CSLB C-46 Solar ContractorPhotovoltaic System InstallationMedium
During a system commissioning, a solar technician observes that a newly installed string inverter is frequently disconnecting from the grid due to 'grid undervoltage' errors, even though the utility grid voltage appears stable. The AC circuit from the inverter to the service panel is a long run. What is the most probable cause of this issue?
- AThe inverter's internal voltage sensors are faulty.
- BThe utility grid is experiencing frequent brownouts.
- CThe inverter's anti-islanding protection is misconfigured.
- DThe AC conductors connecting the inverter are undersized.
Show answer & explanationAnswer & explanation
Correct answer: D. The AC conductors connecting the inverter are undersized.
Longer AC conductor runs, especially if undersized for the current, will experience a greater voltage drop. If the voltage drop is significant enough, the voltage at the inverter's output terminals can fall below the allowed grid undervoltage threshold, causing the inverter to trip and disconnect even if the utility grid itself is stable.
Why the other options are wrong
- A. Faulty sensors are possible but less probable than voltage drop on a long run.
- B. The problem states the utility grid appears stable, ruling out utility brownouts as the primary cause.
- C. Anti-islanding protection detects loss of grid, not undervoltage when the grid is present.
Inverter Voltage Drop
The reduction in voltage between the inverter's AC output and the point of interconnection due to resistance in the AC conductors.
- Increases with conductor length and current.
- Decreases with larger conductor gauge.
- Can cause inverters to trip on undervoltage errors.
Memory trick: Long wires, small gauge, voltage drain, inverter in pain.