Tech Talk: Five tips for AFCI troubleshooting

From on 07/09/2015 in Category Service with 35 Comments

It’s something installers hate to hear and hate to troubleshoot: the dreaded DC-side arc fault. Rarely in solar can such a small phrase bring so much ambiguity and require so much effort to find and fix. Yet over the course of a career, all solar installers will find themselves searching inside junction boxes, combiners and on top of roofs to find that pesky fault.

Sometimes they’re caused by simple installation mistakes like not stripping enough wire length or improper torque. And then there are times when the install was perfect, but the local rodent population fed itself on PV wire long enough to bring down the system.

One thing to remember is that although the inverter has found an arc in the system, it’s often acting as the bearer of bad news. Like the warning lights in a car, the inverter has found a problem that needs to be addressed but is likely outside of the inverter itself.

Tips for finding the arc
  1. Safety first. Make sure to turn off the AC breaker and, if applicable, turn off and lock-out the AC disconnect switch to ensure the inverter is not producing any power. Once the inverter is shut off, wait five minute before opening any covers to ensure the capacitors have time to bleed out excess power.
  2. Open the inverters and any combiner boxes to check for proper torque on all DC terminals. A common test here is to tug each wire to see if any are loose or pull out entirely. If any wires are suspect, tighten them down to proper torque specs.
  3. While the inverters and combiner boxes are open, visually inspect the insulation on the DC conductors where they land. The insulation should be stripped back enough so the wire is solely clamped down, without any insulation touching the terminal. The length of stripped wire is different with each application; for example, with the Sunny Tripower, the DC terminals require .75 inches of insulation to be stripped back.
  4. Visually inspect the homerun connectors going back from the combiner boxes to the modules for each string. The connector-to-connector points for the first and last modules in each string should be easy to find. The homerun wire connector is normally cut and crimped onsite to match the length requirements, giving it a higher probability for causing a fault due to improper crimping.
  5. Walk the array while looking for signs of arcing. Closely inspect the wiring under the modules and inside junction boxes. Damaged wires from rodents are just one example of what to look for. This can be taxing depending on the array location and is often the most difficult and most important step. Make sure to look at the MC4 connectors between modules for a full connection; partial connections that aren’t fully closed are a common cause of arcing.

One thing to remember: an arc fault is not the same as a ground fault, so make sure to follow different testing procedures for ground faults. Once you’re comfortable that everything is checked and in good condition, turn on the AC disconnects or breaker and see if the inverter detects any faults.

Still seeing a fault or in need of deeper troubleshooting tips? Call our Service Line at 877-697-6283 from the system site and we’ll lend a helping hand.

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35 Comments

  • avatar

    Marc

    07/28/2015 at 1:45 pm

    After You’ve checked the DC connections for potential arc faults and have found none, don’t discount the possibility that the inverter is the cause. I’ve been there and seen it happen.

    Reply »
    • avatar

      Justin Dyke

      07/29/2015 at 1:42 pm

      Marc – yes, as much as we’d hate for that to happen it could. If you’ve had it happen with an SMA inverter, hopefully our awesome service team shipped a new out and you were able to get the system back up quickly.

      Best,
      Justin

      Reply »
  • avatar

    Mike

    07/30/2015 at 2:21 pm

    Also make sure the inverter is updated with the latest firmware.

    Reply »
  • avatar

    Bill Sibner

    04/14/2016 at 8:05 am

    I have had about 40% of the inverters I install throw arc faults, most of the time resetting them does the trick. Unfortunately this usually means a trip to the site. I have also installed inverters as replacements on older systems that had worked fine for more than 10 years. Constant afci errors.
    This “technology” is fraught with issues. Manufacturers should refuse to comply with unreasonable code requirements, the next nightmare is going to be “rapid disconnect”

    Reply »
    • avatar

      Mike

      06/28/2017 at 9:25 am

      Agreed Bill. I find that the current firmware has mitigated many of the false arc fault conditions and having a cluster controller enables a remote reset minimizing down time and eliminating a truck roll. That said, there is a safety risk in resetting inverters remotely as there might be a true arc fault condition present and resetting it could result in further damage or even worse…

      Does anyone have info or input regarding inverters detecting high Hz noise as an arc fault? I have discussed this with many in the solar industry, but have not come across any solid documentation supporting this theory.One of those discussions was with SMA tech support and they say it exists, yet there is no documentation. Essentially, the array acts as a large antennae and can pick up high frequencies from cell towers and such and the inverter interprets it as an arc fault.

