Sample Support Report

The O&M team for a 500 kW commercial rooftop PV system reported that all inverters had tripped offline on a low insulation resistance (Riso) fault following overnight rainfall. The system had been down for approximately 4 hours at the time of the support request.

• Inverter event logs (downloaded from monitoring platform)
• Weather data for the previous 24 hours
• Site single-line diagram and string configuration
• Photos of DC combiner boxes and string terminations
• Previous maintenance records for the affected array

• • The Riso fault appeared on all inverters simultaneously, suggesting a common cause in the DC field rather than an individual inverter issue.
• • The fault correlated with overnight rainfall, which is consistent with moisture ingress at a compromised connection point or cable insulation.
• • The system had been in operation for 3 years with no previous Riso events, indicating a new degradation point rather than a design issue.
• • The site's last maintenance inspection was 4 months prior, with no noted concerns on the DC side.

1. 1Perform a binary-split string isolation test using the inverter's built-in insulation measurement function to narrow down the affected string.
2. 2Once the affected string is identified, visually inspect all MC4 connectors and cable runs for signs of corrosion, water ingress, or physical damage.
3. 3If a compromised connector is found, replace it and re-test insulation resistance before re-energizing.
4. 4If no visible damage is found on the isolated string, perform megger testing on individual string cables to locate the insulation fault.
5. 5After repair, monitor Riso values during the next rainfall event to confirm the issue is resolved.

• The specific connector or cable at fault was not identified during this remote session — field testing is required to confirm the exact location.
• If the issue recurs after the initial repair, a full DC field megger test and thermal imaging scan should be scheduled.
• If the fault is traced to a manufacturer defect in a connector or cable, a warranty claim may be warranted — document the findings for the claim package.