Confused about which wire gauge (AWG) you need to build a solar array? Unsurprisingly, different solar array sizes require different size wires. More specifically, the greater the current (Amps) produced by the solar array, the thicker the wires you will need.
But how do you figure all this stuff out?
In this post, we provide a straightforward, 7-step process that will 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 over heating and potentially catching on fire. (But you should also read our solar fusing guidelines to additional safety measures).
And as a bonus, this post will also help you correctly size your solar charge controller.
But before we start, you should know...
To add to the complexity of sizing solar wires, you should know that there are two different sections of wires that you’ll need to account for.
- Section 1: Between the solar panels and charge controller
- Section 2: Between the charge controller and bus bars (or battery)
Depending on the solar array size and configuration, the wire sizes for these two sections can either be the same or completely different. To help you visualize, refer to the simplified solar wiring diagram below.
Why is it possible for these two sections to have different wire sizes? This is because the solar charge controller will adjust the current (Amps) it receives from the solar panels before sending the power to the bus bars (& batteries). Therefore, different amounts of current will be transmitted through these two sections and, as a result, different wire sizes may be required.
This post will help you determine the wire sizes you need to complete BOTH sections.
Best Quality Wires: We only recommend 100% copper wires for the best results. Copper-clad aluminum (CCA) wires are cheaper, but do not safely conduct the same amount of current (A) that pure copper wires can at the same wire gauge.
If you’re ready, let’s get to it
Step 1:
Finalize Solar Array Configuration
The first step to sizing your solar wires is to finalize your solar system setup. To do this, you will need to answer the following four questions:
- Which specific solar panels you will use?
- How many panels will you have?
- What is the total wattage of your solar array?
- Are solar panels 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.
1. Which Specific Solar Panels Will You Use?
This is important because different branded solar panels have slightly different specs and current (A) output. For example, we list the short circuit current “Isc(A)” for three different 200W panels below:
- Renogy 200W: 11.05A
- Newpowa 200W: 11.47A
- BougeRV 200W: 12.21A
Therefore, in order to calculate your solar wire size, you should finalize WHICH solar panels you will use.
2. How Many Solar Panels Will You Have?
The number of solar panels you will have will also impact the total current production of your solar array and wire sizing. If, after using our solar size calculator, you realize you need a 400W solar array, you could choose to either have:
- Four 100W panels, or
- Two 200W panels
In general, at least if you’re installing them on a camper van, it’s better to have fewer – but larger – solar panels.
3. What Is The Total Wattage Of The Solar Array?
Hopefully by this point, you’ll know the total wattage of your solar array. Total watts is one of the most important factors that determine solar wire gauge size. The more watts, the more Amps (current) and the thicker the wire size you’ll need.
4. Are Solar Panels Wired In Series Or Parallel?
If you’re not aware about the differences between series and parallel panel wiring, you might be surprised by just how much your wiring decision here affects total current produced and, consequently, solar wire size.
If you don’t know, check out our series vs. parallel post to learn more.
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 in order to safely transmit higher amperages.
Part 1 Summary
Once you have answers to the above four questions, you’ll have everything you need to start calculating the wire gauges you’ll need to complete your solar installation. In the next steps, we’ll show you exactly how to do these calculations.
Our Example: We decided to go with two Newpowa 180W solar panels, wired in parallel, for a total of 360W.
From the solar panels, to charge controller, to the batteries, and everything in-between, this eBook has you covered. 12+ pages of detailed diagrams, product recommendations, and links to additional resources.
Step 2:
Calculate Max 'Potential' Amps Produced By Array
Assuming you have answers to the previous four questions from Part 1, you can now calculate the maximum ‘potential’ amps produced by your solar array. This is a critical step because the greater the amps produced, the larger the solar wire size you’ll need.
To make this calculation involves a two part process:
- Identify one of your panel’s short circuit current, or “Isc(A)”
- Calculate total current based on series or parallel wiring
1. Identify Short Circuit Current From Single Panel
You can find your panel’s short circuit current by either locating the panel’s specifications sticker on the backside of the panel, or by visiting the panel’s online product page. In the example image below, we locate the short circuit current of Renogy’s 200W panel from their Amazon product page.
In this example, the short circuit current for the 200W Renogy panel is 11.05A.
The short circuit current – sometimes identified as Isc(A) – is the current produced by the panel in the event of a short circuit. It is the ‘maximum’ current that the panel can theoretically produce and is what you should look for when calculating your solar wire size.
2. Calculate Total Short Circuit Current Produced
If you are only planning 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 will have more than one solar panel, keep reading below.
For Series Connections: If wiring multiple panels in series, 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) of each panel adds up, but the current (A) stays the same.
For Parallel Connections: If wiring multiple panels in parallel, the total current produced by the solar array is equal to the sum of the short circuit current of each panel. This is because in parallel connections, the current (A) of each panel adds up, but the voltage (V) stays the same.
Our Example: Our two Newpowa 180W panels have a short circuit current of 11.75A. Since the two panels are wired in parallel, the total current produced is 11.75A + 11.75A = 23.5A
Step 3:
Apply NEC Safety Margin
Traditionally, the National Electric Code (NEC) considers adding 25% to a current-producing device to be a safe margin. However, solar panels are different because a panel gets its wattage rating based on standard light conditions in a laboratory. There are situations where a solar panel can actually produce MORE watts than what it is rated for.