      Reply »
      • avatar

        Carlo

        07/11/2017 at 8:44 am

        Hi Mike, we’ve shared your comment with our service engineers who have provided the following:
        We agree that resetting arc faults remotely is never a good idea. The inverter’s array and DC wiring should always be inspected first before resetting an arc fault event. While we are continually improving the arc fault detection technology that goes into our products, there is always the possibility for a false positive in certain circumstances. The reason for this relates to the characteristics of a series arc the inverter is looking for. There is a slide from a presentation created by Sandia National Labs which shows the characteristics of an arc here. Slide 21 goes over the frequency spectrum of a no arc vs arc scenario. (The main tool used to measure a frequency band is called a spectrum analyzer. Our R&D engineers are trained in how to set these up and use them, but we do not recommend using one for your own analysis.) In this example there is a noticeable dB increase in the 30 to 60 KHz frequency bandwidth when an arc occurs. In order to detect arcs, SMA inverters also measure a large frequency spectrum and continually apply specific algorithms to the data to flag events. There is certainly the possibility that other sources of frequency could make it to the AFCI sensor. If this external noise is within the same bandwidth as an arc, then this could cause a false trip.

        There are a couple things to take into consideration when attempting to filter out other sources of frequency that could be causing the false trip events. If the source is coming from the AC side, an appropriately rated line filter could be used. If the source is from the DC array, we do not recommend using anything to filter the extra noise as this could also filter the actual arc fault frequency and prevent the inverter from properly detecting an event. If the array is acting as an antenna, one way to reduce this effect is to eliminate any large string loops. The positive or negative homerun should run back along the string before pairing with the other homerun.

  • avatar

    chris mathas

    04/15/2016 at 6:58 pm

    I cannot find the reason for error on my Sunnyboy SWR 2500U Inverter . The error message with the yellow light on says: NUW-Idif

    This message is not listed in my User Manual.

    Any Thoughts?

    Thank you
    Chris

    Reply »
    • avatar

      Justin Dyke

      04/18/2016 at 11:03 am

      Hi Chris,

      It’s best for you to call our Service Line for real-time diagnostic and troubleshooting. They can be reached at 877-697-6283 during standard business hours.

      Best,
      Justin

      Reply »
  • avatar

    Vincent Ho

    05/17/2016 at 7:13 am

    I got sunny boy swr2500u inverter, was installed new by home builder in 2005, no fault code, green light is on solid but E-today only 1.5kwh compare to the house next door same system E-today at 14kwh, Dcv from panels at 470v.

    Reply »
    • avatar

      Justin Dyke

      05/17/2016 at 12:20 pm

      Hi Vincent –

      I have forwarded your comment to the SMA Service department, which will be able to discuss that data with you.

      Best,
      Justin

      Reply »
  • avatar

    Steve C

    08/24/2016 at 10:56 am

    Hi, I have the new SMA 6.0 US inverter and when i open my plot screen to see the amount of power generated through the day, i have these spikes shooting off the page every couple of hours and sometimes first thing in the morning i have a event code #3303 and 28205. is there something i should be doing? cant find definition of 28205

    Reply »
    • avatar

      Justin Dyke

      08/24/2016 at 7:07 pm

      Hi Steve –

      That is a great question. I have shared it with our Service Line team and a technical expert should be in contact soon.

      Best,
      Justin

      Reply »
  • avatar

    Joe

    12/07/2016 at 3:46 pm

    Hi I keep getting a red light saying that their is a ground fault. panel voltage is about 515 dc to inverter i found rats had eaten string wiring re paired and reinsulated wiring installed new fuse and turned on ac and then dc started count down and burned fuse again when testing ground fault fuse I am finding the full grid voltage on that circuit dose this mean that the inverter has a short internally this is an old sma1500 system thank you for you help JOE

    Reply »
  • avatar

    Ted

    12/19/2016 at 5:50 am

    Hope someone can help. My installer upgraded our system last summer, adding panels and replacing an SB4000 with an SB5000. We now have 48 panels in 5 strings with two inverters.

    The inverter with three strings generates AFCI errors after running for a while, usually a couple hours. At first I thought it was output related, but it did the same thing yesterday with very low solar influx.

