Solis PV ISO-PRO01 / 02 (Alarm 1033) — PV Insulation Fault

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

What it means: The insulation between your solar array's DC wiring and earth has broken down. Solis states it plainly — PV ISO-PRO means the resistance on the DC side is too low — and logs it as alarm 1033. The LCD shows it with a space, as PV ISO-PRO01 or PV ISO-PRO02, and the two numbers tell you which conductor is at fault: 01 means the negative conductor is finding a path to ground, 02 means the positive conductor is. This is a ground fault on a circuit that is live whenever there is daylight, and Solis is unambiguous that the ground fault must be resolved before the system is energised again.

Why does Solis show PV-ISO-PRO01?

• Water in MC4 connectors, junction boxes or DC conduit after rain — the most common trigger by a wide margin
• DC cable insulation chafed through against a sharp edge on the mounting rail, or crushed under a clamp
• Rodent damage to DC cable, usually where it runs across a roof or through an unsealed conduit
• Field-crimped or mismatched MC4 connectors that were never properly weather-sealed
• Degraded module backsheets on older or low-quality panels, which show low insulation resistance once humidity rises
• Cable jackets broken down by years of direct UV exposure where the run was never put in conduit

The Pakistan factor

Two Pakistani realities turn this from a shutdown into a hazard. The first is the monsoon. Across Punjab and Sindh, July and August drive water into every unsealed MC4 joint, junction box and length of conduit that was terminated without a proper gland, and a large share of Solis insulation faults here appear in the first week of heavy rain and are written off as "it comes back when it dries". It does come back — and the leakage path that opened is still there. The second and more serious one is earthing. Proper array earthing is routinely skipped or reduced to a token rod on Pakistani residential installs, and an earth pit that was marginal when it was dug is often useless after a dry summer. On a system like that, an insulation fault energises the aluminium mounting structure and the roof-level conduit with no low-resistance path to clear it, and this alarm code may be the only warning anyone gets before someone leans on the frame. If your installation has no verified array earth, treat PV ISO-PRO as a keep-everyone-off-the-roof event and get an electrician there the same day.

How to fix it

1. Read the code exactly and write down which variant it is — 01 or 02 — along with the time of day and the weather. Whether it appears only on damp mornings and clears once the roof dries, or stays all day in dry weather, tells your installer roughly where to look. That is genuinely useful and it costs you nothing.
2. Do not touch, unplug, dry out or "reseat" any DC connector, and do not go up to inspect the array. Your strings sit at hundreds of volts DC whenever there is light on the panels. There is no off switch on a solar panel, DC arcs do not self-extinguish the way AC ones do, and this alarm is telling you there is already a fault path to earth somewhere in that circuit.
3. Do not operate the DC isolator to "reset" it either. The Solis manual warns specifically that switching the DC switches while current is flowing damages the inverter, and that damage from that kind of wrong operation is not covered by the warranty.
4. Keep people off the roof and away from the array frame, the mounting rails and any metal conduit until an installer has cleared it. This matters most on installations with weak earthing, where the first sign that the structure has gone live may be someone touching it.
5. Do not clear the alarm and carry on. Restarting an inverter that is reporting an insulation fault simply re-energises a known ground fault.
6. Call your installer and have them do the test properly. Solis's procedure is to isolate the inverter and measure resistance from DC positive to ground and DC negative to ground, then reconnect the strings one at a time to find which string is responsible, then check voltages from PV+ to ground and PV- to ground across every string. That needs an insulation tester, the right PPE and someone who knows how to work on a live DC array.
7. Ask them to check the array's earthing and bonding at the same time, not just the fault itself. A ground fault on a properly earthed array is a shutdown; the same fault on a badly earthed one is a live structure.
8. If every string tests good and the alarm still latches, it is the inverter's own insulation measurement and it goes to the Solis service centre. Nobody should be opening the inverter — the DC capacitors inside stay charged after shutdown.