A conductor is a piece of metal used to conduct electricity, known colloquially as an electrical wire. Wires are very good conductors, which mean that they have very little resistance. In fact, their resistance is so small that often we consider it to be zero. (In other words, we often treat wires as perfect conductors). In United States, conductors are measured by American wire gauge (abbreviated AWG) for smaller ones, and circular mils for larger ones. To give you some idea how thick these wires are; AWG 0000 wire is about 11.7 millimeters in diameter (a little less than one-half inch thick) and at the opposite end of the scale, AWG 40 is less than 0.1 millimeters in diameter (about as thick as a strand of hair from your head). The wiring inside the walls of your home is usually AWG 10 or AWG 12 wire. 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. 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. For a given material, conductors with a larger cross-sectional area have less resistance than conductors with a smaller cross-sectional area. This 3-hr Quick Book 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." Learning Objective At the conclusion of this course, the reader will be able to: Recall the definitions of unit size, mil-foot, square mil, and circular mil. Define specific resistance and recall the three factors used to calculate it in ohms. Describe the proper use of the American Wire Gauge when making wire measurements. State the factors required in selecting proper size wire. State the advantages and disadvantages of copper or aluminum as conductors. Define insulation resistance and dielectric strength. Identify the safety precautions to be taken when working with insulating materials. List the most common insulators used for extremely high voltages. Recall the design and use of coaxial cable."