There are 2 proposals to remove 705.12(D)(6) from the NEC in 2017. They will probably pass if no manufacturer has a product by then.
Here is supporting substantiation from SEIA on their proposal to delete 705.12(D)(6)...
Statement of Problem and Substantiation for Public Input
This Public Input is the result of a consensus process established among two groups of stakeholders: (1) the Solar Energy Industries Association (SEIA) Codes and Standards Working Group, and (2) the Solar America Board of Codes and Standards (SolarABCs) PV Industry Forum. A list of participants in these groups is set forth at SEIA?s Public Input statements for 690.1(a) and 690.2.
The addition of 705.12(D)(6) in the 2014 version has done nothing but create industry confusion on its application, create functional issues and is not supported by major protector manufacturers (as of the writing of this proposal, no suitable devices are widely available on the market). In addition, the requirements are not aligned with how arc-fault has been implemented for AC premise wiring in section 210.12 of the code.
The heading of 705.12(D)(6) mainly targets the AC interconnection method used with groups of utility interactive inverters/AC modules installed in not readily accessible locations (on the exterior surface of any structure), versus inverters with AC outputs that are part of an interior premises wiring system of dwellings where AC arc fault protection of section 210.12 typically applies. Among all utility interactive inverters/AC modules installed on dwellings and other buildings using listed interconnecting cabling methods tested specifically for PV applications, there are no documented cases of an ac arc-fault occurring on the exposed PV ac wiring as described in the justification. With almost 5 million Enphase devices in the field, and over 35 billion unit hours of operation, Enphase has not seen a single case where an ac arc-fault occurred that resulted in any significant damage. Other manufacturers of AC Modules and microinverters involved with this proposal support this claim as well.
When the proposal was written for the 2014 code cycle, it was expected that listed AC arc fault protectors for this application would be available at the time of publication. To date, no vendors have released AFCI breakers that are Listed as suitable for backfeed. In addition, there are significant issues associated with the use of AFCI devices in a back fed application. One such event is transient over voltages produced by inverters during load rejection events (breaker opening) have been shown to damage the AFCI detection circuits. This leads to a loss of arc-fault functionality with no indication that a failure has occurred. Note: In all devices tested to date the overcurrent protection remains effective following a loss of the AFCI function and the loss of AFCI function is not indicated. Nuisance tripping due to advanced inverter functions that will likely be required by 2017 will also be a problem. The implementation of new functional issues and the lack of suitable devices will affect the implementation of microinverter/AC module systems around the country for no valid reason.
The exposed ac conductors referenced in 705.12(D)(6) for not readily accessible inverters/AC modules are an exterior premises wiring system and arc protection of exterior circuits is not required elsewhere in the Code (even for dwelling units in section 210.12). The interconnected cabling for which 705.12(D)(6) seems to apply to are typically located above roofing materials, which carry a fire rating classification, and below PV modules, which are also evaluated for ignition and flame spread. The conductors are fully jacketed, UV resistant, and rated for direct burial along with other specific tests for TC-ER rating. In addition to the TC-ER rating, listed microinverters and AC module systems are often evaluated/listed to additional requirements specific for PV applications. The listed systems using these cables for interconnecting the AC output are installed by qualified/trained personnel following industry practices, manufacturer?s instructions and code for routing and securing. The AC output of these systems are not connected to standard AC receptacles. This is in marked contrast to arc-fault protection required for inside premises wiring of dwellings, where the primary concern is with cord connected equipment where the cord is: in direct contact with unevaluated flammable materials, is subject to mechanical damage, and is typically single insulated cables, e.g. zip cord plugged into convenience outlets.
Section 705.12(D)(6) implies protection is required on any type of structure (not just dwellings) and for any type of supply system (three phase or single phase). Section 210.12 is specifically for dwelling type structures, interior wiring of 120V single phase. Many vendors offer only single pole devices and only a few offer 2-pole breakers suitable for 240 V single phase applications When contacted, manufacturers that produce single pole AFCI breakers have stated they have no plans to produce two pole or 3-pole devices. Currently 3-pole breakers suitable for 3-phase application simply do not exist. All major breaker manufacturers have been contacted and none have indicated any plans to produce 3-pole AFCI breakers. The lack of availability is very problematic since breakers are Listed only for use in electrical panels from the same manufacturer.
It is recommended by the SEIA Codes and Standards Working Group and the SolarABCs PV Industry Forum to remove the requirements of 705.12(D)(6) from the Code.