The 6ES7138-4FR00-0AA0 is a single-channel relay output module for the ET200S distributed I/O system, designed specifically for fail-safe applications. It provides one relay output with two normally-open contacts, rated for 5 A continuous current (thermal continuous current, max. 5 A) and capable of switching both 24 V DC and 24...230 V AC loads. The module achieves SIL 3, Performance Level e, and Category 4 — but only when the control signal comes from a fail-safe digital output (F-DO).
Load voltage and wiring constraints for the relay contacts
The relay output is rated for a signal '1' minimum load current of 5 mA — switching dry contacts below this threshold may not reliably wet the circuit. Maximum switching frequency is 2 Hz with resistive load and 0.1 Hz with inductive load, so this module is not intended for high-speed cycling. Load voltage L+ draws up to 100 mA from the control voltage supply (without load). The module draws a maximum of 10 mA from the backplane bus. Galvanic isolation exists between channels and backplane bus, and between channels and load voltage L+. Cable length is limited to 200 m for both shielded and unshielded runs — the same limit applies regardless of shielding, which is unusual and suggests the limiting factor is the relay coil drive, not noise immunity.
Current derating and thermal limits across ambient temperature
The module delivers 6 A per channel up to 50 °C ambient, derating to 5 A at 60 °C (with the caveat that voltage is limited to max. 24.8 V at the higher temperature). Total module current is capped at 8 A maximum. Power loss is 2.1 W typical — this is the heat the module dumps into the ET200S rail. In a dense cabinet, check that the total rail dissipation stays within the terminal module's thermal budget.