Analysis by Marcus & Team
Troubleshooting false isolation resistance readings in hybrid inverters. Learn common causes and solutions for residential solar + storage systems.
Marcus leads the technical research department at Storage Faults. Together with a team of systems analysts, he specializes in translating complex solar storage error codes into actionable diagnostic steps for the US market.
Typically, a healthy residential PV system should have an isolation resistance of greater than 1 MΩ. Values below this indicate a potential fault.
Capacitive coupling between PV conductors and the grounded racking system can create a false low isolation resistance reading, especially in large arrays. This is due to the AC impedance effect of the capacitance at the inverter's switching frequency.
NEC 690.12 requires that PV systems have a rapid shutdown function that can de-energize the PV conductors within the array boundary to 30 volts or less within 30 seconds of initiation. This is typically achieved using a rapid shutdown device (RSD) at each module or string.