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Self-clears

Fox ESS 10min Volt Fault

Updated June 2026 · Reviewed for technical accuracy · ~2 min read

10min Volt Fault (often shown as Error 28) means the rolling 10-minute average grid voltage has climbed above the upper limit. Unlike an instant spike, this is a sustained high-voltage condition averaged over 10 minutes, frequently caused by high PV export in strong sun on a weak local network. The inverter disconnects and reconnects automatically once the average falls back into range, so a one-off is normal.

What usually causes it

  • Strong PV export on a sunny day. When your system pushes a lot of power out, it can lift the voltage at your connection point, and a weak local network shows this most.
  • A weak or long supply network. Homes far from the local transformer, or on rural feeders, see voltage rise more easily under export.
  • Grid voltage already running high. If the incoming supply sits near the top of the allowed band, even modest export tips the 10-minute average over.
  • It only appears in bright daylight. That timing points to your own export lifting local voltage rather than an inverter fault.

How to handle it safely

  1. Note when it happens. If it shows only in strong midday sun and clears later, that is the classic export-driven pattern, not a hardware problem.
  2. Let it self-clear. The inverter drops off and reconnects on its own once the 10-minute average voltage returns to range. A single daily event needs no action.
  3. Watch for a daily pattern. If it repeats every bright day, log the dates and times so your installer or supply network has clear evidence.
  4. If it persists daily, ask your DNO (the local supply network operator) to check the supply voltage, or have your installer review the export and voltage protection settings.

Quick decision flowchart

10min Volt Fault appears
↓ note the time of day
✅ Only in bright sun, then clears → normal export-driven event, the inverter reconnects on its own.
❌ Every day or stays for long spells → log it and request a DNO supply check or installer settings review.
↓
If it keeps happening daily, the local supply voltage likely needs adjusting, not your inverter.

Related Fox ESS codes

Grid Volt Fault Grid Freq Fault Grid Lost Fault

FAQ

Why does 10min Volt Fault only show on sunny days?

In strong sun your system exports the most power, and pushing power out raises the voltage at your connection point. On a weak local network that can lift the rolling 10-minute average above the upper limit. The inverter then waits and reconnects once the average drops back, which is why it clears as the sun moves on.

Do I need to do anything to clear it?

For a one-off, no. The Fox ESS disconnects and reconnects by itself when the 10-minute average voltage returns to range. You only need to act if it appears every bright day, in which case log the times and ask your DNO to check the supply voltage or have your installer review the export and voltage settings.

Helpful guides

Error codes explained How to safely restart your inverter Inverter not turning on

Sources

  • Fox ESS H1/AC1 inverter user manual and FoxCloud alarm list (Error 28, 10min Volt Fault = 10-minute average grid voltage above the upper limit).
  • Fox ESS installer guidance on grid voltage protection and export limit settings, and DNO supply voltage checks for persistent over-voltage.
⚠️ Safety disclaimer. Solar inverters carry lethal DC and AC voltage even when "off". This guide covers observing the fault and logging when it happens only. Any change to voltage protection settings, AC wiring or supply work must be done by a licensed installer, electrician or your supply network operator.