Inverex Nitrox F20 — DC Over-Current
What it means: A hardware protection inside the inverter has detected excessive current on the DC side, meaning the PV input or the battery input. Inverex's hybrid fault table lists F20 as "DC over current fault of the hardware" with the cause "DC side over current fault", and it names one everyday scenario explicitly — an inverter running off-grid that is started into a large load may report F20. The identical description appears in the Nitrox three-phase string inverter manual, so the meaning is stable across the Nitrox range.
Why does Inverex show F20?
- A large inrush load such as a pump, deep freezer or AC compressor starting while off-grid, which the manual calls out by name
- A PV or battery wiring problem, which is the manual's first check
- Undersized battery cable, or a loose or hand-crimped battery terminal
- A string wiring fault or a mis-wired parallel PV connection
- A genuine hardware fault in the DC stage
The Pakistan factor
Water pumps are the usual trigger in Pakistan. A 1 hp or 1.5 hp motor drawing six to eight times its running current for a second or two at start is exactly the inrush the manual is describing, and it lands hardest during load shedding, when the inverter is off-grid and has no mains to lean on. Cable is the second local cause — battery leads cut short and thin to save money at install, or a lug crimped by hand onto an aluminium conductor, give a connection that behaves perfectly at low load and fails at inrush. Both are worth ruling out before anyone concludes the inverter itself is faulty and pays for a board.
How to fix it
- Note exactly what was switching on at the moment it tripped. If F20 appears the instant a pump, freezer or AC compressor starts while the system is off-grid, you already have your answer — the manual describes that scenario directly.
- Reduce the load connected to the inverter and try again, which is the manual's advice. Start large motors one at a time rather than together, and avoid starting one at the moment the system transfers to battery.
- Power-cycle in the order the manual specifies — turn OFF the DC switch and the AC switch, wait a full minute, then turn the DC and AC switches back on. Do not skip the wait; it is there to let the DC bus discharge.
- If it trips with only modest load, or trips again after a correct power-cycle, stop. Checking the PV and battery connections means working on live DC wiring and inside terminal compartments, and that is installer work rather than homeowner work.
- Do not open the inverter, do not disconnect PV strings or battery cables to test, and do not bypass or hold in the DC breaker. The array is live in daylight and a battery bank cannot be switched off the way a mains circuit can.
- Persistent F20 under normal load is a hardware fault. Escalate to your installer or an Inverex service centre with the serial number, install date and a photograph of the fault screen, which is the escalation the manual asks for.