The 3RW4038-2BB05 is rated 72 A at 40 °C, derating to 62 A at 50 °C and 60 A at 60 °C. For a 40 °C panel ambient, this soft starter handles a 37 kW (50 hp) motor at 400 V — the derating curve matters if your enclosure runs hot. The integrated bypass contactor eliminates the continuous I²R loss through the thyristors after start, so the 72 A rating applies to the bypass path, not the SCRs. This keeps the enclosure heat rise lower than a non-bypassed design at full load.
Mounting and clearance — what fits in the panel
Size S2 envelope: 160 mm height, 55 mm width, 170 mm depth. Screw and snap-on mounting to DIN rail — the snap-on foot saves rail space vs through-bolt mounting. Clearance requirements: 60 mm above, 40 mm below, 30 mm at the sides. These are the minimum air gaps for natural convection cooling — stacking devices tighter forces derating. Mounting position restrictions: with the optional fan, the unit can be rotated ±90° and tilted ±22.5° front/back; without the fan, rotation is limited to ±10°. For vertical panels without the fan, keep the unit within 10° of plumb.
Termination and wiring — main and control
For a 72 A motor circuit, 16 mm² stranded is typical — the dual clamping point accepts two conductors per pole for daisy-chaining. Auxiliary contact terminals accept 2x (24... 14) AWG. The control supply is 24 V AC/DC at 50/60 Hz — confirm your control transformer matches; 24 VDC is also acceptable since the rectifier is internal. Maximum motor cable length is 300 m — beyond that, capacitive charging current from the cable can cause nuisance overcurrent trips during start. For long cable runs, add an output reactor.
Protection and control features
Built-in motor overload protection and intrinsic device protection — the soft starter monitors both motor current and its own thyristor temperature. Adjustable current limitation lets you set the start current between 20% and 100% of the rated motor FLA. Minimum load is 20% of the rated current — below that, the motor current may be too low for the overload detection to function accurately. External reset input allows remote fault reset from a PLC or pushbutton. Fault indication via a red LED — the display version shows the fault code for diagnostics. Thyristors are used for the power switching; the inside-delta circuit is not supported, so the unit must be wired in-line with the motor.
Sourced through authorized distribution channels. For current pricing and availability against your BOM quantity, submit an RFQ — the unit is quoted to order with confirmed lead time at quote issuance.