Photovoltaic Module Arc Fault Testing: Standards, Methods, and Safety Compliance

Photovoltaic (PV) arc fault testing is a critical safety evaluation that verifies whether solar power equipment can detect and interrupt dangerous DC arc faults before they ignite fires in PV installations. This article explains the technical principles of arc faults in PV systems, the applicable standards such as UL 1699B and IEC 63027, the test samples, testing items, test methods, and typical applications of arc fault testing for photovoltaic modules and related system components.

Technical Overview

An arc fault in a photovoltaic system is a hazardous, high-temperature plasma discharge that occurs when current flows across an unintended gap or a degraded contact within a DC circuit. Unlike AC arcs, which naturally extinguish at every current zero-crossing, DC arcs in PV strings can sustain themselves indefinitely because the DC source has no periodic zero crossing. The arc core temperature can reach several thousand degrees Celsius, which is sufficient to melt copper conductors, carbonize insulation, and ignite surrounding materials such as connector housings, cable jackets, and roofing.

There are three principal arc fault categories relevant to PV installations. Series arc faults occur within a single current path, typically caused by broken conductors, corroded or mismatched connectors, loose screw terminals, or cracked solder joints inside a module junction box. Parallel arc faults occur between conductors of different polarity, often triggered by insulation failure, rodent damage, or crushed cables. Ground arc faults occur between an energized conductor and grounded structures. Among these, series arc faults are the most difficult to detect because the fault current remains within the normal operating range of the string.

Arc fault testing is designed to evaluate arc fault circuit interrupter (AFCI) functionality, detection algorithms, and interruption performance under repeatable, laboratory-generated arc conditions. The dominant reference standards include UL 1699B for PV DC arc-fault circuit protection, IEC 63027 for DC arc detection and interruption devices used in PV power systems, and the installation requirements of NEC Article 690.11 for PV systems operating above 80 V DC. Accredited third-party laboratories conduct these tests as part of product certification, safety compliance, and design verification programs.

Testing Samples

PV Modules and Module-Level Components

Crystalline silicon and thin-film photovoltaic modules, including their junction boxes, bypass diodes, internal busbars, and factory-attached cables, are evaluated for their susceptibility to series arc initiation and their behavior when an arc is induced at typical operating currents. Module-level power electronics with integrated shutdown or arc detection functions are also tested at this level.

Inverters with Integrated Arc Fault Protection

String inverters, residential inverters, and hybrid energy storage inverters that embed DC arc fault detection and interruption circuitry represent the most common test samples. Testing verifies that the inverter's detection algorithm responds to arc signatures generated on the DC input side within the required time and energy limits.

Standalone Arc Fault Detection and Interruption Devices

Dedicated AFCI devices, arc fault detection devices (AFDD), DC combiner boxes with arc fault protection, rapid shutdown devices, and recombiner units equipped with arc detection modules are tested as independent protective equipment.

Cables, Connectors, and System Accessories

DC connectors, extension cables, branch connectors, and wiring harness assemblies may be included in test programs to characterize arc generation behavior, contact degradation, and fire propagation resistance when subjected to controlled arcing events.

Testing Items

Typical arc fault test programs cover the following evaluation items:

• Series arc fault detection test across the rated current range of the device
• Parallel and ground arc fault detection tests where required by the applicable standard
• Arc detection time measurement and cumulative arc energy limitation verification
• Arc interruption and circuit isolation verification, including confirmation that the arc does not reignite
• Inhibition (immunity) testing to confirm the device does not trip falsely in the absence of a genuine arc
• Repeatability testing over multiple arc events at identical test points
• Detection performance under varying source voltage, load current, temperature, and cable length conditions
• Annunciation and alarm output verification, including remote indication and automatic re-arming behavior
• Dielectric withstand and insulation resistance verification after arc events
• Endurance testing of the interruption means across repeated fault clearing cycles

Testing Methods

The core of arc fault testing is a controlled arc generator that produces a repeatable, characterized arc while high-speed instrumentation records voltage, current, and arc energy. A typical test setup includes a PV array simulator or real PV string source, the device under test, an arc generator inserted in series with or parallel to the DC circuit, and a data acquisition system sampling at sufficient bandwidth to capture the high-frequency arc signature superimposed on the DC waveform.