    The installer replaced the inverter, thinking we had a bad unit. Still get AFCI errors.

    Tried isolating the string with the problem. Here’s where it gets stranger. No single or pair of strings generates AFCI errors if the positive leg is disconnected from one of the strings. When all three strings are connected, it always generates AFCI errors after a period. When any of the negative legs are disconnected, it faults when all three positive legs are connected.

    The installer claimed he tried switching the wiring between inverters and still the same inverter faults. However, looking at the wiring, it doesn’t appear possible that he tested this since there are straight runs from the three strings through conduit, to the disconnect.

    Can anybody think of what might cause the system to run fine with two strings and not three?
    I believe the system is configured with 3-strings of ?x230w panels, and 2-strings of ?. The open circuit voltage on each of the 3-strings is about 374v. I’d expect a string of 10 to give closer to 480VDC. However, if the installer left the original 3-strings of 8, then this would be close to the rated 48v/panel.

    Any clues?

    Reply »
    • avatar

      Jessica

      01/16/2017 at 5:32 pm

      Hi Ted, someone from our service team would be glad to assist with this. Please reach out to service@sma-america.com or 1 877-697-6283. If that doesn’t work let us know here and we’ll follow up. Thank you!

      Reply »
  • avatar

    Steve

    12/26/2016 at 6:31 pm

    I have found the latest SMA are fraught with false faults. For example, my current installation, two strings of 12 modules. Inverter throws an arc fault. Ok, standard troubleshooting, I swap the strings. If there is a wire problem, the fault should move. It doesn’t. Again we see faults. Swap the SMA out for Fronius, good bye arc faults. And yes, on the latest firmware. I have found that almost every site is throwing faults if using SMA string inverters. We use the same panels everywhere, TrinaSmart. In most of these configurations there are not even any junctions, it is PVWire straight from the string to the inverter, less than 30 ft. At this point we are seriously limiting our SMA installs, hopefully they will fix this someday. If SMA ever updates there arc fault to work, please let us know. I prefer them to other vendors, but this problem has taken them off our equipment list.

    Reply »
    • avatar

      Jessica

      01/18/2017 at 2:41 pm

      Steve, we are so sorry to hear this! I’ve passed your comment along to our service team and someone should be reaching out to you to discuss.

      Reply »
    • avatar

      Don

      02/22/2017 at 1:21 pm

      I have done the same thing. I swapped strings and arc fault stayed on string A I than replaced the SMA with a new one, Same thing. My wire is a single piece to two different TrinaSmart arrays with 255 watt panels with 12 on each. I turned off the Arc fault because after testing its not my wiring. It appears to happen every day about the same time when I was getting my arc fault.

      Reply »
  • avatar

    Amy

    01/09/2017 at 12:20 pm

    Our Old Sunny Boy was replaced, original install 2006. The new unit has been in for less than 2 weeks and it shut down with “Elec Arc Detected – Check DC generator. All 40 panels are on the roof, we’ve never had rodent issues. Did a reset, still getting the same message.

    Reply »
    • avatar

      Amy

      01/09/2017 at 12:24 pm

      The original sunny boy had issues with the fans, we used an external fan and it was functioning without any trouble up to the day it was replaced.

      Reply »
    • avatar

      Jessica

      01/18/2017 at 2:38 pm

      Hi Amy,

      Sounds like our service team may need to provide you with some guidance. Please reach out to our service team service@sma-america.com or 1 877-697-6283. Thank you!

      Reply »
      • avatar

        Amy

        01/26/2017 at 12:47 pm

        Had tech from the solar company that did the install troubleshoot the problem – All 4 strings were swapped/tested – none of the wiring appeared to be an issue but he checked everything anyway and did some minor tightening then reset the inverter. It seemed fine the rest of the day then same error message next day. No snow or rain, seasonably cold and sunny here. Tuesday they’ll be returning to do a visual check of the panels/panel boxes and connections on the roof to rule out anything else.

  • avatar

    Richard

    02/19/2017 at 6:38 pm

    Hi, just noticed a error message. Varistor defekt. Installer doesn’t know what that means. Invertor SMA SB5000TL-2, installed 06/14. Its still working ok. Tried speaking to Service line but put through to empty line.

    Reply »
    • avatar

      Jessica

      03/08/2017 at 9:37 am

      Hi Richard, the Varistor/Defekt error may be only on European inverters. We will need the Serial Number to determine if SMA America can service it. Please reach out to the service team at 1 877-697-6283 or service@sma-america.com. Thanks!

