Cable Sizing Calculator
AS/NZS 3008.1 current-carrying capacity with full derating — grouping (Table 22), ambient temperature, and installation method. Volt drop checked to AS/NZS 3000 cl. 3.6 (≤5%). Copper conductors.
Circuit details
V75 = standard TPS, V90 = XLPE singles or twin
Column numbers are the printed columns of the AS/NZS 3008.1.1 rating table, so the figure can be checked against the page.
The ladder does not stop at 6. This used to flat-rate everything above 6 at 0.57, which over-rates a 20-circuit bunch by about a third.
Reference ambient is 40°C in air and 25°C in soil. Roof spaces routinely reach 50–60°C, and that is where the derating bites hardest.
How this works: Every figure comes from the same verified AS/NZS 3008.1.1:2017 dataset the rest of the app uses — this page now asks the server for it rather than keeping its own copy. Ratings are read from the installation-method column of Table 10 (V75) or Table 11 (V90) — they are not scaled off a clipped-direct base. Grouping is Table 22 item 2 in air, Table 25(2) buried. Ambient is Table 27(1) in air, Table 27(2) in soil. Resistance is Table 35 a.c. resistance at the conductor's rated temperature. Volt drop: 2×I×R×L/1000 (single phase) or √3×I×R×L/1000 (three phase); limit 5% per AS/NZS 3000 cl. 3.6.
Where the standard prints a dash, this tool says so and offers no number. The 2017 edition is the source; AS/NZS 3008.1.1:2025 is current and these figures have not been re-checked against it.
Where the standard prints a dash, this tool says so and offers no number. The 2017 edition is the source; AS/NZS 3008.1.1:2025 is current and these figures have not been re-checked against it.
Always verify final cable selection against AS/NZS 3008.1 tables on the job. Apply additional derating for thermal insulation, high-temperature locations, and harmonic loading as required. This tool is a guide — a licensed electrician must confirm the design.