What makes the better flexible stranded conductor: copper or aluminium?

Stranded conductors: pros and cons, and applications

A stranded conductor is composed of a number of thinner conductors twisted together into a cohesive cable. It is widely used in applications which require considerable movement – such as robotics and in vehicles – or where the wire needs to be bent into complex shapes – such as electronic devices and circuit boards. A stranded conductor can be manufactured in a variety of configurations, the most common being concentric (true, equilay, unidirectional or unilay), bunched and rope.

Copper or aluminium?

Both copper and aluminium can be stranded. However, a key difference is that stranded aluminium is only available at nominal cross-sectional areas of 10 mm2 and above. Copper, on the other hand, is available in very low conductor cross-sections, for example 0.5 to 10 mm2. The reason lies with the difference in tensile strength and fatigue endurance limit of the two materials. Taking 100 for copper, the relative values for aluminium are respectively 35 and 62, as can be seen from the table below.

Material Properties

Comparative Values

Copper

Aluminium

Ultimate tensile strength

100

35

Stress fatigue endurance limit

100

62

 

The differences in tensile strength and fatigue endurance limit, and hence cross-sectional area, mean that so-called ‘finely stranded’ and ‘extra finely stranded’ conductors (0.5 to 6 mm2) are only available in copper, and the finest aluminium conductors available are significantly stiffer than the finest copper conductors.

Stranded aluminium does offer better control of skin effect than stranded copper. This is due to greater skin depth and natural strand insulation through an oxide layer. However, this advantage only plays a significant role for conductor cross-sections above 800 mm2.

Conclusion

Copper is more widely available as a stranded conductor than aluminium, and the strands can be of a much smaller diameter, resulting in a more flexible cable.

References

Conductor stranding http://www.calmont.com/?pgid=46

Electric cables BICC Handbook 3rd edition

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