Which of the following describes a double-insulated tool?

A double-insulated tool is designed to enhance user safety by reducing the risk of electric shock. The key characteristic of such tools is that they do not require a grounding connection, as they are built with an extra layer of protection to insulate users from any potential electrical faults.

In these tools, the two layers of insulation effectively separate the user from live electrical components, which helps prevent accidental electrical contact. This design makes it safe to use in various environments, especially where grounding may be difficult or impractical.

The other options describe characteristics that do not align with the concept of double insulation. Tools with a grounding wire would require a grounding connection, while those designed for high-voltage applications do not necessarily imply double insulation. Similarly, the requirement for special training to operate does not pertain specifically to double insulation, as many tools can be used safely with the appropriate precautions, regardless of their insulation type.