What this fail-safe starter does in a safety circuit
The Siemens 3RK1308-0CD00-0CP0 is a fail-safe direct-on-line starter module that integrates three digital inputs and a load controller in a single 30 mm-wide housing. It is designed for safety-related motor starting in SIL 3 / PL e applications, with the safe state defined as the load circuit open. The module supports both PROFINET and PROFIBUS DP protocols, allowing it to slot into a safety CPU's fieldbus slice without a separate gateway. The 4-byte input and 2-byte output process data map directly to the safety program's I/O addresses.
Trip class and current adjustment — what the range means
The trip class is adjustable to OFF, 5, or 10. OFF disables the overload protection (for use with an external overload relay); class 5 suits fast-starting loads like short-cycle conveyors, while class 10 covers standard motor starts. The minimum load is 50 % of the smallest adjustable rated current, so the module cannot protect a motor drawing less than half the setpoint. The ON-delay is fixed at 35 ms, and the OFF-delay ranges from 35 to 50 ms. These timing windows are set by the safety logic, not field-adjustable on the module itself.
The module mounts by plugging into a base unit on a DIN rail. It occupies 30 mm of rail width, 150 mm deep, 142 mm tall. Clearance above and below is 50 mm each for air circulation and cable bending radius. Vibration resistance is 15 mm at 6 Hz, then 2 g up to 500 Hz; shock resistance is 6 g for 11 ms.