Copper vs Aluminium Cable — The Engineering and Economic Case in 2026

Aluminium’s electrical resistivity is 2.826 × 10⁻⁸ Ω·m compared to copper’s 1.724 × 10⁻⁸ Ω·m. This gives aluminium approximately 61% of copper’s conductivity by volume. To carry the same current, an aluminium conductor needs approximately 1.6 times the cross-sectional area of a copper conductor.

However, aluminium’s density is 2,700 kg/m³ versus copper’s 8,960 kg/m³ — roughly 30% of copper’s weight. When you combine the 1.6× area penalty with the 0.30× density advantage, an aluminium conductor carrying the same current weighs approximately 48% of the equivalent copper conductor (1.6 × 0.30 = 0.48).

This mass advantage compounds through the entire installation:

The cost advantage varies with commodity prices, but the structural relationship is stable: aluminium delivers the same current-carrying capacity at roughly half the material cost and half the weight, in a conductor that is 1.6 times larger in cross-section.

Certain applications are so clearly suited to aluminium that specifying copper requires justification:

LV mains and submains (≥95 mm²)

Large cross-section power cables are the core aluminium market. A 300 mm² Al/XLPE cable carries approximately the same current as a 185 mm² Cu/XLPE cable (per AS/NZS 3008.1.1:2017, Table 13). The aluminium cable costs roughly 45% less and weighs roughly 50% less. On a 200 m cable run, the material cost difference can exceed AUD $15,000 per circuit.

For long cable runs (building risers, site distribution), the weight saving is particularly valuable — lighter cables require smaller cable tray, less support hardware, and fewer installation labour-hours. The total installed cost saving (not just material) typically reaches 30–40%.

Busbars

Aluminium busbars are standard in switchboards rated above 800 A. The size penalty is accommodated within the switchboard enclosure (which has fixed dimensions regardless of busbar material), and the weight reduction simplifies handling during assembly. Modern aluminium alloy busbars (6101-T61 or equivalent) have adequate mechanical strength for bolted connections.

Overhead lines

Distribution and transmission overhead conductors are almost universally aluminium or aluminium alloy (AAAC, ACSR). The weight advantage is critical for span length and tower loading. Copper overhead conductors are effectively obsolete in new construction.

Underground distribution mains

Utility-owned underground cables above 95 mm² are predominantly aluminium globally. The termination and jointing is performed by trained utility crews using type-tested hardware. At utility scale, the material cost saving runs to millions of dollars per major project.

Aluminium’s limitations are real, well-understood, and manageable — but they add cost and complexity that can erode the material savings:

Small cross-sections (≤16 mm²)

Below 16 mm², the 1.6× size increase makes aluminium conductors stiffer and harder to handle in tight spaces. Socket outlets, switches, and small distribution boards are designed for copper conductors. Aluminium at these sizes is not prohibited by standards, but the practical challenges and termination limitations make copper the default.

Termination and jointing

This is the critical issue. Aluminium forms a tenacious oxide layer (Al₂O₃) within seconds of exposure to air. This oxide is an excellent insulator — it increases contact resistance at terminals. Under cyclic thermal loading (the conductor heats under load, cools when unloaded), aluminium’s higher coefficient of thermal expansion (23.1 × 10⁻⁶/K vs copper’s 16.5 × 10⁻⁶/K) causes the conductor to expand and contract more than the terminal, gradually loosening the connection.

The combination of oxide formation and thermal cycling is responsible for virtually all aluminium conductor failures. The conductor itself does not fail — the connection does. This is why aluminium requires:

• Anti-oxidant compound (inhibitor paste) at all mechanical connections
• Bi-metallic lugs or terminals rated for aluminium (marked Al or Cu/Al)
• Correct torque values (typically higher than copper) maintained with calibrated tools
• Periodic retorquing during the first year of operation (after initial thermal cycling)

Conduit installations

The 1.6× cross-section increase directly affects conduit fill calculations. A circuit that fits comfortably in 32 mm conduit with copper conductors may require 40 mm or 50 mm conduit with aluminium — an increase that can exceed the conductor cost saving, particularly in installations with many bends or long conduit runs.

