Reversing starter with IP65 enclosure and PROFIBUS DP
The Siemens 3RK1303-2AS51-1AA0 is a reversing starter in an IP65-rated enclosure, designed for direct-on-line reversing of three-phase motors up to 4 A at 400 V AC-3 duty. That AC-3 rating is the motor-switching current — the rating that governs real motor loads, not the resistive AC-1 figure. It handles reversing applications like conveyor direction change or pump valve positioning without external contactor interlocking. Control voltage is 24 V DC, with a permissible range of 20.4 to 28.8 V DC. The unit communicates via PROFIBUS DP, making it a fieldbus-integrated motor starter rather than a standalone contactor block. Two parameterizable digital inputs are available via M12 sockets, and the motor protection is thermistor-based. The short-circuit protection is rated at 100 kA at 400 V, meaning the unit can safely interrupt a fault current up to that level without upstream device coordination issues. The IP65 rating means the enclosure withstands hose-directed water and dust ingress — suitable for washdown environments or outdoor installation without a separate cabinet.
Dimensions and mounting
The unit measures 250 mm high by 130 mm wide by 107 mm deep. It uses hybrid plug/socket connections for the supply voltage line-side and load-side outgoing feeder, both per ISO 23570. The communication interface uses a hybrid plug as well, with a separate hybrid socket for the PROFIBUS DP transmission. This is a pre-wired, pluggable system — not a DIN-rail mount contactor you wire in the field.