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SolarEdge Inverter PV Isolation Resistance Warning in the Morning

Troubleshoot SolarEdge PV isolation resistance errors. Common causes, diagnosis, and solutions for residential PV systems. Safety and NEC compliance.

Frequently Asked Questions

•What is the typical isolation resistance threshold for a SolarEdge inverter?

The typical isolation resistance threshold is usually around 1 MΩ, but refer to your specific SolarEdge inverter's datasheet for the exact value.

•Can I use a standard multimeter to measure isolation resistance?

No, you need a megohmmeter (insulation tester) to apply a high DC voltage (e.g., 500V or 1000V) and accurately measure high resistance values.

•How often should I have my PV system professionally inspected?

It is recommended to have your PV system professionally inspected at least once every 3-5 years, or more frequently if you notice any performance issues or warning signs.

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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.

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Technical Background:

A SolarEdge hybrid inverter converts DC power from the PV array into AC power for the home or grid. It uses sophisticated Maximum Power Point Tracking (MPPT) algorithms to optimize energy harvest. The inverter constantly monitors the insulation resistance between the PV array's DC conductors (positive and negative) and ground. A low resistance indicates a path for current to leak to ground, creating a safety hazard and reducing system efficiency. The inverter's anti-islanding protection will trigger if grid voltage or frequency is out of spec. Rapid shutdown is NEC compliant using SolarEdge optimizers.

Symptoms:

The SolarEdge monitoring app displays a "PV Isolation Resistance Low" or similar warning message, specifically in the morning hours after sunrise. This indicates a potential ground fault or leakage current within the PV array. The inverter may reduce power output or shut down completely, depending on the severity of the fault.

Possible Causes:

Moisture ingress: Morning dew or condensation on damaged PV panel insulation, connectors, or wiring can significantly reduce isolation resistance.
Damaged wiring: Rodent damage, physical stress, or improper system can compromise wire insulation.
Faulty PV panel: Micro-cracks or defects in PV panel cells can create leakage paths, especially when wet.
Connector issues: Loose or corroded connectors can create leakage paths to ground.
Grounding errors: Improper grounding of the PV array or inverter can contribute to isolation faults.
Inverter fault: In rare cases, the inverter's internal insulation monitoring circuitry may be faulty.

Solution:

1

*Safety First:** Disconnect the DC supply to the inverter using the DC disconnect switch (NEC 690.15). Ensure rapid shutdown is activated via the SolarEdge portal. Lockout/Tagout procedures must be followed.
2

*Visual inspection:** Conduct a thorough visual inspection of all PV panels, wiring, and connectors for signs of damage, moisture, or corrosion. Pay close attention to the lowest point of the array where water may accumulate.
3

*String Testing (with DC Disconnect Open):** Use a multimeter to measure the open-circuit voltage (Voc) of each PV string. Compare the readings to the expected values based on the panel specifications and temperature. Significant deviations may indicate a faulty panel or wiring issue.
4

*Isolation Resistance Testing (with DC Disconnect Open):** Use a megohmmeter (insulation tester) to measure the isolation resistance between the positive and negative DC conductors and ground for each string. A reading below the inverter's specified threshold (typically 1 MΩ) indicates a fault. Perform this test under dry conditions.
5

*Component Isolation:** If a low isolation resistance is detected, isolate individual components (panels, connectors, sections of wiring) to pinpoint the source of the leakage. This may involve disconnecting and testing individual panels.
6

*Repair or Replace:** Repair or replace any damaged components, ensuring proper wiring practices and weatherproofing. Use appropriate connectors and sealants.
7

*System Re-Test:** After completing repairs, re-test the isolation resistance and string voltages to ensure the fault has been resolved. Restore the DC supply to the inverter and monitor its performance.

Safety Warning:

PV systems operate at high DC voltages, posing a significant electrical shock hazard. Only qualified electricians should perform testing and repairs. Always disconnect the DC supply and follow proper lockout/tagout procedures before working on the system. Arc flash protection is mandatory when working on energized DC circuits. NEC 690 provides guidelines for safe PV system system and maintenance. NEC 705 addresses interconnected power sources.

Prevention:

• Regular visual inspections: Check for signs of damage, corrosion, or moisture ingress.
• Torque verification: Periodically check the torque of all electrical connections.
• Rodent control: Implement measures to prevent rodent damage to wiring.
• Panel cleaning: Clean PV panels to maintain optimal performance and prevent the buildup of dirt and debris that can trap moisture.
• licensed technician inspection: Schedule periodic licensed technician inspections by a qualified solar installer.

Expert Tip:

Use a thermal camera to scan the PV array in the early morning hours. Areas with significant temperature differences may indicate moisture accumulation or faulty connections contributing to the isolation fault. Check the SolarEdge monitoring portal for historical data and error logs to identify trends and patterns.