PV DC Arc-Fault Protection: NEC 690.11 vs IEC 63027

အမြန်အဖြေ

PV DC arc-fault protection is a dedicated safety function for detecting hazardous arcing in photovoltaic circuits. It is not automatically provided by a fuse, DC miniature circuit breaker (MCB), surge protective device (SPD), isolator, or ordinary residential AC arc-fault device.

The two references most often compared serve different purposes:

NEC 690.11 is a North American installation-code requirement. In recent NEC editions, PV systems with DC circuits operating at 80 V DC or more between conductors generally require listed PV arc-fault protection, subject to the adopted NEC edition, its exceptions, local amendments, and the Authority Having Jurisdiction (AHJ).
IEC 63027:2023 is an international product performance and test standard for equipment that detects, and optionally interrupts, DC arcs in PV circuits up to 1500 V DC. It does not by itself require every country or every PV project to install such equipment.
UL 1699B is a North American product standard used for photovoltaic DC arc-fault circuit protection equipment.

The central engineering point is:

A series arc can carry less current than the normal operating load. Standard overcurrent protection may therefore remain closed while the arc continues producing concentrated heat.

သော့ထုတ်ယူမှုများ

NEC 690.11 tells a designer when an installation requires protection under an adopted NEC framework; IEC 63027 tells a manufacturer or buyer how PV arc-detection equipment is classified and tested within its scope.
IEC 63027 focuses its test procedures on series arcs. It recognizes detection-only equipment as well as equipment that combines detection with interruption.
A solar inverter marked "AFCI" should not be approved from the acronym alone. Confirm its listing or test standard, protected circuit coverage, voltage/current range, number of strings and channels, interruption method, firmware, and reconnection behavior.
Opening the inverter input may extinguish a series arc in the monitored current path, but it does not prove that every possible parallel or ground-related arc will be cleared. Protection architecture must match the fault type.
Connector mating, crimp quality, terminal torque, cable support, water ingress, and commissioning records remain essential. Arc-fault electronics cannot compensate for poor PV installation practice.

What Is a PV DC Arc Fault?

An arc is a self-sustaining electrical discharge through ionized gas. In a PV array, sunlight keeps the modules energized, and DC current has no natural current zero-crossing like an AC waveform. Once an arc becomes stable, it can continue heating a small area of a connector, conductor, terminal, junction box, or module.

Common initiation points include:

a connector that is not fully seated;
contacts from unapproved connector combinations;
an incorrect or incomplete crimp;
a loose combiner-box or isolator terminal;
a conductor fractured by bending, vibration, or poor cable support;
damaged insulation caused by abrasion, animals, UV exposure, or installation work;
moisture, contamination, or corrosion around a connection;
a failed solder joint, module lead, junction box, or bypass-diode connection.

The system may continue producing power while the defect deteriorates. That makes arc-fault protection a fire-risk control rather than a substitute for ordinary overload protection.

Series Arc vs Parallel Arc vs Ground Fault

These fault types are related but not interchangeable.

Fault type	လက်ရှိလမ်းကြောင်း	Typical origin	Why conventional protection may or may not respond	Main design response
Series arc	Across a discontinuity in the intended current path	Loose connector, broken strand, poor crimp, loose terminal	Arc current is limited by the string and load; it may remain below fuse or breaker pickup	Dedicated series-arc detection and a tested interruption method
Parallel arc	Between conductors at different potentials	Insulation breakdown, damaged positive and negative conductors, contamination	Current may be high, but its magnitude depends on array topology and available source paths	Overcurrent, insulation/ground-fault protection, separation, and fault-specific interruption
မြေပြင်ပြတ်ရွေ့	From a live conductor to grounded metal or earth path	Damaged cable, water ingress, pinched insulation	Fault current may be limited or distributed in ways that do not operate a conventional OCPD	Ground-fault detection, insulation monitoring, bonding, and applicable disconnection

NEC 690.11 and the principal IEC 63027 test scope are concerned with faults caused by a failure in the intended continuity of the PV DC circuit: series arcs.

