Abnormal neutral-to-ground voltage

On CPS three-phase inverters this condition shows up as fault code Protect0790. The manual calls it a zero-to-ground or N2PE voltage anomaly, and it is also flagged as a bit in the Modbus fault register. The manufacturer's first step is to check that the grid connection is good. If the alarm comes back after that, contact after-sales service. The inverter's neutral connection only gives it a measurement reference close to ground potential. A loose neutral wire can make the inverter read the grid voltage wrongly. On site, measure neutral to ground on the AC side along with line to line, line to neutral and line to ground. Only do this with AC on if it is safe. Do not rely on the meter alone: a zero N-G reading can happen by chance. Look to confirm that the neutral-to-ground bond is actually installed. A missing neutral-to-ground bonding jumper at the service entrance or transformer is an installation error. It leaves the system ungrounded, which can push line-to-ground voltages abnormally high and wear out surge protectors over time. Surge protectors that have N-G monitoring blink a red LED and sound an alarm when N-G voltage is excessive, and this needs immediate attention. Do not fit a neutral-to-ground jumper inside the inverter while the neutral conductor is connected, because it can cause damage.

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• sentence 6: support check: partial - Missing jumper being an installation error, ungrounded system and high L-G voltages leading to SPD failure are stated, but 'service entrance or transformer' location is only partly covered and 'wear out over time' is approximated by 'eventually' chasing until failure. -->