Sizing Your Solar Wire

Conductor Considerations

8AWG PV Wire, 90C, OD 0.29”: https://amzn.to/4nvKABQ

10AWG PV Wire, 90C, OD 0.23”: https://amzn.to/4nCISyB

12AWG PV Wire, 90C, OD 0.21”: https://amzn.to/464N5VZ

  • Use pure copper or tin coated copper

  • UL rated for UV exposure and direct burial

  • Figure out the current of your load or solar array.

  • Derate if in conduit or is exposed to high temperatures.

  • Double check minimum gauge with 3% max voltage drop.

  • Select the minimum gauge based on NEC guidelines.

National Electric Code Wire Introduction: https://www.youtube.com/watch?v=RMpglgQgdDA

Maximum Current Rating

Solar Wire 90 Deg C Wire: Numbers to use for Derating.

  • 12AWG: 30A

  • 10AWG: 40A

  • 8AWG: 55A

Note that most terminals are rated for 75Deg C so after derating you will need to make sure the loads are no higher than the ampacity listed in the 75Deg C column.

Max Overcurrent Current Rating

This table lists the Max Overcurrent Protection Ratings for 12-8AWG Conductors.

Ambient Temperature Correction Factors

In MN I am estimating the maximum Ambient Temperature as being around 105 Degrees F. The 90 Degree F Conductor Column gives us a 0.87 correction factor.

Continuous Load Multiplier: A multiplier of 1.25 (or 125%) is applied to continuous loads. 0.8x conductor rating.

Conductor Derating When in Conduit

Max Amapacity x (.8 Continuous Factor) x (.8 Conduit Factor) = Solar Wire in conduit rating

12AWG: 30A x .8 x .8 = 19.2A

10AWG: 40A x .8 x .8 = 25.6A

8AWG: 55A x .8 x .8 = 35.2A

3% Voltage Drop

Long conductors will reduce the efficiency of your solar system. Use these design calculators to ensure you have a large enough wire for your system. Ideally you will want to keep the voltage drop below 3%.

Voltage Drop Calculator: https://www.southwire.com/calculator-vdrop

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