What should the disconnecting means do when connected to an ungrounded conductor within sight of a transformer?

The correct response identifies that the disconnecting means should open all ungrounded conductors. This practice aligns with the safety requirements established in the National Electrical Code (NEC) to ensure that when maintenance or servicing on the transformer is needed, all ungrounded conductors are de-energized. By isolating all ungrounded conductors, it significantly reduces the risk of electric shock to personnel working on or near the equipment.

In transformer applications, opening only a single ungrounded conductor could lead to a hazardous situation due to the presence of voltage on the remaining conductors. Ensuring that all ungrounded conductors are opened creates a safer work environment and minimizes the potential for accidental re-energization during maintenance procedures. This approach is fundamental to promoting electrical safety practices, as it adheres to the NEC’s focus on minimizing risks associated with electrical installations.