OSHA 10-Hour Construction ReviewFocus Four HazardsMedium
A worker is using an electric hand drill on a construction site. The drill's casing is made of non-conductive plastic, and it has a two-prong plug. What type of electrical protection does this tool primarily rely on?
- ADouble insulation
- BGround-fault circuit interrupter (GFCI)
- CGrounding
- DPolarization
Show answer & explanationAnswer & explanation
Correct answer: A. Double insulation
A tool with a non-conductive plastic casing and a two-prong plug is indicative of double insulation. This design provides two layers of insulating material to protect the user from electric shock, eliminating the need for a grounding conductor.
Why the other options are wrong
- B. A GFCI protects against ground faults but is a circuit-level protection, not an inherent tool design feature.
- C. Grounding requires a three-prong plug and a conductive path to earth, which this tool lacks.
- D. Polarization ensures correct connection of hot and neutral wires but does not provide shock protection from internal faults.
Double Insulated Tools
Tools constructed with two layers of insulating material between live parts and the user, providing protection against electric shock without requiring grounding.
- Identified by a square-within-a-square symbol or a two-prong plug.
- Eliminates the need for a grounding conductor.
- Provides an alternative to grounding for electrical safety.
Memory trick: Grounding is for metal, double is for plastic, GFCI for all else drastic!