What this direct starter is and where it lives
The Siemens 3RK1300-0KS01-0AA3 is an EM 300 DS electromechanical direct starter designed for the ET 200X distributed I/O system. It is a self-contained motor starting and protection unit that combines a contactor, bimetal overload relay, and short-circuit protection into one package rated for 0.9 to 1.25 A full-scale setting range. At AC-3 duty on a 400 V supply, it handles 0.37 kW motors — the kind you find on small conveyors, pumps, and agitators out on the plant floor. The IP65 enclosure means this starter is built for washdown environments and dusty industrial zones — it keeps coolant, dust, and moisture out of the switching contacts. That makes it a fit for food processing, packaging lines, or any area where a panel-mount starter would need a separate enclosure. The 134 mm depth, 140 mm width, and 270 mm height give you the envelope for panel layout or direct machine mounting.
What the ratings mean for fit
The 0.9-1.25 A setting range and 0.37 kW at AC-3 400 V tell you the motor current this starter is sized for. AC-3 is the standard duty for squirrel-cage induction motors — starting, stopping, and running under load. The 50 A short-circuit breaking capacity (Icu) at 400 V means the integrated circuit-breaker-style protection can safely interrupt a fault up to that level without welding contacts or cascading upstream. For a 0.37 kW motor on a 400 V line, that is more than adequate headroom. The bimetal overload relay provides Class 10 or 20 thermal protection — it tracks motor heating and trips on sustained overcurrent. The built-in brake output (motor brake contact) handles externally supplied DC brakes, saving an extra interposing relay. PROFIBUS DP communication lets the starter report status and accept commands directly from the PLC without hardwiring every I/O point.
Integration into the ET 200X system
This direct starter mounts directly on the ET 200X rail or can be panel-mounted via the screw fixing points. The main current circuit uses tab terminals — 9-pole motor feeder and 9-pole power connection — so wiring is a plug-and-play affair with the pre-wired connector system. The operating temperature range of 0 to 55 °C covers most indoor industrial environments; derate if you are mounting it inside a non-ventilated enclosure near heat sources. Equipment marking per DIN EN 61346-2 is letter Q, which designates it as a switching device for power circuits. The PROFIBUS DP interface uses the standard 9-pin D-sub connector common to the ET 200X family — no special adapters needed. The IP65 rating on the housing means you can mount it directly on the machine frame without a separate cabinet, as long as the cable glands and connectors are also rated for the environment.