Work out cable ampacity instantly with clear inputs, formula shown and shareable results.
Tabulated ampacity assumes a single circuit at 30 degrees C ambient. Real installations need two corrections: an ambient factor, which follows the square root of the ratio of remaining temperature rise, and a grouping factor for cables bunched together that cannot shed heat independently.
Ampacity correction
I = Itabulated x Ca x Cg, with Ca = sqrt((Tmax - Tambient) / (Tmax - 30))
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.
Bunched cables heat each other, so each must run cooler to stay within its insulation limit. Six circuits together can lose 40% of rating.
Use the tables in the applicable code — BS 7671 Appendix 4, IEC 60364-5-52 or NEC 310 — since the correction factors and base values differ.