NOTE Length (LI) is based on conductor temperatures of  20 °C to determine length (L2) at a higher conductor temperature use formula where T2 = estimated  conductor temperature °C WIRE SIZE Voltage drop chart intermittent flow at 20° tin-plated MIL-W-27759 conductor  VOLTAGE DROP CIRCUIT VOLTAGE 200 1400 1260 1120 980 840 700 560 420 350 280 224 196 168 126 112 98 84. 70 14 115 1600 1200 800 720 640 560 480 400 320 240 200 160 128 112 96 72 64 56 48 40 8  14 200 150 100 90 80 70 60 50 40 30 24 20 16 14 12 8 6 4 1 28 400 300 200 180 160 140 120 100 80 60 50 40 32 28 24 18 16 14 12 10 2  Wire length (ft) 24 22 20 18 16 14 12 10 8 6 4 2 1 1/0 2/0 3/0 4/0 1 1.5 2 3 4 5 7 10 15 20 30 50 70 100 150 200 300 L2 = (254.5) (L1) (234.5) + (T2) AMPERES Figure 4-80.  Conductor graph—intermittent flow. through and over the surface of insulation materials.  Insulation resistance can be measured with a megger without  damaging the insulation. This serves as a useful guide in  determining the general condition of insulation. However, the  data obtained in this manner may not give a true picture of  the condition of the insulation. Clean, dry insulation having  cracks or other faults may show a high value of insulation  resistance but would not be suitable for use. of installation. Rubber, silk, and paper insulation are no longer  used extensively in aircraft systems. More common today are  such materials as vinyl, cotton, nylon, Teflon, and Rockbestos. To aid in testing and repair operations, many maintenance  activities mark wire or cable with a combination of letters  and numbers that identify the wire, the circuit it belongs to,  the gauge number, and other information necessary to relate  the wire or cable to a wiring diagram. Such markings are the  identification code. Dielectric strength is the ability of the insulator to withstand  potential difference and is usually expressed in terms of  the voltage at which the insulation fails due to electrostatic  stress. Maximum dielectric strength values can be measured  by raising the voltage of a test sample until the insulation  breaks down. There is no standard procedure for marking and identifying  wiring; each manufacturer normally develops its own  identification code.  Figure 4-81  illustrates one identification  system and shows the usual spacing in marking a wire.  Some system components, especially plugs and jacks, are  identified by a letter or group of letters and numbers added to the basic identification number. These letters and numbers  may indicate the location of the component in the system.  Interconnected cables are also marked in some systems to  indicate location, proper termination, and use. In any system,  Because of the expense of insulation, its stiffening effect,  and the great variety of physical and electrical conditions  under which the conductors are operated, only the necessary  minimum insulation is applied for any particular type of cable  designed to do a specific job. The type of conductor insulation material varies with the type  4-50 Identifying Wire and Cable