Which method is NOT permitted for identifying equipment grounding conductors larger than 6 AWG?

The method that is not permitted for identifying equipment grounding conductors larger than 6 AWG is tagging the conductor with a string tag marked "equipment grounding conductor." This is because using a temporary or non-permanent method, such as a string tag, does not meet the requirements for clear and long-term identification of grounding conductors.

The purpose of marking these conductors is to ensure that they can be easily identified by anyone working on or near them, which is critical for safety. A string tag could potentially become damaged or removed, leading to ambiguity about the conductor's purpose.

In contrast, the other methods listed—marking with color-coded tape, using a permanent label affixed to the conductor, and using specific identifiers that denote the conductor's function—provide a more reliable and durable means of identification, ensuring clarity and compliance with safety standards. Thus, these methods are acceptable for identifying grounding conductors and help prevent safety hazards during maintenance and operation.