The Siemens 3RW4076-6BB44 is a SIRIUS soft starter in size S12, designed to ramp up and protect three-phase induction motors in industrial control panels. It delivers 432 A at 40 °C, derating to 385 A at 50 °C and 335 A at 60 °C — the 40 °C figure is the one to size against for most enclosed panels. It includes motor overload protection and adjustable current limitation, so you can set the start current to match the load without an external overload relay.
Mounting and wiring in the panel
Mounts via screw fixing — no DIN-rail clip, so plan for direct panel mounting with the vertical surface orientation. The mounting position allows +/-10° rotation (without fan) or +/-90° with an additional fan, which matters for tight enclosures where airflow dictates orientation. Main circuit connection is busbar, accepting stranded 70–240 mm² or finely stranded 50–240 mm². Auxiliary contacts take 2x (0.5–2.5 mm²) solid. Clearance: 100 mm above, 75 mm below, 5 mm at the sides — the side gap is tight, so keep cable ducts and other devices out of that zone.
The 432 A rating at 40 °C is the headline number, but the derated values at 50 °C (385 A) and 60 °C (335 A) are what govern in a warm enclosure or near other heat sources. The 20% minimum load means it needs at least 20% of the rated current to operate correctly — fine for most motors, but check if you are soft-starting a very small motor on a large unit. The operating frequency covers 50–60 Hz, common for global motor bases.