To prevent injury when working on a current transformer, the secondary winding must be what?

The correct answer emphasizes that the secondary winding of a current transformer must be open to prevent injury. When a current transformer operates, its secondary winding generates a proportional current based on the primary circuit's current flow. If the secondary winding is shorted or connected while the primary is energized, it can create dangerously high current levels in the secondary, leading to insulation failure, overheating, or even explosion due to the high energy being trapped in a closed circuit.

Keeping the secondary winding open ensures that there is no path for current to flow, thus minimizing the risks associated with high voltage and potential electrical shock. It is a crucial safety precaution, as it allows the transformer to function correctly without exposing workers to hazardous conditions. Being aware of this requirement is essential for anyone working around electrical equipment, especially those involving transformers.