Methods: Overhead conductor ampacity
calc.line-rating.ampacity · Version 0.1.0
Method
At the maximum conductor temperature, the steady-state current is √((convective cooling + radiated heat loss − solar heat gain) ÷ AC resistance), following the IEEE 738-2023 heat balance: forced convection by the larger of its low- and high-wind correlations with the wind-angle factor, or natural convection if larger; radiation from emissivity and the temperatures; clear-sky solar gain from the sun's position, elevation, and line bearing; and resistance interpolated between the two values entered.
Assumptions
- Weather is steady at the values entered; the rating is for that weather only.
- A clear atmosphere; no ground albedo is added to the solar gain.
- Temperatures are in °C in both unit systems, as IEEE 738 states them.
Sources
- IEEE 738-2023, Standard for Calculating the Current-Temperature Relationship of Bare Overhead Conductors, 2023, Steady-state heat balance: convective, radiated, and solar heat terms and conductor resistance (cited, not reproduced)
- linerate 5.0.0 (Statnett), an open implementation of IEEE 738 and CIGRE 601, 5.0.0, IEEE738 thermal model, used only to generate the stored reference cases
- pypacity 0.1.3, an open implementation of IEEE 738, 0.1.3, Steady-state rating mode, used only to generate the stored reference cases
Worked examples
| Example | Independent source | Tolerance | Last result |
|---|---|---|---|
| A 1.108 in conductor at 40 °C in 2 ft/s wind | This tool's own heat balance for these inputs; the method is checked against linerate's 50 stored cases | ±0.5, ±0.05 | Passed on Oct 31, 2026 |
Known differences from reference engines
None recorded.
Cite this tool
Overhead conductor ampacity, version 0.1.0. gridprims. https://gridprims.com/tools/calc/line-rating/ampacity/