Aluminium Conductor Cable Sizing — Method
Aluminium is the conductor of choice for sub-mains, service entrances and feeders ≥ 50 mm² — the lower metal cost (~1/3 of copper per kg, even at higher cross-section) outweighs the size penalty. Al has 60–65 % the ampacity of Cu for the same cross-section, so aluminium cables are typically one or two IEC standard sizes larger than the copper equivalent. AAC (all-aluminium conductor) and AAAC (aluminium alloy) are common in overhead and direct-buried installations.
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.52.5 (aluminium, XLPE, Reference Method C) 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
- Copper Cable Sizing Calculator — Copper · Cu Conductor
- IEC 60364 Cable Sizing Calculator — IEC 60364-5-52 · International
- Cable Sizing — Installation Method E (Buried / In Ground) — IEC Method D1 · In Ground
- All Electrical Engineering Calculators →
Frequently Asked Questions
About 1.5–1.6× larger cross-section for the same ampacity. IEC 60364-5-52 Method C XLPE: 50 mm² Cu = 179 A, equivalent Al = 70 mm² (171 A) or 95 mm² (212 A). Rule of thumb: go up one or two IEC standard sizes when switching Cu → Al. The cable diameter, conduit fill and bending radius all increase accordingly.
Largely no. The 1965–1973 Al-wired homes in the US showed massive fire-risk from solid Al at 15 / 20 A receptacles. Modern codes (NEC 110.14) require CO/ALR-rated devices for solid Al up to 10 AWG; BS 7671 effectively prohibits Al below 16 mm² in domestic. Stranded Al ≥ 16 mm² (AA-8000 alloy in the US) is still standard practice for service entrances and sub-mains.
Oxide-inhibitor compound (e.g. NoAlOx, Penetrox, Burndy ABO-12) applied between the wire strands and the lug barrel before crimping. The aluminium oxide layer (Al₂O₃) is electrically insulating and forms within seconds of stripping — the inhibitor breaks it and excludes oxygen so it cannot reform. Use only AL- or AL/CU-rated lugs and breakers (NEC 110.14).
Al has higher thermal expansion (23 ×10⁻⁶/K vs 16.5 for Cu) and lower yield stress. Each thermal cycle compresses the Al strands; on cooling they don't fully spring back, so the connector loosens. Modern AA-8000 series Al alloy (with iron / silicon) has higher creep resistance than 1350-H19 — most current standards specify AA-8000 for building wire.
Same Ca and Cg multipliers, just applied to a lower Iz starting point. The k-value for short-circuit is different though — IEC 60364-5-54 gives k = 76 (PVC Al) and 94 (XLPE Al) vs 115 / 143 for copper. Short-circuit sizing for the same fault may force a larger Al cable than ampacity alone.
Usually yes. A typical 200 A copper service uses 2/0 AWG Cu (~67 mm²); the aluminium equivalent is 4/0 AWG Al (~107 mm²). Even at 1.6× the cross-section, the Al cable is roughly 60–70 % the cost of Cu. The conduit may need to step up one trade size, but the total installed cost is generally 30–40 % lower.