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Solar Panel Wire Size Guide

What solar panel wire size (AWG) do you need to build a solar array? Unsurprisingly, different solar array sizes require different wire gauges. The more current (amps) the solar array produces, the thicker the wires you need.

But how do you figure all this stuff out? This post will teach you how to do this, and it’s not that complicated. We promise.

This post provides a straightforward, 7-step process to help you identify exactly what solar wire sizes you need for your entire solar system. Your resulting wire gauge will comply with National Electric Code (NEC) standards to help keep your solar system safe from overheating and potentially catching on fire. (But you should also read our solar fusing guidelines for additional required safety).

Let’s get to it.

Why Correct Solar Wire Sizing Is Important

Incorrect solar wire sizing is a potential fire hazard. If the solar panels force too many amps through too thin of a wire, the metal conductors inside the wire will overheat, burn through the outer insulation, and potentially cause a fire.

The thicker the wire, the more amps the wire can handle before overheating.

That’s why selecting the correct wire gauge is critical for your solar system. This post will help you calculate which sizes you’ll need based on your solar array’s configuration.

Two Wiring Sections You Must Account For

Before we start, you should know that you’ll need to account for the wires in two different sections of a solar system.

  • Section 1: Between the solar panels and the charge controller
  • Section 2: Between the charge controller and the bus bars*

(*The bus bars will be connected to the batteries)

Refer to the simplified solar wiring diagram below.

Solar wiring diagram that highlights the two solar wiring sections to account for.
Two sections of solar wires to account for

Depending on the solar array size and configuration, the wire sizes in these two sections can be the same or different. This is because the solar charge controller, which separates the two wiring sections, will adjust the amps it receives from the solar panels before sending the power to the bus bars (& batteries).

Since the number of amps is the ultimate factor in wire sizing, it’s often likely that the amount of amps entering the charge controller is different than the amount leaving the charge controller. Therefore, different wire sizes may be required.

This post will help you determine the wire sizes you need to complete BOTH sections.

How To Calculate Solar Wire Size (7 Steps)

This 7-step guide will teach you how to calculate your solar system’s wire size. We’ll show you how to determine the maximum amount of amps entering and exiting the solar charge controller, and then we’ll recommend the highest-quality wires that can safely transmit those amps.

Step 1: Finalize Solar Array Configuration

The first step to sizing the solar wires is to finalize your solar system setup. To do this, you will need to answer the following four questions before you can move on:

  1. What is the total wattage of your solar array?
  2. Which specific solar panels will you use?
  3. How many panels will you have?
  4. If you have multiple panels, will the panels be wired in series or parallel?

Below, we explain WHY each of the above questions is critical to calculating which size solar wires you’ll need.

What Is the Total Wattage of the Solar Array?

The total watts produced by the solar system is one of the most critical factors determining solar wire gauge size. The more watts, the more amps produced, and the thicker the wire size you’ll need.

Learn more: Unsure how much solar you need? Use our solar wattage calculator to help.

Which Specific Solar Panels Will You Use?

Knowing which specific panels you are using is important because different-branded solar panels will output different amps, even if they’re all rated for the same number of watts. For example, we list the maximum potential amps for three different 200-watt panels below:

  • Renogy 200W: 11.05A
  • Newpowa 200W: 11.47A
  • BougeRV 200W: 12.21A

Therefore, you must finalize which solar panels you will use before continuing to Step 2.

Solar panel recommendation: We use Newpowa solar panels on our van, and they’ve held up well throughout our travels for the past five years. Newpowa panels are built tough and are generally cheaper ($ per watt) than their competitors. However, you should shop and compare the prices online first.

How Many Solar Panels Will You Have?

The physical number of solar panels you will have will also impact the total amps produced by the solar array and, ultimately, the wire size you’ll need.

Tip: We recommend having fewer – but larger – solar panels for van conversions.

Are Solar Panels Wired in Series or Parallel?

Whether your multiple solar panels are connected in series or parallel will significantly affect the total amps produced by the array. You must decide which method you will use to join multiple panels together.

Learn more: How to wire solar panels in series or parallel.

In short, solar panels that are wired in series produce fewer amps than panels that are connected in parallel. Therefore, panels wired in parallel tend to require thicker wires to transmit higher amperages safely.

Summary

Once you answer the above four questions, you’ll have everything you need to calculate the solar wire gauges for your system. We’ll show you exactly how to do these calculations in the following steps.

