Wire Runs and Voltage Loss

2% Voltage Drop Guidelines
12 volts
Do not exceed 2% for wire runs. A 5% loss is ok on lighting circuits in some cases, butthe next larger wire size cost is usually small and dramatically increases efficiency of batteries.
Amps #14 #12 #10 #8 #6 #4 #2 #1/0 #2/0 #4/0
1 45 70 115 180 290 456 720 . . .
2 22.5 35 57.5 90 145 228 360 580 720 1060
4 10 17.5 27.5 45 72.5 114 180 290 360 580
6 7.5 12 17.5 30 47.5 75 120 193 243 380
8 5.5 8.5 11.5 22.5 35.5 57 90 145 180 290
10 4.5 7 11.5 18 28.5 45.5 72.5 115 145 230
15 3 4.5 7 12 19 30 48 76.5 96 150
20 2 3.5 5.5 9 14.5 22.5 36 57.5 72.5 116
25 1.8 2.8 4.5 7 11.5 18 29 46 58 92
30 1.5 2.4 3.5 6 9.5 15 24 38.5 48.5 77
40 . . 2.8 4.5 7 11.5 18 29 36 56
50 . . 2.3 3.6 5.5 9 14.5 23 29 46
100 . . . . 2.9 4.6 7.2 11.5 14.5 23
150 . . . . . . 4.8 7.7 9.7 15
200 . . . . . . 3.6 5.8 7.3 11
TO SOLVE VOLTAGE DROP PROBLEMS
CONSIDER A HIGH VOLTAGE GEN AND BLADE!

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5% Voltage Drop Table
120v and 24v Five percent is acceptable in most low voltage systems, except 12 volt (see above). NOTE: To obtain a 2% figure from these tables, divide the given distance shown in the table by 2.5.
For calculating distances for 48 volt systems, multiply the 24 volt distances by 2.
For 240 volt systems, multiply the 120 volt distances by 2.
Below stepped lines check ampacity. The (=) indicates over 1000 feet.

Top table = 120/240 volts;  Lower table = 24/48 volts;
or slide page to view voltage -------------------->

Below stepped lines check ampacity. The (=) indicates over 1000 feet.

**IMPORTANT**

Before using these tables, some calculations must first be performed by the system designer to insure accurate current ratings and safety factors are used. For solar modules, the UL-1703 standard requires the short circuit current (lsc) rating be multiplied by 125% before other factors are applied. This is because the electrical performance can increase above the factory rating due to the increased operating temperatures and enhanced irradiances over 1000W/M2 (such as edge-of-cloud effect).


NOTE
The "edge-of-cloud effect" is also a consideration when sizing a charge/voltage controller for solar modules. Use the short-circuit current rating to determine the controller.

The NEC requires the short circuit current ratings of the PV module or array be multiplied by 125% before calculating ampacities of any cable or overcurrent device. This is in addition to the UL rquired 125%! This yields a multiplier of (125%x125%=156%) or 1.56. Although this may seem redundant, good design practice dictates both factors should be used when determining wire size from the solar array to the battery.

Example
When calculating wire size from battery to load, multiply the load current by only 125% (1.25).
Example:  A 24V solar array of four Solarex MSX-120 modules, 2 in series by 2 parallel  modules located 30 ft. from the battery; lsc=7.60 A (one module); 7.60 x 2 = 15.2A (two modules); 15.2A x 1.56 = 23.71A. Using the 24 volt table, locate a value equal to or greater than 24 amps from the left column, follow a line to the right until a distance at or above 30 ft. is found. For this example, using the 24 volt table, we find 25 amps at 36 feet to be the best selection (for not more than 5% loss) indicating a wire size of #8 AWG.

For larger batteries and  inverters (battery to inverter cable connections)
a  minimum 4/0 cable is recommended.




 
 
 

Maximum Ampacity for Copper and Aluminum Wire
Wire Size Copper Aluminum
14 25 .
12 30 25
10 40 35
8 55 45
6 75 60
4 95 75
2 130 100
1 150 115
1/0 170 135
2/0 265 150
4/0 360 205

NEC allows rounding up cable ampacity to next standard fuse or breaker.