Clearance requirements for overhead service conductors have often proven to be a life or death matter. In many cases, the installer adhered to the NEC minimums without considering the actual conditions. Always use these as a starting point, not as the distance you can get by with in an attempt to save money on masts and supports.
The people on the NEC Code Making Panels can’t think of every possibility. Always look at the intention of the clearance requirement to see if the underlying principle would require you, given the conditions (or anticipated conditions), to exceed the requirement.
The clearances are covered in Sec. 230.24(A) through (E). Note that 230.24(C), (D), and (E) refer you to elsewhere in the Code. So the requirements stated in 230.24 are:
- Clearances above roofs, and
- Vertical clearance for overhead service conductors.
Above roofs, the requirement is 8 ft above the roof surface, maintained for 3 ft in all directions. But there are four exceptions.
Vertical clearances are 10 ft, 12 ft, 15 ft, and 18 ft depending upon the specific application (e.g., 18 ft over public streets).