This boundary matters. Research from Sandia has shown that series and parallel arcs can produce similar high-frequency signatures, yet the correct interruption action can differ. Opening a series current path extinguishes that series arc. A parallel arc may remain energized from other array paths, and an unsuitable response can redirect current through the fault. A system should therefore not claim broader arc protection unless that functionality is specifically evaluated.

Why a PV Fuse or DC MCB May Not Clear a Series Arc

Overcurrent protective devices operate when current exceeds a defined time-current threshold. A series arc adds impedance to the normal path. Instead of increasing current, it often reduces it.

Consider a string carrying 9 A in normal operation. If a damaged connector begins arcing in series, current might remain near or below the operating level rather than rising above the string-fuse or breaker threshold. The small arc gap can nevertheless generate enough local temperature to carbonize insulation or ignite nearby polymer material.

That is why the following devices do not automatically provide series-arc protection:

ကိရိယာ	အဓိကလုပ်ဆောင်ချက်	Why it is not a PV arc detector
gPV fuse	Protects PV conductors and modules against defined overcurrent conditions	A series arc may not create sufficient overcurrent
DC MCB or MCCB	Opens overload and short-circuit current within its rated DC application	Thermal-magnetic or electronic overcurrent sensing does not automatically identify an arc signature
SPD	Diverts transient overvoltage energy	It does not continuously analyze string-current noise for series arcs
DC isolator	Provides switching or isolation within its declared rating	It requires an operating command and does not normally detect an arc
Ground-fault detector	Identifies unintended current to ground or insulation deterioration	A conductor-to-conductor series discontinuity may not produce ground current
AC AFDD/AFCI	Detects specified arc signatures in AC final circuits	Residential AC algorithms and product standards do not establish PV DC performance

These devices still remain necessary where the design requires them. Arc-fault protection is an additional coordinated layer, not a replacement for PV-rated DC circuit protection, fuses, surge protection, or safe isolation.

What NEC 690.11 Requires

NEC 690.11 is titled Arc-Fault Circuit Protection (Direct Current). Under the wording used in recent NEC cycles, PV systems with DC circuits operating at 80 V DC or greater between any two conductors require a listed PV arc-fault circuit interrupter or listed system components providing equivalent protection.

The protected system is expected to detect and interrupt arcing caused by a loss of intended continuity in a conductor, connection, module, or other PV DC component.

NEC 690.11 is an installation rule

Its legal effect depends on:

the NEC edition adopted by the state, city, utility, or other authority;
local amendments;
whether the DC circuit is on, in, or associated with a building as addressed by that edition;
whether a stated exception applies to the exact route and facility;
the equipment listing and installation instructions;
the AHJ's acceptance of the submitted design.

Recent code language includes exceptions for specified PV circuits outside or associated with particular building conditions when conductors are installed in qualifying metallic wiring methods or underground. The wording has changed across code cycles. Do not copy an exception from an old drawing note into a new project without checking the locally adopted edition.

Large-scale PV electric supply stations may also be governed by additional Article 691 provisions and project-specific fire-mitigation requirements. "Ground-mounted" alone is not enough information to decide compliance.

NEC 690.11 is not the rapid-shutdown rule

NEC 690.11 and NEC 690.12 address different hazards:

Arc-fault protection detects hazardous discontinuity arcs and initiates interruption.
Rapid shutdown controls conductor voltage around arrays on buildings to reduce responder shock exposure.

One product may participate in both functions, but compliance with one section does not automatically prove compliance with the other.

What IEC 63027:2023 Actually Covers

IEC 63027:2023, Photovoltaic power systems – DC arc detection and interruption, applies to equipment used to detect and optionally interrupt DC arcs in PV system circuits.

Its published scope establishes three important boundaries:

It provides test procedures for detecting series arcs in PV circuits.
It addresses the response of equipment used to interrupt those arcs.
It covers equipment connected to PV systems with a maximum PV source-circuit voltage not exceeding 1500 V DC.

It is a product standard, not a universal installation mandate. National wiring rules, building codes, tender specifications, insurer requirements, or local authorities decide whether and where arc-fault protection must be installed.

