Siemens 3RW3028-1BB04 — SIRIUS Soft Starter, 38 A, S0 Frame
The Siemens 3RW3028-1BB04 is a SIRIUS soft starter in the S0 frame size, rated 38 A at 40 °C, 34 A at 50 °C, and 31 A at 60 °C. Control voltage is 24 V AC at both 50 and 60 Hz. An integrated bypass contact system means the thyristors are shorted out after start, reducing heat dissipation in continuous run. The mounting position allows ±10° rotation and ±10° tilt from vertical.
Derating begins at 40 °C. At 50 °C the current drops to 34 A, at 60 °C to 31 A. Minimum load is 10 % of rated current — below that the soft starter may not trigger reliably. Insulation voltage rated 600 V. Operating frequency 50 … 60 Hz. Maximum motor cable length 300 m — keep that in mind for remote motor runs. No integrated motor overload protection, no intrinsic device protection, no adjustable current limitation, no motor brake output. Inside-delta circuit not supported — this is a standard in-line soft starter, not a six-wire configuration.
Dimensions and Clearances
Width 45 mm, height 125 mm, depth 150 mm. Required clearances: 60 mm upwards, 40 mm downwards, 15 mm at the sides. Solid wire capacity: 2 x (0.5 … 2.5 mm²). Auxiliary contacts accept 2 x (20 … 14 AWG). Front clamping point accepts 1 x 8 AWG or 2 x (16 … 10 AWG).