705.12(D)(6) And Enphase trunk cable

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csoc64

Senior Member
Location
northeast
Does 705.12(D)(6) apply to Enphase single 240V single phase trunk cable? Recently had an inspector tell me I have to install a 70A Arc Fault breaker (replacing a standard 70A 2 pole intertie breaker) in the service panel for an Enphase 240V system. I quoted 690.11 and he in turn quoted 705.12(D)(6). While this obviously would not apply to the 70A intertie breaker, does it apply to the 15A and 20A breakers in the MLO combiner panel because I have trunk cable on the roof (which terminates in a J box on the roof and is hard piped to the MLO)? 2014 code applies.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Does 705.12(D)(6) apply to Enphase single 240V single phase trunk cable? Recently had an inspector tell me I have to install a 70A Arc Fault breaker (replacing a standard 70A 2 pole intertie breaker) in the service panel for an Enphase 240V system. I quoted 690.11 and he in turn quoted 705.12(D)(6). While this obviously would not apply to the 70A intertie breaker, does it apply to the 15A and 20A breakers in the MLO combiner panel because I have trunk cable on the roof (which terminates in a J box on the roof and is hard piped to the MLO)? 2014 code applies.

I don't have the 2014 in front of me to confirm the section, but yes, this is a new requirement in 2014.

It makes sense to me to apply it only to the branch circuit breakers, but hey, if a 70A breaker is cheaper and the inspector is okay with it...;)

I'm glad we don't have to do this in California until 2017.
 

csoc64

Senior Member
Location
northeast
I don't have the 2014 in front of me to confirm the section, but yes, this is a new requirement in 2014.

It makes sense to me to apply it only to the branch circuit breakers, but hey, if a 70A breaker is cheaper and the inspector is okay with it...;)

I'm glad we don't have to do this in California until 2017.
Do you know of anyone supplying 2 pole AFCI breakers that are listed suitable for backfeed?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Do you know of anyone supplying 2 pole AFCI breakers that are listed suitable for backfeed?

I do not know of any GFCI or AFCI breaker that is rated for backfeed. The fact that the electronic circuitry in the breaker consumes power and is connected on the line side of the contacts makes for a certain asymmetry.
 

mwm1752

Senior Member
Location
Aspen, Colo
Thanks.



Nope. See above. Again, I'm glad I haven't yet had to have this conversation with an AHJ.

the UL document link I provided for AFCI clearly states an AFCI breaker is not labeled line/load therefore it is able to be backfed. which contradicts the emphase document
 

SolarPro

Senior Member
Location
Austin, TX
If you can find an AFCI breaker that is not labeled "line" and "load," then, yes, you can backfeed it. In practice, you can't find these because they don't exist.

Long story short, some of the CB manufacturers that met with the CMP during the NEC 2014 proposal process overstated the ease with which they could develop backfeedable AFCI CBs and bring them to market. As a result, we have a requirement than no one can meet.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If you can find an AFCI breaker that is not labeled "line" and "load," then, yes, you can backfeed it. In practice, you can't find these because they don't exist.

Long story short, some of the CB manufacturers that met with the CMP during the NEC 2014 proposal process overstated the ease with which they could develop backfeedable AFCI CBs and bring them to market. As a result, we have a requirement than no one can meet.

Well, the big question is whether installing the CB with the line on the inverter side would be legal since there would occasionally be power flowing just into the GTI and the "load" side would always be live.
Anyway, the "simple" solution is to provide as many small panels as you have branch circuits so that you can connect each GTI to the bus side of one AFCI breaker. :(
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
What would be the danger of using a breaker that's marked 'line' and 'load'? Or would you get nuisance tripping?
I don't know what would happen, physically, but the NEC says you cannot backfeed a breaker that is marked line and load.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Well, the big question is whether installing the CB with the line on the inverter side would be legal since there would occasionally be power flowing just into the GTI and the "load" side would always be live.
Anyway, the "simple" solution is to provide as many small panels as you have branch circuits so that you can connect each GTI to the bus side of one AFCI breaker. :(

I see a potential issue of providing holddowns ...

Also, suppose one had an AC combiner. Would there by any technical issues with providing an AFCI breaker this way that fed the whole AC combiner instead of each branch breaker? (as mentioned by the OP) That would sure be easier.

I don't know what would happen, physically, but the NEC says you cannot backfeed a breaker that is marked line and load.

I know. That's not what I asked.
 

SolarPro

Senior Member
Location
Austin, TX
I don't know the nature of the technical challenges. But presumably it's not as easy to accomplish as the CMP was led to believe. Here's what Tim Zgonena from UL wrote in the substantiation for this new subsection:

AC AFCI equipment and requirements are being developed that include existing AC AFCI protection combined with additional backfeed requirements for this specific purpose. These new requirements and certified equipment are expected to be available by the time of publication of the 2014 NEC. This is an extension of existing requirements and is a significantly easier undertaking in comparison to the development of PV DC AFCIs.

So that was the assumption the CMP was making when it accepted the proposal. But the backfeedable AC AFCI protection was not available last year, and as far as I know still isn't available today. Presumably multiple vendors are working on this, but it could be years before we have listed products for this application. AHJs should just waive this requirement?basically enforcing NEC 2011 as it pertains to microinverters?until these new products make it to market.
 

shortcircuit2

Senior Member
Location
South of Bawstin
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.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I figured you did. Why is it an issue, since backfeeding a line/load marked breaker is forbidden by the NEC? That's my polite way of saying "Who cares?" :D

Mostly because I can easily imagine some of the AHJs around me seeing AFCI breakers available and ignoring the line/load issue, and I would want to have my ducks in a row regarding exactly why it's not only against the code but a bad idea. Nothing harder that convincing an AHJ that they're interpretation is wrong when they've already started enforcing that interpretation.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Mostly because I can easily imagine some of the AHJs around me seeing AFCI breakers available and ignoring the line/load issue, and I would want to have my ducks in a row regarding exactly why it's not only against the code but a bad idea. Nothing harder that convincing an AHJ that they're interpretation is wrong when they've already started enforcing that interpretation.

Got it, but I would think that showing an inspector the specific proscription by the NEC of backfeeding any breakers with line/load designations would be enough.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Got it, but I would think that showing an inspector the specific proscription by the NEC of backfeeding any breakers with line/load designations would be enough.

I've had enough situations where I've shown an inspector an exact section in the code addressing a situation and they still disagreed with me and it took weeks or months to get resolved.
 
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