Solar Arc Fault Troubleshooting Guide

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With heat and electricity building up in PV modules, what are the chances of of a fire breaking out? The chances of solar panels catching fire is very low, but it never hurts to be careful. One often cited possible fire hazard are DC arc faults, so it helps to know how to troubleshoot these before something untoward happens.

The best method to prevent solar panel fire DC arc faults is to use microinverters. Modern solar power systems are also optimized to run DC voltages without causing any risk of fire. As long as a solar panel system is correctly installed, the chances of a DC arc fault fire is low. While it is unlikely, problems can still occur, so troubleshooting knowledge can be invaluable.

What Causes Solar Arc Faults?

Before we can troubleshoot, we should look at the possible causes. There is no single cause for a solar arc, so you need to go over each possibility. That’s why many prefer to leave this to technicians because it is a time consuming process.

  • Outdated fimware
  • Tripping
  • Loose cable wire or connector
  • Damaged inverter cable
  • AFCI board is damaged
  • The solar panel modules are damaged
  • Wires have gotten loose and lying against the array rack
  • Animal chewed wiring
  • DC terminals were not crimped correctly
  • Wire insulation caught in the terminals
  • Temperature change causing the terminal screws to loosen
  • Worn out junction box connectors

Step 1 – Do a Visual Inspection

While it can take a while, solar arcing can leave visual clues about what happened. Sings include the following: Some or all of these may occur.

  • the junction box at the rear of the panel is burned
  • Insulation or connector is burned or melted
  • Wires are discolored

If you suspect loose wiring, gently tug the cable at the wiring box, panel to panel and combiner. If any of the connections are loose you’ll notice it right away. Tugging can also locate poorly crimped connectors. Sometimes the faulty crimping is due to a factory defect. if not repaired this could lead to solar arcing and other problems. If it’s a manufacturer defect, check your solar panel warranty and have it fixed or replaced.

If it’s an outdated firmware, update your inverter as soon as possible. Check your inverter product guide for instructions on how to upgrade it. If it is outdated hardware, contact the manufacturer is there is a possible fix.

Step 2 – Troubleshooting Rooftop Solar Panel Installation

Visual inspection is difficult to do on a roof, but it is possible. If you decide to do this yourself, bring an infrared thermometer and conduct the aforementioned visual inspections. Use the thermometer to check the temperature of the junction boxes, terminals, wires and PV modules. Solar panels can deal with heat, but exceedingly high temperatures can trigger an arc fault.

Step 3 – Use a Voltmeter

A voltermter can help you find a possible arc fault in cable connectors. A megohm meter that locates arc in a particular string can be useful too. You can also use a string tester, which is designed specifically to find ground faults, insulation problems and arcs.

Step 4 – Reset the Inverter

If you used all the methods above and were unable to find the cause, it was probably just a nuisance tripping. Reset the inverter and see if the fault occurs again. If it does there’s a good chance the AFCI circuit is damaged. The best option is to replace the inverter as repairing could be more expensive.

If the arc fault doesn’t repeat, note the condition when it took place. What was the temperature? Was it snowing, raining or was there a strong wind gust? Was it too hot? By taking notes you will be able to compare if the “false trip” occurs again.

Solar Arc Fault FAQ

Where Do Solar DC Arc Faults Happen?

DC arc faults often occur at solar panel DC cabling. It can affect systems that don’t have DC cable protection. If you are not sure about your system, check the installation manual or contact the manufacturer. They can provide information whether there is DC arc fault protection available.

What is the Best Way to Prevent Solar Arcing?

Use a microinverter in your solar power system. If you have a modern solar power system, It should have DC arc protection built in too. Check your system guide for details. Most systems have some kind of integrated protection, though the features vary.

Does Arcing Happen on AC Systems?

No it does not. As voltage alternates in an alternating current, the arc is eliminated. Arcs can only be maintained if the parameters for starting it are always present. That is not possible with AC systems. In DC however, the arc remains with the voltage.

How Can I Avoid Solar Arcing in an Unprotected DC Cabling System?

There is no way to 100% guarantee an arc fault will not happen on an unprotected string inverter DC solar system. It is a mistake to believe that an unprotected DC cabling system will be safe from solar arcing because it is regularly inspected.

Even if you pay a professional solar cleaning service to maintain the system, they can’t do anything if a vermin chews the wire that same night. When the sun is up and the modules start converting energy into current, the wires will get hot. Without protection the risk of a fire is there.

The point is, no amount of inspection can fully guarantee the system will be arc fault free. The only way to do that is if you install a protected DC cabling system with a microinverter.

Will Installing a High Quality Solar System Prevent DC Arc Faults?

The only way to prevent it is to use install a solar power system that has specific protection against DC arc faults. Many high quality PV modules have this feature, so make sure the system you want to buy has it.

But that’s only half of it. The other half is to make certain solar panel installation is correct. Most cases of DC arc faults are due to loose wiring, and it only takes a slight mistake to leave a cable or screw loose. That small mishap could lead to a DC arc fault. It may not be enough to start a fire with today’s solar power systems, but it damage the components.

Are DC Faults More Likely on Older Solar Power Systems?

Yes. As solar systems get older, the wire connectors get worn out. This could result in overheating and eventually to an arc fault. Insects and rats can cause insulation damage. Birds can do the same on the roof. Other components like isolator sealing get worn out too. This is more likely to happen with string inverter systems too.

Can I Prevent DC Faults by Replacing Isolators with a Junction Box?

No, it will not. DC arc faults usually occur because of wire insulation damage, loss of wire continuity and cable joints. Using a junction box in lieu of isolators will not do anything to prevent a DC fault. The only option is to use an optimized and protected DC solar system.

Are DC Isolators the Only Cause of DC Arc Faults?

As stated above, DC arc faults can occur for many reasons and in various locations. Aside from the isolator joint, the fault can happen in the joints, cable, connectors or modules. That is why a visual inspection is necessary to determine the location and root cause.

Can String Inverter Shutdown Mechanisms Prevent DC Arc Faults?

No, it cannot. These devices, usually installed alongside solar panels, will lock down circuits where the arc fault occurs. However it cannot do anything about arc faults that happen on the ground or beneath the solar panels.

What about String Inverters with DC Arc Protection? Do They Work?

These string inverters do provide some protection against DC arc faults, but not all of them. These devices can detect sounds from the cabling, indicating it’s an arc fault. This will be isolated, but it only works for a series and not ground or parallel arc faults. Yes, these string inverters can provide some protection but it is limited.

Conclusion

Solar power safety features have come a long way. But of course we can never be too careful when it comes to fires or troubleshooting solar installation. The bottom line is if your system is correctly installed and maintained, solar fires can be prevented and DC arc faults spotted and remedied before anything unfortunate happens.