Have you looked at the handbook commentaries?
This is the first paragraph that sums it up.
"The basic requirement of 230.2 is that a building or other structure can be supplied by only one service. However, under certain conditions, when a single service may not be adequate to supply a building or structure, 230.2 permits the use of additional services. Sections 230.2(A) through (D) describe those conditions under which more than one service is permitted. If more than one service is installed, 230.2(E) requires that a permanent plaque or directory be installed."
