In the case of a shorted _______________, the respective line contactor and battery relay will deenergize and illuminate the associated battery relay OPEN light and generator FAIL light.

• A. Battery Bus
• B. Line Contactor
• C. Main DC Bus
• D. Battery Relay

Answer: (C)

Short on the main DC bus causes the entire DC distribution to collapse. The line contactor and the battery relay get their control or supply from that bus, so when the bus voltage drops due to the fault, those coils lose power and drop out. With both relays deenergized, the battery relay opens (OPEN light comes on) and the generator/feeder status shows as failed (GEN FAIL light). This arrangement makes sense because the main DC bus is the central point that feeds the generator’s connection path and the battery’s connection path; a fault here removes power from the relays that keep both sources connected to the bus.

If the fault were in the Battery Bus or in the Line Contactor itself, the symptoms wouldn’t reliably produce both the OPEN and GEN FAIL indications in the same way, since those paths and indicators are tied to the main DC bus’s ability to power the relays. A fault isolated to the battery relay, the line contactor, or the battery bus would have a different, less consistent impact on these lights.