The Siemens 3RK1308-0AD00-0CP0 is a SIMATIC-branded direct-on-line motor starter — a compact, fieldbus-capable unit that combines a contactor, overload relay, and communication interface in a single 30 mm-wide housing that plugs into a base unit. It is rated for 9 A at 40 °C, with a short-circuit current rating of 55 kA at both 400 V and 500 V — meaning it can safely interrupt fault currents up to that level without upstream devices needing to clear the fault first. The trip class is adjustable between OFF, 5, and 10, which lets you match the thermal curve to the motor's starting profile — set to OFF for applications where the overload is handled externally, or to 5 or 10 for standard motor protection. It supports both PROFINET and PROFIBUS DP protocols, so it drops into either a PN or a legacy DP network without a gateway.
The module fastens by plugging into a base unit on the DIN rail — no separate wiring for the power bus; the base unit carries the line and load connections. Dimensions are 30 mm wide, 142 mm high, and 150 mm deep, with 50 mm clearance required above and below for ventilation and cable routing. Mounting position is vertical or horizontal, but per the manual derating applies for horizontal orientation — factor that into your thermal budget if the panel layout forces a horizontal mount. Operating temperature range is -25 to +60 °C, with derating required above 40 °C; storage and transport range extends to -40 to +70 °C.
The listed MTBF of 46 a gives a mean time between failures of 46 years under stated operating conditions — a reliability figure that supports long service intervals in continuous-duty applications.
The minimum load is 50 % of the smallest adjustable rated current — meaning the overload protection may not trip reliably below that threshold, so don't use this on a motor drawing less than half the set current. ON-delay time is fixed at 20 ms; OFF-delay is adjustable between 35 and 50 ms — these govern the response to start/stop commands from the fieldbus or local control. Vibration resistance is 15 mm at 6 Hz and 2 g up to 500 Hz; shock resistance is 6 g for 11 ms — suitable for mounting on machinery that sees moderate vibration, but not for high-shock environments like stamping presses without additional isolation.