Answer
Solar AFCI (arc-fault circuit interrupter) protection detects a DC series arc in a PV array and stops power conversion. In the U.S., NEC 690.11 calls for listed PV arc-fault protection on dc circuits at 80 V dc or greater, with exceptions. UL 1699B and IEC 63027 are the product standards. Inverter makers document their own restart steps.
Last updated: November 2026
When an inverter shows an arc-fault alarm, the first question is whether to reset it or go up on the roof. The short answer is to inspect first. This guide explains what the protection does, which rules and standards apply, and how to read the alarm.
An arc is an electric spark that jumps across a gap. A series arc forms where a connection or conductor has failed in the current path, for example a loose PV connector. The NEC is the National Electrical Code. A listed product has been evaluated by a testing lab and appears on its published list.
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Key Takeaways
- NEC 690.11 is the U.S. installation rule. UL 1699B and IEC 63027 are product standards for the devices that meet it.
- The vendor documents read for this page describe series-arc detection. They do not say these AFCI functions detect parallel arcs.
- The inverter model and its firmware (its built-in software) set the restart behavior. Tesla requires a manual reset on its Solar Inverter. SMA offers an optional automatic return on newer CORE1-US models.
- Inspect the PV wiring and connectors before every reset. Solis says to do this even when the trip looks like a nuisance trip.
What Solar PV Arc-Fault Protection Does
A series arc forms across a gap in the path the current is meant to follow. SMA says an arc-fault happens when a conductor, connection, module or other part fails to carry current as intended. That leaves a gap, and the current jumps across it as an arc. SMA lists these as the most common causes: damaged or badly assembled PV connectors, loose terminal connections and damaged modules. The AFCI glossary entry gives the short definition.
In a PV system, the inverter does the detecting. Solis states that its AFCI is designed to detect series arcing in the DC cabling or junction boxes. It alerts the main control CPU and interrupts power conversion, which stops the DC current. Tesla describes the same pattern for its Solar Inverter. Its detection algorithm uses voltage and current. When it detects an arc, the inverter stops converting power and disconnects from the grid.
A parallel arc runs between conductors or to another conductive part. A 2010 Sandia National Laboratories presentation lists parallel arcs as “not in the NEC” at the time. It lists series arcs (NEC 690.11) and ground arcs (NEC 690.5) next to it. The inverter documents cited on this page describe series-arc detection only. So a device sold as AFCI is not documented to cover every kind of arc.
Separate the protection functions
| Function | What to verify |
|---|---|
| PV DC arc-fault protection | Listed detection and interruption scope for the connected PV circuits |
| Ground-fault protection | The equipment’s ground-fault detection and response requirements |
| Overcurrent protection | Ratings and coordination for the relevant circuit and fault conditions |
| Rapid shutdown | The controlled conductors, equipment and initiation method required for the installation |
These functions can share equipment, but each one needs its own check. A rapid-shutdown system does not supply arc-fault protection. SMA’s own troubleshooting guidance says an arc fault is not a ground fault, so you test each one differently.
NEC 690.11, UL 1699B and IEC 63027 Compared
| Document | Type | What it covers | Voltage | Where it applies |
|---|---|---|---|---|
| NEC 690.11 (NFPA 70) | Installation rule | Listed PV arc-fault circuit interrupter, or other listed equivalent, on PV dc circuits; the system must detect and interrupt arcing faults from a break in the intended continuity of a conductor, connection, module or other component | 80 V dc or greater between any two conductors (2023 edition second-revision text) | U.S. projects under the adopted edition; exception for systems not installed on or in buildings |
| UL 1699B | Product standard | PV DC arc-fault circuit-interrupters, arc-fault detectors, interrupting devices, and inverters, converters and charge controllers with integral protection | 1,500 V or less | Equipment listing, named in UL’s scope as for systems described in NEC Article 690 |
| IEC 63027:2023 | Product standard | Detection and optional interruption of DC arcs in PV circuits; test procedures for series arcs and response times of the interrupting equipment | Maximum PV source-circuit voltage up to 1,500 V DC | Equipment testing; not an installation mandate |
These figures come from the NFPA second-revision report, UL’s and IEC’s own store pages and the SMA CORE1-US technical information linked below.
Sources: UL 1699B scope and IEC 63027:2023 from the standards bodies’ own pages. For NEC 690.11, NFPA’s second-revision report for the 2023 NEC (Panel 4, Second Revision 8431, submitted 26 October 2021). The adopted 2023 text itself is behind NFPA’s free-access login, and we did not read it. Check Section 690.11 in the edition your area has adopted.
