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Solar PV Systems Fuse Calculator

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The main reason for me to make a post about PV fuse calculator is the number of times I am asked by customers on whether they need to fuse their PV systems.

Fusing for PV systems is usually recommended as an additional layer of protection for the electrical equipment, as all charge controllers now have over-current protection and you can depend on them to do this job, which in my opinion is enough. Still, in large installations for large projects, fusing is essential and sometimes mandatory as I will explain in this post.

Side note: Protecting the wires is the main use of fuses and protecting the equipment is the secondary use of them

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Fuse Calculator

 

When to NOT Use Fuses in the PV System?
  • When you have a small system with one or two strings.

That is because PV panels manufacturers include an integrated over-current protection device in their panels. So, in a single or two strings, there is no need for an additional fuse.

 

When to Use Fuses for the PV System?
  • Usually, when you have a system of three or more strings.

In this case, you will need to use the fuse calculator below but let us first look at the following examples to know why you need fusing for systems of three or more strings.

 

The integrated over-current protection in the PV panels always equals 1.56 times the short circuit current of the panel and the considered maximum current should be 1.25 times the short circuit current.

 

Examples:

Assuming a single string system, max current = short circuit current (Isc) and protection = 1.56 * (Isc), therefore, the system is protected.

Assuming a two strings system, max current of each string = 1.25 * short circuit current (Isc) and protection = 1.56 * (Isc), therefore, the system is protected.

Now, assuming a three strings system, max current of each string = 1.25 * short circuit current (Isc) * the number of healthy strings (2) = 2.5 * (Isc), therefore, the system is NOT protected and additional fusing is needed.

 

Practical Example #1:
RENOGY 100 Watt 100w Monocrystalline Photovoltaic PV Solar Panel Module

Fuse Calculator

By looking at the nameplate/datasheet of the panel, we will notice the following:

Isc = 5.75A

Max Series Fuse Rating = 15A

Assuming two strings system, max current of each string = 1.25 * 5.75A = 7.1875 < 15A

Therefore, there is NO need to add fusing to this PV panels system if you will install two strings or less.

 

Practical Example #2:
RENOGY 2 Premium 250W Watt monocrystalline solar Panel

 

Fuse Calculator

By looking at the nameplate/datasheet of the panel, we will notice the following:

Isc = 8.87A

Max Series Fuse Rating = 15A

Assuming three strings system, max current of each string = 1.25 * 2 * 8.87A = 22.175 > 15A

Therefore, you need to add fusing to this PV panels system if you will install three or more strings.

 

Recommended Copper Wires Sizes
AWG 16 14 12 10 8 6 4 2
Max Current 18A 25A 30A 40A 55A 75A 95A 130A

 

Solar PV System Fuse Calculator:
Download here for free

 

Where to Get Fuses?

Fuse Calculator

 

Disclaimer: The above guidelines for installation are provided in good faith to help you with the installation. The author shall not be held responsible for purchase or installation actions taken or not taken. There are many details of installation that are assumed to be general knowledge to experienced installers which are not included in the post. These installation guidelines are intended to be strictly recommendations and are not to serve as a step-by-step, fail-safe installation checklist. Selection of an experienced installer is the sole responsibility of the project owner or project manager.

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