Inverex Nitrox F08 — GFDI Relay Failure (Earth-Fault Protection)

⚠ DANGER — this fault involves lethal voltage. Do not attempt a DIY fix. Call a qualified technician.

What it means: F08 is a failure of the earth-fault protection itself, not a battery fault. The GFDI is the ground-fault detection and interruption relay — the component whose entire job is to notice current leaking to earth and shut the system down. In Inverex's hybrid fault table, Chart 7-1, this row reads "GFDI Relay_Failure", and its only remedies concern the backup-load neutral-to-ground connection and contacting support. The Nitrox three-phase string manual states the same family plainly in Table 10.1 as F08 "GFDI grounding touch failure", alongside F04 "Ground fault GFDI" and F07 "GFDI blown fuse". Read it carefully: the inverter is not telling you it has found an earth fault. It is telling you that the device which would find one has declared itself unreliable.

Why does Inverex show F08?

• Failure of the internal ground-fault detection relay or its drive circuit — an internal component fault
• On split-phase (120/240 Vac) or three-phase (120/208 Vac) systems, the backup-load port N line not connected to ground, which is the manual's own first remedy
• An earth-referencing problem on the backup or load side that leaves the relay unable to complete its self-test
• Degraded or missing system earthing, so the relay's reference is not what it expects

The Pakistan factor

This code deserves to be taken more seriously in Pakistan than almost anywhere else, because it removes a protection that local installations lean on harder than they should. Earthing is the routine weak point here — a nominal earth rod that has dried out, was never properly bonded, or was omitted entirely is common enough that the ground-fault relay is doing real work on many systems. F08 says that relay is out of action, and it is precisely the combination of no working earth-fault detection with poor site earthing that lets an insulation failure energise an array frame or roof structure instead of tripping harmlessly. It is also frequently misdiagnosed: F08 is widely repeated in the local market — and in an earlier version of this page — as a battery over-voltage code, which sends the owner to the battery-type setting and the charge profile while the actual fault sits in the earth-fault protection, untouched. Neither Inverex manual supports a battery reading of F08. If you are chasing a genuine battery or charging complaint, this is not the code for it.

How to fix it

1. Stop, and treat this as the end of the DIY path. The system's earth-fault protection has reported itself faulty, and an inverter that cannot be trusted to detect a ground fault should not be left running while you experiment with it.
2. Leave the system shut down using the external AC and DC isolators your installer fitted — AC off first, then the DC/PV isolator — and leave it off until it has been looked at. Do not open the inverter and do not open the backup-load distribution board.
3. Do not clear F08 by restarting over and over. Chart 7-1 offers no restart-and-retry remedy for this row, unlike most other codes in the same table, and that absence is the message.
4. Do not disable, bypass or work around the earth-fault protection to get the power back on. It is the protection that stands between a leakage fault and the metalwork people touch.
5. The manual's one wiring remedy — connecting the backup-load port N line to ground — applies to split-phase and three-phase configurations and is installer work in any case. On a normal Pakistani single-phase 230 V house this remedy usually does not apply at all, which leaves the manual's second instruction as the real one.
6. Call your installer, and escalate to an Inverex service centre with the serial number, install date and a photograph of the fault screen. The manual's own remaining instruction for F08 is simply to contact them for help.