Critical What does this mean?
A safety-rated fault — there may be a risk of electric shock, fire, or equipment damage. Do not try to fix this yourself. Call a qualified electrician.
SolarEdge Inverter 18X86 Isolation Fault — Why It Trips and What to Do
18X86 is a PV isolation fault: your SolarEdge inverter has detected that the solar array is not properly isolated from earth ground, so it refuses to start producing power. The inverter checks the array’s insulation every time it starts, and it will keep this fault latched until the problem is fixed. The installation guide is explicit — the faulty string must be repaired by a qualified, certified installer before it is reconnected.
What should I do first?
Two quick questions — we'll point you to the right starting point.
Is this code still showing on your inverter's display?
Is your system producing power right now?
What this code means
Isolation, in this context, means electrical separation: the DC conductors in your solar array must be insulated from earth ground, with no current path between them and the panel frames, mounting rails, or roof. Every time your inverter starts up, it measures the array’s insulation resistance to verify that separation. If the reading is too low, it concludes current could leak to earth — a shock and fire risk — and raises 18X86 instead of starting.
The guide’s own description is plain: ‘PV Isolation fault. The inverter has detected the PV solar array is not properly isolated from ground earth.’
On single-phase inverters running older CPU firmware (v3.18xx and earlier), this same fault appears on the LCD as the number 134. Newer firmware (v3.19xx and later) displays 18X86.
An isolation fault is not a glitch and not a setting you can change. It means something in the array — a panel, a cable, a connector, or an optimizer — has developed a path to earth. Because the inverter re-tests insulation at every start, the fault will simply return after any restart until the faulty part is found and repaired.
What is this downtime costing you?
Rough estimate while your system isn't producing. Adjust the numbers to match your setup.
≈ – kWh of lost production per day.
Estimate only — assumes ~80% real-world output vs. nameplate. Actual losses depend on weather, shading, panel direction, and your tariff.
Common causes
- ['A damaged solar panel — cracked glass, a punctured or delaminated backsheet — providing a leakage path from the cells to the frame and earth.', 'Damaged DC cabling: chewed, abraded, pinched, or UV-degraded cable insulation touching the mounting structure, especially after storms or roof work.', 'Water ingress in a connector, junction box, or cable run creating a conductive path to earth — isolation faults often appear or worsen in wet weather.', 'A failing power optimizer with compromised internal insulation leaking to its grounded enclosure.', 'Deteriorated connectors or junction boxes where corrosion or contamination has bridged insulation — the guide directs you to check the PV installation for isolation problems and ground faults.']
Safe steps to try
Work top to bottom, ticking off each step as you complete it. 0 of 1 done.
Is your inverter still under warranty?
Before paying for a repair, check — your installer may fix this free.
Based on typical standard warranty terms — always confirm with your warranty card or installer paperwork, as terms vary by model, region, and purchase date.
When to call an electrician
Immediately. 18X86 is one of the faults where the guide removes all ambiguity: ‘The faulty string must be fixed by a qualified (certified) installer before it is reconnected to the inverter.’ Do not attempt to identify the bad string yourself — the manual’s string-by-string isolation procedure involves working around live DC equipment and is technician-only.
Your installer’s visit will follow the guide’s direction: check the PV installation for isolation problems and ground faults, locate the leaking string or component with insulation measurements, and repair or replace the faulty panel, cable, connector, or optimizer. The system stays off until that work is done.
If you smell burning, see smoke or scorch marks, or hear arcing near the array or inverter, switch the system off using the documented shutdown sequence and call a professional immediately — do not wait for a scheduled visit.
Frequently asked questions
Will my system produce any power with 18X86?
No. The inverter refuses to start while the isolation fault is present, and because it re-tests insulation at every start, the fault returns after any restart until the underlying problem is repaired.
Can I find the faulty string myself by disconnecting things?
No. The string-by-string procedure in the guide is explicitly for qualified technicians — it involves working around DC equipment that can be live and dangerous in daylight. Leave the detective work to your installer.
Is an isolation fault dangerous?
It can be. Current leaking to earth is a shock risk, and damaged insulation is also a fire risk. The inverter stopped precisely to contain that risk — treat the array as hazardous until a professional clears the fault.
My LCD shows 134, not 18X86. Is that the same thing?
Yes. 134 is the number this fault displays on single-phase inverters with CPU firmware v3.18xx and earlier; 18X86 is the code on v3.19xx and later. Same fault, same fix.
Could rain have caused it?
Possibly — moisture getting into a damaged connector, cable, or junction box is a classic isolation-fault trigger, and the fault often appears or worsens in wet weather. Tell your installer when it started; the timing helps them find it.
Need a professional?
This fault is a safety risk — do not attempt to fix it yourself. Contact a qualified solar electrician in your area.
Sources: meaning and troubleshooting verified against the manufacturer's documentation — SolarEdge Single Phase Inverter with HD-Wave Technology Installation Guide MAN-01-00250-1.1 (Europe & APAC), Version 1.1 — Appendix A: Errors and Troubleshooting, Error Codes table (18x86 Isolation: ‘PV Isolation fault. The inverter has detected the PV solar array is not properly isolated from ground earth’); cross-confirmed in the North America edition MAN-01-00306-1.1, Appendix A, which maps CPU v3.18xx LCD number 134 → 18x86 Isolation.