Deye SUN Hybrid F24 — DC Insulation Failure (PV Isolation Resistance Too Low)
⚠ DANGER — this fault involves lethal voltage. Do not attempt a DIY fix. Call a qualified technician.
What it means: The inverter measured the electrical insulation between the DC (solar panel) side and earth and found it too low. Deye's manuals give the description as "DC insulation impedance failure" with the plain-English line "PV isolation resistance is too low". In practice this means current has a path from your array to earth that it should not have — through wet or damaged cable insulation, a chafed conductor, water in a connector or junction box, or a damaged module. The inverter has stopped rather than energise an array it can no longer isolate.
Why does Deye show F24?
- Water ingress into a DC connector, junction box or conduit — the classic monsoon and post-wash failure
- Damaged, chafed or rodent-bitten DC cable insulation, especially where cable crosses a sharp roof edge or unbushed conduit entry
- A cracked or delaminated module allowing moisture to the cells
- The inverter's PE (earth) cable not connected to ground, or connected to an ineffective earth — Deye's manual makes checking this step 2
- Loose or badly made PV-to-inverter connections (Deye's manual step 1)
The Pakistan factor
Pakistan produces this fault in three specific ways. First, monsoon and pre-monsoon dust storms drive water into connectors that were crimped by hand and never properly sealed — F24 that starts in July and vanishes in October is nearly always a wet connector. Second, panel washing, which is unavoidable on dusty rooftops here, pushes water into the same places; wash in the evening with the DC isolator open, never onto hot glass at midday. Third, and most serious, earthing: Deye's own step 2 is "check whether the PE cable of inverter is connected to ground", and a large share of Pakistani rooftop installs have either no dedicated earth electrode or a rusted rod with high resistance. On a system with poor earthing, F24 is not a nuisance code — it means the one protective measure that would carry a fault current away is also missing. Treat it as an emergency and leave the system off.
How to fix it
- Stop. This is one of the codes that means leave it off. F24 reports the exact condition that precedes a shock or a roof fire — a live DC array with a leakage path to earth. Do not clear it and carry on.
- Switch the system off using the external isolators your installer fitted, AC first and then the DC/PV isolator, and leave it off. Do not open the inverter, do not open a DC junction box, and do not unplug or "reseat" a DC connector — array DC stays live in daylight whatever the inverter is doing, and it does not trip like AC.
- Keep people and animals away from array framing, mounting rails, conduit and any metal the DC cabling runs near until it has been checked. If anyone has felt a tingle from metal work, say so when you call.
- Note the weather. F24 that appears after rain or after the panels are washed, and clears when everything dries, is a real fault with an intermittent presentation, not a false alarm. Tell the installer the pattern — it is the single most useful thing you can give him.
- Qualified installer only, from here. Deye's own steps are to verify the PV-to-inverter connections are firm and correct and to verify the inverter's PE cable is connected to ground. Both are done with the array isolated and with an insulation-resistance tester, which is not a multimeter and not a homeowner tool.
- If the installer confirms insulation resistance is low with the array isolated and healthy wiring, the fault is in the array or the inverter's measurement circuit and goes to the manufacturer's service route. Deye's manual ends at "seek help from us, if can not go back to normal state".