Where is the reverse current relay (RCR) installed?

• A. Between a DC power source and the DC buses being supplied power
• B. In parallel with the DC buses being supplied power
• C. On the DC buses themselves
• D. At the AC input

Answer: (A)

The key idea is that a reverse current relay is used to stop energy from flowing backward from the DC distribution buses into the power source. It is placed in series between the DC power source and the DC buses it feeds, so if the buses are energized by another source or a higher voltage, the relay opens and prevents backflow into the source. That’s why the correct placement is between the power source and the buses being supplied.

Placing it in parallel with the buses wouldn’t isolate the source from reverse current, and putting it on the buses themselves wouldn’t interrupt the path from the source to the buses. Locating it at the AC input protects the AC side, not the DC reverse-current path.