V
LOAD
=
I R
TEST
I
=
V
LOAD
/
R
TEST
V
OC
=
V
SOURCE +
V
LOAD
V
OC
=
IR
S +
V
LOAD
R
S
=
V
OC -
V
LOAD
I
R
S
=
(V
OC
- V
LOAD
)
V
LOAD
/
R
TEST
R
S
=
V
OC
- V
LOAD
V
LOAD
= 48V - 47.5V
47.5V
=
0.105
R
TOTAL
=
R
CABLE
+ R
SOURCE
R
CABLE
=
R
TOTAL
- R
SOURCE
R
CABLE
=
0.233 - 0.105
=
0.128
Solution
V
DROP
=
I
MAX
R
TOTAL
2
= 8.6 R
TOTAL
R
TOTAL
=
2/8.6
R
TOTAL
=
.233
x
R
TEST
x
10
For example, if you have a 12-gauge wire, solid strand, at room temperature, you use the following
calculation:
Total cable length
=
Total cable length
=
= 75 ft
R
CABLE
DC resis.
1
.128
.0017 /ft
AWG
Strand
DC resistance
1
[Ω
/ft.]
Total cable length
2
[ft]
25°C
75°C
25°C
75°C
12
Solid
.0017
.0020
75
64
DS4243, DS2246, DS4486, and DS4246 Installation and Service Guide
66
Recommended power line sizes