What is the 3RK4320-3DQ51-0BA2 and where is it used?
It integrates motor protection, switching, and bus communication into one unit, so it replaces a separate contactor, overload relay, and gateway for small motor loads on an AS-Interface line. Rated 1.25 A at 400 V in AC-3 duty (switching motor loads), it is sized for fractional-horsepower motors — pumps, small conveyors, or valve actuators — where the CLASS 10 bimetal overload gives fast trip under locked-rotor conditions.
The 1.25 A AC-3 rating at 400 V is the motor-switching current — not the resistive (AC-1) rating. For a 400 V three-phase motor, this typically covers a 0.37 kW (0.5 HP) load. If your motor draws more, this starter will trip on overload or fail to break the stalled current. The 20.4...26.4 V DC control supply powers the electronics and the integrated motor brake output (if used). The brake output is rated for a DC brake — no brake control for 180 V DC or 400 V AC is built in, so external brake switching is needed for those voltages. Two digital inputs are available on the unit for local pushbuttons or limit switches, reducing wiring back to the PLC. The AS-Interface bus carries the I/O and control data over a single two-wire cable.
Dimensions are 245 mm wide × 215 mm high × 205 mm deep. Plan for side clearance to route the AS-Interface cable and the motor power wires; the IP54 housing needs no extra air gap for cooling. Short-circuit protection is provided by an upstream circuit breaker (not a fuse) — the starter itself is not a stand-alone breaker.