Solar Troubleshooting: Hunting SMA String Arc Faults

Happy holidays!!

Fun fact!! not a single fault reported again, with cloudy days, rainy days, and sunny days!!!

It is going to be fun to find where it comes from!!

Go through your wiring, check screws for tightness, reseat the stuff at the SMA “spring clip” end, and let it ride until it becomes enough of a problem to regularly reproduce.

Good luck. It’s certainly a maddening process at times. Just remember, at least you’ve got the access and skills to run it down yourself!

Well its been 20 days and not a single fault reported, cloudy days, sunny days and rainy days, no fault, I’ll keep you posted!

Have a great one!!

@Syonyk… it’s worse than you even know!!!

I found this thread because I too have the dreaded 4301 error and will now embark on the process of troubleshooting the array.

…but this goes back a ways.
I first got the dreaded 4301 error shortly after the 2 string array was connected to my SB 6.0 (same as you have); this occured soon after installation and I had the installer return multiple times to troubleshoot the system. They could find nothing wrong and they were working with SMA tech’s during the troubleshooting process.
I hit the roof when they suggested their next visit would cost me $$ (installion still under installer’s warranty!) as they “had exhausted all avenues of troubleshooting” => in fact, it was I that suggested to them that they should swap the connection of the two 10-cell strings (A to B and vice versa) to determine whether the problem followed the string or the inverter. They agreed and did so and - as I now know from your writeup was inevitable - the “problem” was found to follow the inverter (problem still identified on string A though the strings had been reversed). The solution? They RMA’d the inverter! …and guess what? The problem naturally re-occured with the new inverter! Go figure. So apparently not everyone at SMA is even aware of the faulty error reporting.
I finally had all the panels removed and all connections reseated and that seemed to solve the problem for about a year but now I’m seeing these AFCI disconnects several times a day again. As my panels are roof mounted the troubleshooting process will not be much fun. Might be time to invest in a thermal imager

Yeah… well, welcome to the forum, at least! Bunch of solar nerds here, among other things. Not just blog post comments!

It’s funny. Over on the “Solar Professional Places” (including r/solar, which I was quite banned from back in the day), they talk about how horrid it is to install your own solar, how much more experience and such the Professionals™ bring (contrasting with multiple people out here who’ve DIY’d installs and heard from inspectors that “Wow, this is clean…”).

And then I talk to people who have to deal with the “professionals,” who are… well, your sort of experience, where they’re just utterly clueless. And then I realize that, yeah, DIY may be a pain in the rear, but the $30k+ in savings over paying “professionals” is worth a decent amount of hassle, and, living here, I can troubleshoot stuff an awful lot faster than service calls.

Nope. :confused: They definitely are not all aware of that. The first support person I talked to definitely was not aware, the second… was irritated that not everyone knew this.

Oof. Good luck. Please report back! Do you have optimizers, or are you under NEC 2014 with array boundary rapid shutdowns?

I’m still happy with my DIY ground mount system.

Tigo optimizers for Rapid Shutdown, Monitoring, and Optimization. I don’t use SMA’s rapid shutdown (other than the inverter’s anti-islanding). The Tigo system uses its own mains-connected communication device.
Something I’ve wondered that someone might be able to help with…

I have 20 panels in 2 strings of 10 panels each. One string is mounted entirely on the south facing portion of my roof. The second string is mostly on the west-facing roof (7 panels) but 3 panels are on the south facing roof. That is, there are 13 panels on the south facing roof and 7 on the west facing roof.
Someone told me that the 3/7 panel orientation discrepancy on the one string could be causing voltage differences at certain times of the day that could be causing the AFCI faults.
Does that make sense? Is it a possibility?

The optimizers should be able to handle that situation, non-optimal though it is. But I’m not that familiar with the quirks of Tigo modules.

I will say that “disconnecting a full string at a time” should help run down the issues.

Yeah, that seems a good place to start.
Also thought I’d take a close look at the “jumper” that connects the two portions of the second string.

I have a ground mounted 16 kw solar about 400 feet from the garage where all 4 SMA inverters are located. 7 kw was put in 2014 and 9 kw in 2017. A master electrician did all the wiring but he is mostly retired now. The SMA arc fault came up in February but the Electrician that wired it all came a month ago and did check out all the modules, panels, arrays, combiner boxes and all other wiring at the ground mount site. So he said it confirmed to him that it was the SMA 5.0 inverter located in the garage. The only thing he said I should check out is the inverter GFDI fuse. He said “a piece of cake”. I have not located it yet and thought that maybe you could send me a text photo of the fuse location if I send you my phone number?

Sorry, I work via this forum, I don’t text random people. However, it looks like the GFDI fuse is a fairly easy swap. I’m not sure it’s related to arc faults, though.

Has the arc fault warning been consistently firing, or did it fire once in Feb and hasn’t been an issue since? If it’s not come up again, it could have been some sort of transient interference - high power radio transmitters, home appliance motors, and a range of other things can lead to that sort of noise on lines, hence my advice to just ignore the first one or two. If they keep showing up, then it’s time to get the thermal imager out and look for what’s hot, because something, somewhere, is probably arcing.

It sounds like your installer doesn’t have a good sense of what they’re looking for.