What it is and what it does
The Siemens 3RK1303-5CS41-1AA0 is a reversing starter — a compact, pre-assembled unit that combines two contactors, a solid-state motor protection function, and the interlocking logic for forward/reverse control of a three-phase motor. It is part of the SIRIUS 3RK1303 family, designed for distributed motor control in industrial automation. Its headline motor rating is 9 A in AC-3 duty at 400 V, which means it can switch a standard three-phase induction motor drawing up to that current — roughly a 4 kW motor at 400 V — under the starting and stopping conditions typical of a conveyor, pump, or fan. The unit is rated for an operating voltage of 400 to 500 V AC, and its short-circuit withstand at 400 V is 100 kA, so it can be installed on a bus with high fault current without requiring an upstream current-limiting device. Control power is 24 V DC nominal, with a permissible range of 20.4 to 28.8 V DC, which covers the standard 24 V industrial supply including the ripple and drop typical of a long cable run.
Integration and connectivity
This reversing starter communicates over PROFIBUS DP, so it drops into a Siemens S7 or any other PROFIBUS master network as a remote I/O and motor control node. It does not support PROFINET natively. The unit has two parameterizable digital inputs, each on an M12 socket, for local start/stop or selector switch signals. There are no digital outputs on this variant. The line-side supply connection uses a hybrid plug, and the load-side outgoing feeder uses a socket conforming to ISO 23570. The main energy infeed also uses an ISO 23570 socket. The communication interface uses a hybrid plug and socket arrangement. The enclosure is rated IP65, meaning it is dust-tight and protected against low-pressure water jets. This makes it suitable for mounting directly on a machine frame or in a washdown zone, without needing a separate control cabinet. Physical dimensions are 250 mm high, 130 mm wide, and 107 mm deep — a compact footprint for a reversing starter with integrated protection and fieldbus.
Protection and reliability
Motor protection is solid-state, which provides accurate thermal overload protection without the drift of a bimetal relay. The switching contact is mechanical, so the main power path is a conventional contactor set. Short-circuit protection is provided by fuses, and the unit itself has short-circuit protection built in. The auxiliary contacts are rated for fewer than 1 error per 100 million operating cycles, which is a reliability figure for the control circuit. The minimum operating frequency is 1 cycle per hour, which is typical for a reversing starter not intended for high-speed jogging or plugging duty.
Lifecycle and sourcing
The substance prohibitance date of 05/01/2012 indicates compliance with RoHS and similar substance restrictions as of that date. Standard compliance documentation (RoHS, REACH) is available from the manufacturer.