How to choose the right solar wire size
Wire sizing is best determined in the context of a single line diagram for your system, where the wire run distances, loads, and site specific factors are defined to ensure the wires selected have suitable capacities.
Here is an example of wire calculations from a single line diagram produced by our permitting partner, Illumine-I. To have a single line diagram, or permit plan set drafted for your project, first generate a bill of materials on our Solar Design & Quote Tool, (enter your email address to receive a PDF copy, which you can then send on to Illumine-I), and then see our Permitting Page for details on how to submit the drafting request.
It is important to select wires that are properly sized for the currents and voltages in your solar energy system. Wires that are too small will cause significant voltage drops, and therefore a significant solar energy loss, as well as possible overheating that may cause a fire. You can email info@renvu.com about selecting the proper wire for your needs. Below you will find a detailed explanation on how you need to select the proper wire for the different sections of solar power systems.
Just like water flowing in a pipe, the thicker the wire is - the easier it will be for larger electrical currents to flow in it. Therefore, short wires with large wire cross-sectional area have a small electrical resistance that result will with small voltage drop. Long wires with small cross-sectional area have a large resistance that results in a large voltage drop along the wire.
To compare options, check pricing, and create a bill of materials including Tier 1 solar panels, as well as CEC listed inverters, and racking, see our Solar Design & Quote Tool.
Solar Wire Size Chart
The common scale for wire sizes is the American Wire Gauge, or AWG. Lower AWG stands for larger wire cross-sectional area, and therefore lower resistance and lower voltage drop. The following wire size chart applies to typical DC circuits and some simple AC circuits (single-phase AC with resistive loads, not motor loads, power factor = 1.0, line reactance negligible). It corresponds every AWG value with the wire cross-sectional area, the maximum current allowed for this cross-sectional area, and the wire Voltage Drop Index, or DVI. The DVI is inversely related to the resistance of 1 ft of wire.
To use this chart, you will have to know the system Amperage and the maximum voltage drop that you will accept. Using these values you can easily use this wire size chart to select the wire that is appropriate for your solar system. Different wires will be chosen to connect between your solar panels and the inverter or charge controller, between the charge controller and the batteries, wires between batteries in the battery bank, or between the inverter and the grid.
Step 1: Calculate the Voltage Drop Index (VDI)
To do this you will need to know:
The amperage (the current)
The length of the one-way wire (feet)
Voltage drop %
VDI = (AMPS x FEET) / (%VOLT DROP x VOLTAGE)
Step 2: Determine Wire Size from Chart:
Use the VDI determined from the previous calculation to find the closest wire size in the chart below.
Note: Ampacity is based on the National Electrical Code (USA) for 30 degrees C (85 degrees F) ambient air temperature, for no more than three insulated conductors in raceway in free air of cable types AC, NM, NMC and SE; and conductor insulation types TA, TBS, SA, AVB, SIS, RHH, THHN and XHHW. For other conditions, refer to National Electric Code or an engineering handbook.
Wire size calculations for different sections of the PV system
For each section of your solar energy system you will have to use the appropriate Amperage, cable length, and accepted voltage (and power) loss:
For the wire that connects the solar panel array to the inverter or charge controller, use the total output current of the entire solar array.
In grid tie solar systems, the wires that connect the inverter to the grid are calculated based on the inverter output current and voltage.
In off-grid systems, the wires from the inverter or charge controller to the battery bank can typically be the same as the solar panel cables. An exception to this rule is when the PV array operates at a voltage that is higher than the inverter or charge controller. In this case, the inverter or charge controller transformer will reduce the voltage and as a result, increase the current that goes to the batteries. The output current of the inverter or charge controller should be the current used for the calculation of these wires. The wires between batteries in a battery bank are typically used for a higher current than that of the PV system, because of the current required by the power inverter.