AFD, AFI, and AFPE

IEC terminology separates the sensing and interruption functions:

Term	အဓိပ္ပာယ်	လုပ်ဆောင်ချက်
AFD	Arc-fault detector	Detects an arc and generates the relevant indication or command
AFI	Arc-fault interrupter	Receives a command and interrupts the arc current path
AFPE	Arc-fault protection equipment	Combines arc detection and interruption as a complete protective function
AFS	Arc-fault sensor	Sensing element or channel associated with the detection architecture

This distinction prevents a common purchasing error: an AFD can detect an arc without independently interrupting it. If the product is detection-only, the project must identify the compatible AFI, communication link, fail-safe behavior, and verified complete system.

Classification and coverage matter

IEC 63027 classification is intended to describe practical installation characteristics, including:

protection coverage within the PV system;
integrated, stand-alone, or distributed implementation;
detection-only versus detection-and-interruption functionality;
maximum monitored strings and inputs;
number and allocation of detection channels or sensors;
reconnection method after operation.

Two inverters can both advertise "IEC 63027 arc detection" while covering different numbers of strings, different conductor sections, or different interruption functions. Obtain the classification and test evidence for the exact model and firmware rather than approving a family-level brochure.

NEC 690.11 vs IEC 63027 vs UL 1699B

ကုသိုလ်ကံ	NEC 690.11	UL 1699B	IEC 63027:2023
Document role	Electrical installation code requirement	North American product safety standard	International product performance and test standard
အဓိကအသုံးပြုပုံ	Determines when listed PV DC arc-fault protection is required in an adopted NEC jurisdiction	Supports evaluation/listing of PV DC arc-fault circuit protection equipment	Classifies and tests PV DC arc detection and optional interruption equipment
Legal effect	Enforced when adopted, interpreted by the AHJ	Relevant through listing, specification, and code acceptance	Becomes contractually or legally relevant when adopted by a market, installation rule, or project specification
Voltage boundary	Recent editions use 80 V DC or greater between conductors, subject to edition and exceptions	Use the product's listed scope and ratings	Equipment connected to PV source circuits up to 1500 V DC
Principal fault focus	Series arcing caused by failure of intended continuity	PV DC arc-fault protection within the standard's scope	Test procedures for series-arc detection and interruption response
Interruption	Required as part of the protective result	Evaluated as part of the listed protection function	Optional at equipment scope: AFD may detect only; AFPE includes interruption
Project evidence	Adopted code, drawings, listed equipment, instructions, AHJ acceptance	Listing/certification record and model markings	Classification, certificate/test evidence, ratings, firmware and installation limitations

UL Solutions identifies UL 1699B as the standard for photovoltaic DC arc-fault circuit protection. A claim of "meets NEC 690.11" should therefore be supported by the appropriate listing or listed equivalent system components, not only by an internal arc-detection algorithm.

IEC 63027 Is Not IEC 62606

The similar terminology can mislead buyers:

IEC 62606 addresses arc-fault detection devices (AFDDs) for household and similar AC circuits within its scope.
IEC 63027 addresses DC arc detection and interruption equipment for photovoltaic systems.

A residential AC AFDD tested to IEC 62606 is not automatically suitable for a 1000 V or 1500 V PV string. The waveform, source behavior, switching noise, insulation system, environmental conditions, and interruption problem are different.

For the AC final-circuit device category, see VIOX's separate guide to IEC 62606 AFDD protection.

Where PV Arc-Fault Protection Can Be Located

The correct location depends on the tested protection coverage, array topology, string count, and interruption method.

Inverter-integrated protection

The detector analyzes one or more DC inputs, and the inverter or associated switchgear interrupts the current path after detection.

အားသာချက်များ

fewer external components;
access to MPPT and current data;
event logging and remote diagnostics may be available;
common in string-inverter designs.

Questions to resolve

How many strings can be connected to each monitored input?
Is every string independently monitored or are several combined before one sensor?
Does opening the inverter input de-energize the complete protected section?
Is the function dependent on a specific firmware version or setting?
What cable section between the array, combiner, and inverter is within the tested coverage?

Combiner-box or string-level protection

Detection closer to the array can improve fault localization and reduce the number of strings represented by one sensing channel. The AFD or AFPE may be integrated into a PV combiner box or installed as dedicated string equipment.

