The ABB PSTB370 softstarter, order code 1SFA894015R7020, carries two distinct current ratings that govern how you wire it. In-line connection (the standard configuration, with the softstarter in the motor supply) is rated 370 A — that's your go-to figure for sizing the main circuit, the contactor upstream, and the cable. Inside-delta connection, where the softstarter sits inside the motor's delta winding, jumps to 640 A because each phase handles only a portion of the line current. That 640 A figure is not a higher rating for the same wiring — it's a different topology that lets a smaller unit control a larger motor. At 400 V, the corresponding power ratings are 200 kW in-line and 355 kW inside-delta. The adjustable ramp time spans 0 to 120 seconds, so you can dial in the acceleration for any load from a centrifugal pump to a high-inertia conveyor. The initial voltage during start is set between 30% and 70%, and a step-down voltage special ramp from 100% down to 30% is also available for loads that need a soft deceleration. The current limit function lets you cap the inrush between 1.5 and 7 times the set motor current, and the starting capacity is 3x Ie for 15 seconds — enough to break away most loads without tripping. Communication is via a standard FieldBusPlug, meaning you can snap in a PROFIBUS, DeviceNet, or other fieldbus module without extra wiring. The control supply accepts 100–250 V AC, and there's a separate 24 V DC control circuit for the logic. Three signal relays — run, fault, and bypass — give you dry contacts back to the PLC, and an overload signal relay is also present. The built-in electronic overload protection eliminates the need for a separate thermal relay, saving panel space and wiring.
Main circuit terminals are bars — expect to bolt your cable lugs directly, not clamp stranded wire. The connecting capacity hole diameter is 10.5 mm, so M8 or 5/16" bolts fit. Control circuit terminals use a screw clamp with a tightening torque of 0.5 N·m, accepting 1 x 2.5 mm² rigid wire. The supply circuit also takes 1 x 2.5 mm² rigid. The main terminals are rated IP00 per IEC 60529 and IEC 60947-1 — that means no finger protection at the power connections; the unit needs to live inside an enclosure with a door or cover. The ambient operating temperature range is 0 to +50 °C. If your panel runs hotter than that, you'll need to derate or add forced ventilation. The service factor is 115%, giving you a 15% continuous overload margin above the rated current — useful for intermittent duty cycles.