Question 52 QMED02 - Electrician-Refrigerating Engineer

The Correct Answer is C **Explanation of why option C is correct:** Option C states: "Unless the power tool is an approved double-insulated type, an ungrounded power tool has the potential to cause a fatal accident due to electrical shock." This statement is true based on fundamental electrical safety principles for portable power tools. 1. **Standard Tools (Non-Double-Insulated):** Tools that are not double-insulated rely on grounding (a dedicated third wire connected to the tool's metal casing) as the primary safety mechanism. If an internal fault occurs (e.g., a hot wire touches the metal casing), the ground wire routes the current safely away, tripping the circuit breaker. 2. **Ungrounded Tool (Standard Type):** If a standard, non-double-insulated tool is used without a proper ground (i.e., it is "ungrounded," either through a faulty cord or being used with an ungrounded outlet/adapter), and an internal fault occurs, the metal casing becomes energized (live). If a user touches the energized casing while simultaneously contacting a ground source (like concrete, plumbing, or another grounded object), they become the path for the current, resulting in a severe, potentially fatal, electrical shock. 3. **Double-Insulated Tools:** Double-insulated tools are explicitly designed with extra layers of non-conductive material and do not require a grounding conductor, making them safe even without a third (ground) prong. Therefore, the danger of lethal shock from an ungrounded tool applies specifically to the standard, non-double-insulated type. **Explanation of why the other options are incorrect:** * **A) Power tools other than those as approved as double-insulated require the use of two conductor cables, two-prong plugs, and ungrounded receptacles.** * **Incorrect.** Tools that are *not* double-insulated must be grounded. Grounding requires a **three-conductor** cable, a **three-prong** plug, and a **grounded** receptacle (or GFCI protection). Two-conductor cables/plugs are used only for double-insulated tools. * **B) Double-insulated power tools require the use of three conductor cables, three-prong plugs, and grounded receptacles.** * **Incorrect.** Double-insulated tools are specifically designed to be safe *without* a grounding wire. They typically use a **two-conductor** cable and a **two-prong** plug, although sometimes they may be fitted with a three-prong plug where the third prong is non-functional or plastic. Requiring three conductors and grounding is standard procedure for *non-double-insulated* tools, not double-insulated ones. * **D) A power tool fitted with a three-conductor cable and three-prong plug may be safely used with an ungrounded outlet as long as a three prong receptacle to two prong plug adapter is used.** * **Incorrect.** Using a grounding adapter (often called a "cheater plug") with a three-prong tool in a two-prong (ungrounded) receptacle defeats the purpose of the grounding safety system unless the adapter's grounding pigtail or lug is properly attached to a verifiable ground (like a grounded box screw). If the adapter's grounding mechanism is ignored (which is common practice), the tool is effectively ungrounded and poses a serious shock hazard, making the usage unsafe.