In our experience, these situations are not uncommon. If we experience exceptionally clear, sunny days and are at a high altitude, our 360W-rated array has, at times, produced over 400W.
Therefore, to apply the appropriate NEC safety margin to a solar panel, follow this two-part process.
- Calculate NEW max current of solar array
- Apply 25% safety margin to NEW max current
1. Calculate NEW Max Current Of Solar Array
For solar panels, the NEC considers the maximum current of a solar array to be 25% above the total short circuit current produced by the array. For example, if your array’s total Isc(A) is 23.5A, the NEW max total current is 23.5A * 1.25 = 29.375A
2. Apply 25% NEC Safety Factor
Take your new max current and, again, add a 25% safety margin. For example, 29.375A * 1.25 = 36.72A
Essentially, you are adding a 25% buffer TWICE to your solar array’s total short circuit current. If you want to save a step, you can multiply the total short circuit current by 1.56 to get a similar result, which is approved by the NEC.
Step 4:
Calculate (Section 1) Solar Wire Size
Now that you have applied the NEC safety margin to your solar array’s current output, you’re now ready to calculate the solar wire size you need for Section 1.
Do You Remember? Section 1 represents the wires that connect the solar panels to the solar charge controller.
Take the final current (A) you calculated in Step 3 (after the NEC safety margin) and refer to our table below to identify which solar wire size you need to complete your ‘section 1’ wiring. (To locate the correct row, your current (A) should be within range listed in the blue ribbons)
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.
* Note: Ancor branded red & black wires are sold separately. It’s annoying, but they produce high quality wires. So you will need to also buy a spool of black wire of the same gauge size.
Example: From Step 3, we have 36.72A. Using the table above, we should be using 8 AWG wires to connect the solar panels to the charge controller. Realistically, you could get away with 10-gauge wires, but to maximize safety and be NEC compliant, we recommend following the table above.
Good To Know: All our wire recommendations below are 100% copper & ‘marine grade’; meaning they comply with various boating standards and 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 correct charge controller size you need is directly related to the total wattage of your solar array. You must get a charge controller before you can identify the solar wire size you need 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 30A-rated controller will output a maximum 30A current.
Use our table below to help you identify your ideal charge controller size based on the total wattage of your solar array. (To find the correct row, your solar array wattage should be within the range listed in the blue ribbon)
Why do we only recommend Victron controllers? Victron controllers are workhorses. We’ve been using a 30A Victron charge controller for 4 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.
But we understand that Victron charge controllers are not the cheapest. Therefore, you can first identify the amp-rating of the charge controller you need from the above table, then search for a more affordable model on Amazon.
Step 6:
Apply NEC Safety Margin
Just like in Step 3, you will need to apply a safety margin to be compliant with NEC standards. However, unlike in Step 3, you only need to add a 25% buffer once. You DO NOT need to do this twice since the charge controller is the power producer and not the solar panel.
Therefore, take the amp-rating of your selected charge controller and add a 25% margin.
Example: A 30A-rated controller will output a maximum 30A current. After adding the 25% buffer, we get 30A * 1.25 = 37.5A
Step 7:
Calculate (Section 2) Solar Wire Size
Now that you’ve applied the NEC safety margin, you’re ready to calculate the solar wire size you need to connect the charge controller to the bus bars (Section 2).
To do this, take the current you calculated in Step 6 and identify your correct wire size from the table below. (The amps you calculated should fall within the range listed in the blue ribbons)
Example: From Step 6, we have 37.5A. Using the above table as reference, we should be using 8 AWG wires to connect the charge controller to the bus bars.
Too Long, Didn't Read...
Solar Wire Size Summary
The below diagram is a summary showing you what wire sizes you’ll need to connect the solar panels to the charge controller and then subsequently to the bus bars (or batteries).
1. The size of the solar wires between the panels and the controller is determined by the maximum output current of the solar array.
2. The charge controller amp rating is determined by the total wattage produced by the array.
3. The size of the solar wires between the controller and the batteries (or bus bars) is determined by the amp rating of the controller.
Now that you’ve selected your solar wires, you might be ready to start wiring everything together. If that’s the case, check out our epic solar system guide for a step-by-step installation tutorial.
Download our eBooks for useful electrical, solar & plumbing diagrams. They are completely FREE.
Use This Solar Design...
Sample Solar Wiring Diagram (<440W)
If you would rather use a premade design, you can refer to the below solar wiring diagram. This solar system is designed for a max solar array of 440W with panels wired in series. The following wire sizes are used:
* Note: If you’re wondering why we use 2/0 AWG wire here, read our camper van wire size guide for more informatin.
For a complete product breakdown of this wiring diagram, download our free solar wiring eBook.
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 a tedious process and, understandably, not particularly exciting. However, the biggest argument why you should take the time to do your calculations correctly is for YOUR safety.
You want to keep you, 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’ll also need to install the correct fuses and/or circuit breakers to further 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, please send us an email to the address listed in our footer.
Happy building!
Similar Posts
