It’s something installers hate to hear and hate to troubleshoot: the dreaded DC-side arc fault. Rarely in solar can such a small phrase bring so much ambiguity and require so much effort to find and fix. Yet over the course of a career, all solar installers will find themselves searching inside junction boxes, combiners and on top of roofs to find that pesky fault.
Sometimes they’re caused by simple installation mistakes like not stripping enough wire length or improper torque. And then there are times when the install was perfect, but the local rodent population fed itself on PV wire long enough to bring down the system.
One thing to remember is that although the inverter has found an arc in the system, it’s often acting as the bearer of bad news. Like the warning lights in a car, the inverter has found a problem that needs to be addressed but is likely outside of the inverter itself.
Tips for finding the arc
- Safety first. Make sure to turn off the AC breaker and, if applicable, turn off and lock-out the AC disconnect switch to ensure the inverter is not producing any power. Once the inverter is shut off, wait five minute before opening any covers to ensure the capacitors have time to bleed out excess power.
- Open the inverters and any combiner boxes to check for proper torque on all DC terminals. A common test here is to tug each wire to see if any are loose or pull out entirely. If any wires are suspect, tighten them down to proper torque specs.
- While the inverters and combiner boxes are open, visually inspect the insulation on the DC conductors where they land. The insulation should be stripped back enough so the wire is solely clamped down, without any insulation touching the terminal. The length of stripped wire is different with each application; for example, with the Sunny Tripower, the DC terminals require .75 inches of insulation to be stripped back.
- Visually inspect the homerun connectors going back from the combiner boxes to the modules for each string. The connector-to-connector points for the first and last modules in each string should be easy to find. The homerun wire connector is normally cut and crimped onsite to match the length requirements, giving it a higher probability for causing a fault due to improper crimping.
- Walk the array while looking for signs of arcing. Closely inspect the wiring under the modules and inside junction boxes. Damaged wires from rodents are just one example of what to look for. This can be taxing depending on the array location and is often the most difficult and most important step. Make sure to look at the MC4 connectors between modules for a full connection; partial connections that aren’t fully closed are a common cause of arcing.
One thing to remember: an arc fault is not the same as a ground fault, so make sure to follow different testing procedures for ground faults. Once you’re comfortable that everything is checked and in good condition, turn on the AC disconnects or breaker and see if the inverter detects any faults.
Still seeing a fault or in need of deeper troubleshooting tips? Call our Service Line at 877-697-6283 from the system site and we’ll lend a helping hand.
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