What must electrical hand tools using a regular 120-volt system have unless they are double-insulated?

Electrical hand tools using a regular 120-volt system are required to be 3-wire grounded unless they are double-insulated. The grounding provides an essential safety mechanism that reduces the risk of electric shock or electrocution. In a standard 3-wire system, the ground wire provides a path for electrical current to safely return to the ground in case of a fault, helping to prevent excess voltage from reaching the user.

Double-insulated tools, meanwhile, are designed with two layers of insulation that isolate the user from any live electrical parts, eliminating the necessity for grounding. However, if a tool is not double-insulated, proper grounding is vital for ensuring that any potential fault current has a safe path, thereby enhancing the safety of using such tools.