What this soft starter delivers
The Siemens 3RW4026-2BB15 is a SIRIUS soft starter in the Size S0 frame, rated 25 A at 40 °C. That 25 A figure is the continuous motor current it can handle in standard ambient — at 50 °C it derates to 23 A, and at 60 °C to 21 A, so if your panel runs hot you size off the derated number, not the headline. It carries an integrated bypass contact system, meaning once the motor is up to speed the thyristors are shorted out — no continuous heat dissipation from the semiconductors, which keeps the enclosure cooler and extends component life. Control supply is 110-230 VDC, a single DC rail that covers most industrial control voltages without needing a separate transformer tap.
Depth is 155 mm, so account for that when spacing the backplane. Main current circuit uses spring-loaded terminals; auxiliary and control circuits also use spring-loaded terminals. Accepts 2x (0.25... 2.5 mm²) solid or stranded — strip length is whatever the terminal spec calls for, but 8 mm is typical for this class. Clearance: 60 mm upwards, 40 mm downwards, 15 mm at the sides — those are the minimum air gaps for heat dissipation, not suggestions.
Protection and control features
Built-in motor overload protection and intrinsic device protection — the soft starter monitors its own temperature and the motor current. Adjustable current limitation lets you set the starting torque profile without external hardware. External reset is supported — useful if the starter is inside a locked panel and you want a remote reset button on the door. Minimum load is 20 % of the rated current; below that the internal current sensing may not trip reliably. Rated insulation voltage is 600 V, and the pollution degree is 3 per IEC 60947-4-2 — that's conductive pollution typical of industrial environments, so no derating needed for dusty or mildly humid panels.