Installation and repair of power cables: Copper vs. aluminium

Ease of bending

Copper conductors, when compared to aluminium conductors having the same current rating, have a smaller cross-sectional area and are thus easier to bend and shape when jointing and terminating cables.

Extent of brittleness

Copper is less brittle than aluminium. This is particularly evident when using 3-core cables, where core manipulation is required for correct phasing etc. The larger the cable core size, the more difficult it is to shape and bend the cores while maintaining the correct electrical clearances within cable termination enclosures/compartments.

For example, it is sometimes not possible to terminate a 3-core 300 mm2 aluminium cable into a typical cable termination enclosure, whereas this is possible using a 3-core 185 mm2 copper cable. In the case of the 300 mm2 aluminium cable, it would be better to use a trifurcation joint or termination (with long tails) and opt to bring only the individual cores (i.e. 1-core) into the cable termination enclosure. Alternatively, a larger cable termination enclosure would need to be specified and designed – which is often not possible for certain types of equipment.

“Cold flow”

Aluminium exhibits a property known as “cold flow” in which the aluminium tends to flow out of a compression termination, causing a loose connection that can overheat. Next to new installation techniques and termination devices, it still takes a trained, competent electrician to terminate properly. Copper is much more forgiving.  

Corrosion

As aluminium corrodes quickly, compared to copper, every installation or repair action requires attention from the jointer to remove any oxide layer, which by definition will cause problems due to the insulating properties of the oxide layer.

The table below summarizes the basic differences between copper and aluminium for power cables.

 

Copper

Aluminum

Higher conductivity (A/mm2)

60% of copper’s conductivity (A/mm2)

Smaller cable surface area possible, so more flexible cable

Larger cable surface area leads to less flexibility of cable

Highly ductile so less brittle

Less ductile so more brittle

More expensive

Less expensive

Heavier

50% lighter than copper

“Cold flow” properties

6x more “cold flow” properties than copper

Less prone to oxidation

More prone to oxidation in air leading to localized heating at contact points (oxides exhibit poor conductivity)

No galvanic (bi-metallic) action at terminal equipment

Galvanic action – contact with brass/copper terminal equipment – leads to poor contacts

Reference

Aluminium Wiring: Understanding the Problem and the Solutions. The Hartford Loss Control Department, 2002

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