The Siemens SIRIUS 3RW4038-1TB04 is a size S2 soft starter rated 72 A at 40 °C, 62 A at 50 °C, and 60 A at 60 °C — so the 40 °C figure is the one to spec against for a standard panel environment; above that, the 50 °C and 60 °C ratings give you the thermal derating curve without guessing. It uses thyristors for the soft-start ramp and includes an integrated bypass contact system, which means the thyristors are only in circuit during start/stop — no continuous dissipation from the semiconductors once the motor is at speed.
Mounting is screw and snap-on, sized for a 55 mm wide footprint on DIN rail or a backplate; the size S2 frame keeps it compact for a 72 A device. Clearance requirements: 60 mm above, 40 mm below, 30 mm at the sides — plan the enclosure layout accordingly, especially if you're adding the optional fan (which changes the allowable mounting angles). Main circuit connections use screw-type terminals accepting 2x (1.5... 25 mm²) stranded or 2x (0.5... 2.5 mm²) solid; auxiliary contacts take 2x (20... 14) AWG. The back and front clamping points each handle 16... 2 AWG.
Operating temperature range is -25... +60 °C; storage from -40... +80 °C. Derating starts at 40 °C, which the 50 °C and 60 °C current ratings already reflect. Minimum load is 20 % of the rated current — below that, the soft starter may not trigger the thyristors reliably, so don't use it on a motor drawing less than about 14.4 A at 40 °C ambient. No inside-delta circuit configuration — this is a standard in-line soft starter, not a six-wire delta variant. Maximum motor cable length is 300 m. External reset input is available; fault indication via a red display.