Home › Fox ESS › DCI Fault
Stop, call a pro

Fox ESS DCI Fault

Updated June 2026 · Reviewed for technical accuracy · ~2 min read
This is a safety and grid-code fault, not a routine glitch. Your Fox ESS measured too much DC current flowing into the AC output and shut down on purpose to protect the grid. You can attempt one controlled power cycle, but if it returns, stop resetting and call a qualified installer. Never open live DC connectors or AC terminals yourself.

DCI Fault means the inverter's certified monitoring has detected an unacceptable DC component (DC offset) being injected into the AC output. Grid codes such as G98 and G99 set a strict limit on this DC current for safety, and exceeding it usually points to an internal fault inside the inverter, so it stops exporting until the problem is cleared.

What usually causes it

  • An internal AC-coupling or power-stage fault. This is the most common cause. The inverter's own circuitry is letting a small DC current leak through to the AC side beyond the regulatory limit.
  • A loose or poor earth (ground) connection. A compromised earthing path can disturb the inverter's DC injection measurement.
  • A loose AC terminal or connection. Poor contact on the AC output side can upset the reading and trigger the trip.
  • A transient sensor glitch. Rarely, a one-off measurement upset clears with a single power cycle and does not return.

How to handle it safely

  1. Do one controlled power cycle. Turn off the inverter, then switch off the PV (DC) isolator, the AC isolator and the battery isolator. Leave everything off for about 15 minutes so the unit fully discharges.
  2. Reconnect in order and restart. Switch the battery, grid (AC) and PV (DC) back on, then power the inverter up. Watch whether the DCI Fault clears and stays clear.
  3. Have the earthing and AC connections checked. Confirming the earth and AC terminals are sound is electrical work, so leave any inspection or tightening to a licensed installer.
  4. If it recurs, stop resetting. A repeating DCI Fault indicates an internal AC-coupling problem in the inverter. Repeated resets will not fix it. Contact your installer and quote the exact fault.
When to call a professional. If DCI Fault comes back after a single power cycle, the inverter is telling you it can no longer guarantee a clean AC output, which is a real grid-safety issue. Do not keep restarting it and do not attempt any work behind the covers. Book your Fox ESS installer or a qualified solar electrician to diagnose the internal fault, as the unit may need a warranty repair or replacement.

Related Fox ESS codes

Res Cur Fault ISO Fault Relay Close Fault

FAQ

Can I just keep resetting the inverter to make DCI Fault go away?

No. You can try one controlled power cycle in case it was a transient glitch. If the fault returns, repeated resets will not fix it and could let the inverter export an unsafe AC output. A recurring DCI Fault points to an internal problem that needs an installer.

Is a DCI Fault dangerous to my house or the grid?

The inverter shuts down precisely so it is not dangerous. Too much DC current in the AC output can affect grid equipment and trip protection devices, which is why grid codes limit it. By stopping, your Fox ESS is doing its job. The risk is in ignoring it or forcing it to run, so leave it off and get it checked.

Helpful guides

Error codes explained How to safely restart your inverter

Sources

  • Fox ESS H1/AC1 inverter user manual and FoxCloud alarm list (DCI Fault = DC injection in the AC output exceeds the permitted limit).
  • Fox ESS installer guidance on grid-code (G98/G99) compliance, earthing and AC connection checks for DC injection faults.
⚠️ Safety disclaimer. Solar inverters carry lethal DC and AC voltage even when "off". This guide covers a controlled power cycle using the external isolators only. Any AC wiring, earthing, RCD or internal work must be done by a licensed installer or electrician.