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

[GlowNDAark]

Hi Everyone,
I did the online search to find a forum to discuss 1500VDC rated AFCI device on ground mount project, and I found this! Glad to be here. I am looking forward to learn and contribute. Here is what I am evaluating and could use your opinions and practical experience. I am working on a design of a large ground mount solar farm (>15MW DC) with 1500VDC UL listed central inverters. PV modules and combiner boxes are also UL listed for 1500VDC. The design is at 90PCT stage. The implemented code cycle for the AHJ is NEC2014.
NEC 2014 690.11 requires AFCI devices for all systems greater than 80VDC . My research tells me that 1500VDC device AFCI is some what of a "purple cow". Digging down further I could come up with 2 options
- Per NEC 90.4, maybe get a waiver for AFCI protection for this project if AHJ chooses to refer to NEC 2011; which requires AFCI protection only for PV systems located on "Buildings" under the basis that product UL safety standard does not exist.
- Go with NEC 2017 and follow 690.11 exception. Please note that the system is located on a site where excavation is not allowed, (the design currently has ladder tray) than option is to go with enclosed cable tray - which is adding cost and design change to the project.
I have not made a final decision to either go in with a request for waiver to AHJ or provide enclosed cable tray for the whole system. I am evaluating construction feasibility for enclosed cable tray and the risk of not having AFCI on the ground mount array.

How has your experience been for satisfying 690.11 requirement for 1500 VDC PV Systems? Thanks

 

[electrofelon]

Hi Everyone,
I did the online search to find a forum to discuss 1500VDC rated AFCI device on ground mount project, and I found this! Glad to be here. I am looking forward to learn and contribute. Here is what I am evaluating and could use your opinions and practical experience. I am working on a design of a large ground mount solar farm (>15MW DC) with 1500VDC UL listed central inverters. PV modules and combiner boxes are also UL listed for 1500VDC. The design is at 90PCT stage. The implemented code cycle for the AHJ is NEC2014.
NEC 2014 690.11 requires AFCI devices for all systems greater than 80VDC . My research tells me that 1500VDC device AFCI is some what of a "purple cow". Digging down further I could come up with 2 options
- Per NEC 90.4, maybe get a waiver for AFCI protection for this project if AHJ chooses to refer to NEC 2011; which requires AFCI protection only for PV systems located on "Buildings" under the basis that product UL safety standard does not exist.
- Go with NEC 2017 and follow 690.11 exception. Please note that the system is located on a site where excavation is not allowed, (the design currently has ladder tray) than option is to go with enclosed cable tray - which is adding cost and design change to the project.
I have not made a final decision to either go in with a request for waiver to AHJ or provide enclosed cable tray for the whole system. I am evaluating construction feasibility for enclosed cable tray and the risk of not having AFCI on the ground mount array.

How has your experience been for satisfying 690.11 requirement for 1500 VDC PV Systems? Thanks

I dont have an answer for you, but just wanted to say it is cool to hear about 1500VDC systems out there! I was not aware there was equipment available for 1.5KV yet. I have been on a 2.5Meg and we were just ranting/dreaming of how much work it would save if it was 1.5KV.... I am a big fan of central inverters too.

 

[pv_n00b]

NEC 2014 690.11 requires AFCI devices for all systems greater than 80VDC . My research tells me that 1500VDC device AFCI is some what of a "purple cow". Digging down further I could come up with 2 options
- Per NEC 90.4, maybe get a waiver for AFCI protection for this project if AHJ chooses to refer to NEC 2011; which requires AFCI protection only for PV systems located on "Buildings" under the basis that product UL safety standard does not exist.
- Go with NEC 2017 and follow 690.11 exception. Please note that the system is located on a site where excavation is not allowed, (the design currently has ladder tray) than option is to go with enclosed cable tray - which is adding cost and design change to the project.
I have not made a final decision to either go in with a request for waiver to AHJ or provide enclosed cable tray for the whole system. I am evaluating construction feasibility for enclosed cable tray and the risk of not having AFCI on the ground mount array.

How has your experience been for satisfying 690.11 requirement for 1500 VDC PV Systems? Thanks

Under the 2014 NEC all 1,500V systems were behind the fence since there was a lack of 1,500V UL listed equipment until recently, so leaving out AFCI was not a problem. Under the 2017 NEC the AFCI exclusion that would cover almost all ground mount arrays covered it. As far as I know, there are no products that will provide an AFCI function for 1,500V arrays and since they are not required under the 2017 NEC there will probably never be any. So that leaves you with the two choices you listed. Either will get you what you need. If you have an AHJ that requires you to fully comply with 2014 then you are out of luck.

