The Siemens 3RK1903-3CA00 is an F-CM (Failsafe Contact Multiplier) module for the ET200S PROFISAFE distributed I/O system. It provides 4 floating safety contacts rated for 2 A DC-13 at 24 V, designed to couple separate safety circuits without merging them into the main PROFIsafe logic. The safe state is load circuit open — meaning on any fault or bus loss, the contacts drop out and the downstream load is isolated. Safety integrity is SIL CL 3 per IEC 61508 and Category 4 per EN ISO 13849-1, with a Safe Failure Fraction of 99% and average diagnostic coverage (DCavg) of 99%. The PFHd value is 4E-10 1/h — that is a probability of dangerous failure per hour so low it effectively qualifies for continuous-duty safety functions without periodic proof testing in most applications. Hardware fault tolerance is 1 (HFT = 1), meaning the module can tolerate a single fault and still maintain the safety function. This is a bus-communicating module — it plugs onto the TM-FCM30 terminal module and communicates via PROFIsafe over the ET200S backplane. It does not provide its own short-circuit protection (that must be handled upstream or by the connected load). The control supply voltage range is 20.4...28.8 V DC.
Sourcing & Lifecycle
Compliance documentation is standard for Siemens industrial safety components: the module carries a substance prohibition date of 05/01/2012 (RoHS compliance), and the safety case is built on IEC 61508 and EN ISO 13849-1. No UL or CSA listing is stated in the available spec data, so verify with the factory if a specific agency mark is required for your jurisdiction.
Panel Integration
The module is 30 mm wide, 196.5 mm high, and 117.5 mm deep — it mounts on a TM-FCM30 terminal module in the ET200S rail system, not directly on DIN rail. The 30 mm width matches the standard ET200S electronic module footprint, so it occupies one slot in the I/O station. No additional wiring space is needed beyond what the terminal module provides. Electrical endurance is rated at 200,000 operating cycles typical; mechanical service life is 10,000,000 cycles typical. The DC-13 rating at 2 A means it switches inductive DC loads (solenoids, contactor coils) at that current — the 24 V coil in a typical contactor is well within range.