Sizing against the thermal envelope
The 3RW4028-2TB04: That derating starts at 40 °C, so if your enclosure runs hotter than that — common with drives or transformers sharing the cabinet — size the bypass rating for the 60 °C figure, not the 40 °C headline. The integrated bypass contact system means once the motor is at speed, the thyristors are shorted out — no continuous heat dissipation from the power semiconductors, just the bypass contact resistance.
Termination and panel fit
Main current circuit and auxiliary/control circuits both use spring-loaded terminals — no screw torque to check, no re-torquing after thermal cycling. The main circuit accepts 2x (16... 10) plus 1x 8 AWG; auxiliary side takes 2x (24... 14) AWG. Mounting is screw or snap-on onto DIN rail, Size S0 footprint: 45 mm wide, 150 mm tall, 155 mm deep. Clearance needs: 60 mm above, 40 mm below, 15 mm at the sides. Mounting position matters — with the optional fan the unit can rotate ±90° on a vertical surface or tilt ±22.5° front/back; without the fan, rotation is limited to ±10°.
Protection and control logic
Built-in motor overload protection and intrinsic device protection cover the soft starter itself and the downstream motor — no separate overload relay needed for most applications. Adjustable current limitation lets you set the starting current between 20 % and 100 % of the rated current — useful for gentle starts on pumps or conveyors where mechanical shock is the concern. External reset input and a red fault signal LED give the panel operator a clear indication and remote reset capability without opening the enclosure.