What hazard is most likely if the transformer secondary is not properly isolated to prevent backfeed?

• A. Backfeed into the system
• B. Short circuit
• C. Ground fault
• D. Insulation failure

Answer: (A)

When a transformer's secondary isn’t properly isolated to prevent backfeed, energy on that secondary can be pushed back into the rest of the electrical system. This backfed energization can make parts of the system that are supposed to be de-energized or isolated become live, creating shock and arc-flash hazards for workers, as well as potential misoperation of protective devices and equipment damage.

This is the best answer because it directly describes the hazard caused by the lack of isolation: energy flowing back into the system (backfeed). The other options describe faults or failures that are not the immediate consequence of insufficient secondary isolation—short circuits and ground faults are fault conditions with low-impedance paths to cause high fault currents or grounding paths, while insulation failure is a deterioration issue that may occur over time, not the specific backfeed risk highlighted here.