Specifications

AC 43.13-1B CHG 1 9/27/01
Page 11-22 Par 11-66
TABLE 11-7. Examples of determining required tin-
plated copper wire size and checking voltage drop using
figure 11-2
Voltage
drop
Run
Lengths
(Feet)
Circuit
Current
(Amps)
Wire Size
From
Chart
Check-
calculated volt-
age drop (VD)=
(Resistance/Ft)
(Length) (Cur-
rent)
1 107 20 No. 6
VD= (.00044
ohms/ft)
(107)(20)=
0.942
0.5
90 20 No. 4
VD= (.00028
ohms/ft)
(90)(20)=
0.504
4
88 20 No. 12
VD= (.00202
ohms/ft)
(88)(20)=
3.60
7 100 20 No. 14 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
Wire
Size
Circuit
Current
(Amps)
Maximum
Wire Run
Length
(Feet)
Check-calculated
voltage drop
(VD)= (Resis-
tance/Ft) (Length)
(Current)
1
No. 10
20 39
VD= (.00126
ohms/ft)
(39)(20)= .98
0.5
---- 19.5
VD= (.00126
ohms/ft)
(19.5)(20)=
.366
4
---- 156
VD= (.00126
ohms/ft)
(156)(20)=
3.93
7 ---- 273 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:
))()5.234(
))(5.254(
2
1
2
TC
LC
L
+°
°
=
For aluminum conductor wire, the formula is:
)()1.238(
))(1.258(
2
1
2
TC
LC
L
+°
°
=
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:
TTTT II
R21 1
=+ −()(/
max2
)