Electrician's Licensing Practice Exam

Must all metallic boxes be grounded according to NEC?

1. Yes, unless there is no grounding conductor

2. No, they can be left ungrounded

3. Only non-metallic enclosures need grounding

4. Yes, all must be grounded regardless

The correct answer is: Yes, unless there is no grounding conductor

Grounding metallic boxes is an essential safety requirement outlined in the National Electrical Code (NEC). The correct answer is based on the understanding that metallic boxes are generally required to be grounded to ensure safety and protect against potential electrical shocks. When a grounding conductor is present, it allows for any fault current to safely return to the ground, thereby reducing the risk of electric shock or fire. However, if there is no grounding conductor available, the NEC permits the use of ungrounded metallic boxes. In such cases, while it is strongly advised to use grounded enclosures whenever possible for safety reasons, the code acknowledges situations where grounding might not be feasible. This scenario is particularly relevant in older wiring systems or certain installations where a grounding conductor isn't part of the circuit. The other choices do not accurately reflect the guidelines specified by the NEC. Grounding non-metallic enclosures, for example, is generally unnecessary because they do not conduct electricity. Similarly, the idea that all metallic boxes can be left ungrounded without any conditions does not align with the requirements of the NEC, which aims to promote safety in electrical installations. The importance of grounding is highlighted as a protective measure against electrical hazards, reinforcing the need for proper grounding practices in systems that require them.