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What Would Be The Best Conductor Material for Electrical Cables
What Would Be The Best Conductor Material for Electrical Cables (photo credit: penstonecommunications.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.

HV copper cable
HV copper cable (photo credit: businessinsider.com)

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.

CharacteristicCopper 300 m2Aluminium 500 m
Overall diameter (mm)66.583.9
Minimum bending radius (mm)550700
Max DC resistance/km at 20o C (ohm)0.06010.0617
Approx. voltage drop/A/m (mV)0.1900.188
Continuous current rating, drawn in to duct (amp)496501

(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.

More about this is described in the following paragraphs.


Economic Selection of Cables for Industry

The function of a power cable is to distribute electric power as efficiently as possible from a source to a point of utilisation. Unfortunately, due to their electrical resistance, cables dissipate in the form of heat some of the power carried, so that 100% efficiency is not achieved.

An idea of the extent of this heat loss can be obtained from the comparison that modern cables are capable of operating at temperatures as high as those of central heating systems.

The energy lost by using cables at such temperatures has to be paid for and becomes a surcharge on the cost of operating whatever equipment is being supplied. This surcharge continues for the life of the process involved and into the future for any subsequent use of that circuit.

The cost of energy is an important component of industrial and commercial running costs and every effort should be made to contain it as much as possible. The environmental and conservational aspects of wasted energy are important factors, even though they may be partly subjective, and it is evident that pressures from this direction will increase.

It may be observed that heat losses from a cable go hand in hand with a lower voltage at its delivery end. This may impair the efficient operation of the supplied process, thus further degrading the cost efficiency of production.

It therefore makes good sense to adopt distribution designs which go as far as is practicable to reduce energy losses.

In theory it would be possible to reduce the lost power to a negligible amount by increasing the size of the cable; however, as this also increases the cost of the cable it tends to cancel the savings from better distribution efficiency and a compromise has to be struck.

The best time to incorporate high-efficiency distribution is at the design stage when additional costs are marginal. It can prove to be difficult to reinforce a circuit at a later date.

The problem is to identify a conductor size which reduces the cost of the wasted power without incurring excessive cable costs. The basic approach to this problem was formulated by Lord Kelvin in 1881 and has been applied to numerous situations where cost (or weight) and efficiency need to be taken together to obtain an optimum solution.

Reference // Electrical energy efficiency of motors, cables, busbars and transformers

About Author //

author-pic

Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on

4 Comments


  1. KER Group
    Apr 11, 2016

    Thanks for taking the time to put this article together for us engineers and technicians, good work!


  2. Derek [Bill] Bailey
    Apr 09, 2016

    Last paragraph:
    ” The basic approach to this problem was formulated by Lord Kelvin in 188129 and has been applied to numerous situations where cost (or weight) and efficiency need to be taken together to obtain an optimum solution.

    Reference // Electrical energy efficiency of motors, cables, busbars and transformers

    What would be the correct year please?
    Would you be so kind as to state Lord Kelvin’s formula that you mention or a reference to undertake more research?

    Regarding the reference given, would it be possible to supply more detail re the authors et al.

    Thank You


  3. GNANAVEL
    Apr 09, 2016

    Dear Sir, Thank you for your effort to make other engineers and technicians to have the knowledge by sharing this.
    I wish to know the same in detail and also i wish to know the cable routing design for a project. (Sewage Treatment Plant.
    I am working as electrical engineer in a project company in Oman.

    Hope I will get the details from you.

    Thank you once again.

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