WiremanWireman · PV ground fault or arc-fault alarm: troubleshooting for electricians · 2023 NEC ·
PV ground fault or arc-fault alarm
Insulation and arc faults on the DC side: moisture, damaged wire, bad connectors and how to isolate the string.
Before you start
How much electrical experience do you have?
This sets how much detail each step shows. You can change it any time.
Showing detail
How it works
Modern string inverters check how well the whole DC array is insulated from ground before they start each morning, and they watch for leakage while running. A wet connector, a conductor rubbed through on a rail, or a cracked module back sheet lets current leak to the frame. Separately, the inverter’s arc-fault detector listens for the electrical noise of a DC arc, usually a loose or mismatched connector, and stops the system until someone resets it.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Which alarm is it?
- Ground fault, isolation or insulationWhen does the ground fault show up?
- Mornings or after rain, clears laterMoisture reaching a damaged spot
- All the time, even dryTest: Find which string has the fault
- Clears when one string is outTest: Insulation-test the faulted stringExpect: High readings, similar to the good strings. Very low or falling readings point to the fault.
- Much lower than the good stringsInsulation failure on one string
- Similar to the good stringsFault that only shows under certain conditions
- Never clears, even with all strings outFault inside the inverter or its DC wiring
- Clears when one string is outTest: Insulation-test the faulted stringExpect: High readings, similar to the good strings. Very low or falling readings point to the fault.
- Arc faultTest: Inspect connectors and terminations
- Burned or melted connector or terminalArcing connection
- Mixed brands or loose-looking connectorsCross-mated or poorly mated connectors
- Nothing visibleHidden connection or nuisance detection
- Ground fault, isolation or insulationWhen does the ground fault show up?