How the NEC rule changed between editions
A Sandia National Laboratories presentation reproduces the 2011 text. It shows that the 2011 NEC applied the rule to PV systems with dc circuits on or penetrating a building. The maximum system voltage had to be 80 V or greater. The 2011 NEC also required manual restart. SMA states that an inverter with arc-fault protection may return to operation automatically. This applies as of the 2017 NEC and UL 1699B Edition 1. For projects permitted under the 2014 NEC or earlier, SMA tells installers to ask the authority having jurisdiction. The later wording in the second-revision report drops the building-only phrasing. It keeps an exception for systems not on or in buildings. Read the exception in the edition your authority having jurisdiction enforces. That is the office or official that enforces the code for the project. The NEC Article 690 glossary entry gives an overview.
UL 1699B summary
UL’s public scope says the requirements cover DC PV arc-fault circuit protection devices for systems described in NEC Article 690. The protection is meant to reduce the effects of arcing faults that may start a fire if the arcing continues. The scope also states that the devices are not meant to detect glowing connections. So an AFCI is not a general overheating detector. UL lists a published date of 22 August 2018 and a last revision of 9 July 2024. SMA certifies its CORE1-US inverters to UL 1699B Edition 1 (August 2018).
The test steps are in the full standard, which is sold. On 28 October 2026 UL’s store listed UL 1699B at USD 402 to USD 998, depending on the purchase option. IEC’s webstore listed IEC 63027:2023 (published 3 May 2023) at CHF 380. Searches for a “free” copy end at unofficial files. If you need the test conditions, buy the standard from UL or IEC.
Inverters With Built-In AFCI
The table lists inverters documented in the vendor manuals and technical notes cited below. It is not a complete market list. Each row repeats that vendor’s wording.
| Vendor | Model | AFCI as documented | Standard named by the vendor | Restart behavior |
|---|---|---|---|---|
| SMA | Sunny Tripower CORE1-US STP 33-US-41, STP 50-US-41, STP 62-US-41 | Integrated; detects series arc-faults in the PV modules and array wiring; inverter stops operation | UL 1699B Edition 1 (August 2018); NEC 690.11 | Setting-dependent: manual reset (permanent inhibition) or automatic return after about 10 minutes, firmware 03.12.21.R or later |
| SMA | Sunny Tripower CORE1-US STP 50-US-40 | Listed in the note’s firmware table | Not stated for this model in the note | AFCI with permanent operation inhibition only; the enhanced option is not available |
| Tesla | Solar Inverter | Detects series arcs within the PV array using voltage and current; stops converting power and disconnects from the grid | NEC 690.11, UL 1699B and UL 1998 | Manual reset on site only, using the mobile app via remote command; the fault cannot clear automatically |
Sources: SMA CORE1-US technical information (version 1.1) and the Tesla Solar Inverter installation manual. Solis North America documents series-arc detection and interruption for its inverters in a knowledge-base article, without a model list or a standard.
Check the datasheet of the exact model you specify. A feature list that says “AFCI” does not tell you the listing, the firmware or the restart setting.
Restart Behavior Differs Between Products
The same standards allow different restart designs, so there is no single rule for all inverters. Tesla documents a manual reset for its Solar Inverter. SMA’s CORE1-US offers three settings. You choose one with the Device > AFCI switched on parameter. The first is AFCI off (not recommended). The second is AFCI on with permanent operation inhibition, where the inverter waits for a reset. The third is AFCI on without permanent inhibition, where the inverter returns after about 10 minutes. SMA says there is no limit to the number of automatic resets in that mode.
SMA tells installers to monitor inverters in automatic-return mode and to look into repeat events right away. If the cause cannot be checked right away, SMA says to put the inverter in a non-operational state. SMA also states that Canadian codes (CSA C22.1 and C22.2 No. 292-18) had not been harmonized with automatic return. So installations in Canada need the authority’s answer first.
Troubleshooting an Arc-Fault Alarm
Inspect the site before you reset an arc-fault alarm. Solis states that you must inspect the site every time an arc fault occurs. This is true even when it looks like a nuisance trip. A nuisance trip is a false alarm. SMA describes the inverter as the bearer of bad news, meaning the fault is usually outside the inverter.
Alarm codes on the SMA CORE1-US
| Event ID | SMA’s description | SMA’s corrective measure |
|---|---|---|
| 4301 / 4302 | Series arc detected in string group ABC / DEF | Inspect the PV wiring and array to locate and correct the cause |
| 8206 / 8210 | Inverter is waiting to be reset after an arc-fault detection | Inspect, correct the cause, then reset the operation inhibition |
| 8208 | AFCI self-test failed at startup: interference level too high | Contact the SMA Service Line |
| 8209 / 8212 | AFCI self-test failed at startup: signal level too low | Contact the SMA Service Line |
A self-test failure and an arc event need different responses. Codes are specific to each maker. Another vendor’s code with a similar number means something else.
Step by step
- Record the event. Note the model, serial number, firmware version, event code, affected input group, date, time and weather.