This architecture must account for:

the number of parallel strings;
current flowing from healthy strings toward a fault;
sensor allocation and channel independence;
DC interruption voltage and polarity;
environmental temperature and enclosure protection;
communications and auxiliary-power failure;
coordination with string fuses, disconnects, and inverter controls.

A standard combiner box does not become an AFPE merely because it contains fuses, an SPD, and a DC switch.

Module-level or distributed protection

Distributed sensors or interrupters can narrow the protected zone and improve localization. They also increase component count, rooftop exposure, communications complexity, and replacement considerations.

The project should verify what happens when:

one module device loses power or communications;
only part of a string opens;
the central controller is unavailable;
firmware versions differ across devices;
a parallel fault remains energized from adjacent strings.

Coordinating AFCI With Fuses, Breakers, SPDs, and Isolators

A complete PV DC protection design assigns one job to each protective layer.

ကာကွယ်ရေးအလွှာ	Detects or controls	Coordination question
စထရင်ဖျူး (String fuse)	Reverse-current and defined overcurrent conditions	Does its rating coordinate with module maximum series-fuse rating and parallel-string current?
DC breaker	Overload/short-circuit protection and switching where declared	Is it rated for PV DC voltage, polarity, fault current, and time-current duty?
SPD	Lightning-induced and switching overvoltage	Is the SPD suitable for the PV voltage architecture and grounding arrangement?
DC isolator	Manual or commanded switching/isolation	Can it interrupt the declared DC load, and is it included in the AFPE interruption path?
Ground-fault/insulation monitoring	Leakage or insulation deterioration	What faults remain undetected in an ungrounded or functionally grounded array?
AFD/AFPE	Series-arc signature and tested interruption response	What circuit section, string count, operating range, and fault scenarios are covered?

An AFPE may command an inverter, contactor, solid-state switch, or PV-rated DC isolating device to interrupt the series current path. The executing device must be part of the evaluated architecture. Adding a shunt-trip accessory to an unrelated DC breaker does not by itself establish IEC 63027 or UL 1699B performance.

How PV Connectors and Terminations Create Series Arcs

PV connectors are frequent points of concern because they combine a small contact interface with outdoor temperature cycling, moisture, cable movement, and long service life.

Cross-mating connector brands

Products described as "MC4 compatible" are not necessarily qualified as one connector pair. Contact geometry, plating, spring force, seal compression, tolerances, cable-gland dimensions, and assembly tools can differ. Use connector combinations permitted by the module, connector, and project documentation.

Incorrect crimping

Wrong dies, worn tools, incorrect strip length, unsupported cable size, or a conductor not fully inserted can leave a high-resistance joint. A pull test alone does not prove low electrical resistance, while an electrical test alone does not prove mechanical retention. Follow the connector manufacturer's complete assembly and inspection process.

Loose terminals and damaged cable

Combiner terminals, fuse holders, DC switches, and inverter inputs can develop weak connections when conductor preparation, torque, or strain relief is wrong. Cable abrasion under modules can create both series discontinuities and insulation faults.

Good arc-fault prevention therefore starts before the electronics:

use documented connector combinations;
use calibrated and specified crimp tools;
follow terminal torque values from the actual component;
support cables away from sharp edges and standing water;
maintain bend radius and strain relief;
record string and connector installation details;
inspect alterations and replacement connectors with the same discipline as the original installation.

Commissioning PV Arc-Fault Protection

Commissioning should prove both the protective function and the installation context without creating an uncontrolled arc.

Record:

inverter, AFD, AFI, and AFPE model numbers;
listing or IEC classification and certificate reference;
firmware and enabled protection settings;
maximum corrected string open-circuit voltage;
operating-current range and number of strings per input;
sensor/channel mapping;
protected conductor sections;
interruption device and control path;
alarm, event-log, communications, and reset behavior;
connector families, crimp tools, torque records, and inspection results.

Use only the manufacturer's approved functional test or commissioning method. Do not create an improvised live DC arc to prove operation. Insulation-resistance and continuity testing must also follow inverter, optimizer, SPD, and AFPE instructions so test voltage is not applied through connected electronics that cannot tolerate it.

Troubleshooting Solar AFCI Trips

An arc-fault trip should be treated as a potentially genuine wiring defect until investigation shows otherwise. Repeated resetting without inspection can re-energize a damaged connection.

