In a multi-source electrical system, what happens to non-highest sources during a fault?

• A. They remain fully connected and power the bus.
• B. Non-highest sources are always active.
• C. They automatically become the primary source.
• D. Non-highest sources are isolated or fail-safe to prevent backfeed.

Answer: (D)

When a fault occurs in a multi-source electrical system, protection logic isolates non-highest sources so they do not push power back into the faulted path. This prevents backfeeding, which could cause circulating currents, damage equipment, or energize a faulted source. The highest-priority source stays connected to supply the bus, while the other sources are opened off or held in a safe, fail-safe state by protective devices. Only after the fault is cleared and the system is proven safe would re-energization or reallocation of sources occur.