 

[Lorenze]

Two Options

Two Options

Under the 2014 NEC all 1,500V systems were behind the fence since there was a lack of 1,500V UL listed equipment until recently, so leaving out AFCI was not a problem. Under the 2017 NEC the AFCI exclusion that would cover almost all ground mount arrays covered it. As far as I know, there are no products that will provide an AFCI function for 1,500V arrays and since they are not required under the 2017 NEC there will probably never be any. So that leaves you with the two choices you listed. Either will get you what you need. If you have an AHJ that requires you to fully comply with 2014 then you are out of luck.

Just to chime in here, I believe you have two options:

1. Apply NEC 2017 691.10 allowing for no AFCI protection for systems rated at 5MW and above.
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.

 

[pcanning87]

Any Updates?

Any Updates?

Has anybody found a product yet that complies with 1500V AFCI? We're getting more inspectors taking a look at this and asking why we don't do string inverters, which I believe can comply. I'd be open to a stand-alone pass-through box, and potentially a non-UL listed (IEC listed?)product if available.

 

[Besoeker]

I dont have an answer for you, but just wanted to say it is cool to hear about 1500VDC systems out there!

There are. And not just for PV. We made inverters directly connected at 3.3kV. The DC link was about 4.5kV. Not for the faint-hearted.

 

[pv_n00b]

Has anybody found a product yet that complies with 1500V AFCI? We're getting more inspectors taking a look at this and asking why we don't do string inverters, which I believe can comply. I'd be open to a stand-alone pass-through box, and potentially a non-UL listed (IEC listed?)product if available.

There is nothing I know of and since the latest code does not require it I doubt anyone will build and sell one. Since you are building under the 2014 NEC build behind the fence or point the AHJ to 90.4. Sounds like you just have the odd hard to work with AHJ.

What 1,500V string inverters provide AFCI?

 

[pcanning87]

There is nothing I know of and since the latest code does not require it I doubt anyone will build and sell one. Since you are building under the 2014 NEC build behind the fence or point the AHJ to 90.4. Sounds like you just have the odd hard to work with AHJ.

What 1,500V string inverters provide AFCI?

Thanks, being proactive with the AHJs is basically our approach at this point. We're under 2017 NEC, which at least in my interpretation does require AFCI on source circuits, and possibly require AFCI on output circuits as well unless they are in metallic conduit or below grade.

The manuals for the Chint 100 & 125kW 1500V string inverters claim to have UL1699B listed DC AFCI, although I haven't dug into it since we're yet to design with a 1500V sting inverter. I'm not sure about Sungrow, Huawei, etc.

 

[pv_n00b]

Thanks, being proactive with the AHJs is basically our approach at this point. We're under 2017 NEC, which at least in my interpretation does require AFCI on source circuits, and possibly require AFCI on output circuits as well unless they are in metallic conduit or below grade.

If your system is 5MW or greater then it falls under 691 and 691.10 states:

691.10 Arc-Fault Mitigation. PV systems that do not comply
with the requirements of 690.11 shall include details of fire
mitigation plans to address dc arc-faults in the documentation
required in 691.6.

That's a get out of jail free card.

 

[pcanning87]

If your system is 5MW or greater then it falls under 691 and 691.10 states:

691.10 Arc-Fault Mitigation. PV systems that do not comply
with the requirements of 690.11 shall include details of fire
mitigation plans to address dc arc-faults in the documentation
required in 691.6.

That's a get out of jail free card.

Totally agree, unfortunately most of our systems are under 5MW.


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[BillK-AZ]

Arc Fault Detection Module

Arc Fault Detection Module

If your inverter has a suitable control input, you may be able to use one of these Arc Fault Detection Modules
http://www.dcsunvolt.com/ArcFaultDetectionModule.shtml

This is detection only, one of the PV circuit DC conductors (2,000V PV wire) passes through this device and any arc fault rf signal is detected. The isolated Form-C relay output can be used to shut down the inverter via a control input.

 

[pcanning87]

If your system is 5MW or greater then it falls under 691 and 691.10 states:

691.10 Arc-Fault Mitigation. PV systems that do not comply
with the requirements of 690.11 shall include details of fire
mitigation plans to address dc arc-faults in the documentation
required in 691.6.

That's a get out of jail free card.

Also, Massachusetts unfortunately deleted Article 691 as part of their state amendments.


