Part I is for the electrician, installer, or other person involved in selecting
and installing cabinets and boxes. Part II is for the manufacturers of those
You must place or equip it so as prevent moisture from accumulating inside it,
and you must mount it at least 6mm (1/4") from the mounting surface [312.2].
The maximum distance is 6mm (1/4") [312.3].
Openings through which conductors pass shall be adequately closed [312.5(A)].
That rule holds, even if no conductors are actually present in the opening.
You'll find the space requirements in Table 312.6(A). Every conductor has a
maximum bend radius; bend a conductor too severely, and you damage its
insulation. By allowing enough room at terminals, an electrician can terminate
wires without being forced to exceed the bend radius.