Which statement correctly describes the function of the reverse current relay (RCR)?

• A. It is installed between the DC power source and the DC buses being supplied power
• B. It regulates AC voltage
• C. It charges the batteries
• D. It prevents backflow from the DC buses

Answer: (D)

In a DC power system with multiple sources feeding a common bus, it's essential to prevent current from flowing backward into a source or into another source. The reverse current relay is designed to do just that: it allows forward flow from a power source into the DC buses when the source is supplying, but it blocks current if the bus would push current back toward the source. This protects sources (like generators or batteries) from being discharged or damaged by reverse feeding and keeps the distribution stable when sources change state. It isn’t about regulating voltage or charging batteries, or about AC voltage; its primary role is to stop backflow.