Step 2: Calculate Maximum Amps Produced by Array

Assuming you’ve answered the previous four questions from Step 1, you can now calculate the maximum amps produced by the solar array. This is a critical step because the more amps produced, the larger the wire size you’ll need.

Making this calculation involves a two-part process:

  1. Identify one of your panel’s short circuit current, or “Isc(A)”.
  2. Calculate the total current based on series or parallel wiring.

Identify Short Circuit Current – Isc(A) – From Single Panel

The short circuit current – sometimes identified as Isc(A) – is the current produced by the panel in the event of a short circuit. The short circuit current is the ‘maximum’ current that the panel can theoretically produce and is what you should look for when calculating your solar wire size.

You can find your panel’s short circuit current from the panel’s specifications sticker on the backside of the panel or by visiting the panel’s online product page. Below, we locate the short circuit current of Newpowa’s 200W panel from their Amazon product page, which is 11.47 Amps.

Specification data for a Newpowa 200 watt solar panel, with specific indication of the panel's short circuit current, which is important for the solar wire size.
Newpowa 200-watt solar panel specs

Calculate the Total Short Circuit Current Produced From the Array

If you only plan to have one solar panel in your array, the short circuit current you identified above will be the total current produced by your solar system.

But if you have more than one solar panel, how you connect these solar panels – series or parallel – will affect the maximum amps produced by the array.

Series connections: The total current produced by the solar array is only equal to the short circuit current of one of your panels. This is because, in series connections, the voltage (V) produced by each panel adds up, but the amps stay the same.

Parallel Connections: The total current produced by the solar array is equal to the sum of the short circuit currents of each panel. This is because, in parallel connections, the amps produced by each panel add up, but the voltage stays the same.

Example: Two Newpowa 200W panels have a short circuit current of 11.47 amps each. The two panels are wired in series, so the total current produced stays at 11.47A.

Step 3: Apply Safety Margins

The National Electric Code (NEC) exists to help keep people and property safe from electrical hazards. This step will show you how to comply with NEC code 690.8, which deals specifically with solar wire sizing.

In short, you must apply the following buffers to comply with the NEC code.

  1. Add 25% to the solar array’s maximum amps for a NEW maximum.
  2. Apply a 25% NEC safety margin to this new maximum current.

We’ll delve deeper into each of these two steps below.

Add 25% to the Solar Array’s Maximum Amps

For solar panels, the NEC considers the maximum current of a solar array to be 25% more than the total current produced by the array. Therefore, you must multiply the total amps you calculated in Step 2 by 1.25.

This is the NEW maximum amps produced by your solar array.

Why? This is because solar panels can sometimes produce MORE watts than what they are rated for in a lab. Our 360-watt solar array sometimes produces over 400 watts during exceptionally sunny days at high altitudes. Therefore, the NEC assumes that any solar array has the potential to produce 25% more power than what it is technically rated for.

Example: If your solar array’s maximum amps is 11.47A, the NEW maximum total current is 14.34A. (11.47A * 1.25 = 14.34A)

Apply the 25% NEC Safety Margin to the New Maximum Current

Take your new maximum amps and add a 25% safety margin. The NEC considers this new figure the starting point when selecting the appropriate solar wire size.

Example: The new maximum current from the previous example was 14.34A. By adding the 25% safety margin, we get 17.93A. (14.34A * 1.25 = 17.93A)

Step 4: Calculate Solar Wire Size For Section 1

Now that you have applied the NEC safety margin to your solar array’s maximum amps, you can determine the solar wire size you need for Section 1.

Remember: Section 1 represents the wires that connect the solar panels to the solar charge controller.

Take the amps you calculated in Step 3 – after the 25% NEC safety margin – and refer to the table below to identify which wire size you need to complete Section 1. The amps should fall within one of the three ranges in the light-blue row.

Note: We recommend a maximum of 8 AWG wires for Section 1. If the max current (after the NEC safety margin) is over 40A, consider wiring your panels in series to reduce the current.

Example: From Step 3, we have 17.93A. Using the table above, we should use 12 AWG wires to connect the solar panels to the charge controller.

Good To Know: All our wire recommendations above are ‘marine grade,’ meaning the wire jackets resist corrosion when exposed to UV light, salt water spray, and rain. This is important because parts of these wires will be outside and constantly exposed to the harsh outdoor environment.