For series arc fault tests, the arc is commonly generated by one of the following methods:

• A moving-electrode arc generator that draws a controlled arc between separated conductors, following the electrode geometry defined in UL 1699B
• A guillotine or blade-type cable severing fixture that cuts a current-carrying conductor to create a realistic conductor-break arc
• A separable contact fixture that simulates loose or corroded terminal connections in a junction box or connector

Test currents are stepped across the operating range of the device, for example from low currents near the minimum detection threshold up to the rated current, while the source voltage is maintained at specified levels up to the maximum system voltage. During each arc event, the laboratory records the time from arc initiation to detection, the time to interruption, and the total delivered arc energy in joules. Compliance criteria generally require detection and interruption within a time limit that caps cumulative arc energy, with UL 1699B and IEC 63027 defining specific trip-time and energy ceilings that must not be exceeded at each test point.

Parallel and ground arc tests apply an arc across conductors of different potential or between an energized conductor and ground, often initiated along a carbonized insulation path or across a defined electrode gap, to verify detection of higher-energy fault modes. Inhibition tests then expose the device to non-arc electrical noise sources, such as normal inverter switching behavior, load transients, and PWM signatures, to confirm that nuisance tripping does not occur during normal system operation.

All testing is performed in a controlled laboratory environment with fire-resistant enclosures, arc shields, and remote operation to protect laboratory personnel, since deliberate arc generation produces intense ultraviolet radiation, molten metal ejecta, and toxic decomposition gases.

Applications

Photovoltaic arc fault testing supports multiple engineering and compliance objectives across the solar industry:

• Certification of inverters, AFCI devices, and protective electronics to UL 1699B and IEC 63027 for market access in regions requiring arc fault protection
• Compliance demonstration for NEC Article 690.11 requirements on PV systems operating above 80 V DC in North American installations
• Fire risk assessment and forensic investigation support for rooftop, ground-mount, and building-integrated PV systems
• Validation of detection algorithm performance during product development, firmware updates, and model extensions
• Comparative quality evaluation of connectors, junction boxes, and module designs regarding arc susceptibility
• Due diligence and periodic safety verification for utility-scale, commercial, and residential solar portfolios
• Support for insurance assessments and post-incident root cause analysis following suspected arc-related PV fires

FAQ

What is a photovoltaic arc fault? A photovoltaic arc fault is an unintended, sustained electrical discharge through air or degraded material in a DC circuit, caused by factors such as broken conductors, loose connectors, or insulation failure. Because DC arcs do not self-extinguish at zero crossing, they represent a major fire hazard in PV systems.

What standards govern PV arc fault testing? The primary standards are UL 1699B for PV DC arc-fault circuit protection, IEC 63027 for DC arc detection and interruption devices in photovoltaic power systems, and IEC 63049 and related IEC documents covering PV safety and rapid shutdown. Installation codes such as NEC Article 690.11 define where arc fault protection is required.

What is the difference between series and parallel arc faults? A series arc fault occurs within a single current path and the fault current equals the normal string current, making it difficult to detect with overcurrent devices. A parallel arc fault occurs between conductors of different polarity or to ground and can draw currents well above normal levels. Series arcs are the primary target of most arc fault detection standards.

How quickly must an arc fault be detected and interrupted? Standards specify maximum cumulative arc energy and trip-time limits, and devices are typically required to detect and interrupt an arc within a few seconds under specified test conditions so that delivered arc energy remains below the defined safety threshold.

Is arc fault testing mandatory for PV products? Requirements depend on the target market and installation code. In jurisdictions adopting NEC requirements, PV systems above 80 V DC must include arc fault protection, which in practice requires testing and certification of the protective device by accredited third-party laboratories before market entry.

Can arc fault testing be performed on an installed PV system? Laboratory certification testing is performed on equipment samples, while field testing typically involves functional verification using portable arc simulation tools combined with thermographic inspection and connector torque checks to assess arc risk in operating systems.