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Troubleshooting DC Arc Faults

DC arc faults are one of the most difficult and time consuming faults to detect, especially if they occur infrequently. The steps listed in this article are the most comprehensive ways to troubleshoot a DC arc fault. 

  1. Check the inverter - The primary alert system of any PV installation is the inverter. Look up any arc fault codes within the inverters manual, and if available, activate the inverters "self test" for arc faults. ALL UL1699B listed inverters are required to perform an arc fault circuit test after a power cycle. Turn the inverter on and off and ensure the arc fault testing system is working correctly. If it's not working correctly the inverter should have a (hopefully obvious) way of indicating that the failure is internal to the unit. 
  2. Inspect the easy stuff - A full system inspection takes a lot of time and labor. Start with the easy stuff, check the DC connections at the inverter, physically remove them and re-land them. Inspect any terminals that may be loose on the FACTORY connections of the inverter. Many inverters ship from far away places and during shipping some connections may loosen. If you found a loose wire, tighten it up and ensure the system will run without triggering an arc fault.
  3. Verify the connections on the DC circuit - Most arc faults are caused by NOT pushing the module connections together. Even a small gap can cause an arc fault. Ensure all of the DC connections between modules, including the home runs are SECURELY connected. Make sure that none of those connections are being exposed to pooling water. Check any junction boxes that may have water or moisture in them. Remake those connections to ensure they are properly assembled. The DC homeruns can be made incorrectly in the field. Disconnect the homeruns and inspect the internal connections. check If there are any signs of melting, disfiguring, arcing or dark colored metal inside. Replace any connections that may be suspect, as avoiding a return trip is paramount. 
  4. Try to run the inverter with only 1 string at a time, if you know the arc fault occurs at certain times of the day, try to run the inverter with each individual string around this time. Typically TRUE arc faults occur during the highest producing times of the day. 
  5. If all of the above fails, its time to look into replacing the inverter.

There are a couple things NOT to check for. 

  1. While troubleshooting an arc fault - do not treat the troubleshooting like a ground fault.
  2. Do not assume good voltage means there is not an arc fault.
  3. Do not measure current - current released during an arc fault will not be detectable by most multimeters technicians carry. 

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