MYTH: Aluminium Cable Is Always Cheaper Than Copper

The Aluminium "Savings" That Cost You More

The myth: "Aluminium cable is cheaper than copper — always use it for large feeders."

The reality: Aluminium has a crossover point below which copper is cheaper installed, not just purchased.

The Conductivity Gap

Aluminium conductivity = 61% of copper (IEC 60364-5-52 Annex B)

To match copper current rating, aluminium needs:

• ~1.6× the cross-sectional area
• Larger conduit/cable tray
• Bigger glands, lugs, and terminations
• Anti-oxidant compound (prevents oxidation)
• More labor (heavier, stiffer cable)

Cost Breakdown: 50m Run, 3-Phase, 100A

Aluminium "savings": -$300 conductor cost, +$515 ancillary costs = $215 more expensive installed.

The Crossover Point

Aluminium becomes cost-effective when:

1. Cable run >150m (conductor cost dominates)
2. Cable size ≥120mm² (conduit/gland premium flattens)
3. Open cable tray (no conduit cost penalty)
4. Low-congestion installation (easier handling of stiffer cable)

For short runs (<100m) and small cables (<95mm²), copper wins on total installed cost.

The Hidden Risks

Aluminium terminations require:

• Torque wrench (specific N·m per lug size) — over-tightening causes cold flow
• Inspection schedule (re-torque after 6 months, then annually per AS/NZS 3000)
• Oxide inhibitor (prevents high-resistance joints)
• Bimetallic lugs (if connecting to copper busbars)

Copper: tighten to finger-tight + 1/4 turn. Done.

Standards Perspective

AS/NZS 3008 Table 3: Lists both copper and aluminium current ratings. Aluminium needs 1.5-1.8× area for equivalent rating.

BS 7671 Regulation 521.5: Requires suitable terminations and protection against galvanic corrosion for aluminium.

NEC 110.14: Requires terminals and lugs to be identified for aluminium use — many aren't.

Real Project: 200-Circuit Commercial Fitout

Scenario: Replace 200 × 4mm² Cu subcircuit cables with aluminium to "save money."

Reality:

• Need 200 × 6mm² Al (nearest equivalent rating)
• Conduit upsizes from 25mm to 32mm on 60% of runs
• Switchboard lugs: standard copper to bespoke aluminium-rated
• Termination labor: +15 minutes per circuit (anti-ox, torque wrench)
• Re-inspection after 6 months (contractual obligation per AS/NZS 3000)

Result: $27,000 "savings" on cable became $42,000 extra cost installed + ongoing inspection liability.

Try It Yourself

Use ECalPro cable sizing calculator:

1. Size a 50m run at 80A, 3-phase, 0.85 pf
2. Note the copper size and cost
3. Switch to aluminium
4. Add conduit, gland, labor premiums
5. Compare total installed cost

Takeaway: Aluminium saves money on large, long feeders. For subcircuits and short runs, copper is often cheaper installed. Always calculate total cost, not just $/m cable.