To allow a feeder to be derived from an autotransformer, what is required?

• A. A grounded conductor electrically connected to a grounded conductor from the system that supplies the autotransformer.
• B. A completely isolated grounding conductor from the system.
• C. A separate feeder panel for the autotransformer.
• D. No grounding connection is required.

Answer: (A)

Grounding and a reliable fault-path are essential when deriving a feeder from an autotransformer. To derive a feeder safely, the grounding conductor of the derived feeder must be electrically connected to the grounded conductor of the system that supplies the autotransformer. This creates a common return path for fault currents and a solid reference point, allowing protective devices to operate correctly and keeping exposed surfaces at a safe potential. Without this connection, the derived feeder could float, leading to hazardous voltages and unreliable protection. A completely isolated grounding path or no grounding connection would not provide the necessary fault path, and a separate feeder panel doesn’t address the grounding requirement.