What this reversing starter is built for
The Siemens 3RA6250-1CB33 is a SIRIUS compact reversing starter — two contactors mechanically interlocked in one package, with an integrated overload relay. It handles forward/reverse motor control in a single 90 mm wide unit, saving panel space over two separate contactors plus a mechanical interlock. Control voltage is 24 V AC/DC, so it works off a standard 24 VDC control supply or a 24 VAC transformer without rewiring. The coil holds at 24 V nominal; verify the dropout threshold against your PLC output card's low-side capability. The overload relay offers adjustable Trip Class 10 and 20 — set Class 10 for standard motor protection on conveyors and pumps, Class 20 for high-inertia loads like fans or centrifuges that need a longer start curve before tripping.
Breaking capacity and fault coordination
For a panel fed by a transformer with 50 kA available fault current, this unit provides adequate SCCR headroom without an upstream current-limiting fuse. The 1 500 W rated power at 400 V and 4 A at 480 V / 600 V set the motor-size ceiling. For a 1.5 kW reversing application on 400 V three-phase, this is a direct fit.
Mounting and wiring in the panel
The 90×170×165 mm footprint (W×H×D) fits a standard distribution board depth. Wiring terminals accept solid conductors from 0.5 to 4 mm², or two conductors 0.5 to 2.5 mm² per clamp — enough for a 4 mm² motor supply cable and a 1.5 mm² control loop in the same terminal. The plug-in main current circuit speeds replacement: pull the main plug, swap the unit, reinsert. The 60 °C upper operating limit means it can sit next to a drive or transformer inside a sealed enclosure without derating, provided the enclosure's internal temperature stays below that ceiling.