chances for short circuits and to protectpersonnel. Atmospheric conditions, voltagerequirements, and environmental and operatingtemperatures are factors to consider in selectingthe type of insulating material for a particular job.SINGLE CONDUCTORS.— A single con-ductor may consist of one solid wire or a numberof stranded, uncovered, solid wires that share incarrying the total current. A stranded conductorhas the advantage of being more flexible thana solid conductor, making it more adaptablefor pulling through any bends in a conduit.Common types of single conductors are shownin figure 9-12.Conductors vary in diameter. Wire manufac-turers have established a numerical system,called the American Wire Gage (AWG) Standard,to eliminate the necessity for cumbersome circularmil or fractional-inch diameters in describing wireFigure 9-13.—Comparison of standard wire gauge numberto wire diameters.sizes. Figure 9-13 shows a comparison of one-halfactual wire diameters to their AWG numericaldesignations. Notice that the wire gauge numberincreases as the diameter of the wire decreases.The wire size most frequently used for interiorwiring is No. 12 AWG and is a solid conductor.No. 8 and larger wires are normally used for heavypower circuits or as service entrance leads tobuildings.The type of wire used to conduct current fromoutlet boxes to sockets in the lighting fixtures iscalled “fixture wire.” It is stranded forflexibility and is usually size 16 or 18 AWG.MULTIWIRE (CABLE) CONDUCTORS.—A multiwire conductor, called a CABLE, is anassembly of two or more conductors insulatedfrom each other with additional insulation or aprotective shield formed or wound around thegroup of conductors. The covering or insulationfor individual wires is color coded for properidentification. Figure 9-14 shows common typesof multiwire conductors.Figure 9-14.—Types of multiwire insulated conductors(cables).9-9
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