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 | 11-66. General
AC 43.13-1B CHG 1
9/27/01
TABLE 11-7. Examples of determining required tin-
plated copper wire size and checking voltage drop using
figure 11-2
Voltage
drop
1
0.5
4
7
Run
Lengths
(Feet)
107
90
88
100
Circuit
Current
(Amps)
20
20
20
20
Wire Size
From
Chart
No. 6
No. 4
No. 12
No. 14
Check-
calculated volt-
age drop (VD)=
(Resistance/Ft)
(Length) (Cur-
rent)
VD= (.00044
ohms/ft)
(107)(20)=
0.942
VD= (.00028
ohms/ft)
(90)(20)=
0.504
VD= (.00202
ohms/ft)
(88)(20)=
3.60
VD= (.00306
ohms/ft)
(100)(20)=
6.12
TABLE 11-8. Examples of determining maximum tin-
plated copper wire length and checking voltage drop
using figure 11-2.
Maximum
Voltage
drop
1
0.5
4
7
Wire
Size
No. 10
---
---
---
Circuit
Current
(Amps)
20
Maximum
Wire Run
Length
(Feet)
39
19.5
156
273
Check-calculated
voltage drop
(VD)= (Resis-
tance/Ft) (Length)
(Current)
VD= (.00126
ohms/ft)
(39)(20)= .98
VD= (.00126
ohms/ft)
(19.5)(20)=
.366
VD= (.00126
ohms/ft)
(156)(20)=
3.93
VD= (.00126
ohms/ft)
(273)(20)=
6.88
(2) As an alternative method or a means
of checking results from figure 11-2, continu
ous flow resistance for a given wire size can be
read from table 11-9 and multiplied by the wire
run length and the circuit current. For inter
mittent flow, use figure 11-3.
(3) Voltage drop calculations for alumi
num wires can be accomplished by multiplying
the resistance for a given wire size, defined in
table 11-10, by the wire run length and circuit
current.
(4) When the estimated or measured
conductor temperature (T2) exceeds 20 °C,
such as in areas having elevated ambient tem
peratures or in fully loaded power-feed wires,
the maximum allowable run length (L2), must
be shortened from L1 (the 20 °C value) using
the following formula for copper conductor
wire:
L2 = (254.5 °C)(L1)
(234.5 °C)+)(T 2)
For aluminum conductor wire, the formula is:
L2 = (258.1 °C)(L1)
(238.1 °C) + (T 2)
These formulas use the reciprocal of each ma
terial’s resistively temperature coefficient to
take into account increased conductor resis
tance resulting from operation at elevated tem
peratures.
(5) To determine T2 for wires carrying a
high percentage of their current carrying capa
bility at elevated temperatures, laboratory
testing using a load bank and a high-
temperature chamber is recommended. Such
tests should be run at anticipated worse case
ambient temperature and maximum current-
loading combinations.
(6) Approximate T2 can be estimated
using the following formula:
T2 = T1 + (TR − T1 )( I 2 / I max )
Page 11-22
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