What it is and what it does
The Siemens 3RK1300-0JS01-1AA1 is an EM 300 RS electromechanical reversing starter designed for the ET 200X distributed I/O system. It integrates a reversing contactor, bimetal overload relay, and PROFIBUS DP communication into a single IP65-rated enclosure — a self-contained motor control unit for a reversing application, not a collection of separate parts wired in the field. Rated at 0.25 kW at AC-3 duty on a 400 V supply, with a setting range of 0.7 to 1.0 A. The bimetal overload provides motor protection, and the unit includes a brake contact (DC 24 V / 3 A) for externally supplied brakes — a common requirement on hoist or conveyor reversing drives where a holding brake must release before the motor starts. Operating voltage is 400 to 500 V AC, with an ambient temperature range of 0 to 55 °C. The short-circuit breaking capacity (Icu) at 400 V is 50 A, meaning the integrated short-circuit protection (circuit-breaker design) can safely interrupt a fault up to that level without upstream devices needing to clear it first — relevant for coordination studies on the line.
Integration and mounting
This is a panel-mount unit sized for the ET 200X family: 270 mm high, 140 mm wide, 134 mm deep. The IP65 rating means the housing and all connections withstand washdown — it can be mounted directly on a machine frame or in a small junction box without an additional enclosure, provided the cable glands are properly sealed. Main current circuit connections use tab terminals — a fast, tooled connection method common in automotive and conveyor applications. The PROFIBUS DP interface is integrated, so the starter communicates directly with the PLC over the fieldbus; no separate gateway or I/O block is needed for the reversing function. The switching contact is electromechanical, not solid-state. That means it's a traditional contactor pair with mechanical interlocking — the bimetal overload handles the thermal protection, and the unit's own circuit-breaker design handles short-circuit protection upstream. For a line-down replacement, verify that the existing motor feeder and power connection are 9-pole (as specified in the description) to match the connector pattern.