This article is documented in the 2001 ROP Purposal 9-113 on page 674. It references UL Standard 896A for service equipment. The other standard is UL 67 for panelboards it addressed the connections of equipment grounding conductors, but appears to have been deleted as of Sept. 20 of 2002.
The issue of parraleling the grounded circuit conductor is not necessarily one that the NEC will address directly. Ultimately the condition you describe is a practical application. Granted one that most professionals would consider unorthodox. If you reference Article 90.1 Purpose, and specifically 90.1 (C), Intention, which states, “This Code is not intended as a design specification or an instruction manual for untrained persons”, you can see how the document handles unforeseen contingencies. Maybe the Code could use direct language to prevent such an installation but beyond 310.4 and 408.21 the Code is reluctant to dictate circuitry.
Charlie p
