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What is a Solar Fuse and Why or When Do You Need It?

Solar fuse
Solar fuse
Resource: https://www.rv.net/forum

A solar fuse is a type of fuse used in PV installations. It provides protection against overcurrent conditions, which helps prevent fires or damage to electrical components. Check out this post to learn more about the fuses for PV systems, how they protect solar systems, and more. The topics we will discuss include:

  • What is a solar fuse?
  • Why use a solar fuse?
  • Solar fuse location in a PV system
  • Types of fuses for PV systems
  • Solar fuse price

What is a Solar Fuse?

A solar fuse, or PV fuse, is a device that electricians use to protect solar circuits against excessive currents, also called overcurrents. An overcurrent refers to the abnormal flow of electricity that occurs due to a number of factors, such as:

The solar fuse, like most other fuses, uses a conductor that melts when exposed to too much current. This causes the circuit to break and interrupts the flow of electricity, thus preventing further damage or fire.

Solar fuses are specifically designed to protect solar circuits. That means they will adequately respond to fault currents that characterize PV systems. For that reason, solar power fuses must always be used in PV installations.

Why Use a Solar Fuse?

The primary reason for using photovoltaic fuses is to prevent the wiring from becoming too hot (due to fault currents) and causing a fire. In addition, fuses help protect solar equipment or devices from damage that can be caused by short circuits and other faults.

These solar components include panels, inverters, and solar batteries. In short, properly sized solar PV fuses ensure the longevity of your power investment. This makes it a critical safety device that should not be overlooked.

Types of Solar Fuses

Solar fuses can be different designs. They are also mostly classified based on their acting speed. In light of that, electricians usually have to choose between two main types of solar fuses – the fast-blow fuse and the slow-blow fuse.

The main difference between the two PV fuse types is in how they respond to an over-current. A fast-blow fuse will blow or melt almost immediately when exposed to an over-current, while a slow-blow fuse can handle small surges or inrush currents without blowing.

A fast-blow fuse is usually used to protect smaller circuits such as those found in electronic devices or circuits that will not experience any large inrush currents.

On the other hand, slow-blow PV fuses are best at protecting larger circuits such as those found in motors or power supplies, as they can handle the initial inrush current without blowing.

Solar fuse between the solar charge controller and battery
Solar fuse between the solar charge controller and battery
Resource: https://www.youtube.com/watch?v=Mes6ShwTqPw

Solar Fuse Location

Solar power fuses are typically installed at the point where they will protect a specific solar component, such as panels, cables, batteries, and so on. For that reason, it’s recommended to place them in these 4 places:

  • At the panel cables to protect parallel-wired modules or strings
  • Between the solar fuse block or combiner box and charge controller
  • Between the charge controller and battery or battery bank
  • Between the battery and inverter.

Solar Panel Fuses

Solar panel fuses are meant to protect individual panels and their cables. You install them on each cable of the panel, usually using a solar fuse block or in a combiner box. However, whether or not you need them will depend on the design of your system.

Solar panel fuses are necessary when you have three or more panels connected in parallel. That’s because, in this configuration, a single faulty panel could cause other panels to drive current through it.

Because the current in a parallel connection is additive, the fault current would be equivalent to a sum of the other panel currents. This would heat up the faulty panel cables to a point of even causing a fire.

If you have the panels in series, on the other hand, you will not need them fused. That’s because the current will not increase if one panel becomes faulty (panels in series only offer increased voltage and not current).

Solar Fuse Block Fuse

After the solar panel fuses in a parallel system (or outputs in a series wired system) are combined, a fuse must be installed. This type of solar DC fuse will provide protection to the wiring between the combined fuse block and the charge controller or if yours is a grid-tied system, the cables to the grid-tie inverter.

The manufacturer will most likely have stated this solar fuse size, or you can calculate it using the provided ratings in your solar system. The industry standard is to base your calculations on the short circuit current rating,(ISC), of the solar array or strings.

You can then calculate the required size using this formula: Fuse current rating = 1.56 x Isc

Solar Charge Controller Fuse

The role of the solar charger controller fuse is to protect the wiring from the solar charge controller to the battery bank. In its absence, the wire to the charge controller could become too hot during a fault current, and potentially catch fire.

In order to size the solar controller fuse, you would need to refer to the charge controller manual – if it comes fused, and whether it’s a PWN or MPPT controller.

That’s because whereas a PWN’s current is generally constant, an MPPT charge controller has its current fluctuating and the fuse sizing must accommodate for this.

Solar Battery Fuse

This is the last solar DC fuse. The solar battery fuse here is used to refer to the fuse that is located between the battery and the inverter.

The fuse protects both the wiring and the battery. Without it, a short circuit could cause a fire, as it would draw too much current from the battery.

The sizing of the solar inverter fuse is a bit more complicated, as you must factor in not only the inverter design but also the battery capacity.

Note that some inverters come already fused on either side (DC and AC) and you must consult its manual for the correct rating to use.

Solar Inverter Fuse

The other side of the inverter is the AC side. On this side, AC fuses or circuit breakers may be used. This is also the load side, and the fuses or breakers will protect the wiring from the overcurrents caused by faulty appliances.

A solar inverter fuse may be installed in the inverter or close to it. In the event of a fault such as a short circuit, the fuse will cut off power to prevent the wires from becoming too hot and causing a fire.

 Types of solar fuses
Types of solar fuses
Resource: https://www.youtube.com/watch?v=GyzrxAwxtgA

Solar Fuse Price

How much would solar PV fuses cost you to install? The price tag of a solar fuse will mainly be based on its size, type, and brand. However, you can expect to pay anywhere from $15 to $60 for most solar fuses.

Size is one of the main factors that affect the solar fuse price. The larger the fuse, the more expensive it will be. This is because larger fuses can handle more current and are therefore more expensive to manufacture.

As mentioned earlier, there are different types of these fuses. These will also have an impact on the price. Different fuse brands will also cost different amounts. To get the best deal, therefore, you may want to compare the prices of different companies.

Conclusion

A solar fuse ensures the cables in your solar system do not overheat and cause a fire when a fault current flows through them. PV fuses also help to protect the electrical components in your system from damage caused by over-currents from short circuits. Because of this, it is important to choose the right type and size of fuse for your application. Also, be sure to install the fuse in the correct location, as that will ensure proper protection.

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