314.23 Supports. Enclosures within the scope of this article
shall be supported in accordance with one or more of
the provisions in 314.23(A) through (H).
(B) Structural Mounting.
(1) Nails and Screws. Nails and screws, where used as a
fastening means, shall be attached by using brackets on the
outside of the enclosure, or they shall pass through the
interior within 6 mm (1?4 in.) 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.