) in the formula for calculating area, plus the need to figure wire radius when you’ve been given diameter. The sole purpose for having this special unit of measurement is to eliminate the need to invoke the factor π (3.1415927. This special unit is called the circular mil (sometimes abbreviated cmil). However, electricians and others frequently concerned with wire size use another unit of area measurement tailored specifically for wire’s circular cross-section. We could also, if we wanted, express the area of the wire in the unit of square mils, calculating that value with the same circle-area formula, Area = πr 2:Ĭalculating the Circular-mil Area of a Wire For the illustrated example, we would say that the diameter of the wire was 101.9 mils (0.1019 inch times 1000). These are fairly small numbers to work with, so wire sizes are often expressed in measures of thousandths-of-an-inch, or mils. Calculating the area of the cross-section with the formula Area = πr 2, we get an area of 0.008155 square inches:
The diameter is shown as being 0.1019 inches. The wire cross-section picture shown above is, of course, not drawn to scale. We could speak of a wire’s diameter, but since its really the cross-sectional area that matters most regarding the flow of electrons, we are better off designating wire size in terms of area. Wire size can be measured in several ways. The greatest benefit of stranded wire is its mechanical flexibility, being able to withstand repeated bending and twisting much better than solid copper (which tends to fatigue and break after time). Stranded wire is composed of smaller strands of solid copper wire twisted together to form a single, larger conductor. Solid copper wire is just as it sounds: a single, solid strand of copper the whole length of the wire. Two Basic Varieties of Electrical Wire: Solid and StrandedĮlectrical wire is usually round in cross-section (although there are some unique exceptions to this rule), and comes in two basic varieties: solid and stranded. The same general principle holds for the flow of electrons through conductors: the broader the cross-sectional area (thickness) of the conductor, the more room for electrons to flow, and consequently, the easier it is for flow to occur (less resistance). It should be common-sense knowledge that liquids flow through large-diameter pipes easier than they do through small-diameter pipes (if you would like a practical illustration, try drinking a liquid through straws of different diameters).
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