FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 11. Aircraft Electrical Systems | 5. Electical Wire Rating | 11-68. Instructions for Use of Electrical Wire Chart
AC 43.13-1B CHG 1
9/27/01
(1) The wire size should be sufficient to
prevent an excessive voltage drop while car
rying the required current over the required
distance. (See table 11-6, Tabulation Chart, for
allowable voltage drops.)
(4) The circuit has continuous opera
tion.
(5) Estimated conductor temperature is
20 °C or less.
(2) The size should be sufficient to pre
vent overheating of the wire carrying the re
quired current. (See paragraph 11-69 for al
lowable current carrying calculation methods.)
b. Two Requirements. To meet the two
requirements (see paragraph 11-66b) in se
lecting the correct wire size using figure 11-2
or figure 11-3, the following must be known:
(1) The wire length in feet.
(2) The number of amperes of current to
be carried.
(3) The allowable voltage drop
permitted.
The scale on the left of the chart represents
maximum wire length in feet to prevent an ex
cessive voltage drop for a specified voltage
source system (e.g., 14V, 28V, 115V, 200V).
This voltage is identified at the top of scale
and the corresponding voltage drop limit for
continuous operation at the bottom. The scale
(slant lines) on top of the chart represents am
peres. The scale at the bottom of the chart rep
resents wire gauge.
STEP 1: From the left scale find the wire
length, 50 feet under the 28V source column.
STEP 2: Follow the corresponding horizontal
line to the right until it intersects the slanted
line for the 20-amp load.
(4) The required continuous or inter
mittent current.
(5) The estimated or measured con
ductor temperature.
(6) Is the wire to be installed in conduit
and/or bundle?
(7) Is the wire to be installed as a single
wire in free air?
c. Example No. 1. Find the wire size in
figure 11-2 using the following known infor
mation:
(1) The wire run is 50 feet long, in
cluding the ground wire.
STEP 3: At this point, drop vertically to the
bottom of the chart. The value falls between
No. 8 and No. 10. Select the next larger size
wire to the right, in this case No. 8. This is the
smallest size wire that can be used without ex
ceeding the voltage drop limit expressed at the
bottom of the left scale. This example is plot
ted on the wire chart, figure 11-2. Use figure
11-2 for continuous flow and figure 11-3 for
intermittent flow.
d. Procedures in Example No. 1 para
graph 11-68c, can be used to find the wire size
for any continuous or intermittent operation
(maximum two minutes). Voltage (e.g.
14 volts, 28 volts, 115 volts, 200 volts) as in
dicated on the left scale of the wire chart in
figure 11-2 and 11-3.
(2) Current load is 20 amps.
(3) The voltage source is 28 volts from
bus to equipment.
e. Example No. 2. Using figure 11-2, find
the wire size required to meet the allowable
voltage drop in table 11-6 for a wire carrying
Page 11-26
Par 11-68