Sageon III Power System
Installation
PM990-8800-00, Rev. 9
2-3
Selecting and Sizing DC Power Cables
Protective circuits, overall system performance, and safety depend on the proper sizing of DC cables for current and acceptable DC
voltage drop. The minimum size allowable is the larger of the wire size per the National Electrical Code or the calculated wire size.
Use the following method to determine the wire size.
1.
Calculate the minimum area in circular mils (CM) required for copper wire using the following formula:
22.2 x I x L
CM =
V
where:
CM = minimum area of circular mils in the cable
I = maximum current (in amps)
L = one-way cable length (in feet)
V = allowable loop voltage drop (in volts)
Example: Assume a maximum output current of 100 amperes, an allowable loop voltage drop of 0.25 volts, and a distance of
50 feet between the Power system and the load.
I = 100 amperes
L = 50 feet
V = 0.25 volts
(22.2)(100)(50)
CM =
(0.25)
CM = 440,000 circular mils
2.
After calculating the minimum area in circular mils, select the proper copper wire size from Table 2-1; always choosing the next
larger wire size if the area rating falls between values. For the above example, select 500 MCM wire.
3.
Determine the minimum wire size for ampacity according to the code authority having jurisdiction in your location.
4.
Select the larger of the sizes calculated for voltage drop or ampacity.
TABLE 2-1 WIRE SIZING
SIZE
AWG
NO.
AREA
IN CM
CURRENT
CARRYING
CAPACITY*
DIA
BARE
COND
INCHES
RHW DIA
OVER INS
INCHES
RHW
BEND
RADIU
S
INCHE
S
OPE
N
AIR
ENCLOSE
D
14
12
10
8
6
4
2
1/0
2/0
4/0
350 MCM
500 MCM
750 MCM
4,110
6,530
10,380
16,510
26,250
41,740
66,370
105,500
133,100
211,600
350,000
500,000
750,000
15
20
30
45
70
100
135
185
210
300
425
525
660
15
20
30
45
65
85
115
150
175
230
310
380
475
0.064
0.081
0.102
0.146
0.184
0.232
0.292
0.373
0.418
0.528
0.681
0.814
0.998
0.19
0.21
0.24
0.31
0.40
0.45
0.51
0.63
0.68
0.78
0.98
1.12
1.34
0.95
1.05
1.20
1.55
2.00
2.25
2.55
3.15
3.40
3.90
4.90
5.60
6.70
* Data based on NEC Handbook 2011, Table 310-17 adjusted for 50°C (122°F) ambient temperature.
