Which of the following is not recognized as an equipment grounding conductor in the NEC?

The correct answer indicates that the 1/2" flexible metal conduit in lengths over 10' is not recognized as an equipment grounding conductor according to the National Electrical Code (NEC). This is because, while flexible metal conduit (FMC) can be used as a grounding path, it is subject to certain limitations when it comes to length and rigidity.

FMC, particularly when exceeding a length of 10 feet, does not ensure a continuous grounding path because the flexibility of the conduit may not provide a consistent and reliable bond to grounding systems, especially if subjected to mechanical stress or vibration. As a result, its effectiveness as a grounding conductor diminishes over longer distances.

In contrast, the other options, including rigid metal conduit and EMT, are inherently designed to provide robust grounding pathways. Rigid metal conduit and EMT are integral to the grounded system due to their solid construction, offering optimal reliability. Thus, they are fully recognized as suitable equipment grounding conductors under NEC guidelines.

The inclusion of flexible nonmetallic conduit in the answer choices highlights the distinction between materials recognized for grounding; nonmetallic conduits typically do not conduct electricity and therefore cannot serve as effective grounding conductors.