- Solar and energy
- Solar inverter
18x86
SolarEdge 18x86 on a solar inverter: PV array isolation fault
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
The inverter found that the PV array is not properly isolated from earth and will not start producing. Note the time and the weather and call your installer. Do not touch panel cables or connectors.
Safety first
Stop and check this first
- Do not disconnect connectors or touch panel cables. SolarEdge warns that an earth fault can leave hazardous voltage on metal parts that are normally earthed.
- Do not reconnect a string with an earth fault. SolarEdge states only a certified PV installer repairs it before it goes back on the inverter.
Safe checks you can perform
- Code and message on the inverter screen
- Time of the fault and weather
- Last isolation value in the monitoring platform
- Locating the leaking string
Leave these tasks to a qualified professional
- Do not attempt this professional task: Inverter Isolation Status diagnostics
- Do not attempt this professional task: Insulation tester test
- Do not attempt this professional task: Module versus optimizer test
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Inverter Isolation Status diagnostics
What they doThe installer opens Diagnostics, Isolation Status on the inverter display or in SetApp to read the isolation resistance and the leak position percentage from DC+.
They must show youthe screen with R Iso and the percentage.
In writingthe string checked and the module identified.
Insulation tester test
What they doWith everything disconnected, they test each home run cable to earth with an insulation tester, then the string, then each optimizer and module pair.
They must show youthe measured values against the limits in the SolarEdge document.
In writingeach reading and the component it belongs to.
Module versus optimizer test
What they doThey disconnect the suspect module from its optimizer, connect only the optimizer to the string and start the inverter to see if the fault remains.
They must show youa start without the error after removing the part.
In writingthe replaced part, its reference and the final pairing.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Code and message on the inverter screen
- Who:
- you, with no tools and without opening anything.
- How:
- look at the inverter screen, or SolarEdge monitoring if you have access, and write down the full code.
- Result that matters:
- that it reads 18x86 Isolation and whether the inverter is producing or stopped.
- If it shows 18x86 Isolation:
- an isolation fault is confirmed; call your installer.
- If it shows another code:
- this page does not apply; look up that exact code.
- Evidence to keep:
- photo of the screen with date and time visible.
Evidence: Appendix A: Errors and Troubleshooting (Single Phase Inverter with HD-Wave Technology Installation Guide, MAN-01-250-1.2)
Time of the fault and weather
- Who:
- you, with no tools.
- How:
- each time you see the error, note the time and whether there was rain, dew or fog.
- Result that matters:
- whether the fault matches early morning moisture or also appears in dry weather.
- If it only appears in damp mornings and then clears:
- SolarEdge says it can return; report it now, as it is easier to locate while active.
- If it also appears in dry weather:
- it points to a permanent leak in the installation.
- Evidence to keep:
- list of dates, times and weather for each occurrence.
Evidence: Isolation Fault Troubleshooting - Application Note, Version 1.4
Last isolation value in the monitoring platform
- Who:
- your installer, with installer access to the SolarEdge platform.
- How:
- read the Last Isolation Value parameter of the inverter in the monitoring platform.
- Result that matters:
- the measured value against the 600 kΩ single phase or 1 MΩ three phase limit.
- If it is below the limit or within 10 % above it:
- SolarEdge says to troubleshoot on site.
- If it is at least 10 % above:
- SolarEdge suggests waiting until the error recurs.
- Evidence to keep:
- screenshot of the value with its date.
Evidence: Isolation Fault Troubleshooting - Application Note, Version 1.4
Locating the leaking string
- Who:
- qualified PV installer.
- How:
- with the inverter off and the DC voltage at a safe level, connect one string at a time and check whether the error returns.
- Result that matters:
- which string triggers the fault.
- If the error appears with one string only:
- that string holds the leak.
- If it appears with several:
- more than one string is faulty and each is checked separately.
- Evidence to keep:
- report listing the strings tested and the result for each.
Work on the PV DC side with hazardous voltage and arc risk when disconnecting. With an earth fault, normally earthed metal parts can carry voltage. Qualified personnel only.
Evidence: Appendix A: Errors and Troubleshooting (Single Phase Inverter with HD-Wave Technology Installation Guide, MAN-01-250-1.2) · Isolation Fault Troubleshooting - Application Note, Version 1.4
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Solar and energy
- Brand
- SolarEdge
- Product type
- Solar inverter
Known code variants
- SolarEdge 18x86
- SolarEdge error 134
- SolarEdge error 18x86 Isolation
- SolarEdge fallo de aislamiento
- SolarEdge isolation fault
What it means
SolarEdge checks the resistance between the DC conductors and earth every time the inverter starts. If the total falls below 600 kΩ on single phase or 1 MΩ on three phase units, it shows Isolation (error 134 on firmware 3.18xx and earlier). The leak can sit in a module with defective insulation, unshielded wiring, a power optimizer or an internal inverter fault. The code confirms a leak, not where it is in the string.
Warnings and stop conditions
- Highsource verified
Do not disconnect connectors or touch panel cables. SolarEdge warns that an earth fault can leave hazardous voltage on metal parts that are normally earthed.
Evidence: Isolation Fault Troubleshooting - Application Note, Version 1.4
- Mediumsource verified
Do not reconnect a string with an earth fault. SolarEdge states only a certified PV installer repairs it before it goes back on the inverter.
Evidence: Appendix A: Errors and Troubleshooting (Single Phase Inverter with HD-Wave Technology Installation Guide, MAN-01-250-1.2)
Symptoms and causes
Probable causes · in order
- PV module with defective insulationPossible
The leak is inside the panel itself. It shows when the technician disconnects the module from its optimizer and the fault clears on the next start.
Evidence: Isolation Fault Troubleshooting - Application Note, Version 1.4
- Damaged DC wires or connectorsPossible
Unshielded wires or damaged connectors between an optimizer and its module or between neighbouring optimizers. SolarEdge asks to check these first in the area the diagnostics point to.
Evidence: Isolation Fault Troubleshooting - Application Note, Version 1.4
- Faulty power optimizerPossible
The leak follows the optimizer: if the technician connects it to the string without its module and the fault returns, the optimizer is the source.
Evidence: Isolation Fault Troubleshooting - Application Note, Version 1.4
- Morning moisturePossible
SolarEdge warns the fault can disappear and come back shortly after, especially when morning moisture causes it. Clearing on its own does not remove the leak.
Evidence: Isolation Fault Troubleshooting - Application Note, Version 1.4
- Internal inverter faultPossible
SolarEdge lists it among the possible sources of leakage to earth. It is only considered once the strings and their components have tested correctly.
Evidence: Isolation Fault Troubleshooting - Application Note, Version 1.4
Virtual technician
Does 18x86 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
SolarEdge Technologies · manual
- 2
Isolation Fault Troubleshooting - Application Note, Version 1.4
SolarEdge Technologies · 2019 · official_doc
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