Do Solar Panels Need A Fuse?

  • By: Preetam
  • Date: August 28, 2021
  • Time to read: 4 min.

A solar fuse is a unique device used in solar power and photovoltaic systems.

Fuses applied in these systems are referred to as either Solar PV Fuses, PV Fuses, Solar Panel Fuses, or Fusible P Fuses.

Ampere ratings and wide voltage ranges determine the size of the Solar Panel Fuse.

Although fuses are not necessary for systems to operate appropriately, I generally recommend using them for safety reasons.

Additionally, the fuse size depends on the number of solar panels and the connection used; parallel, series, or parallel/series.

Why should I install Fuses in My Photovoltaic Installations?

According to the world economic forum, the world will add about 70,000 panels per hour for the next five years.

In Photovoltaic installations, DC fuses are generally used to prevent the system from overheating or catching fire.

Besides, they also prevent the modules from serious damage if a short circuit takes place.  

Typically, the fuses also play their conduction role. Suppose an electrical fault occurs whereby there is an abnormally high current.

In that case, the energy transfer due to the electrical fault makes the fuse melt since the fuse consists of a wire element or a metal strip.

When Should you Fuse and When Should Not Fuse your Solar Panels?

It is unclear how a person should determine when a fuse is needed and when it is not in a PV string output.

So, how can you easily determine where to fuse and avoid potential issues with the system and prevent redundant or unnecessary components in the system?

Generally, some string inverters come with string fuses, while others only provide placeholders, whereby the user decides whether to use them or not.

However, the presence of string fuses when you purchase these items depends on the manufacturer.

As we all know, the reason for installing fuses is to protect the wire and, secondly, to protect the electrical component.

Although it is advisable to fuse every PV outlet, it can be repetitive in two strings or smaller systems.

This is because the manufacturers of modules should integrate OCPD (over-current protection devices) of at least 1.56 times the module short-circuit current or ISC.

Therefore, no other OCPD is required in a single string system at the string output since the internal fusing protects it and no other current source can back feed through the circuit.

Suppose we have a two-string system. In this case, every string in this state can generate a current 1.25 times the system’s ISC rating.

If a short circuit occurs, the un-faulted module strings can force their current over the faulted string.

Since the faulted string can contain 1.56 times its ISC rating, the system is still protected. You do not need to fuse it.

In other cases, suppose a system has three module strings connected in parallel? Are you required to fuse the system’s strings, or is fusing not necessary in this case? If a fault occurs in one string, the other strings in good condition force the current through the faulted string.

Therefore, the current 2.5 times the module’s ISC rating flows through the defective string.

In most scenarios, the integrated over-current protection devices of the defective string will exceed its limit.

Therefore, you should install fuses on each string’s output to protect the equipment and the wiring from damage.

How to Appropriately Fuse a Solar PV System

If you do not have adequate knowledge in the electrical field, you should consult an electrician to maintain safety.

So, how can I appropriately fuse my solar panel?

Solar Panel Fusing

Commercial solar panels with over 50 watts contain ten gauge wires with the ability to handle up to thirty amps of the flow of current.

If a person connects these panels using the series method, there is no current flow increase; therefore, fusing is unnecessary for this string.

 However, this is not usually the case when connecting the panels using the parallel method, since the current is additive.

For example, suppose you have four panels capable of producing 15 amps. In this case, a short in a single panel can direct all sixty amps towards the short-circuited machine.

The wires directed to that panel will surpass to30 amps making the wire-pair catch fire.

Therefore, you need a thirty-amp fuse for each panel.

Moreover, the system needs twenty amp fuses if the panels are less than fifty watts and use only twelve gauge wires.

Charge Controller to Battery Fuse or Breaker

When using a Pulse Width Modulated charge controller, the wire size and the fuse can match since the worst-scenario amps flowing to and from the controller are similar.

On the other hand, the MPPT charge controllers can reduce the voltage and increase the current flowing; hence the fuse and the exact wire sizes must be recalculated.

Fuses play a significant role in preventing wires from overheating and preventing electric equipment from damage when a short circuit occurs.

Although these devices are not necessary for equipment like solar panels to work, they act as safety measures.

Therefore, we recommend you to install them in your solar systems.

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