The Siemens 3RK1301-0BB20-0AA4 is a SIMATIC direct motor starter rated for 3 kW at 400 V, 50 Hz, with an adjustable trip class 10 and 10A — meaning it protects motor windings during start-up by letting the overload relay ride through the inrush without nuisance tripping, while still clearing a stalled rotor fast enough to keep the copper from cooking. It is a direct-start design (no reversing), so it suits fixed-direction loads like pumps, fans, or conveyors in a controlled start sequence. This starter is part of the SIMATIC motor starter family, built for integration into a Siemens automation architecture. It communicates over PROFINET and PROFIBUS DP, so it reports motor status, current draw, and trip events directly to the PLC without hardwiring each auxiliary contact back to a digital input module. The 2-byte input and 2-byte output process image keeps the bus traffic lean — one starter per slot on the terminal module. The supply voltage is 24 V DC nominal, with a permissible range of 20.4 to 28.8 V DC, so it holds in during a sagging 24 V bus common in mills where long cable runs and multiple loads pull the rail down.
The starter mounts pluggable on a terminal module — it snaps onto a base unit that carries the power and bus wiring, so replacing a failed starter means pulling the module off its base without disturbing the field wiring. That is a real time-saver on a line-down callout: swap the top half, not the whole harness. Mounting position is vertical or horizontal, which gives flexibility in a crowded panel. The enclosure is IP20, so it belongs inside a cabinet, not on the machine frame. Physical dimensions are 290 mm high, 65 mm wide, and 150 mm deep. Depth of 150 mm means it clears most 200 mm deep enclosures, but check the terminal module depth plus wiring bend radius for a shallow gland plate.
That storage range covers unheated warehouses and truck beds in winter. The starter is rated for shock at 5 g / 11 ms and vibration at 2 g, so it survives the mechanical environment of a typical industrial panel with contactors and breakers cycling nearby. Pollution degree is 3 at 400 V and 2 at 500 V per IEC 60664, meaning it is designed for industrial atmospheres with conductive dust or occasional condensation — no conformal coating required for most panel environments. EMC compliance is to CISPR 11, industrial environment (ambience A), so it is intended for factory floor use, not residential or light commercial.