Answer
Solar PV arc-fault protection detects signs of electrical arcing and interrupts the affected circuit or power conversion. A series arc can occur at a damaged conductor or poor connection without tripping ordinary overcurrent protection. Requirements depend on the adopted electrical code and listed equipment. Investigate inverter alarms using the exact manufacturer instructions before authorizing a restart.
An inverter arc-fault alarm needs investigation. Clearing it without understanding the cause can return a damaged PV circuit to service. This guide explains the protection function and the records installers and designers need to evaluate an alarm; it does not replace the equipment’s service instructions.
What solar PV arc-fault protection does
A series arc occurs across a break in the intended current path, such as a defective connection. Current can continue across that gap while remaining below an overcurrent device’s trip level. Arc-fault detection and interruption address this failure mechanism; a fuse rating alone does not establish that it is covered.
A parallel arc involves a path between conductors or another conductive part. Do not assume a device marketed as AFCI detects every arc configuration. The Tesla Solar Inverter manual specifically describes series-arc detection using voltage and current information, followed by stopping conversion and disconnecting from the grid.
DC has no alternating-current zero crossing. That does not mean every DC arc persists indefinitely or that an AC arc necessarily remains extinguished after a zero crossing. Avoid using a simplified AC/DC comparison as a prediction of fire behavior.
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 they are not interchangeable. A rapid-shutdown system is not proof that arc-fault protection is installed. A PV ground-fault protection function also should not be described as identical to every personnel-protection GFCI.
NEC 690.11: build a project-specific compliance record
For U.S. work, identify the adopted NEC edition, local amendments and the authority having jurisdiction. Confirm the actual requirements of Section 690.11 in that edition before approving an equipment selection or exception.
This article does not certify the current code text for your jurisdiction. In particular, do not carry an older building-only description into every newer edition, or treat all ground-mounted systems as exempt. Circuit type, voltage and wiring arrangement matter. A microinverter label also does not replace checking the actual DC circuit and the separate AC installation requirements.
Use this review checklist:
| Record | Why it is needed |
|---|---|
| Adopted code edition and amendments | Establishes which requirements govern the permit |
| DC circuit identification and operating voltage | Identifies the circuits being evaluated |
| Array location and conductor routing | Supports review of an exception, if claimed |
| Exact inverter or protection-device model | Connects the design to its listing and instructions |
| Protection configuration and firmware | Records the behavior actually commissioned |
| Inspector or designer review of any exception | Makes the reasoning traceable instead of relying on a product category |
An NEC Article 690 overview can help organize the review, but the adopted code and approved equipment documentation govern acceptance.
UL 1699B and IEC 63027: what the public scopes establish
UL’s public UL 1699B scope covers PV DC arc-fault detectors, interrupting devices and equipment with integral protection. It describes equipment rated up to 1,500 V and explicitly excludes detection of glowing connections. Consequently, AFCI should not be presented as detecting every overheating connection.
UL 1699B is distinct from UL 1699 for AC branch-circuit AFCI. Check the certification of the exact product, including any conditions of use. The presence of the letters “AFCI” on a feature list does not establish suitability for a particular PV system.
IEC 63027:2023 covers DC arc detection and optionally interruption in PV circuits, including series-arc test procedures and interruption response times. Its scope extends to systems with maximum PV source-circuit voltage not exceeding 1,500 V DC. This is a product-standard scope, not a universal installation mandate or proof of automatic equivalence with another certification.
The full standards contain test conditions that public summaries do not reproduce. Do not turn an isolated energy or time value into a universal field threshold, or promise that a device will detect every dangerous condition.
Restart behavior differs between products
Vendor-reported example: Tesla’s manual specifies a manual reset for its Solar Inverter arc-fault event. SMA’s CORE1-US technical information describes optional automatic return for specified STP 33/50/62-US-41 models with the stated firmware, while its STP 50-US-40 entry does not have that enhanced handling option.
This difference disproves a universal “all AFCI devices require manual restart” statement. It does not authorize changing another inverter’s settings. SMA also directs qualified technicians to investigate recurring events and recommends stopping operation when investigation and correction cannot be completed. Confirm the permitted behavior for the local installation and exact device.
Reviewing an alarm without assuming a nuisance trip
An intermittent alarm is not automatically a false alarm. Absence of visible melting does not establish that no fault exists. Solis’s North American troubleshooting guidance calls for inspection before resetting an arc-fault event and lists potential causes including connection problems, damaged wiring, firmware and detection hardware.
For the owner, the useful first action is to record the alarm and contact the installer or service provider. Electrical inspection and testing belong with qualified personnel using the manufacturer’s procedures. Do not open PV connectors under load or assume that switching off AC removes voltage from sunlit DC circuits.
Give the service team usable evidence
Record:
- 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.
- Frequency of events and whether they followed installation or maintenance changes.
- Available commissioning records, circuit drawings and previous service findings.
A self-test failure and an arc-detection event can call for different responses. SMA’s CORE1-US documentation, for example, distinguishes arc events from interference or signal-level failures during self-test. The same numeric code should not be presumed to mean the same thing across manufacturers.
Use the exact assembly and service specifications
SMA’s installer troubleshooting guidance discusses termination, stripping, crimping, connector mating and damaged wiring. Use it as context, then consult the current manual for the actual equipment. There is no single torque, strip length or pull-test value suitable for every PV connector and terminal.
Do not add ferrites, change sensitivity, swap strings or apply insulation-test voltage using a generic blog procedure. The service plan must account for equipment compatibility, isolation, test limits and the manufacturer’s approval. Ask support to interpret unresolved events rather than repeatedly resetting them.
Make the design and handover reviewable
Keep the circuit drawings, selected equipment, connector specifications and protection settings consistent across the design, installation and commissioning records. Record substitutions and their review. A product family name or “MC4-compatible” description does not document an approved mating combination.
After service, keep a record of the identified cause, repaired components, configuration changes, verification and authorization to resume operation. These records make a later recurring event easier to investigate.
Review SurgePV’s solar design workflow if you need to evaluate how project information is organized. Confirm the available documentation outputs for your workflow; design software does not certify an AFCI installation or replace field inspection.
Frequently asked questions
Is AFCI protection required for every solar installation?
Check the locally adopted electrical code, circuit voltage, installation arrangement and applicable exceptions. NEC 690.11 addresses PV DC arc-fault protection in U.S. projects, but a rooftop-versus-ground-mount label alone does not establish compliance.
Does solar AFCI detect series and parallel arcs?
Do not assume both. The Tesla Solar Inverter manual describes series-arc detection, and IEC 63027 includes series-arc test procedures. Confirm the protection scope of the exact listed device and system configuration.
Is manual restart always required after a PV arc-fault alarm?
No universal rule applies to every inverter and jurisdiction. Tesla documents a manual reset for its Solar Inverter, while SMA documents optional automatic return for specific CORE1-US models and firmware. Follow the approved configuration and investigate recurring events.
What is UL 1699B?
UL 1699B is the standard for photovoltaic DC arc-fault circuit protection. Its public scope covers detectors, interrupting devices and equipment with integral protection. It is different from the AC branch-circuit AFCI standard UL 1699.
Can I disable AFCI to stop inverter trips?
Do not bypass required protection to clear an alarm. Have a qualified PV service technician investigate the event, follow the model-specific isolation and inspection instructions, and involve manufacturer support if the cause remains unresolved.
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.
