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Thread: How to Comply w/NEC 2017 690.11 Arc-Fault Circuit Proection (DC)-Strings > 3 Modules?

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    How to Comply w/NEC 2017 690.11 Arc-Fault Circuit Proection (DC)-Strings > 3 Modules?

    Is there any DC Arc-Fault protection equipment currently available that can satisfy the requirements of NEC 2017 690.11 for PV source and output circuits with over three 60 cell PV modules in series?

    If "no" how do we get this by the AHJ code inspector or is there "equivalent protection?"

    2017 NEC 690.11 states:
    PV systems operating at 80V dc or greater between any two conductors must be protected by a listed PV arc-fault circuit interrupter or other component listed to provide equivalent protection.

    Thanks!

    Ken Clifton
    Salisbury, NC, USA

  2. #2
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    Most inverters include this feature.

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    How about any Combiners or Arc-Fault Protection devices for Combiners?

    Thanks, yes at the inverter, but with a string inverter mounted somewhere on the outside wall of the building and the array on the roof, it might be 75 ft away — and most arc faults happen up in the array or one of the combiners.

    Is there anything to protect the PV source circuits before hitting the combiners?

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    Quote Originally Posted by pclifton View Post
    Thanks, yes at the inverter, but with a string inverter mounted somewhere on the outside wall of the building and the array on the roof, it might be 75 ft away — and most arc faults happen up in the array or one of the combiners.

    Is there anything to protect the PV source circuits before hitting the combiners?
    It isn't necessary. AF detectors in the inverter will shut down the PV wherever the AF occurs. Note that only series AFs are detected, so shutting down the inverter will stop the fault wherever it is.

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    To expand on what ggunn said, with a series arc if you remove the load then the arc stops. In this case the inverter acts as the load on the PV panels.

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    AF detectors in the inverter will shut down the PV ...

    Quote Originally Posted by ggunn View Post
    It isn't necessary. AF detectors in the inverter will shut down the PV wherever the AF occurs. Note that only series AFs are detected, so shutting down the inverter will stop the fault wherever it is.
    Thanks. I am confused, but I don't see how the inverter which is a load, can shut down the series of PV modules (the source). Breaking the circuit at the load-end does not stop arcing that is happening 75 feet up stream possibility up on the roof. Nothing short of turning the sun off would prevent that arcing without some kind of AFCI before the insulation failure.

    I am looking for a DC AFCI that can handle more than a 40A PV output circuit. Here is a excerpt from an article describing this issue:

    Unfortunately, the product safety standard for dc arc-fault circuit protection, UL 1699B, at this time covers products working at currents up to 40 A only. It is difficult, if not impossible, to find arc-fault detectors for larger 200 A–400 A PV output circuits.

    See this SolarPro Mag (down close to the bottom in - ARC-FAULT PROTECTION WAIVER section) link: http://solarprofessional.com/article...1#.WvmmtZ-YV8c

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    Quote Originally Posted by pclifton View Post
    Thanks. I am confused, but I don't see how the inverter which is a load, can shut down the series of PV modules (the source). Breaking the circuit at the load-end does not stop arcing that is happening 75 feet up stream possibility up on the roof.
    ...
    Yes, you are confused. If the inverter opens the circuit it stops acting as a load. If it stops acting as a load, there is nowhere for current to go in the circuit. If there is nowhere for current to go, then any bad connection in the circuit will stop arcing.

    The requirement is to protect against series arcs only (i.e. bad connection). It is not required to detect arcs between positive and negative, or to ground. Ground-fault detection and interruption addresses that.

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    Series Arc-Faults Only?

    Quote Originally Posted by jaggedben View Post
    The requirement is to protect against series arcs only (i.e. bad connection). It is not required to detect arcs between positive and negative, or to ground. Ground-fault detection and interruption addresses that.
    Strange, when I read the definition of an Arc-Fault here on this forum at: https://www.mikeholt.com/mojonewsarc...n~20020124.htm it says:
    Arcing faults can occur in one of two ways, series arcing faults or parallel arcing faults, but the most dangerous of these is the parallel arc...snip...Typically, series arcs do not cause enough heat to create a fire.

    According to what you say, it does not matter if the conductors in the PV source circuits develop an Arc-Fault and there is no protection...
    Where exactly does the NEC mention that only series Arc-Faults need to be protected?

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    Quote Originally Posted by pclifton View Post
    Strange, when I read the definition of an Arc-Fault here on this forum at: https://www.mikeholt.com/mojonewsarc...n~20020124.htm it says:
    Arcing faults can occur in one of two ways, series arcing faults or parallel arcing faults, but the most dangerous of these is the parallel arc...snip...Typically, series arcs do not cause enough heat to create a fire.

    According to what you say, it does not matter if the conductors in the PV source circuits develop an Arc-Fault and there is no protection...
    Where exactly does the NEC mention that only series Arc-Faults need to be protected?
    The code doesn't use the word 'series' but it uses this language which amounts to the same thing:
    "The system shall detect and interrupt arcing faults
    resulting from a failure in the intended continuity of
    a conductor, connection, module, or other system
    component in the dc PV source and dc PV output
    circuits."

    Note the language doesn't refer to a fault to ground or another conductor.
    Again, ground fault protection, which has been required for a long time, would address most parallel arc faults.

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    Thanks

    Quote Originally Posted by jaggedben View Post
    The code doesn't use the word 'series' but it uses this language which amounts to the same thing"
    Thank you.

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