String level AFCI on the DC side

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Carultch

Senior Member
Location
Massachusetts
I'd like to see if anyone can recommend a solution for string-level AFCI. What I need is a device that does the 690.11 arc fault feature, but does not combine the strings.

I have a project that uses the European version of SMA Sunny Tripower inverters, which do not allow you to "pre-parallel" your strings in advance of connecting to the inverter, and does not already contain AFCI, which the project requires.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I'd like to see if anyone can recommend a solution for string-level AFCI. What I need is a device that does the 690.11 arc fault feature, but does not combine the strings.

I have a project that uses the European version of SMA Sunny Tripower inverters, which do not allow you to "pre-parallel" your strings in advance of connecting to the inverter, and does not already contain AFCI, which the project requires.

I thought that all SMA inverters now have DC AFCI. Not so?
 

SolarPro

Senior Member
Location
Austin, TX
Are you using the Tripower 60-US?

http://www.sma-america.com/products/solarinverters/sunny-tripower-60-us.html#Downloads-137582

That's a model that SMA has in its quiver via an acquisition. It has a different feature set than other SMA inverters.

You could use a SolarBOS arc-fault combiner:

http://www.solarbos.com/products/combiner-boxes/afci-combiners

My impression is that this is an expensive option. But I don't what else is out there. There's a reason 3-phase string inverters with integral dc arc-fault protection have taken over the market.

FWIW, 2017 NEC will provide a waiver for dc arc-fault protection for systems that are not on buildings, provided the dc conductors are underground or above ground in metal conduit. Engineers designing large-scale PV electric supply stations, which are covered in a new article (691), can also forego dc arc-fault protection and meet NEC 2017 requirements.
 

SolarPro

Senior Member
Location
Austin, TX
Right, because they don't use "plumbing pipe" to build PV systems in Europe. They just plug the field wring harness into the inverter.

If this is power plant application, the simplest way to meet the dc arc-fault protection requirements might be argue that these should not apply.
 

BillK-AZ

Senior Member
Location
Mesa Arizona
Apparently no interruption. From the Installation Instructions:

"Make sure the alarm signal can be well heard and proper follow up in case of an alarm is guaranteed. "
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I could have sworn those did interruption but apparently I stand corrected.
It does seem kind of silly just to trigger an alarm. What if something happens on a commercial installation during a weekend when no one is on the premises?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
What if it's during the week but none of the 50 people on site have any clue about the significance of a PV arc-fault?

If it's going to just trigger an alarm, maybe it should trigger the building fire alarm system that automatically calls the FD. (Or would that be too much of a nuisance? :roll:)
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
What if it's during the week but none of the 50 people on site have any clue about the significance of a PV arc-fault?

If it's going to just trigger an alarm, maybe it should trigger the building fire alarm system that automatically calls the FD. (Or would that be too much of a nuisance? :roll:)
What if it's in the middle of the nigh... Oh, wait. Never mind. :D
 

Carultch

Senior Member
Location
Massachusetts
What if it's during the week but none of the 50 people on site have any clue about the significance of a PV arc-fault?

If it's going to just trigger an alarm, maybe it should trigger the building fire alarm system that automatically calls the FD. (Or would that be too much of a nuisance? :roll:)

That's why AFD is a joke, and AFCI is what you really need.

Mike Holt once said he could summarize the entire NEC in one sentence: "If there is a problem with a circuit, turn it off".
 
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