NetApp DS4246 - Page 66

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