As per NFPA70, the outside overhead branch circuits or feeder have to be of covered conductor if a nearby building or structure is within 3m or 10ft.
Outside overhead branch circuit, feeders conductor insulation issue
For any purpose we have to use outside branch circuits and feeders like receiving power from a grid pole to the building, powering from separated substation to the near buildings, wiring from one building to another building.
Wiring from from substation to buildings or buildings to buildings are done by covered conductor usually. If in a certain establishment the substation is inside the area and 11KV service power is fed to the substation from the grid pole, then there is an issue arises. Because usually the 11KV wiring is done by bare conductor by the grid service provider.
When outside overhead branch circuit or feeders is of covered conductor
As per (NFPA70- 225.4 Conductor Covering)-
As per (NFPA70- 225.4 Conductor Covering) the Equipment grounding conductors and grounded circuit conductors can be bare or naked.
Why the recommendation- “Outside overhead branch circuit or feeders is of covered conductor”