Overhead Conductor Clearance Calculator
Find the minimum vertical clearance of an overhead span under NEC 230.24 (service conductors) and 225.18 (outside branch circuits and feeders). Pick what the span crosses and enter the voltage to ground; the tool returns the required height over sidewalks, driveways, streets, railroad rails, or a roof.
How to use this calculator
- Choose the conductor type: overhead service conductors (NEC 230.24) or an outside branch circuit or feeder (NEC 225.18). Only outside feeders expose the railroad-rail clearance.
- Select the location the span crosses: a sidewalk or pedestrian-only area, residential property or a driveway, a street or truck-traffic area, over railroad track rails, or above a roof.
- For the pedestrian and residential locations, enter the nominal voltage to ground. For a 120/240 V single-phase or 208Y/120 V system it is 120 V; for 480Y/277 V it is 277 V; for a 480 V delta it is 480 V.
- Read the minimum vertical clearance and the exact NEC subsection it comes from. Street and roof clearances do not depend on voltage, so the voltage field is hidden for those.
- Hold the full clearance over the whole span, and check the roof reductions or the clearance-from-buildings rules separately where they apply.
NEC reference
This calculator implements the NEC 2020 vertical clearances of overhead spans 1000 V nominal or less: 230.24(B) for the ground clearances of overhead service conductors, 230.24(A) for the clearance above roofs, and 225.18 for outside branch circuits and feeders (including the 24.5 ft clearance over railroad rails, which 230.24 does not list) with 225.19(A) for their roof clearance. The residential and commercial non-truck category splits at 300 V to ground (12 ft at or below, 15 ft above). Clearance from buildings, the point of attachment, and clearances over swimming pools are separate rules and are out of scope here.
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
Overhead clearance heights, 1000 V or less
The required height depends on what the span crosses, and for one category on the nominal voltage to ground. The values are the same for overhead service conductors (230.24) and outside feeders (225.18); only the railroad row is unique to outside feeders.
| Location the span crosses | Clearance | NEC |
|---|---|---|
| Sidewalks, platforms, pedestrian-only areas (150 V to ground or less) | 10 ft | 230.24(B)(1) / 225.18(1) |
| Residential property, driveways, commercial non-truck areas (300 V to ground or less) | 12 ft | 230.24(B)(2) / 225.18(2) |
| Same areas, above 300 V to ground | 15 ft | 230.24(B)(3) / 225.18(3) |
| Public streets, roads, truck-traffic parking, vehicle areas | 18 ft | 230.24(B)(4) / 225.18(4) |
| Over railroad track rails (outside feeders only) | 24.5 ft | 225.18(5) |
| Above a roof surface (base value) | 8 ft | 230.24(A) / 225.19(A) |
The 10 ft pedestrian row applies only at 150 V to ground or less. Above 150 V over a pedestrian-only area this tool reports the higher residential-category clearance (12 ft or 15 ft), which never under-clears.
Voltage to ground, not system voltage
The clearances key on the nominal voltage to ground, which is the classic place these get read wrong. A 120/240 V single-phase service is 120 V to ground and a 208Y/120 V or 480Y/277 V wye system is 120 V or 277 V to ground, all at or below the 300 V breakpoint. An ungrounded or corner-grounded 480 V delta, however, is 480 V to ground, so a feeder over a driveway jumps from the 12 ft row to the 15 ft row. Reading the clearance off the 480 V system voltage would miss that either way, but reading it off a 277 V phase-to-neutral figure on a delta would under-clear it.
Worked example: a service drop across a yard and driveway
A 120/240 V overhead service drop (120 V to ground) crosses a back yard and the homeowner's driveway. Over the residential property and driveway the required clearance is 12 ft under 230.24(B)(2). If that same drop continued over the public street out front it would need 18 ft under 230.24(B)(4), and where it passes over a sidewalk reachable by pedestrians it needs 10 ft under 230.24(B)(1). If it crossed the roof of an attached porch it would need 8 ft of clearance above the roof under 230.24(A), maintained 3 ft back from the roof edge.
Now take an outside 480 V delta feeder (480 V to ground) run to a detached shop across the same driveway. Because it is over 300 V to ground, the driveway clearance rises to 15 ft under 225.18(3), and if the run crossed railroad spur rails it would need 24.5 ft under 225.18(5).
Common mistakes
- Using the system voltage. The rows are indexed by voltage to ground. A 480 V delta is 480 V to ground and needs the 15 ft residential row, not the 12 ft one.
- Treating a truck-traffic driveway as residential. A driveway on other than residential property, or any parking area subject to truck traffic, is the 18 ft vehicle row, not the 12 ft residential row.
- Looking for the railroad clearance under 230.24. The 24.5 ft railroad-rail clearance is a 225.18 outside-feeder rule; 230.24 for service conductors does not list it.
- Applying a reduced roof clearance without the conditions. The 3 ft and 18 in roof reductions need a specific slope or a short overhang to a through-roof raceway and a voltage at or below 300 V. Absent those, the 8 ft base holds.
Frequently asked questions
How high does a service drop have to be over a driveway?
Under 230.24(B) the clearance over residential property and driveways is 12 ft at 300 V to ground or less and 15 ft above 300 V. A standard 120/240 V service is 120 V to ground, so 12 ft applies over a residential driveway.
What are the NEC overhead conductor clearance heights?
230.24(B) and 225.18 set 10 ft over pedestrian-only areas (150 V to ground or less), 12 ft over residential property and driveways (300 V or less), 15 ft over those areas above 300 V, and 18 ft over streets and truck-traffic areas. Outside feeders add 24.5 ft over railroad track rails.
What is the clearance above a roof?
230.24(A) requires 8 ft above the roof, kept 3 ft in from the roof edge. It drops to 3 ft for a steep roof (4 in 12 or greater) at 300 V or less, and to 18 in for a short overhang run to a through-roof raceway. Outside feeders use the same base under 225.19(A).
System voltage or voltage to ground?
Voltage to ground. A 120/240 V or 208Y/120 V system is 120 V to ground and 480Y/277 V is 277 V, all at or below 300 V. A 480 V delta is 480 V to ground, which crosses into the 15 ft row. Keying on voltage to ground avoids under-clearing a 480 V delta.
How do 230.24 and 225.18 differ?
230.24 covers overhead service conductors and 225.18 covers outside branch circuits and feeders. The 10, 12, 15, and 18 ft ground clearances match; 225.18 alone adds the 24.5 ft clearance over railroad track rails.
Related calculators
- Working Space Clearance Calculator: the horizontal working space in front of equipment per NEC 110.26(A).
- Service Size Calculator: size the service disconnect, conductors, and grounding electrode conductor.
- Dwelling Service Conductor Calculator: size the service-entrance conductors under the Table 310.12 dwelling allowance.
- Conduit Support Spacing Calculator: maximum spacing between conduit supports by type and trade size.
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