The Color of the Trust

Decades of reliable service have allowed copper to attain the position as the most efficient electric conductor in the manufacture of commercial and industrial electric wires and cables.

Copper has the highest conductivity among all metals used in engineering applications. This means that a copper cable, being smaller than an aluminum cable, has an equivalent current-carrying capacity.

When being installed, conductors are subject to inevitable bending and mechanical abuse. Copper conductors, however, are stronger and more resistant than aluminum conductors. This is a real advantage both in distribution as well as in terminal boxes, where copper conductors can bend further, coil tighter and be pulled with greater force without drawing nor breaking. To the contrary, aluminum is softer and has a lower degree of elasticity than copper, due to which it draws in the required area when being installed under great mechanic tension.

Copper is and has been throughout its history, a highly suitable metal for electrical installations. Unlike this experience, aluminum connections may result weak due to:

• The critical installation procedures require to guarantee a good connection.
• The insulating oxide that is always present.
• A higher thermal expansion factor than copper.
• An actual threat of corrosion.

Many installations with aluminum conductors have been subjected to the ANSI C119.4500 heat cycle trial, at times modified by a 100 Cycles Current (CCST) low immersion trial (At least 1,600 cycles should be applied in order to obtain results that are close to real life conditions). Field experience has shown that many installations already tested with these standards easily fit the requirements, but fail when exposed to real operating conditions. This occurs because the criteria of the performance of trials are not based on the new theories of the electric contacts and their deterioration.

Adequate copper connections become less heated than their aluminum equivalents, what guarantees a longer useful life cycle.

The Insulated Conductors Committee of the IEEE has accurately determined the current-carrying capacity of a wide range of wires and cables, and the installation conditions, which are published in norm IEEE-835-1994. Engineers and systems designers worldwide utilize this norm. Their charts show that due to copper’s inherent higher conductivity, the current-carrying capacity of copper conductors is approximately 1.6 times higher than that of aluminum conductors in the same transverse section.

Given that a copper cable is smaller in diameter and requires less insulation, shielding and bushings than an aluminum cable, it is more flexible and requires less effort when bended and placed in position during installation. Copper cables are less spacious, whereby their transportation to the installation site is also easier, as a smaller reel will be required. Likewise, by being smaller in size, it may be installed in places with limited spaces.

Aluminum alloys are more active metals than copper, due to which they corrode in the presence of humidity (water). This sensitivity to corrosion reduces the useful life of a cable. Humidity may permeate into the cable during transportation, handling, outside storage or through unintentional damage or defects in cable connections or terminals.

Copper cable will not be seriously corroded by water. But when water comes in contact with the aluminum conductor of an insulated wire or cable, a severe corrosion will cause the aluminum to transform into hydroxide and hydrogen gas. Hydroxide has greater volume than metal and its formation will cause a damaging expansion to the cable’s insulating structure, eventually destroying it. Hydrogen gas produced may frequently reach high pressures with harmful results.

The case of a Canadian company may illustrate the implacable nature of corrosion, where an aluminum conductor was contaminated through hand perspiration during handling and was later installed onto the terminal. In humid conditions but without applying tension, 70% of conductors and/or connections were so corroded that they become useless after two days.

Aluminum conductors require special protection and can not be used as equivalents not to replace copper conductors in certain critical applications. As an example, the Electricity Code of Canada allows only the use of copper conductors in fire alarms and circuits of fire-prevention pumps.

In order to decide a purchase, it is important to make an economic comparison between copper and aluminum cables. It is evident that the cost of aluminum cables is sometimes lower than the cost of copper cables. But a real economy should not be measured only by the initial cost. This is the reason for considering the life cycle cost, which includes useful life, installation, materials, maintenance, repairs and possible replacement together with the potential responsibility for a poor performance during service.

The analysis of parameters involved shows that the key factor is the "useful life". In this regard, the alternative for a longer useful life has a lower total cost and provides higher value. Only the copper cable eliminates the risk of projecting the cable’s useful life because, unlike aluminum, the useful life of copper is based on real factual on-site performance and not only on speedy short-term laboratory tests. The curves in the graph below show the high cost of an early failure of an aluminum cable. The examples correspond to failures at 10, 20 and 30 years.

Commercial and industrial electric cables are long-term assets, essential to a healthy financial investment, the profitability of which is directly affected by their efficiency. Throughout history, reliability of copper is and has been unbeatable. That is why copper is "The Color of Trust" for commercial and industrial electric cables.

Source: Canadian Copper and Brass Development Association