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

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

Answer: (C)

The Main DC Bus is the centralized power node that feeds the line contactors, battery relay, generators, and the rest of the electrical system. A short on this bus creates a fault condition that protective circuits respond to by deenergizing the sources connected to it. When the main DC bus short occurs, the line contactor and the battery relay lose coil power and drop out, which in turn lights the battery relay OPEN indicator and the generator FAIL indicator to signal that the system has isolated the fault. This protection keeps the bus from being damaged and prevents reverse or undesired current flow. So the component that’s shorted is the Main DC Bus.