Vibration environments

Aluminium is more susceptible to fatigue failure from vibration than copper. In industrial environments with significant vibration (adjacent to rotating machinery, on vibrating structures), copper is preferred. Aluminium conductors in these environments require additional securing and strain relief.

Each major standard addresses aluminium conductors with specific provisions:

AS/NZS 3008.1.1:2017

Provides separate current-carrying capacity tables for aluminium conductors (Tables 14–22). Derating factors apply equally to copper and aluminium. Clause 4.3 requires that terminations for aluminium conductors be suitable for the purpose, with anti-oxidant treatment where specified by the terminal manufacturer. The standard does not prohibit aluminium at any cross-section but notes that common accessories may not be rated for aluminium below 16 mm².

BS 7671:2018+A2:2022

Regulation 521.4 requires aluminium conductors to be terminated using means specifically designed for aluminium. Appendix 4, Table 4D3A provides voltage drop values for aluminium conductors separately from copper. The IET On-Site Guide notes that many socket outlet and switch terminals are not rated for aluminium, effectively limiting aluminium to larger cross-sections in practice.

IEC 60364-5-52:2009+A1:2011

Clause 523.1 provides current-carrying capacity tables for both copper and aluminium. Clause 526.2 requires connections between dissimilar metals to be made using appropriate means to prevent electrolytic corrosion — a direct reference to the copper-aluminium junction problem.

NEC/NFPA 70:2023

Section 110.14 requires conductors to be terminated using devices identified for the conductor material. Terminals marked “AL-CU” or “CO/ALR” accept both materials; terminals marked “CU” or unmarked accept copper only. Article 310 provides separate ampacity columns for aluminium in Tables 310.16 through 310.21.

Commodity prices fluctuate, but the copper-aluminium cost ratio has been remarkably stable over the past decade. As of Q1 2026:

• LME copper: approximately USD $8,800/tonne (USD $8.80/kg)
• LME aluminium: approximately USD $2,600/tonne (USD $2.60/kg)
• Ratio: copper is 3.38× the price of aluminium per kilogram

For a concrete example, consider a 100 m submain cable run rated at 400 A:

The aluminium option saves approximately $1,570 per circuit (53%). On a project with 20 such circuits, the total saving exceeds $31,000 — real money in any project budget.

The insulation cost is slightly higher for aluminium because the larger conductor requires more insulation material. The termination cost is higher because bi-metallic lugs and anti-oxidant compound add cost. But these additions are small compared to the conductor material saving.

Aluminium’s higher resistivity means higher voltage drop per metre for the same current. This can be the deciding factor on long cable runs where voltage drop is the limiting constraint rather than current-carrying capacity.

For a 400 A circuit at 0.8 power factor, approximate voltage drop values (per AS/NZS 3008.1.1:2017 mV/A/m method):

• 240 mm² Cu: ~0.190 mV/A/m
• 400 mm² Al: ~0.185 mV/A/m

At these sizes, the voltage drop is comparable because the aluminium conductor is large enough to compensate. However, if you compare at equal cross-section (both 240 mm²), the aluminium voltage drop would be approximately 1.6× higher.

The practical implication: size aluminium by current-carrying capacity first, then verify voltage drop. In most cases, the aluminium conductor sized for current also meets voltage drop limits. On very long runs (>200 m) at moderate loads, voltage drop may require an additional size increase — but even with this increase, aluminium often remains cheaper than copper.

Standards referenced: AS/NZS 3008.1.1:2017 (Tables 13–22, mV/A/m tables), BS 7671:2018+A2:2022 (Regulation 521.4, Appendix 4), IEC 60364-5-52:2009+A1:2011 (Clauses 523.1, 526.2), NEC/NFPA 70:2023 (Section 110.14, Article 310). Commodity prices: LME settlement, March 2026.