Factors Which Affect The Selection of Copper or Aluminum Conductor
| Factor | Copper | Aluminum | |
| 1 | Conductivity | Higher conductivity (A/mm2) | 60% of copper's conductivity (A/mm2) |
| 2 | Bending Copper conductors, when compared to aluminum 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. | Smaller cable surface area possible, so more flexible cable | Larger cable surface area leads to less flexibility of cable |
| 3 | Brittle Copper is less brittle than aluminum. 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. | Highly ductile so less brittle | Less ductile so more brittle |
| 4 | Cost | More expensive | Less expensive |
| 5 | Weight | Heavier | 50% lighter |
| 6 | Cold Flow Aluminum exhibits a property known as "cold flow" in which the aluminum 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. | Cold Flow properties | 6x cold flow effect |
| 7 | Corrosion As aluminum 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. | Less prone to oxidation Copper does not react with water | More prone to oxidation in air leading to localized heating at contact points (oxides exhibit poor conductivity) |
| 8 | Galvanic termination effect | No galvanic (bi-metallic) action at terminal equipment | Galvanic action – contact with brass/copper terminal equipment – leads to poor contacts |
| 9 | Fatigue Strength Copper conductors can withstand larger vibration amplitudes and for much longer than aluminum conductors without cracking or breaking.Fatigue occurs when a material is subjected to repeated loading and unloading stresses. If the stresses are above a certain threshold and the number of repetitions is large enough, microscopic cracks begin to form. Progressively, a crack can reach a critical size and then propagate suddenly, leading to a fracture.Fatigue strength is defined as the value of stress at which failure occurs after a given number of cycles. These are the comparative values of fatigue strength for high conductivity copper and low alloyed aluminum respectively:Another application area in which fatigue strength plays a role is overhead transmission lines. Due to wind excitation, the electrical conductors experience so called aeolian vibrations in the 5 to 50 Hz range. | AnnealedFatigue strength (N/mm²) = 62No. of cycles x 106 = 300Half HardFatigue strength (N/mm²) = 115No. of cycles x 106 = 300 | AnnealedFatigue strength (N/mm²) = 20No. of cycles x 106 = 50Half HardFatigue strength (N/mm²) = 45No. of cycles x 106 = 50 |
| 10 | Short Circuit Heating | Copper conductors retain adequate mechanical strength to be able to withstand the large electromagnetic forces during short-circuits in spite of the intense heating | |
| 11 | Yield Strength | Copper conductors can withstand higher pulling forces than aluminum conductors without necking or breaking.Tensile Strength Annealed=200 N/mm20.2% Proof Stress Annealed (N/mm2)<120 | Therefore, when long runs of aluminum conductor cables are pulled through containment systems, and subjected to high pulling forces, these can stretch and "neck-down", reducing the current carrying capacity of the cables which may result in dangerous overheating. In extreme cases, mechanical drawing in of aluminum conductor cables over long or multidirectional routes can even result in irreparable physical damage.Tensile Strength Annealed=50-60 N/mm20.2% Proof Stress Annealed (N/mm2)=20-30 |
| 12 | Weight for same conductivity (Comparative) | 100% | 54% |
| 13 | Cross section for same conductivity (Comparative) | 100% | 156% |
| 14 | Nicks, scratches, minor damage | Better | WorseWhere aluminum conductors are subject to nicks, scratches or "ringing", these flaws can lead to "fatigue failure" when subjected to movements due repeated expansion and contraction or vibration. The significantly higher rate of thermal expansion in aluminum compared with copper when exposed to thermal cycling due to load changes can create sufficient movement such that minor flaws in the aluminum conductor may deteriorate into areas of high resistance, causing hot spots or even breakage of the conductor. |
| 15 | Termination Preparation | Less Work | More workIt is clear that whilst effective terminations may be made in aluminum conductors, the required skill level is also higher if problems relating to dissimilar metals, galvanic corrosion, stress breakage and creep are to be avoided. This additional skill and effort required for reliable aluminum conductor terminations carries a cost premium.A further consideration when exposing the conductor to the atmosphere is the formation of surface contaminants. Oxides, chlorides and sulphides of the base conductor metal are common when the conductor is exposed to the atmosphere at terminations. The principal difference is that the oxides of aluminum are effective electrical insulators, whereas the oxides of copper, whilst not as conductive as copper, remain conductive when formed. The key difference is that aluminum conductors require surface preparation to remove these oxides (usually by mechanical means such as wire brushing) immediately before any further attempt to terminate is made, and also require ongoing protection by means of contact compounds that exclude air (and also moisture). |
| 16 | Cross Sections | low cross-sections, such as 0.5 to 10 mm | stranded aluminium is only available in nominal cross-sectional areas of 10 mm2 and above |
| 17 | Thermal Expansion | linear coefficients of expansion Copper = 17?10E-6 | Coefficient of thermal expansion for aluminium is 35% greater than that of copper.linear coefficients of expansion Aluminium = 23.10E-6 |
As of 2007: The 7.8 km long cable will be the world's first 3-core XLPE submarine cable to achieve a voltage rating of 245 kV, beating Nexans' current world record of 150 kV, set by the Horns Rev offshore wind farm in Denmark.
Devicenet cable section