Step 5: Select Solar Charge Controller

The total wattage of your solar array determines the correct solar charge controller size. You must select a charge controller before identifying the solar wire size for Section 2. This is because every charge controller has an amp rating, which is the maximum amps that the controller can output through the solar wires to the bus burs (and battery).

Example: A charge controller rated for 30 amps will output a maximum 30A current to the bus bars.

Use the table below to help you identify your ideal charge controller size based on the total wattage of your solar array. Your solar array wattage should be within the range listed in the light-blue row.

Example: Our two 200-watt solar panels produce a total of 400 watts. Therefore, we should select a 30A solar charge controller.

Why Victron charge controllers? Victron controllers are workhorses. We’ve been using a 30A Victron charge controller for five years, and it’s been working day in and day out without trouble. We also love its Bluetooth & smartphone app features. Read our Victron charger controller review for more info.

Step 6: Apply NEC Safety Margin To Charge Controller Amp Rating

To begin calculating the wire size for Section 2, you must apply a 25% safety margin to the solar charge controller’s amp rating to comply with NEC standards. The resulting amount is what we will use to determine the solar wire size you need.

Example: A 30A controller will output a maximum 30A current. After adding the 25% buffer, we get 37.5A. (30A * 1.25 = 37.5A)

Step 7: Calculate Solar Wire Size (Section 2)

After applying the NEC safety margin, you can calculate the solar wire size you need to connect the charge controller to the bus bars (Section 2).

To do this, take the amps you calculated in Step 6 and identify the correct wire size from the table below. The amps you calculated should fall within the range listed in the light-blue row.

Example: From Step 6, we have 37.5A. Using the above table as a reference, we should use 8 AWG wires to connect the charge controller to the bus bars.

Solar Wire Size Summary (TL;DR)

The diagram below shows what wire sizes you’ll need to connect the solar panels to the charge controller and the bus bars.

  1. The solar array’s maximum current determines the size of the solar wires between the panels and the controller.
  2. The total wattage produced by the solar array determines the amp rating of the solar charge controller.
  3. The amp rating of the solar charge controller determines the size of the solar wire between the controller and the batteries.
Wiring diagram with a summary of factors that determine solar wire size
Solar wire size summary

Now that you’ve selected your solar wires, you might be ready to start wiring everything together. Check out our solar system guide for a step-by-step installation tutorial.

Solar Wiring Diagram (Less Than 440W)

If you prefer to follow a premade design, you can refer to the solar wiring diagram below. This solar system is designed for a max solar array of 440W with panels wired in series.

Free download: Get this wiring diagram as a PDF.

Solar wiring diagram for medium systems with max 4400W solar array
Solar wiring diagram for medium systems (max 440W)

Solar Wire FAQ

How do I calculate solar cable size?

To calculate the correct solar cable size, you will first need to know the maximum current (amps) produced by the solar array. Then, you must add the NEC safety margin to the maximum current to ensure you select the proper wire gauge for the solar system.

What cable do I need for a 100W solar panel?

A typical 100W solar panel outputs about six amps of current. As a result, you can use a 14 AWG wire for a 100W panel.

What is the best wire for a solar setup?

Pure copper wires are the best for a solar system. These wires can safely transmit more amps than copper-clad wires. Make sure your wires are also ‘marine grade.’ This means the wire jackets are more corrosion-resistant to UV light, salt, and water.

Conclusion: Proper Solar Wire Size Is All About Safety

If you’ve gotten this far in the post, congratulations! Calculating the correct wire sizes for your solar system is tedious and, understandably, not particularly exciting. However, the biggest argument for taking the time to do your calculations correctly is for YOUR safety.

You want to keep yourself, your loved ones, and your home safe from electrical faults and fires.

But proper wire size is just one-half of the safety equation. You must also install the correct fuses and circuit breakers to protect the solar wires from over-current events. Read our post “How To Fuse A Solar System” to learn more about how to determine what you need.

If you have any questions regarding the best solar panel wire size for your system, please comment in the section below.

Happy building!

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2 Comments

  1. Eric,
    I have the Victron 100 V / 50 Amp controller. By your calculations, I would need a 4 AWG wire from the controller to a bus bar. 50 + (50×25%) = 62.5 Amps. A 4 AWG wire will not fit in the controller.

    1. Hi Cyndi, you are absolutely right here. I’ve reviewed the Victron 100/50 controller and the device has a max wire size is 6 AWG. I’ve also reviewed the Windynation wire and this wire should safely carry 50A*1.25 of current. Thank you for catching our slip up here, I’ve updated the table to reflect this.

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