The Siemens 3RK1903-3DA00 is a PM-D FX1 failsafe power module designed for the MS Failsafe F-RS and F-DS system family. It provides power distribution and overvoltage protection for up to six independent shutdown groups, with bus communication integrated on the module. The safe state is load circuit open — meaning when a safety demand occurs, the module opens its output contacts to remove power from the guarded zone. Rated for 20.4 to 28.8 V DC control supply, this module is sized for standard 24 V DC industrial safety circuits. It carries a SIL Claim Limit of 3 per EN 62061 and SIL CL 3 per IEC 61508, with a safe failure fraction of 99 % and average diagnostic coverage of 99 %. That puts it in Category 4 per EN ISO 13849-1 — the highest performance level for safety-related control systems, meaning it can handle single faults without losing the safety function and detects most dangerous failures automatically. The PFHD value of 6E-11 1/h (probability of dangerous failure per hour) is extremely low — three orders of magnitude below the SIL 3 threshold — so this module is well into the safety margin for high-demand or continuous-operation applications like press guarding, robot cell access, or conveyor hazard zones.
The module measures 30 mm wide by 196.5 mm tall by 117.5 mm deep. Depth of 117.5 mm means it stays within the typical 120 mm enclosure clearance, so no need for a deeper gland plate or extended rear panel. The design is for safety circuits — it snaps onto the DIN rail via the base module and connects through the backplane bus, so no additional wiring for power distribution between modules. The 30 mm width leaves room alongside other safety I/O slices in the same row.
Endurance and compliance
Electrical endurance is rated at 200,000 operating cycles typical; mechanical service life at 10,000,000 cycles typical. Short circuit protection is built in. The module is Type B according to IEC 61508-2, meaning it uses complex components (microcontrollers, ASICs) and requires a higher diagnostic coverage than simple electromechanical safety relays. Hardware fault tolerance is HFT = 1, so the system can tolerate one fault without losing the safety function. Substance prohibitance date of 05/01/2012 aligns with RoHS compliance.