AWG
Strand
DC resistance
1
[Ω
/ft.]
Total cable length
2
[ft]
25°C
75°C
25°C
75°C
12
7/20
.0015
.0018
85
71
12
19/25
.0017
.0020
75
64
12
65/30
.0018
.0022
71
58
12
165/34
.0016
.0019
80
67
1
Data from Alpha Wire, wire manufacturer
2
Combined positive and negative run
Example 2
This example uses the following given values:
Given
V
DROP
= 2V
Maximum voltage drop through input source
and cable
V
MIN
= 40V
Minimum input voltage
I
MAX
= 8.6A
Maximum input current at 40V
R
SOURCE
0
Solution
V
DROP
= I
MAX
R
TOTAL
R
TOTAL
= V
DROP
I
MAX
R
TOTAL
= 2/8.6
R
TOTAL
= 0.233
R
TOTAL
= R
SOURCE
+ R
CABLE
R
CABLE
= R
TOTAL
-
R
SOURCE
R
CABLE
= 0.233 - 0
R
CABLE
= 0.233
For example, if you have a solid-strand, 12-gauge wire at room temperature, you use the following
calculation:
Total cable length
=
Total cable length
=
R
CABLE
DC resis.
1
.233
.0017 /ft
= 136 ft
DS4243, DS2246, DS4486, and DS4246 Installation and Service Guide
67
Recommended power line sizes