Start with evidence, not with a disabled setting

Qualified personnel should review:

exact event code and timestamp;
affected MPPT input, string, channel, or sensor;
DC voltage and current before operation;
weather and irradiance conditions;
inverter switching, grid, or communication events;
recent maintenance, module replacement, or cable work;
history of the same fault moving between channels or remaining in one string.

Then follow the equipment manufacturer's isolation and diagnostic process. Inspect connectors, crimps, terminals, cable routing, water ingress, abrasion points, combiner components, and DC isolators. Absence of visible burning does not prove that no intermittent arc occurred.

Sources of unwanted operation

Detection algorithms must distinguish arc noise from normal high-frequency behavior. Challenging conditions can include:

inverter switching spectra;
MPPT operating transitions;
long DC cable runs and coupling between adjacent strings;
DC/DC converters or module-level power electronics;
external electromagnetic interference;
unstable connectors that generate real intermittent noise before visible damage;
incorrect sensor allocation or unsupported string configuration;
outdated or mismatched firmware.

The corrective action is not automatically to lower sensitivity or disable AFCI. First remove physical defects, verify the supported array configuration, and apply only manufacturer-approved firmware and settings.

Solar AFCI and AFPE Procurement Checklist

Buyer question	Evidence to request
Which market requirement is being met?	Adopted NEC clause and listing, IEC 63027 classification/test evidence, or named local installation requirement
Is the product an AFD or complete AFPE?	Functional block diagram identifying detector, interrupter, communication path, and auxiliary power
What circuit section is protected?	Coverage diagram from modules through combiner and inverter inputs
What are the electrical limits?	Maximum PV voltage, Voc range, Vmpp range, Isc, Impp, polarity, and environmental derating
How many strings and inputs are supported?	Maximum strings per input, number of inputs per sensor, and independent channel count
How is the arc interrupted?	AFI type, DC interruption rating, command path, and fail-state behavior
What fault type is tested?	Series-arc test scope plus any separately evaluated parallel-arc or ground-fault functionality
How is reconnection controlled?	Manual/automatic rules, lockout behavior, inspection requirement, and event retention
Does firmware affect compliance?	Certified firmware version, change-control policy, update procedure, and setting restrictions
How are nuisance events handled?	EMC tests, supported topology, diagnostic logs, service procedure, and technical support
What certifications are valid?	Certificate number, issuing body, exact model, manufacturing site if relevant, and current status
How will the system be commissioned?	Approved test procedure, records, alarms, communications, and maintenance instructions

Avoid specifications that say only "inverter shall include AFCI." That phrase does not identify the standard, protected zone, number of monitored strings, interruption function, or acceptance evidence.

အသုံးများသော သတ်မှတ်ချက် အမှားများ

Treating NEC 690.11 and IEC 63027 as equivalent documents

One is an installation-code provision; the other is a product performance and test standard. A project may reference both, but they answer different questions.

Assuming detection always includes interruption

IEC 63027 allows detection-only equipment within its scope. Confirm whether the supplied system is an AFD or complete AFPE.

Counting only inverter DC inputs

The number of physical inputs does not prove the number of independent arc sensors or monitored strings. Obtain the classification and channel map.

Using a standard DC breaker as “solar AFCI”

A DC breaker can execute a trip command only if it is suitable for that function and integrated into an evaluated system. Its ordinary overcurrent element does not automatically detect a series arc.

Disabling protection after repeated trips

An intermittent connector or cable defect may produce arc-like signals before heat damage is obvious. Investigate the circuit and supported configuration before changing protection settings.

Confusing arc fault with arc flash

PV arc-fault protection aims to detect sustained unintended arcs that can create fire. Arc-flash analysis addresses incident thermal energy and worker exposure during high-energy faults. They are related to arcing physics but are not the same study or protective function.

အမြဲမေးလေ့ရှိသောမေးခွန်းများ

Does IEC 63027 require AFCI on every solar installation?

No. IEC 63027 is a product test and performance standard. Installation requirements come from national rules, local codes, project specifications, insurers, or AHJs.