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[pcanning87]

If your inverter has a suitable control input, you may be able to use one of these Arc Fault Detection Modules
http://www.dcsunvolt.com/ArcFaultDetectionModule.shtml

This is detection only, one of the PV circuit DC conductors (2,000V PV wire) passes through this device and any arc fault rf signal is detected. The isolated Form-C relay output can be used to shut down the inverter via a control input.

That’s interesting, I hadn’t seen it before. I’ll check it out, thanks.


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[ggunn]

Totally agree, unfortunately most of our systems are under 5MW.


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Why is that unfortunate? There is plenty of work in this business in systems of less than 5MW.

 

[pcanning87]

Why is that unfortunate? There is plenty of work in this business in systems of less than 5MW.

Just in reference to this particular issue.


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[pv_n00b]

If your inverter has a suitable control input, you may be able to use one of these Arc Fault Detection Modules
http://www.dcsunvolt.com/ArcFaultDetectionModule.shtml

This is detection only, one of the PV circuit DC conductors (2,000V PV wire) passes through this device and any arc fault rf signal is detected. The isolated Form-C relay output can be used to shut down the inverter via a control input.

According to the datasheet it's only rated for 1,000Vdc.

 

[pv_n00b]

Thanks, being proactive with the AHJs is basically our approach at this point. We're under 2017 NEC, which at least in my interpretation does require AFCI on source circuits, and possibly require AFCI on output circuits as well unless they are in metallic conduit or below grade.

The manuals for the Chint 100 & 125kW 1500V string inverters claim to have UL1699B listed DC AFCI, although I haven't dug into it since we're yet to design with a 1500V sting inverter. I'm not sure about Sungrow, Huawei, etc.

According to the Chint manual it does have DC arc-fault detection. So that is an option. Either the AHJ will severely limit your choices in equipment or they let you off with 90.4. It's not unusual for the NEC to introduce a requirement that is not commercially available at the time of publication as a way to encourage manufacturers to provide for it, or sometimes a manufacturer will slip in a requirement because they have something they are ready to supply. AHJs usually allow for this by not requiring compliance until there many choices on the market, but not all AHJs do that.

 

[BandGap1.1eV]

I did some exhaustive research on this recently and found very few answers. All 1500V inverter manufacturers I found will claim AFCI compliance, but when you dig deeper the UL 1699 standard (there are at least 4 variants) they are certified to is only for 1000V. The one nugget of hope right now is Innovative Solar who has listed a 1500V disconnecting combiner with an AFCI option.

https://docs.wixstatic.com/ugd/196ee4_4c76cb8476144760b2b3940031e247f9.pdf

I've reached out but have not heard back regarding whether is actually a 1500V AFCI option (UL 1699B-bulletin).

https://standards.globalspec.com/std/10264847/ul-1699b-bulletin

Further interpretation of the exception in 690.11 requires defining a "PV output circuit". Based on my (and others) interpretation this refers to the output circuit from a DC combiner since 690.31(B) separately to "PV source circuits" and "PV output circuits" as separate entities.

If you direct bury a combiner output circuit or install in a metal raceway, any arc fault that occurs will rapidly evolve into a ground fault and shut shown the system through the GFDI circuitry. This all means the DC string wiring still needs AFCI protection since you cannot reasonably be expected to direct bury string wiring.


This is bringing back flashbacks. I need a hug.

 

[jaggedben]

Further interpretation of the exception in 690.11 requires defining a "PV output circuit". Based on my (and others) interpretation this refers to the output circuit from a DC combiner since 690.31(B) separately to "PV source circuits" and "PV output circuits" as separate entities.

I don't have the 2017 in front of me to read the new exception, but the difference between source and output circuits has been well defined for many code cycles and shouldn't be too open to interpretation. Which is to say, I agree with you.

 

[pv_n00b]

I did some exhaustive research on this recently and found very few answers. All 1500V inverter manufacturers I found will claim AFCI compliance, but when you dig deeper the UL 1699 standard (there are at least 4 variants) they are certified to is only for 1000V. The one nugget of hope right now is Innovative Solar who has listed a 1500V disconnecting combiner with an AFCI option.

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 actually one of my ongoing complaints about several of the UL Standards related to PV, they are encapsulating various levels of testing in the same standard so knowing the product is listed does not tell me what they listed it to do. It also shows that UL does no policing of ads, data sheets, etc to ensure that the manufacturer is accurately presenting the capability of the product. UL is supposed to review installation manuals for compliance, but I have found that hit or miss. And what someone gets out of a support call depends on who is answering the call.

I have found a few manufacturers over the years who misrepresented their equipment and when reported to UL little was done, in one case UL actually changed the standard to conform to what the manufacturer was misrepresenting the product as being able to do under the listing.

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.