330 mm high. Clearance requirements: 90 mm upward, 10 mm forward, 10 mm downward, 12 mm at the side, and 0 mm backward (–,).