The ABB PSTB370 soft starter (order code 1SFA895015R7020) carries two current ratings that govern how you wire it into the motor circuit. In-line connection is rated 370 A (Ie), which is the current through the main terminals when the starter is wired in series with the motor leads. Inside-delta connection is rated 640 A — a 73% higher figure because each phase handles only the winding current, not the line current. That inside-delta rating lets you downsize the starter for the same motor kW: at 400 V, the in-line power rating is 200 kW, while inside-delta reaches 355 kW. Pick the wiring topology first, then size the starter. The ramp time is adjustable from 0 to 120 seconds, giving you a wide window to match the acceleration profile of conveyors, pumps, or fans. Initial voltage during start is set between 30% and 70% of line voltage, and a separate step-down voltage special ramp (100% down to 30%) handles deceleration or soft stopping.
Integrated protection and control signals
Built-in electronic overload protection is standard — no separate overload relay needed. The current limit function is adjustable from 1.5 to 7 times the rated current Ie, and starting capacity is 3x Ie for 15 seconds. Three dedicated signal relays (run, fault, bypass, overload) give you discrete dry contacts for the PLC or annunciator panel. A red LED indicates a fault condition; a yellow LED signals protection activation. The control supply voltage accepts 100...250 V AC, and a separate 24 V DC control circuit is available for the logic interface. Communication is via a standard FieldBusPlug — the starter accepts a plug-in fieldbus adapter for PROFIBUS, DeviceNet, or similar protocols, but the base unit ships without the module installed.
Main circuit terminals are bars with a 10.5 mm hole diameter — expect to use ring lugs or busbar connections, not wire ferrules. Control circuit terminals accept rigid 1 x 2.5 mm² wire with a tightening torque of 0.5 N·m. The supply circuit connection is also rigid 1 x 2.5 mm². Ambient operating temperature range is 0 to +50 °C, with a 115% service factor for continuous overload capability. Degree of protection at the main terminals is IP00 — the starter is intended for enclosure mounting, not standalone outdoor use.