Disconnecting means for ungrounded conductors within sight of a transformer must do what?

• A. Open only the grounded conductor
• B. Open all ungrounded conductors
• C. Open only the ungrounded conductor that is touched
• D. Open the grounding conductor

Answer: (B)

When working near a transformer, any ungrounded (hot) conductors within sight must be fully de-energized by opening every ungrounded conductor at the disconnecting means. This ensures there is no live path that a person could touch, and it prevents any of the conductors from energizing one another through the transformer or through interconnected circuitry. The grounding conductor is not opened because it serves as a safety Earth path and ground reference; leaving it connected maintains fault current paths and equipment grounding.

Opening only one ungrounded conductor or only the grounded or grounding conductor would not guarantee that all parts of the circuit are de-energized, leaving a risk of shock or arc-flash. The rule focuses on ensuring all possible live paths (the ungrounded conductors) are disconnected so the area is safe for work.