What the 72 A rating means for your motor load
The Siemens 3RW4038-2BB14 is a SIRIUS soft starter rated 72 A at 40 °C, which means it handles motor starting current for loads up to roughly 37 kW on a 400 V three-phase system — the current rating is the one that governs the real motor fit, not the frame size. The integrated bypass contactor means the thyristors are shorted out once the motor is up to speed, so heat dissipation in the cabinet drops to near zero during run — a real advantage for dense DIN-rail layouts where every watt counts.
Panel integration — DIN rail and clearances
Clearance rules: 60 mm upwards, 40 mm downwards, 30 mm at the side. If you add the optional fan, the mounting surface can tilt ±90° rotatable and ±22.5° front-to-back; without the fan, only ±10° rotatable and ±10° tilt.
Wiring and control connections
Main power circuit uses screw-type terminals accepting 2x (1.5... 25 mm²) stranded or 2x (0.25... 2.5 mm²) solid. Auxiliary and control circuits use spring-loaded terminals for 2x (24... 14) AWG. Control supply voltage is 110...230 V DC — note that's DC only, not AC, so don't feed it from a standard 230 V AC control transformer without a rectifier. The maximum motor cable length is 300 m.