1500VDC AFCI device for Ground Mount PV System and Code Interpretation

[jaggedben]

2.9 DC Arc-fault Protection
The Standard wire-box inverters include DC Arc-fault detection compliant with UL 1699B. The inverter will detect electrical noise that is indicative of a DC series arc. Upon detection of an arc-fault, the inverter will cease operation.

Is the electrical noise that is indicative of a DC series arc meaningfully different at 1500V vs. 1000V? I mean, presumably the inverter's parts are rated for 1500V, and it just seems to my non-inverter-designer brain like the noise detection method would not need to be different. Like, you're measuring the voltage and current in either case, and your components for doing so are rated for the voltage they'll see. And the brains of the inverter does the analysis.

This might be a little different for a combiner box like the OP asked for, where we're looking for components that are rated for 1500V that go inside an enclosure and there are also independent 'thinking' components for the noise analysis that also need to go in that box and need to be rated for the higher voltage or appropriately isolated or something.

 

[ggunn]

Is the electrical noise that is indicative of a DC series arc meaningfully different at 1500V vs. 1000V? I mean, presumably the inverter's parts are rated for 1500V, and it just seems to my non-inverter-designer brain like the noise detection method would not need to be different. Like, you're measuring the voltage and current in either case, and your components for doing so are rated for the voltage they'll see. And the brains of the inverter does the analysis.

I'm not an inverter designer, either, but what it is detecting is an AC noise component riding on a DC voltage. It seems to me that the magnitude of the DC offset to the AC waveform shouldn't matter.

 

[BandGap1.1eV]

One might assume that if a manufacturer has a 1,500V inverter and states that it has arc-fault protection that the arc-fault protection might actually work at 1,500V.



This is from the Chint 100kW-125kW manual:

2.9 DC Arc-fault Protection
The Standard wire-box inverters include DC Arc-fault detection compliant with UL 1699B. The inverter will detect electrical noise that is indicative of a DC series arc. Upon detection of an arc-fault, the inverter will cease operation.

So it looks like it provides 1,500V AFCI protection to 1699B. If it does not then this is a problem that should be reported to UL, for what it's worth.

This is the frustrating part. Based on what I found there are multiple "editions" of 1699B.

1699B-1 was released in 2011 and covered 1000V systems.
1699B-2 was released in 2013 and clarified some language around the term “device”.
1699B-3 was released in 2017 but only applies to residential breakers (20A, 120V, 60 Hz).
1699B-BULLETIN was released in 2018 and finally ups the voltage threshold to 1500V.

https://standardscatalog.ul.com/standards/en/outline_1699b_1
https://standardscatalog.ul.com/standards/en/outline_1699b_2
https://standardscatalog.ul.com/standards/en/standard_1699_3
https://standards.globalspec.com/std/10264847/ul-1699b-bulletin

 

[pv_n00b]

This is the frustrating part. Based on what I found there are multiple "editions" of 1699B.

1699B-1 was released in 2011 and covered 1000V systems.
1699B-2 was released in 2013 and clarified some language around the term “device”.
1699B-3 was released in 2017 but only applies to residential breakers (20A, 120V, 60 Hz).
1699B-BULLETIN was released in 2018 and finally ups the voltage threshold to 1500V.

https://standardscatalog.ul.com/standards/en/outline_1699b_1
https://standardscatalog.ul.com/standards/en/outline_1699b_2
https://standardscatalog.ul.com/standards/en/standard_1699_3
https://standards.globalspec.com/std/10264847/ul-1699b-bulletin

Yes, this is the problem with listing to an outline and not waiting for the standard to be finalized. UL 1699B is not a UL Standard, it is an Outline of Investigation and that means it is still under active development. I did not know that 1699B was an outline until I looked it up. Some AHJs will not accept a listing to an outline as a true UL Listing and I agree with them. I wish UL did not allow the practice of listing to outlines.

In the case of the PV AFCI, there is no UL Standard to list too, so being "listed" to 1699B is meaningless. But I would have to believe that even unlisted the AFCI is designed to operate at 1,500V, at least with the same level of assurance I give to any information put out by a manufacturer about their product. When dealing with an AHJ that insists that the AFCI has to be Listed I would just show them on the UL website that there is no UL Standard for PV DC AFCIs to be listed too at this time and one is under development. The AHJ then has the choice of accepting that the UL Standard does not exist and allowing the equipment under 90.4 or they could just not allow any PV installations in their area.

 

[jcrawford]

This topic has been of great interest to me as well. I see references to taking the 691.11 exception in this thread. What kinds of fire mitigation plans have others used to satisfy 691.11?

 

[Carultch]

2. Apply 90.4 given that there are no products currently available that are listed specifically for arc-fault detection and interruption. UL1699B is written with a maximum system voltage of 1000Vdc. Therefore, until 1699B test procedures are revised to 1500Vdc, 1500V arc-fault products will not be available to the PV industry.

It seems unreasonable to specifically plan anything that relies on a 90.4 exception, when you have the option of planning something else. I get that if the code requires a new technology that isn't available yet, it is a reasonable judgement allow compliance with the previous code cycle on that particular issue, forgoing the new technology. Or if you are locked in to an inverter by a utility ISA, and no DC BOS equipment exists yet for this particular inverter to comply with a new standard, a 90.4 exception is reasonable to give.

However, it is another matter entirely to deliberately go down the road of a 1500V system, knowing in advance that compliance is not possible with a mature rule that has been in place for 3 cycles. A 1000V system seems like the obvious limit any time AFCI is required, until the technology can catch up with 1500V. If anything, a 1500V system has a much higher risk of arcing than 600V and 1000V counterparts, and needs AFCI the most.