Wire Size Considerations
Wind/Solar Hookup Basics and Beyond.
It is very important that the wire you choose is large enough to carry the amount of current from your charge sources, batteries and loads or you WILL experience a substantial loss of energy. Very undersized wire can lead to high heat build up in the wire which could lead to failure of the wire and surrounding devices, as well as the possibility of fire and/or injury. The cost of wire can be a substantial investment and may dictate where items are placed. The closer you can get your charge sources to the batteries, the better as far as power transmission is concerned. Inverters need to be very close to the batteries.
The longer the cable run, the larger the wire must be in order to prevent large voltage drops (loss of power) due to the resistance of the wire. The most amount of power you would ever want to lose in a cable run of an alternate energy system is about 5 percent, yet 2 to 4 percent is by far a better target.
A common mistake in sizing wire is to turn to the NEC wire size charts to determine how much amperage a wire can safely handle. This method of sizing wire will lead to a very inefficient system since these tables are generally based on higher voltage (110/220 volts A/C), and the main concern is safely transmitting the power without heat build up. In a low voltage system, we are of course concerned with safety, yet what dictates wire size even more is loss of power. A 10% loss of power in a 12 volt line is 1.2 volts! This may completely prevent some devices from operating.
It is very important that certain circuits, like lighting circuits having fluorescent bulbs, have low losses. 12 volt fluorescent bulbs do not operate well with even a 10% loss. Circuits having larger motors simply should not be undersized or you may find the motor does not start up properly. Always insure your inverter wire is well within this 2% drop. For battery interconnects, a 1% or 1/2% drop is even better. A 5% (and perhaps 10%) drop might be acceptable in solar panels since the cost of the wire may exceed the cost of the solar panels when there is a large distance involved. An exception is wire used for diversion or dummy loads; in this case a 10% loss is probably acceptable.
2% Voltage Drop Guidelines -- 12 volts
This table represents the maximum distance (in feet, one way) that can be achieved with a given wire size and amperage to maintain less than a 2% loss of power.
| 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 |
The interactive wire-size calculator from the WordPress site is not included here. Use the existing catalog item "Wire Size Calculator" (ccode WireCalculator) for the calculator.
Source: getawaypower.com/2019/02/wire-size-considerations/
