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Home / Code Guides / Service Mast

Service Mast Requirements — Overhead Clearances & Support

A service mast has one structural job — holding up the utility’s service drop — and one code job: keeping those conductors far enough from people, vehicles, roofs, and windows. The clearance numbers in NEC 230.24 are the heart of it, and the utility’s own standards layer on top, so a mast job always means checking two rulebooks.

RequirementModel Code StandardSection
Clearance above gradeService-drop conductors need 10 feet of clearance above finished grade and walkways (measured from the lowest point of the drip loop), 12 feet over residential driveways, and 18 feet over public streets and roads subject to truck trafficNEC 230.24(B)
Clearance over roofsConductors passing over a roof generally need 8 feet of vertical clearance, reduced to 3 feet where the roof slope is 4-in-12 or steeperNEC 230.24(A)
Overhang exceptionWhere conductors cross only the roof overhang and terminate at a through-the-roof mast, clearance can drop to 18 inches — provided no more than 6 feet of conductor passes over no more than 4 feet of roof measured horizontallyNEC 230.24(A) Exc. 3
Mast supportThe mast must have adequate strength (or be braced/guyed) to withstand the strain of the service drop, and only power service conductors may attach to it — no cable TV, phone, or fiber lines on the mastNEC 230.28
Point of attachmentThe drop’s attachment point on the building must be at least 10 feet above finished grade, positioned so the required clearances in 230.24 can actually be metNEC 230.26
Drip loops & service headThe service head goes above the point of attachment where practicable, and drip loops must be formed so water drains off the conductors rather than following them into the mastNEC 230.54
Clearance from openingsOpen service conductors need 3 feet of clearance from windows that open, doors, porches, and fire escapes — conductors run above the top of a window are exemptNEC 230.9

Worth knowing

  • The utility’s service standards manual governs the drop itself and often dictates mast diameter (2-inch rigid metal conduit is the common minimum), attachment hardware, and roof flashing details — get their spec sheet before buying material.
  • Couplings in the mast above the roofline are prohibited by most utilities and many inspectors because they create a hinge point — use a single length of rigid conduit through the roof.
  • A mast bent by drop tension is a common storm-damage finding; where the drop span is long, guying or a stouter mast is cheaper than the repair, which usually involves the utility, a permit, and an emergency electrician.
  • These rules cover overhead services; underground (lateral) services trade clearance problems for burial depth and conduit rules in NEC 300.5.
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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