- Make the circuit safe. Follow the manufacturer’s steps to isolate it. Do not open PV connectors under load. Switching off AC does not remove voltage from sunlit DC circuits.
- Inspect visually. Solis lists these signs of arcing. Look for discolored wiring and racking, melted connectors and insulation, and burned junction boxes on the back of modules.
- Check terminations and connectors. A termination is where a wire ends and connects. SMA’s installer tips cover three things. One is insulation stripped far enough that only bare wire is clamped. Another is field-crimped home-run connectors. The third is module-to-module connectors that are not fully mated. Solis recommends a gentle tug on DC cables to find loose or badly terminated wires. It adds that factory crimps and module junction boxes have caused arcing too.
- Check firmware. Solis lists out-of-date firmware and a damaged AFCI board as possible causes.
- Reset only after the inspection. If the event returns, inspect again and call the manufacturer’s service line. Do not just reset again.
Follow the manufacturer’s manual for any electrical test.
Pro Tip
Photograph the connectors and junction boxes before you touch them, and attach the event code to the photos. Intermittent arcs often leave no visible mark after cleaning, so the record may be the only proof the service team gets.
Give the Service Team Usable Evidence
- Exact model, serial number and firmware version.
- Full event text, event code and affected input group, if reported.
- Date, time and time zone, plus weather and operating conditions.
- How often the events occur and whether they followed installation or maintenance work.
- Commissioning records (the start-up checks), circuit drawings and earlier service findings.
Make the Design and Handover Reviewable
Keep the circuit drawings, chosen equipment, connector specifications and protection settings the same across design, installation and commissioning records. Record any substitutions and who reviewed them. A product family name or an “MC4-compatible” label does not prove that two connectors are an approved match.
After service, record the cause and the parts you repaired. Also record any settings change, the checks you made and who approved the return to operation.
Document protection settings with the design
Keep circuit drawings, equipment choices and settings in one project record. Bring a real project to a guided demo and see how SurgePV organizes them.
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For site safety rules in other markets, see solar fire safety in Europe. If you are choosing software for string and BOM documentation, choosing solar design software covers what to ask in a trial project.
Frequently Asked Questions
Is AFCI protection required for every solar installation?
No. NEC 690.11 applies to PV dc circuits at 80 V dc or greater between any two conductors. It has an exception for systems not installed on or in buildings. So the answer depends on circuit voltage, location and the code edition your authority adopted. Check Section 690.11 in that edition. Ask the authority having jurisdiction about any exception.
What is UL 1699B?
UL 1699B is the product standard for photovoltaic DC arc-fault circuit protection. Its public scope covers PV DC arc-fault circuit-interrupters, arc-fault detectors and interrupting devices. It also covers inverters, converters and charge controllers with built-in protection, rated 1,500 V or less. It does not cover detection of glowing connections. It is separate from UL 1699, the AC branch-circuit AFCI standard.
Which inverters have built-in AFCI?
Several string inverters include it. SMA documents built-in AFCI certified to UL 1699B Edition 1 for the Sunny Tripower CORE1-US models STP 33-US-41, STP 50-US-41 and STP 62-US-41. Tesla documents AFCI in its Solar Inverter, compliant with NEC 690.11, UL 1699B and UL 1998. Check the datasheet or manual of the exact model before you specify it.
Does solar AFCI detect series and parallel arcs?
The vendor documents we read describe series-arc detection. SMA says its CORE1 AFCI detects series arc-faults in the PV modules and array wiring. Tesla says its detection targets series arcs within the PV array. IEC 63027 covers test procedures for series arcs. Confirm the scope of the exact listed device.
Is manual restart always required after a PV arc-fault alarm?
No. Tesla documents a manual on-site reset for its Solar Inverter. SMA documents an optional automatic return after about 10 minutes for CORE1-US STP 33/50/62-US-41 models on the stated firmware. For the STP 50-US-40, SMA documents permanent inhibition with manual reset. SMA says automatic return is allowed as of the 2017 NEC and UL 1699B Edition 1.
How do I troubleshoot an inverter arc-fault alarm?
Record the event code and the affected input. Then inspect the PV wiring, connectors and terminations before you reset. Solis says to inspect every time, even for a suspected nuisance trip. Look for discoloration, melted connectors, burned junction boxes, loose terminations and connectors that are not fully mated. Contact the manufacturer if the event repeats or a self-test fails.
Can I disable AFCI to stop inverter trips?
No. SMA’s CORE1-US parameter table marks a setting with no arc-fault protection as not recommended. Find and fix the cause instead. If you cannot find the cause, call the manufacturer’s service line.
Where this fits
This article is part of SurgePV's Solar Design hub, which works through the topic from first principles to the decisions a project team actually has to make.