Is an IEC 62606 AFDD suitable for a PV DC string?

Not on the basis of IEC 62606 alone. That standard addresses AC AFDD applications within its scope. PV DC equipment requires appropriate voltage, source-circuit, detection, interruption, and environmental evaluation, such as the relevant IEC 63027 evidence.

Does NEC 690.11 apply to every ground-mounted PV system?

Not necessarily. Applicability depends on the adopted NEC edition, circuit voltage, relationship to buildings, wiring method, any Article 690 or 691 exception, local amendments, and AHJ interpretation. Review the exact project rather than relying on the label "ground mount."

Can an inverter-integrated AFCI protect strings connected through a combiner box?

Only within its evaluated configuration. Confirm the maximum parallel strings, sensor allocation, protected conductor length and zone, combiner arrangement, and interruption path. Combining more strings than the tested limit can change both arc signal strength and fault current paths.

Does a PV fuse or DC MCB replace solar AFCI?

No. Those devices protect against specified overcurrent conditions. A series arc may remain below their operating threshold, so dedicated arc detection may still be required.

What is the difference between solar AFCI and AFPE?

Solar AFCI is common North American terminology for PV arc-fault circuit interruption. AFPE is IEC terminology for equipment combining arc-fault detection and interruption. Always verify the applicable standard and function rather than treating the acronyms as universally interchangeable.

Do microinverter systems need NEC 690.11 protection?

Many microinverter architectures keep individual module DC circuits below the NEC voltage threshold, but the answer depends on the actual circuit voltage and the adopted code. Confirm the equipment architecture and AHJ requirements.

Can an AFCI trip be reset remotely?

Only if the product, applicable standard/listing, installation rules, and operating procedure permit it. A remote reset should not bypass a required inspection or repeatedly re-energize a suspected damaged connection. Check the declared reconnection method and event history.

Final Engineering Rule

PV DC arc-fault protection must be specified as a system function, not a three-letter feature on an inverter brochure.

For NEC projects, confirm the adopted version of NEC 690.11, the 80 V circuit boundary, any valid exception, equipment listing, conductor route, and AHJ acceptance. For IEC projects, confirm whether the equipment is an AFD or AFPE, its IEC 63027 classification, voltage/current range, monitored strings and channels, protected zone, interruption method, firmware, and reconnection behavior.

Then coordinate that function with PV fuses, DC breakers, SPDs, isolators, ground-fault protection, connectors, cable routing, and commissioning records. A fuse, DC MCB, SPD, or isolator remains valuable, but none should be presented as dedicated PV series-arc protection unless the complete system has been evaluated for that function.

နည်းပညာဆိုင်ရာ ကိုးကားချက်များ

စာရေးသူအကြောင်း

ဂျိုး

မင်္ဂလာပါ၊ ကျွန်တော်ကတော့ လျှပ်စစ်လုပ်ငန်းနယ်ပယ်မှာ အတွေ့အကြုံ ၁၂ နှစ်ရှိပြီဖြစ်တဲ့ ကျွမ်းကျင်ပညာရှင် Joe ဖြစ်ပါတယ်။ VIOX Electric မှာ ကျွန်တော့်ရဲ့ အဓိကရည်ရွယ်ချက်ကတော့ ကျွန်တော်တို့ရဲ့ ဖောက်သည်တွေရဲ့ လိုအပ်ချက်နဲ့ကိုက်ညီတဲ့ အရည်အသွေးမြင့် လျှပ်စစ်ဆိုင်ရာဖြေရှင်းချက်တွေကို ပံ့ပိုးပေးဖို့ပဲ ဖြစ်ပါတယ်။ ကျွန်တော့်ရဲ့ ကျွမ်းကျင်မှုနယ်ပယ်တွေကတော့ စက်မှုလုပ်ငန်းသုံး အလိုအလျောက်စနစ်များ (Industrial Automation)၊ လူနေအိမ်သုံး ဝိုင်ယာသွယ်တန်းခြင်းနှင့် လုပ်ငန်းသုံး လျှပ်စစ်စနစ်များပဲ ဖြစ်ပါတယ်။.

PV DC Arc-Fault Protection Explained: NEC 690.11, IEC 63027, and Solar AFCI