Ground fault alarms can be caused by a range of site-side issues, including AC wiring faults, incorrect polarity, poor earthing, abnormal grid supply conditions or high earth electrode resistance on TT systems. In some cases, the issue may also relate to the inverter’s internal sampling circuit, but this should only be considered once the external installation checks have been completed.
The following guidance is intended to help installers carry out a structured ground fault investigation before escalating the issue to Fox ESS Technical Support.
1. Fully Power Cycle the System
Shut the system down completely:
- AC isolator OFF
- Battery isolator OFF
- PV isolator OFF
Leave the system powered down for several minutes, then restart the system in the correct sequence.
2. Check AC Wiring
Confirm the AC connection wiring is correct:
- L to N
- L to E
- N to E
Inspect for:
- Loose terminations
- Damaged conductors
- Signs of overheating
3. Verify Grid Supply Voltages
Disconnect the grid-side L, N, and PE connections from the inverter and measure:
- N to PE
- Expected reading: approximately 0V
- L to PE
- Expected reading: approximately 220/230V
If readings are abnormal, investigate the incoming supply and earthing arrangement before reconnecting.
3. Confirm Inverter Output Connections
Check that the inverter output terminals are correctly fitted:
- L connected to L
- N connected to N
Confirm conductors are fully terminated and secure on the circuit board terminals.
5. Measure Voltage Between N and PE
Measure the voltage between Neutral and Earth.
If reading is around 110V:
- Suspect an abnormal or missing PE connection.
- Recheck all earthing and PE wiring connections.
- If reading is around 220/230V:
- Suspect L and N are reversed.
- Recheck polarity of the AC connections.
- If reading is below 60V:
- Wiring is likely correct.
- Possible inverter sampling circuit fault.
- TT System Checks – Earth Electrode Resistance
For TT systems, confirm the earth electrode resistance is within acceptable limits.
Recommended Checks
- Measure the resistance of the earth electrode using suitable test equipment.
- Inspect all earthing connections for corrosion, damage, or loose terminations.
Guidance
High earth electrode resistance can cause ground fault alarms and unstable inverter operation.
If resistance readings are high:
- Inspect the rod installation
- Check clamps and connections
- Consider installing additional rods or improving the earthing arrangement
As a general guide, I would like to see the earth electrode resistance below 100 ohms for stable inverter operation and reliable fault detection.
Additional Notes
Ensure firmware is up to date before further fault finding. If all checks pass and the fault remains, gather the following before escalation:
- Fault code
- Photos of wiring
- Voltage readings
- Earth resistance readings
