Hi Bob. Let me start by quoting the 2005 text.
(1)Nails and Screws. Nails and screws, where used as a fastening meanse, shall be attached by using brakcets on the outside of the enclosure, or they shall pass through the interior within 1/4" of the back or ends of the enclosure, Screws shall not be permitted to pass through the box unless exposed threads in the box are protected using approved means to avoid abrasion of conductor insulation.
Now, back to the question at hand. When I read the code, it gives me two options on how I can support a box with internal screws.
Option 1: I use brackets outside the box.
Option 2: I use screws that
pass through the box, within a 1/4" of the
back or ends of the enclosure. In your example 3, the screws, in my opinion, are not passing
through the box...they are peircing the side of it. Also, even if they were passing through the box, they are not within a 1/4" of the back or ends of the box.
