One Inverter Trips on Grid Overvoltage While Others Run Fine

Why this matters

When one inverter in a multi-inverter system keeps tripping on grid overvoltage (a 59.2 / over-voltage trip per IEEE 1547) while its siblings run clean, the instinct is to blame that inverter. It is usually innocent. An inverter trips on overvoltage when the voltage AT ITS AC TERMINALS exceeds the trip threshold, and the inverter that trips is almost always the one electrically FARTHEST from the point of common coupling, where conductor voltage rise stacks on top of an already-high utility voltage. The fix is rarely a new inverter - it is conductor sizing, the voltage trip settings, or the utility's service voltage. This tree finds which.

Symptom presentation

Monitoring shows one inverter logging repeated AC over-voltage faults and dropping offline, typically clustered around midday peak production on sunny days, while the other inverters on the same site keep producing. The tripping inverter recovers and reconnects after the mandated reconnect delay, then trips again. Production from that inverter is chronically short because it spends peak hours faulted. The customer sees one "string" or one part of the array underperforming on the bill.

Quick checks

Measure AC voltage at the tripping inverter's terminals UNDER LOAD (midday, full production) and compare to the same measurement at the utility service / point of common coupling. Then:

• Measured voltage at the tripping inverter near or above the inverter's overvoltage trip point (commonly around 264 V on a 240 V nominal, per IEEE 1547 default 1.10 pu) while the service voltage is meaningfully lower: voltage rise on the conductors to that inverter is the cause.
• Utility service voltage itself already high (e.g., 248 to 252 V at the meter with the array off): the utility is delivering high voltage and even small added rise pushes the far inverter over.
• All inverter terminal voltages similar yet only one trips: suspect that inverter's settings or a measurement/wiring issue on its AC side.

Note WHICH inverter trips and its conductor run length back to the interconnection. The longest run almost always trips first.

Isolation tree

Branch A - Conductor voltage rise (the usual cause). PV export current pushes voltage UP along the AC conductors, so the far inverter sees the highest terminal voltage. Confirm: the tripping inverter has the longest and/or smallest-gauge AC run, and its terminal voltage rises with production while the service voltage stays lower. The differential between service voltage and inverter terminal voltage IS the voltage rise. NEC voltage-drop guidance (informational 3 percent branch / 5 percent total) applies in reverse here as voltage rise. Remedy: upsize the AC conductor to that inverter, shorten the run, or move the interconnection point closer.

Branch B - Already-high utility service voltage. If the meter reads high with the array off (above the ANSI C84.1 Range A upper limit, ~252 V on a 240 V nominal service), the utility is the root cause and every inverter is close to the edge - the far one just crosses first. Confirm with the array fully off, measuring at the service over a day. Remedy: file a high-voltage complaint with the utility to adjust the transformer tap; do not mask a genuine utility overvoltage by loosening trip settings beyond IEEE 1547 limits.

Branch C - Trip settings mismatch. The tripping inverter may carry tighter or default overvoltage settings while the others were set to a different (utility-approved) profile, or its IEEE 1547 voltage ride-through profile differs. Confirm by comparing the voltage trip thresholds and grid profile across all inverters. They should match the utility-required profile. Remedy: align all inverters to the correct, utility-approved IEEE 1547 settings - never widen beyond what the utility and standard permit.

Branch D - AC wiring fault on the tripping inverter. A loose terminal, a corroded lug, an undersized or shared neutral, or a high-resistance connection on that inverter's AC side creates localized voltage anomalies that read as overvoltage. Confirm by inspecting and torque-checking the AC terminations and measuring for an abnormal voltage difference across a connection. Remedy: repair the connection.

Branch E - Inverter measurement fault. Last and least likely: the inverter's internal voltage sensing is reading high. Confirm by comparing the inverter's reported AC voltage to a calibrated meter at the same terminals. A consistent offset indicts the inverter. Remedy: RMA the inverter only after the conductor, utility, and settings branches are cleared.

Confirming diagnosis

The decisive data pair is service voltage versus tripping-inverter terminal voltage, measured simultaneously at peak production. A large positive differential (terminal higher than service) confirms conductor voltage rise (Branch A). A high service voltage with the array off confirms a utility problem (Branch B). Matching terminal voltages with only one inverter tripping points to settings or wiring on that unit (Branch C/D). A meter-versus-inverter discrepancy at the same terminals confirms a sensing fault (Branch E). Logging over a full sunny day ties the trips to peak export, the hallmark of voltage rise.

Remediation

For conductor rise, upsize the AC conductor or relocate the interconnection to cut the run and bring rise under the design target. For utility overvoltage, open a service-voltage complaint so the utility corrects the transformer tap; document readings against ANSI C84.1. Align every inverter to the utility-approved IEEE 1547 voltage trip and ride-through profile. Repair any loose or corroded AC termination and torque to spec. RMA the inverter only as a last resort. After remediation, log a full sunny day and confirm the formerly tripping inverter stays connected through peak production with terminal voltage held below the trip threshold.

References

• IEEE 1547 - Standard for Interconnection and Interoperability of Distributed Energy Resources (voltage trip limits, ride-through, overvoltage 1.10 pu default).
• NEC Article 705 - Interconnected Electric Power Production Sources (interconnection point, conductor and overcurrent context).
• NEC Article 690 - Solar Photovoltaic Systems (conductor sizing and inverter output circuit, with NEC 210.19/voltage-drop informational guidance applied as voltage rise).
• ANSI C84.1 - Electric Power Systems and Equipment Voltage Ratings (Range A/B service voltage limits) and UL 1741 inverter interconnection requirements.