Reference Installation Method A1 / A2 Cable Sizing — Method
IEC Reference Method A1 (single-core conductors in conduit in a thermally insulated wall) and A2 (multi-core cable in the same conduit) give the lowest ampacity of any IEC reference method — because the insulation around the conduit traps heat. Typical for plasterboard partition walls with rockwool or PIR insulation. Always verify the installation truly is Method A — clipped-direct on the wall (Method C) gives ~20 % higher ampacity for the same cable.
Where:
- Ib — design current of the circuit (A), from the load calculation
- Ca — ambient temperature correction (1.00 at 30 °C reference)
- Cg — grouping / bunching factor (1.00 for a single circuit)
- Ci — thermal-insulation factor (1.00 if the cable is in free air; 0.50 if fully buried in insulation)
Then pick the smallest cable cross-section in IEC 60364-5-52 Table B.52.4, Method A1 column whose tabulated ampacity Iz ≥ It.
Related cable sizing calculators
Other standard- and method-specific cable-sizing calculators in the same series — same procedure, different reference tables and defaults:
- Cable Sizing Calculator (universal) — the seed page covering all standards in one tool
- Cable Sizing — Installation Method C — IEC Reference Method C · Clipped Direct
- Cable Sizing — Installation Method E (Buried / In Ground) — IEC Method D1 · In Ground
- IEC 60364 Cable Sizing Calculator — IEC 60364-5-52 · International
- All Electrical Engineering Calculators →
Frequently Asked Questions
Method A1: insulated conductors (single-core) installed in a conduit in a thermally insulated wall. The conduit can be metallic or non-metallic. The insulation surrounds the conduit on all sides, restricting heat dissipation. This is the worst-case heat scenario in IEC 60364-5-52, so its ampacity values are the lowest in Table B.52.4.
A1 = single-core insulated conductors in conduit in insulated wall. A2 = multi-core (sheathed) cable in the same conduit-in-insulated-wall configuration. A2 ampacity is ~5 % lower than A1 because the multi-core sheath adds another thermal layer. Both are penalty methods — avoid where possible.
Heat from copper losses (I²R) must conduct through: cable insulation → conduit wall → thermal insulation → wall finish → ambient air. Each layer adds thermal resistance. The insulated wall blocks the convective heat-loss path that would exist in Method B (conduit on a wall surface). Result: 1.5 mm² Cu Method A1 = 17.5 A vs Method C clipped direct = 22 A — same cable, 26 % less ampacity.
No, that would over-derate the cable and waste copper. Use Method B1/B2 for conduit on a non-insulated wall surface, or Method C for clipped direct. Method A specifically requires the conduit to be surrounded by thermal insulation — typical of new-build partition walls but not of fixed masonry walls.
Marginally. IEC 60364-5-52 treats Method A1 the same for steel, PVC and corrugated conduit — the conduit's thermal resistance is small compared to that of the surrounding insulation. The wall insulation type and thickness dominates the result.
BS 7671 Section 523.9 / IEC 60364-5-52 ¶ 523.7: if a cable passes through ≤ 50 mm of thermal insulation, no derating is required; 50–100 mm requires Ci = 0.88; 100–200 mm requires Ci = 0.78; 200–400 mm requires Ci = 0.63; ≥ 400 mm or fully buried requires Ci = 0.50 (effectively Method A). Always size for the worst-case section of the run.