PSTB720 soft starter, 720 A in-line
The ABB PSTB720 soft starter 1SFA895018R7000 is a 720 A in-line unit rated for 400 kW at 400 V, handling motors up to 690 V AC on the main circuit. The 720 A in-line rating means it directly switches the motor current without needing an inside-delta configuration for most applications up to that current. Built-in electronic overload protection eliminates the separate overload relay, saving panel space and wiring. Ramp time is adjustable from 0 to 120 seconds, giving you control over acceleration for pumps, conveyors, or compressors.
Inside-delta capability for higher power
When wired in inside-delta configuration, the PSTB720 handles 1247 A and 710 kW at 400 V — roughly 73% more current capacity than the in-line connection. This matters when the motor is larger than the in-line rating but you want to keep the same soft starter frame. The inside-delta wiring places the soft starter in the motor's delta legs, so each phase carries less current. The unit supports this natively with a switch for inside-delta connection.
Control and communication
Control supply voltage is 100-250 V AC; a separate 24 V DC control circuit handles the logic. Communication is via FieldBusPlug (Standard) — a modular plug-in interface for fieldbus connection, not hardwired. Analog output 0-10 V can feed a PLC or panel meter with the motor current or ramp status. Three signal relays — run, fault, and bypass — plus an overload signal relay give discrete status for each state. Main circuit terminals are bars with a 12.5 mm hole for cable lugs; control circuit terminals tighten to 0.5 N·m.