What electrical trait identifies a double insulated tool?

• A. It has three prongs
• B. It has two prongs
• C. It uses a battery
• D. It has no plug

Answer: (B)

Double insulation means a tool is designed so it doesn’t need a grounding connection for safety, using extra insulation instead. The practical way to identify this in common use is the two-prong plug, which has no ground pin. That two-prong design signals that the tool relies on insulation rather than a grounding conductor for safety. A three-prong plug would indicate a ground connection, which is not a feature of double-insulated tools. Some tools may be battery-powered and thus don’t have a plug at all, but for corded tools, the two-prong plug is the telltale sign. Many double-insulated tools also carry the square-in-square symbol on their label to denote Class II construction.