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The satisfactory performance of any modern aircraft depends to a great degree on the continuing reliability of electrical systems and subsystems. Improperly or carelessly installed or maintained wiring can be a source of both immediate and potential danger. The continued proper performance of electrical systems depends upon the knowledge and technique of the mechanic who installs, inspects, and maintains the electrical wire and cable of the electrical systems. 

The procedures and practices outlined in this section are general recommendations and are not intended to replace the manufacturer’s instructions in approved practices. 

For the purpose of this discussion, a wire is described as a single solid conductor, or a stranded conductor, covered with an insulating material. [Figure 4-73] The term “cable,” as used in aircraft electrical installations, includes the following: 

1. Multiconductor cable—two or more separately insulated conductors in the same jacket. 

2. Twisted pair—two or more separately insulated conductors twisted together. 

3. Shielded cable—one or more insulated conductors, 

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covered with a metallic braided shield. 

4. Radio frequency cable—a single, insulated center conductor with a metallic braided outer conductor. The concentricity of the center conductor and the outer conductor is carefully controlled during manufacture to ensure that they are coaxial. 

## Wire Size 

Wire is manufactured in sizes according to a standard known as the American wire gauge (AWG). The wire diameters become smaller as the gauge numbers become larger. The largest wire size shown in Figure 4-74  is number 0000, and the smallest is number 40. Larger and smaller sizes are manufactured but are not commonly used. 

Wire size may be determined by using a wire gauge. [Figure 4-75]  This type of gauge measures wires ranging in size from number 0 (zero) to number 36. The wire to be measured is inserted in the smallest slot that just accommodates the bare wire. The gauge number corresponding to that slot indicates the wire size. The slot has parallel sides and should not be confused with the semicircular opening at the end of the slot. The opening simply permits the free movement of the wire all the way through the slot. 

Gauge numbers are useful in comparing the diameter of wires, but not all types of wire or cable can be accurately measured with a gauge. Large wires are usually stranded to increase their flexibility. In such cases, the total area can be determined by multiplying the area of one strand, usually computed in circular mils (commonly used as a reference to wire size) when diameter or gauge number is known by the 

