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: 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. 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. 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  covered with a metallic braided shield. 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,  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. Figure 4-72.  Firing end cleaning. Figure 4-73.  Two types of aircraft wire. Wire Size 4-45 Conductors Wire single solid conductor Solid conductor Standed conductor A B High-voltage air surface gap Yes Yes Yes No High-voltage surface gap High-voltage recessed surface gap Low-voltage shunted surface gap Gap Description Typical Firing End Configuration Clean Firing End