Copper vs aluminium cable: What is the difference?

Quick answer: Copper has lower electrical resistance than aluminium at the same conductor size. Aluminium’s main advantage is its lower weight. Choosing between them involves conductor size, voltage drop, terminations and installation conditions, as well as the cable price. An aluminium cable is not a direct replacement for a copper cable of the same mm² rating.

The main differences

Why equal conductor sizes are not equivalent

Conductor resistance depends on resistivity, length and cross-sectional area: R = ρ × L / S. Here, R is resistance, ρ is material resistivity, L is conductor length and S is cross-sectional area. At the same length and temperature, aluminium’s higher resistivity produces greater voltage drop and I²R losses for the same conductor size.

To obtain roughly equal resistance, aluminium needs about 1.6 times the cross-sectional area of copper. A 10 mm² copper conductor and a 16 mm² aluminium conductor are therefore a useful approximate comparison. This is not a guarantee of equal current-carrying capacity. Alloy, construction and temperature affect the result; use the actual cable’s published resistance and current ratings for design.

Insulation temperature limits, installation method and grouping with other loaded circuits also affect the allowable current. Do not interchange copper and aluminium figures in a cable current-carrying capacity table. Longer circuits need a separate voltage-drop check too.

Where each material is commonly used

Copper is widely used in building wiring, panel connections, control circuits and purpose-built flexible machine cables. Aluminium is common in power distribution, overhead lines and larger fixed feeders. These examples do not establish what is permitted in a particular installation; the design and applicable wiring rules determine that.

For a moving connection, conductor material alone is not enough. The cable must be designed for repeated flexing or cable-chain service as appropriate. A stranded conductor does not automatically make a cable suitable for continuous movement. See the guide to solid and stranded conductors for the distinction.

Terminations deserve particular attention

Aluminium’s surface oxide can impede electrical contact. Joint design must also account for thermal cycling and changes in contact pressure as the conductor deforms over time. This makes connector selection and the specified tightening or crimping method essential. Extra tightening cannot compensate for an unsuitable connector.

A terminal designed for copper may not accept aluminium. Approval may be limited to particular sizes and conductor classes, and some products require a specified contact compound. Adding compound does not make an unapproved terminal suitable for aluminium. Follow the product instructions for surface preparation, compound use and tightening torque.

Can copper and aluminium be joined?

Yes, using a connector approved for the transition. Twisting the wires together and covering them with tape is not an acceptable substitute. Moisture can promote galvanic corrosion at a copper–aluminium interface. Depending on the application, use an approved Al/Cu connector or a bimetallic lug, with the correct conductor sizes, classes and environmental rating.

A bimetallic lug combines an aluminium conductor barrel with a copper contact section designed for the interface. Inserting aluminium into an arbitrary copper lug does not provide the same arrangement. For compression connections, the lug, crimping dies and crimp sequence must form an approved combination.

Is CCA cable the same as copper cable?

CCA means copper-clad aluminium. Its copper exterior surrounds an aluminium core, so it should not be treated as an all-copper conductor. Check the declared material, cross-sectional area and resistance in the data sheet rather than relying on appearance. Tinned copper can look silver too; colour alone is not a reliable way to identify conductor material.

Which option costs less overall?

Compare designs that meet the same electrical requirements, rather than the price per metre of equal-size cables. Include connectors, installation labour, space requirements and operating losses. A larger conductor may require different glands, terminals or routing arrangements. A saving on the cable itself may therefore be offset elsewhere in the installation.

Installation note: Changing an existing circuit’s conductor material requires a new cable sizing assessment. If a termination smells burnt, melts or overheats, stop using the circuit. Isolate it if you can do so safely and have a qualified electrician inspect it. Terminations must not be inspected or worked on while energised.