The Siemens SIRIUS 3RA6120-1CP32 is a compact starter — a direct starter design that combines a motor-protective circuit breaker and a contactor in a single 45 mm wide package. That's the number that decides whether this unit clears a short-circuit on its own or forces a cascade. The trip class is adjustable between Class 10 and 20, so you can match the overload curve to the motor's start profile — handy when swapping between a standard pump and a high-inertia fan on the same line. Mounting is screw-and-snap onto standard DIN rail, any orientation, vertical or horizontal. Wire range accepts 0.5 to 4 mm² solid, or 2x 0.5 to 2.5 mm² — enough for most motor branch circuits up to the rated power. The control voltage is AC/DC 110 to 240 V, 50/60 Hz, drawing 6 W AC or 5.1 W DC maximum — so a single 24 VDC supply won't drive this one; it needs the line-voltage coil.
In the panel
At 45 mm wide, 170 mm tall, and 165 mm deep, it fits the standard SIRIUS compact starter footprint — you can replace an older 3RA61 without re-drilling the subplate. The screw terminals on the main circuit are sized for the wire range above, and the two LEDs give a quick visual on status (trip / on). Ambient range is -20 to +60 °C operating, -55 to +80 °C storage; pollution degree 3 means it's fine in a typical industrial panel without conformal coating. Vibration resistance is tested to 4–5.8 Hz at 15 mm amplitude and 5.8–500 Hz at 20 m/s² — tough enough for a machine-mounted enclosure.