SIRIUS MCU motor starter for AS-Interface networks
The Siemens 3RK4320-3FR51-0BA0 is a SIRIUS MCU motor starter designed for direct-on-line starting of three-phase motors over an AS-Interface bus. It integrates the motor protection, switching, and AS-i communication into a single IP55-rated enclosure, eliminating separate contactor, overload relay, and gateway wiring. The Class 10 bimetal overload protects against sustained overcurrents typical of stalled rotor conditions. Operating voltage is 340 to 440 V AC at 50/60 Hz, with a DC control supply of 20.4 to 26.4 V DC for the AS-Interface bus power and logic.
AS-Interface integration and mounting
This motor starter communicates natively via the AS-Interface protocol — no PROFIBUS or PROFINET onboard. Mounting is flexible: the 182 mm wide, 220 mm tall, 145 mm deep enclosure can be rotated ±180° on a vertical surface and tilted forward or backward by ±22.5°. That range covers most panel layouts where a flat mounting plate or machine frame is available. IP55 protection means it's dust-protected and can handle low-pressure water jets — suited for machine-mounting in environments with occasional washdown or condensation, though not for submersion or high-pressure cleaning.
Motor protection and short-circuit coordination
The bimetal overload relay inside provides Class 10 trip protection. Short-circuit protection is handled by upstream circuit breakers (the starter itself does not include a built-in breaker). The design supports Type 1 or Type 2 coordination depending on the upstream breaker selected; Siemens publishes coordination tables for the SIRIUS family.