Copper Cable or Aluminum Cable: Which Should I Buy?

How do copper and aluminium conductors compare electrically?

Copper has higher conductivity than aluminium. For comparable resistance and current duty, a copper conductor is generally smaller than an aluminium conductor. The exact equivalence must be checked against the cable standard and a design calculation, not assumed from a general rule.

Resistance per kilometre drives voltage drop and losses. As a reference point, plain copper conductors in classes 1 and 2 have a maximum DC resistance at 20 °C of 1.15 Ω/km at 16 mm², according to IEC 60228. An aluminium conductor of the same size has higher resistance, which is why it usually needs a larger cross-section for the same duty.

Voltage drop limits come from the installation rules, not from the conductor material. IEC 60364-5-52 Annex G (informative) gives 3 % for lighting and 5 % for other uses on an installation supplied directly from a public low-voltage network, and 6 % and 8 % for a private low-voltage supply. National rules may differ, so check the rule that applies to your project.

Does the conductor material change the short-circuit check?

Yes. The adiabatic check uses S = I × √t / k, where S is the cross-section in mm², I is the fault current in A and t is the time in seconds. The k value depends on the conductor and insulation: 115 for copper with PVC, 143 for copper with XLPE, 76 for aluminium with PVC and 94 for aluminium with XLPE (IEC 60364-5-54 and IEC 60364-4-43). Because the aluminium k values are lower, the same fault needs a larger cross-section.

Worked example: a 10 kA fault cleared in 0.4 s on copper with PVC insulation gives S = 10,000 × √0.4 / 115 ≈ 55 mm², so the next standard size is 70 mm². The check is valid for faults up to about 5 s. For fast fuses and breakers, use the let-through I²t value from the manufacturer instead.

How do weight and size affect handling and installation?

Aluminium is much lighter than copper. Based on material density, copper conductor weighs about 8.89 kg per km for each mm² of cross-section, and aluminium about 2.70 kg per km for each mm². The lower weight can reduce handling effort and may simplify long runs.

The larger diameter of an aluminium cable affects conduit fill, bending radius, tray capacity and terminations. Copper is more compact and is often preferred where space is limited. The minimum bending radius depends on the cable construction and standard edition, so take the value from the manufacturer's datasheet rather than from a general rule.

How do copper and aluminium compare side by side?

The table summarises the main differences. Use it as a starting point for the specification, then confirm each row against the cable datasheet and the equipment maker's instructions.

Density values are material properties used for weight estimates, not cable masses. The k values apply only to the adiabatic short-circuit check. Confirm terminal approval against the equipment instructions.

What should be checked at the connections?

Use lugs and terminals identified for the conductor material and size. Surface preparation, oxide control, tightening method and inspection should follow the equipment and connector instructions. Mixed-metal interfaces need suitable approved hardware, not improvised joints.

• Check equipment terminals for the conductor material.
• Include connector and oxide-control requirements in the specification.
• Do not substitute at equal cross-section without a calculation.

How should the commercial comparison be made?

Compare cable cost, supports, tray size, pulling effort, terminations, losses and maintenance. A lower initial cable price may not produce the lowest installed or lifetime cost. If aluminium requires a larger cable, verify that switchgear lugs, glands, bend space and tray capacity still work with the new size.

Metal prices change over time and affect quotations, so ask suppliers to state the price basis clearly. The guide on copper price and cable quotation explains how to compare quotes on the same basis.

Equal cross-section does not mean equal performance. The useful comparison includes cable losses and termination labour, not only the conductor purchase price.

Frequently asked questions