HOW-TO GUIDE
How to Diagnose DC Arc Fault Warnings in a Solar Inverter
By the OhmSavvy Research Team ·
DC arcs are a fire risk: do not touch the array or its wiring
- Solar panels generate voltage whenever light reaches them, and a residential string can be several hundred volts DC. Switching off the inverter or the AC breaker does not make the roof wiring dead.
- Unlike AC, a DC arc has no zero crossing to put it out, so a connector pulled apart under load can draw a sustained arc. Never unplug PV connectors, and never open the inverter's DC compartment, combiner boxes, junction boxes or rapid-shutdown devices.
- Smoke, a burning smell, sparking or scorch marks on the roof, conduit or inverter: get everyone out, call 911 and tell the dispatcher the building has solar panels.
What the arc fault code means
The US National Electrical Code requires DC arc-fault protection for PV systems on or in buildings that operate at 80 V DC or more, which covers almost every string-inverter installation. The protection is usually built into the inverter. It watches the DC input current for the irregular, broadband high-frequency noise that an arc produces, and when the signature crosses its threshold it stops power conversion. With no load drawing current, a series arc loses the energy that keeps it burning.
Most inverters then latch the fault: the display, LED pattern or monitoring app shows an arc fault code, often with the input or MPPT channel it was seen on, and production stays off until someone resets it. European installations follow different rules; dedicated arc detection is not required everywhere in the EU, but many inverters sold there include it and test to the IEC 63027 standard for PV arc detection. Where your inverter has it, the behavior is the same.
Note that the inverter only knows the arc is somewhere on that input. It can't say which connector or which module, so the code starts the search rather than ending it. Don't confuse it with the AC arc-fault breakers in your house panel, which protect branch circuits and trip for different reasons, as covered in why an AFCI breaker keeps tripping.
Symptoms and likely causes
| Symptom | Likely cause | What to check | Who should fix it |
|---|---|---|---|
| Arc fault returns after every reset, same input | Real series arc at a connector, splice or terminal | Which MPPT input the app names; production history | Installer |
| Trips in the morning or after rain | Moisture in a connector or junction box; damaged insulation | Weather and time stamps on each event | Installer |
| Trips on hot afternoons | Thermal expansion opening a loose joint | Event times vs temperature and peak output | Installer |
| Fault after roof work, storm or pest activity | Crushed, chewed or abraded cable, displaced connector | Look from the ground for hanging wires or debris | Installer; roofer only with installer present |
| Occasional trip, no pattern, nothing found | Nuisance detection from electrical noise | Firmware version; nearby new equipment | Installer with inverter maker |
| Arc code plus burn smell or marks | Arc has already damaged equipment | Nothing: evacuate if needed, call 911 | Fire service, then installer |
Connectors are the classic weak point. A PV plug that wasn't pushed fully home, was crimped poorly, or was mated with a different brand of "compatible" connector can develop resistance, heat and eventually a gap. Module junction boxes, field splices and terminals inside combiners and the inverter itself are the other usual sites.
Real arcs vs false trips
Arc detectors work by recognizing noise, and other things make noise. Long DC cable runs can pick up interference, some detectors react to switching from nearby inverters or communications equipment, and early firmware on some models was more sensitive than later releases. A single trip that never repeats after a reset, with no weather link and nothing visible, leans toward a nuisance event. Even then, record it, because a slowly degrading connector can trip occasionally for months before it fails outright.
A pattern is far more telling than one event. Trips that cluster at the same time of day, the same weather, or the same input channel point to a physical cause that changes with temperature or moisture. A trip after a hailstorm, a re-roof or a squirrel problem points squarely at damaged wiring. Treat every repeat as real until a qualified person has proved otherwise.
1What the owner can do
- Record the event. Photograph the inverter display or save a screenshot of the app: fault code, date, time, input channel and how much the system was producing just before the trip. Note the weather.
- Check the history. Most monitoring apps keep an event log. A list of previous arc faults, with timestamps, is the most useful thing you can hand the installer.
- Look, from a safe distance. From the ground, with binoculars if needed, check for cables hanging under the array, debris, nesting material, or dark marks. At the inverter, look for discoloration, melted plastic or a smell, without opening any cover. Don't climb onto the roof.
- Reset once, by the manual. If nothing looks or smells wrong, follow the manufacturer's reset procedure, which may be a button, a menu step or an AC/DC switch sequence on the outside of the unit. If the fault returns, leave the system off and stop resetting.
- Contact the installer. Send the photos and event log, and ask whether the inverter maker's support team should review the data remotely. Many inverters upload detailed logs the installer can read before visiting.
2What the installer tests
A qualified technician shuts the system down by the documented procedure, then works through the string methodically with tools rated for PV voltages. Typical steps include comparing each string's current with a DC clamp while the system runs, checking open-circuit voltage at isolated points, testing insulation resistance from the conductors to ground, and scanning connectors and junction boxes with a thermal camera, since a high-resistance joint runs hotter than its neighbors. Many also run an IV-curve tracer, which plots each string's current against voltage and reveals resistance, mismatch and damaged modules that a single number can hide.
These checks involve energized DC conductors at voltages that can exceed what general-purpose meters are rated for, so the meter needs a CAT rating and DC voltage range above the system's maximum. The repair itself is usually replacing a connector pair with matching parts from one manufacturer, re-making a crimp with the specified tool, or replacing a damaged cable or module. For background on reading a single panel safely, see how to test a solar panel with a multimeter.
Why an arc fault needs a professional inspection
PV-rated meters installers use for string checks
CAT III 1500V solar clamp: 1500 V DC, DC current to 999.9 A, DC power and a polarity alarm.
Budget AC/DC clamp to 1000 A with 1000 V DC, CAT III 1000V. For smaller residential strings.
Hands-on Tested. CAT III 1000V / CAT IV 600V True RMS meter for open-circuit voltage checks.
As an Amazon Associate I earn from qualifying purchases. Prices and availability are shown on Amazon.
Frequently asked questions
Can I turn off arc-fault detection to stop the nuisance trips?
No. Arc-fault protection on rooftop PV is a code requirement in the US for most systems, and it is the main safeguard against a DC arc starting a roof fire. Disabling it can also void the inverter warranty and the installation's approval. If the trips are false, the installer and inverter maker can investigate the cause, update firmware or adjust settings within what the manufacturer permits.
How many times can I reset the inverter after an arc fault?
Follow the inverter manual, and as a rule reset once. If the fault comes back, the inverter is telling you the condition is still there, and each restart re-energizes whatever arced. Leave the system off and call the installer. Some inverters retry on their own a limited number of times before locking out; that lockout is deliberate.
Do microinverter systems get DC arc faults?
Much less often. With microinverters, each panel's DC wiring is a short run at module voltage, and the roof wiring carries AC. Systems with a high-voltage DC string, including those with power optimizers, are the ones where DC arc detection matters most. Your installation paperwork or the inverter label shows which type you have.
Is the system safe to leave in daylight while I wait for the installer?
Shutting the inverter down stops the current that sustains an arc, which is why AFCI works. The panels and DC wiring are still energized whenever light falls on them, so keep people and pets away from any damaged cable, and if your system has a rapid-shutdown initiator, its label explains how to use it. Any smoke, smell or sparking means 911.
Does an arc fault mean my solar panels need replacing?
Usually not. Most arcs happen at a connector, splice or terminal, and the repair is often a pair of correctly crimped, matched connectors or a new section of cable. A panel is replaced only when the arc is inside its junction box or the module itself is cracked or burned. The installer's inspection, not the error code alone, decides which parts have to go.
