705.12(D)(6) And Enphase trunk cable

[ggunn]

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.

Then as an engineer you revert to a Scottish brogue and say, "I cannae rewrite the laws of physics, Cap'n! She's gonna blow!"

 

[mwm1752]

If there is an arcing issue with a panel feeder do individual branch circuit AFCI breakers in that panel trip?

If not the only way to truely protect the cords would be immediately after the micro inverter--- so the AFCI protection could only be logically be integrated in the inverter for this code to apply. As the code is written does not the AFCI protection pertain to the complete string as it travels from Micro inverter to Micro inverter to last j box tie?

If so, the is a mechanical way of installing protection that exists presently.

 

[shortcircuit2]

If so, the is a mechanical way of installing protection that exists presently.

How?

 

[SolarPro]

If there is an arcing issue with a panel feeder do individual branch circuit AFCI breakers in that panel trip?

Presumably that is the goal. But since there aren't any listed products, it's sort of a moot point. It's hard to analyze how something works when it doesn't exist yet.

While I agree that it makes a lot of sense for microinverters to provide this functionality, the only way to accomplish that is to rewrite or amend the product safety standard. If you start expediting that process today, you might be able to complete the project in 3 to 5 years.

 

[mwm1752]

How?

There are alot of if's & then's -- If the AFCI trips when there is a line side issue, then combine all of your microinverter outputs in a subpanel, IE: 2- 240v volt 20 amp backfed breakers in a 12 circuit ML 125 A Panel --- feed out of the panel to the AC tie with a 40A AFCI breaker. Arcing issues appear on either cord feed from the microinverters the AFCI trips. Refer ot the big IF -- I have not heard of a panel tripping multiple AFCI circuits due to a line side fault.
To put it in perspective the inverters have DC AFCI protection - the question is is the AFCI protection for the inverter or for the input wiring?

 

[jaggedben]

...
To put it in perspective the inverters have DC AFCI protection - the question is is the AFCI protection for the inverter or for the input wiring?

Although I think that DC Arc Fault protection is hardly relevant to this discussion, I will just point out that microinverters don't have it because it's not required for DC system voltages under 80 volts.

Here's a different point that is relevant...

If there were any arcing in the exposed microinverter AC cabling (or in fact anywhere in the AC interconnection wiring all the way back to the utility transformer), it is highly likely that the inverters would register an AC voltage out of range event and shut down for at least 5 minutes. How this interplays with an AFCI breaker is a good question.

 

[shortcircuit2]

There are alot of if's & then's -- If the AFCI trips when there is a line side issue, then combine all of your microinverter outputs in a subpanel, IE: 2- 240v volt 20 amp backfed breakers in a 12 circuit ML 125 A Panel --- feed out of the panel to the AC tie with a 40A AFCI breaker. Arcing issues appear on either cord feed from the microinverters the AFCI trips. Refer ot the big IF -- I have not heard of a panel tripping multiple AFCI circuits due to a line side fault.
To put it in perspective the inverters have DC AFCI protection - the question is is the AFCI protection for the inverter or for the input wiring?

I was wondering what mechanical protection you were referring to?

 

[SolarPro]

To put it in perspective the inverters have DC AFCI protection - the question is is the AFCI protection for the inverter or for the input wiring?

Do they? I've heard microinverter manufacturers claim that their products can detect dc arc-faults. But it seems like kind of a moot point. Microinverters are generally exempt from the dc arc-fault protection requirements in 690. If you review 690.11, you'll see that it only applies to systems with a max operating voltage of 80 volts or greater. If the Code or product safety standard doesn't require this functionality, I wouldn't assume that all microinverters have it. (I see jaggedben has already covered this ground.)

In any case, since the dc source (the PV module) is current-limited, there's no need to protect the input wiring to the microinverter. Assuming the products are designed and used correctly, the PV module can never generate an overcurrent condition that would damage the dc input conductor to the microinverter. So ac AFCI is for the trunk cable only.

 

[iwire]

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

What a surprise, the manufacturers overstated their own abilities. :roll:

 

[Carultch]

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.

I can easily find a breaker that isn't marked "line and load". All I need is sandpaper, and I can make any breaker not marked "line and load".

I think the backfeed suitability of a breaker needs to be labeled with an AFFIRMATIVE marking, as opposed to the absence of a marking.

 

[SolarPro]

I can easily find a breaker that isn't marked "line and load". All I need is sandpaper, and I can make any breaker not marked "line and load".

I think the backfeed suitability of a breaker needs to be labeled with an AFFIRMATIVE marking, as opposed to the absence of a marking.

It sounds like that's the way things are heading, in part because breakers listed "line" and "load" are increasingly being tested and listed for back-fed applications. Historically those markings are how you identify breakers that have been tested with current in both directions, as illustrated by the language in 690.10(E). But that language is expected to change in NEC 2017.