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How to Determine Solar Panel Fuse Size

Solar fuse installation points in a solar power system
Solar fuse installation points in a solar power system
Resource: https://www.youtube.com/watch?v=fZGj2cVnlHc

When it comes to fusing solar panels, the general rule of thumb is that the larger the wattage of the panel, the larger the fuse size should be. Use this guide to determine the right solar panel fuse size for your system, based on its specific wattage.

Solar Panel Fuse Size

Solar panel fuses are available in many different sizes. Solar panel fuse size refers to the amperage rating of the fuse or, in other words, the maximum amount of current that the fuse can safely carry.

The ampere rating is usually printed on the side of the fuse, and it will be represented by a number followed by the letter “A” (for example, “3A” or “15A”).

The letter represents the maximum current that the fuse can pass without blowing. So, a 30 Amp fuse for solar panel protection can safely carry up to 30 amps, and a 40 Amp fuse as much as 40 amps of current.

Why Fuse Solar Panels?

We fuse solar panel strings to protect the wiring (and the entire system) from the effects of fault currents such as those that result from short circuits.

A fault current or overcurrent would heat the wires and that heat could lead to a fire. The fuse “blows” or “opens” the circuit by melting and interrupting the flow of current before that happens.

Solar Panel Fuse Calculator

Solar panel fuse rating presents an important safety consideration. The wrong size can cause the fuse to either blow too easily or not blow at all in an overcurrent situation.

To calculate a solar panel fuse size, we need to obtain the maximum short circuit current (Isc) of the panels or panel strings. This will usually be on the sticker located on the back of the panel.

After we have the value, we can use the following formula to determine the minimum rating of the fuse needed for our application: Fuse size = 1.56 x Isc. Continue below for specific examples of these calculations.

Solar fuse box
Solar fuse box
Resource: https://www.youtube.com/watch?v=-64CyKEjwX0

What Solar Panel Fuse Size Do You Need?

Solar fuse installation can be a DIY project, or you could have a professional electrician do it for you. Either way, you’ll need to know the proper solar panel fuse size for your system. This sizing guide for solar panel fuses will help you choose the right size for the following panels arranged in both series and parallel.

  • 90-watt solar panels
  • 150-watt solar panels
  • 200-watt solar panels
  • 300-watt solar panels

Important! Note that these panels will usually require 30A fuses at the individual level. Our calculations are, therefore, aimed at finding the fuse to use between the array and the charge controller, at the combiner box or block.

What Fuse Size for 90W Solar Panel?

Suppose you have three of these 90-watt panels in series, each with an Isc of 4.6 amps. You’ll need a solar fuse size that can carry (4.6 x 1.56) = 7.1 amps, so an 8-amp fuse would be the smallest you could use in your system.

For 3 of these panels or 3 strings in parallel, you’ll need a fuse that can carry (7.1A x 3) = 21.3 amps, so a 25-amp fuse would be the type to look for. That’s because manufacturers only make these fuses in specific sizes.

What Fuse Size for 150W Solar Panel?

Let’s assume you have 150-watt panels arranged in series with each panel having Isc rating of 8.2 amps. In this case, you’ll need a fuse that can carry (8.2 x 1.56) = 12.8 amps. Rounding off the value, we find that your system would require a 15-amp fuse as the smallest size.

If you have the panels in parallel instead, you’ll need a fuse that can carry (12.8A x 3) = 38.4 amps. Again, rounding off the figure to the higher value, a 40-amp solar fuse would be the smallest you could use.

What Fuse Size for 200W Solar Panel?

What if you have three, 200-watt panels in series, and each has an Isc of 10 amps? Again, using our solar fuse calculator formula, we would need to multiply 10 x 1.5, which gives 15.6 amps. That means you would need to install a 20-amp fuse.

If the panels were in parallel, you’ll need your fuse rated (15.6A x 3) = 46.8 amps. In this case, we recommend using a 50-amp fuse as the smallest size. Remember, this fuse rating should match the size of the array wiring.

What Fuse Size for 300W Solar Panel?

For three 300-watt panels wired series, and assuming each panel comes rated of 11.7 amps for Isc, you’ll need a fuse that can protect against a minimum of (11.7 x 1.56) = 18.2 amps. Rounded off, the solar panel fuse rating for this system would be 20 amps.

And for the panels of this rating in parallel strings, you’ll need a fuse that’s rated (18.2A x 3) = 54.6 amps. Rounded off, the minimum size for this application would be 60 amps.

Note that these calculations to find the right solar panel fuse size are based on the most important parameters. Several other variables would need to be considered as well but these wouldn’t have as much impact. These include:

  • Wiring size and material
  • Array voltage
  • Operating temperature

We also advise that you follow the manufacturer’s recommendations for overcurrent protection devices. Many companies include guidelines to be used in determining the proper fuse size. Also, make sure you’re using the correct type of fuse.

Conclusion

Solar panel installations must be properly fused, or else serious damage to wiring equipment could result. In the worst of these fault current situations, the hot cables or equipment could cause a fire. If you are unsure about what solar panel fuse size to use, or have any other questions about installing solar fuses, our advice is to always consult with a qualified professional.

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