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 continuous flow at 20 °C tin-plated MIL-W-27759 conductor  EXAMPLE 1 EXAMPLE 2 No. 8 wire at 20 amps No. 12 wire at 20 amps No. 14 wire at 20 amps VOLTAGE DROP CONTINUOUS CIRCUIT VOLTAGE 200 700 630 560 490 420 350 280 210 175 140 112 98 84 63 56 49 42 35 7 115 800 600 400 360 320 280 240 200 160 120 100 80 64 56 48 36 32 28 24 20 4  14 100 75 50 45 40 35 30 25 20 15 12 10 8 7 6 4 3 2 0.5 28 200 150 100 90 80 70 60 50 40 30 25 20 16 14 12 9 8 7 6 5 1  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 4-79.  Conductor graph—continuous flow.  amperes, the line indicating the value of 20 amperes should  be selected from the diagonal lines. Follow this diagonal  line downward until it intersects the horizontal line number  50. From this point, drop straight down to the bottom of the  graph to find that a conductor between size No. 8 and No.  10 is required to prevent a greater drop than 1 volt. Since the  indicated value is between two numbers, the larger size, No.  8, should be selected. This is the smallest size that should be  used to avoid an excessive voltage drop. If the installation is for equipment having only an intermittent  (maximum 2 minutes) requirement for power, the graph in  Figure 4-80  is used in the same manner. Two fundamental properties of insulation materials (e.g.,  rubber, glass, asbestos, and plastic) are insulation resistance  and dielectric strength. These are entirely different and  distinct properties. Suppose that you want to install a 50-foot conductor from  the aircraft bus to the equipment in a 28-volt system. For this  length, a 1-volt drop is permissible for continuous operation  with a conductor temperature of 20 ºC or less. By referring  to the chart in  Figure 4-79 , the maximum number of feet a  conductor may be run carrying a specified current with a  1-volt drop can be determined. In this example, the number  50 is selected. Insulation resistance is the resistance to current leakage  Assuming the current required by the equipment is 20  4-49 Conductor Insulation 7.  Whether it is a single conductor in free air 6.  Whether the wire to be installed is in a conduit or in  a bundle 5.  The estimated or measured temperature of the  conductor 4.  Whether the current to be carried is intermittent or  continuous  2.  The number of amperes of current to be carried 3.  The amount of voltage drop permitted