The Siemens 3RW4038-2BB15 is a SIRIUS soft starter rated 72 A at 40 °C, which means it handles motor starting current for loads up to that full-load ampacity — typically a 37 kW motor on 400 V three-phase, though the exact motor power depends on the service factor and duty cycle. The integrated bypass contactor means this unit does not need a separate external bypass — the thyristors are shorted out after start, which cuts heat dissipation and extends relay life. That saves one panel component and the wiring to it. Control supply is 110-230 VDC, so it works on standard DC control buses found in most industrial panels. The operating frequency is 50/60 Hz, covering both mains standards without a setting change.
Dimensions: 55 mm wide, 160 mm high, 170 mm deep. Clearance: 60 mm above, 40 mm below, 30 mm at the sides. Auxiliary and control circuit terminals are spring-loaded, accepting 2x (0.25... 2.5 mm²) solid. The mixed terminal types are common on this class — screw for power, spring for signals — so have both screwdriver and ferrule tools ready. Without the fan, vertical surface only with +/-10° rotation and +/-10° tilt. For most panel layouts, vertical is the default.
Motor overload protection is built in, along with intrinsic device protection and adjustable current limitation. The minimum load is 20%, so it works on lightly loaded motors without nuisance tripping.