AS-Interface Ground Fault Module with Relay Output
The Siemens 3RK1408-8KG00-0AA2 is an AS-Interface ground fault detection module designed for monitoring the AS-i cable for earth faults. The module's relay output is rated DC-12 at 1 A, with a mechanical endurance of 2,000,000 operating cycles. For inductive loads, the manufacturer recommends freewheel diodes across the load to extend relay life. The auxiliary supply (Uaux) should be protected by a 2 A slow-blow fuse. Switching capacity is specified at 24 V for 500 mA and 48 V for 200 mA — these are the DC-13 resistive/inductive load ratings that govern real-world contactor or indicator lamp switching. The module draws up to 40 mA from the AS-Interface bus for its own electronics.
Ground Fault Detection Logic
The module detects an earth fault when the AS-Interface cable voltage to ground (Ugnd) falls between 10% and 90% of the nominal Uas-i. It provides a remote reset input and two signaling relay outputs for fault annunciation. If repeaters are used in the network, each AS-Interface segment requires its own ground fault detection module — one per power supply unit. The module does not perform overvoltage detection and has no counter function. Its sole purpose is ground fault monitoring on the AS-i bus, making it a targeted component for maintaining bus integrity rather than a general-purpose I/O slice.
Lifecycle Status: Not Recommended for New Designs
The 3RK1408-8KG00-0AA2 carries a manufacturer lifecycle status of NRND (Not Recommended for New Designs). This means Siemens will continue to support existing installations and fulfill orders for current production runs, but the part should not be specified into new BOMs.
Its 22.5 mm width matches the standard AS-interface module footprint, allowing side-by-side mounting with other SIRIUS 3RK1 devices. The spring-loaded terminals accept 2 x (0.25 – 1.5) mm² solid or stranded wire (2 x (0.25 – 1.0) mm² with end sleeves). IP20 rated — suitable for enclosed control panels only, not for washdown or outdoor locations. The rated temperature for all electrical specifications is 25 °C.