Al or Cu conductor…
The conductivity of copper is 65% higher than that of aluminium which means that the conductor size of similarly rated cables is proportionately smaller. Correspondingly less expense is then incurred in providing for insulation, shielding and armouring the cables themselves. Transport of the less-bulky cables is easier and so is installation. In limited spaces in cable ducts, the smaller volume and better ductility of copper cables can have an even larger benefit.Copper cables are easily jointed because copper does not form on its surface a tough, non-conducting oxide. The oxide film that does form is thin, strongly adherent and electrically conductive, causing few problems.Cleaning and protection of copper is easy and if joints are made as recommended they will not deteriorate to any great extent with age, which saves on maintenance costs.
For the same nominal current rating, the cable with the aluminum conductor is significantly larger in diameter, carries a proportionally greater volume of insulation and is not so easily installed because of being less flexible. Aluminum is notoriously difficult to joint reliably. Table 1 compares aluminum and copper conductors for equivalent current rating.
Table 1 – Comparison between Copper and Aluminum Conductors in XLPE Insulated Steel- Wire Armoured Cables.
| Characteristic | Copper 300 m2 | Aluminum 500 m2 |
| Overall diameter (mm) | 66.5 | 83.9 |
| Minimum bending radius (mm) | 550 | 700 |
| Max DC resistance/km at 20o C (ohm) | 0.0601 | 0.0617 |
| Approx. voltage drop/A/m (mV) | 0.190 | 0.188 |
| Continuous current rating, drawn in to duct (amp) | 496 | 501 |
These notes have largely been derived from reference to BS 7450 which is identical to IEC 1059. Both of these give full details of the variables to be considered and the ways in which optimum cable size determinations can be made.
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