What Would Be The Best Conductor Material for Electrical Cables

HV copper cable (photo credit: businessinsider.com)

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 aluminium conductor is significantly larger in diameter, carries a proportionally greater volume of insulation and is not so easily installed because of being less flexible. Aluminium is notoriously difficult to joint reliably. Table 1 compares aluminium and copper conductors for equivalent current rating.


Table 1 – Comparison between Copper and Aluminium Conductors in XLPE Insulated Steel- Wire Armoured Cables.
 

Characteristic	Copper 300 m2	Aluminium 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

(Cable: to BS 5467 (& IEC 502) 4-core, stranded conductors, XLPE insulation, PVC bedding, steel wire armour, PVC oversheath, rated at 0.6/1.0 kV)



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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