Part II of NEC Art. 230 provides the requirements for overhead service conductors. The bulk of Part II is devoted to clearances and supports. Part II starts off by requiring that all overhead service conductors be insulated or covered [230.22]. The next set of requirements is for the size and rating [230.23]. Some minimum sizes are specified, and the conductor ampacity must be sufficient for carrying the load, as calculated per Art. 220.
What may be puzzling about this set of requirements is the one stating the conductors must be large enough to “have adequate mechanical strength.” Adequate for what? And how do you calculate the strength, using what material data and what equations?
There’s a reason for this vagueness: the NEC is relying on the installer to exercise engineering/craft judgment. The strength requirement isn’t specified in any detail, but is there as a reminder to add that consideration when performing the design and installation. If you’re qualified to do the work, you’ll know whether the conductors have adequate mechanical strength for the support provided for a given span.
