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DC Error Troubleshooting Basics

How do we troubleshoot DC Errors? Most inverters look for errors in similar ways, no matter who the manufacturer is, they still use either isolation testing, or a current sensor to determine if you have a ground fault in a PV system. (isolation testing is where the inverter measures the ohms between ground and the DC circuit, if its below a certain threshold it trips the inverter and calls out a ground fault. Current sensing is a GFDI breaker that trips offline when there is current moving between the negative conductor and ground. You typically see isolation testing on floating arrays, and GFDIs/current sensing on grounded arrays). 

Knowing how your Inverters look for faults can help determine how you troubleshoot them. The manual for the inverter is the first key in determining how to troubleshoot. 

  1. Start at the inverter, do you have an error code? If you do, look it up in the manual! What does it say?
  2. Is the inverter powered on? Check out the display if it has one, look at the DC values INSIDE of the inverter. Are they normal? RECORD THEM! WRITE them down!
  3. It doesn't matter if they are good or bad, measure the DC voltage at the inverter. If possible disconnect the DC from the inverter (this can be difficult for a central, move to step 4 for a central)
  4. Now measure the DC at the array, whether this is a combiner box, or the DC strings attached to the inverter, disconnect them and measure. RECORD THEM! WRITE THEM DOWN!
  5. Still haven't seen anything weird? Voltage levels are acceptable, they aren't bleeding down, they don't fluctuate at all? Interesting. Now try hooking up just one input at a time. Does the fault code change? Does it go away or stay the same? 
  6. Finally ensure all the connections are secure, make sure MC connectors are locked and there is no gap, and tighten DC connections at every point (inverter terminations, combiner boxes, between modules, and home runs. 
  7. If you brought a spare string inverter, hook it up. See if it runs without the error. If it does, you now have an RMA you need to process. 

When checking DC voltages make sure you record Positive to Negative, Positive to ground, and Negative to ground. 

The best thing you can do during this entire bit of troubleshooting is to WRITE DOWN what you have done. Manufacturers are going to ask you what troubleshooting you performed. You have to prove to them that you did everything in your power to ensure the issue isn't on your side. 

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