230.28 Service Masts as Supports. Only power service-drop or overhead service conductors shall be permitted to be attached to a service mast. Service masts used for the support of service-drop or overhead service conductors shall be installed in accordance with 230.28(A) and (B).
(A) Strength. The service mast shall be of adequate strength or be supported by braces or guys to withstand safely the strain imposed by the service-drop or overhead service conductors. Hubs intended for use with a conduit that serves as a service mast shall be identified for use with service-entrance equipment.
(B) Attachment. Service-drop or overhead service conduc- tors shall not be attached to a service mast between a weath- erhead or the end of the conduit and a coupling, where the coupling is located above the last point of securement to the building or other structure or is located above the building or other structure.
Why do you say that the code is silent? I get that the code doesn't have a formula but it is not silent. There are other instances where the code forces a judgment call. Take for example a GEC. The code says that it can be without protection unless it is exposed to physical damage. There is no example or description and the reader is left to use their imagination.