Description of Electrical Conductors
A. Bhatia, B.E.
For the purpose of electronics and electrical engineering, materials are classified according to their electrical resistance, which describes how readily they allow electric current to pass when a voltage is applied. A conductor is a piece of metal used to conduct electricity. Apart from conductors, materials are classed as insulators (very poor conductors), semi-conductors (materials whose ability to conduct electricity can be controlled), and superconductors which (below a critical temperaure, usually cryogenic) offer no significant electrical resistance, allowing circular currents, once established, to flow indefinitely.
This 3-hr course provides general requirements, classifications and application information for electrical conductors. The course is based entirely on Naval Education and Training Materials (NAVEDTRA 14176), Electricity and Electronic Training Series; Module-4 and covers Chapter 1 titled “Electrical Conductors”.The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.
At the conclusion of this course, the student will be able to:
This course is aimed at students, professional electrical & electronics engineers, service technicians, energy auditors, operational & maintenance personnel, facility engineers and general audience.
Conductors are usually surrounded by and/or supported by insulators and the insulation determines the maximum voltage that can be applied to any given conductor. The ampacity of a conductor, that is, the amount of current it can carry, is related to its electrical resistance; a lower-resistance conductor can carry more current. The resistance, in turn, is determined by the material of the conductor and its size.
Many factors determine the type of electrical conductor used to connect components. Some of these factors are the physical size of the conductor, its composition, and its electrical characteristics. Other factors that can determine the choice of a conductor are the weight, the cost, and the environment where the conductor will be used. For a given material, conductors with a larger cross-sectional area have less resistance than conductors with a smaller cross-sectional area.
In this course, you are required to study Naval Education and Training Materials (NAVEDTRA 14176), Electricity and Electronic Training Series; Module-4, Chapter 1 titled “Electrical Conductors”:
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All conductors contain movable electric charges which will move when an electric potential difference (measured in volts) is applied across separate points on a wire (etc) made from the material. This flow of charge (measured in amperes) is what is meant by electric current. In most materials, the amount of current is proportional to the voltage (Ohmís law) provided the temperature remains constant and the material remains in the same shape and state. The ratio between the voltage and the current is called the resistance (measured in ohms) of the object between the points where the voltage was applied. The resistance across a standard mass (and shape) of a material at a given temperature is called the resistivity of the material. The inverse of resistance and resistivity is conductance and conductivity.
Non-conducting materials lack mobile charges, and so resist the flow of electric current, generating heat. In fact, all materials offer some resistance and warm up when a current flows. Thus, proper design of an electrical conductor takes into account the temperature that the conductor needs to be able to endure without damage, as well as the quantity of electrical current. The motion of charges also creates an electromagnetic field around the conductor that exerts a mechanical radial squeezing force on the conductor. A conductor of a given material and volume (length x cross-sectional area) has no real limit to the current it can carry without being destroyed as long as the heat generated by the resistive loss is removed and the conductor can withstand the radial forces. This effect is especially critical in printed circuits, where conductors are relatively small and close together, and inside an enclosure: the heat produced, if not properly removed, can cause fusing (melting) of the tracks.
Since all conductors have some resistance, and all insulators will carry some current, there is no theoretical dividing line between conductors and insulators. However, there is a large gap between the conductance of materials that will carry a useful current at working voltages and those that will carry a negligible current for the purpose in hand, so the categories of insulator and conductor do have practical utility.
Of the metals commonly used for conductors, copper, has a high conductivity. Silver is more conductive, but due to cost it is not practical in most cases. Compared to copper, aluminum has worse conductivity per unit volume, but better conductivity per unit weight. In many cases, weight is more important than volume making aluminium the 'best' conductor material for certain applications. For example, it is commonly used for large-scale power distribution conductors such as overhead power lines.