      Reply »
  • avatar

    Janice Roberts

    03/04/2017 at 11:55 am

    I have a 5 year old Sunny Boy 3000 inverter. I have got my solar panels insured and I have bee told that the voltage is too high what reads 400v on the pannel readout. I have paid to have a switch fitted to reduce the voltage. Is this correct or have I been cheated out of my money? Please help me put my mind at rest. Janice

    Reply »
    • avatar

      Mike

      06/07/2017 at 9:25 am

      Hello Janice – The maximum DC voltage for the Sunny Boy 3000-US is 500V. What you are seeing on the inverter display is operating voltage, and this is likely much less than the maximum array voltage. That maximum is usually calculated based on the coldest historical temperature at your home, and depends on the exact type of PV module you are using in your system. Your system should have a small plaque, maybe affixed to the inverter, that shows maximum system voltage. That is the number that should be under 500 VDC. Do I understand correctly that you had a third party install this “switch” and not the original installer? Have you contacted your system installer? They should be able to verify the maximum system voltage for you also.

      Reply »
  • avatar

    Christopher Vandemore

    03/13/2017 at 10:12 pm

    What a horrible product. What is the bad news being borne? That video made it sound like this actually provided some sort of feature. If it is so important did you install it in all existing inverters? Are those installations just going to burn up? The video also says that someone would be informed. How does one see that red light when the city now forces it to be on the roof? And seriously I’m supposed to tap the case to read cryptic misspelled messages 120 characters shorter than a tweet? And why exactly is the Ethernet hidden behind a panel? And why is this thing so huge? And how on earth will I ever recoup my investment when this stupid thing goes down every time it is sunny?

    Reply »
    • avatar

      Jessica

      03/15/2017 at 11:17 am

      The AFCI requirement was a safety enhancement written into the 2011 National Electric Code (NEC). New NEC versions are issued every three years and adopted by states on a non-uniform basis. Manufacturers have specific requirements for compliance and must be certified to UL safety standards in the U.S. Local Authorities Having Jurisdiction (AHJ) are tasked with enforcing the code via inspections. The AFCI requirement does not necessitate rooftop installation of any additional equipment. Further code revisions in 2014 and 2017 have added new requirements, however, so it is important to understand which code version your area has adopted so that you can select the appropriate technology. Solar inverters, like TVs, phones, computers, or other electronic devices, carry some risk of malfunction but that risk is very small. SMA has more than four million inverters installed worldwide with an impeccable safety and reliability record. SMA offers comprehensive training and support to solar installers for proper installation of our products. If you’ve already purchased a unit and are having issues, please contact our Service Line at 1-877-697-6283 and they will be happy to assist.

      Reply »
  • avatar

    Bill Neukranz

    04/07/2017 at 12:39 pm

    My US6000 Sunny Boy inverter, installed very later 2009, has been trouble free until now. I disconnected each of my three strings to measure open circuit string voltages (3 strings total). After reconnection I cannot get the inverter to engage. The green light continuously blinks and the message is “waiting.”

    Please help. Many thanks!

    Reply »
    • avatar

      Carlo

      05/02/2017 at 10:29 am

      Hi Bill, if the system was turned on after reconnection by turning on DC disconnect then AC breaker/disconnect, the inverter will wait five minutes with the green light blinking – as required by code – before it reconnects. This can be prevented in the future by connecting AC first, then DC. To address your specific concern, I recommend contacting service directly at 1-877-697-6283.

      Reply »
  • avatar

    Rabi Hachem

    06/06/2017 at 2:57 am

    Dear Sir,

    what do you prefer to install between the PV string and the DC input of a SunnyBoy SB5000TL-21 to control the ON and OFF switching of the inverter ?
    I am using a load-breaker but an internal flame is appearing when i’m switching it Off (no load on the AC output when i put the load- breaker OFF).
    There should be something more efficient to cut off that spark inside the breaker, some kind of a fast switch which can resist the string DC voltage.

    Thanks and regards

    Rabi

    Reply »
    • avatar

      Mike

      06/14/2017 at 2:01 pm

      Rabi – any correctly rated DC disconnect should be acceptable. The switch must be rated for maximum system voltage and be capable of safely breaking the DC connection while the inverter is under maximum load. I am concerned, however, if you are seeing an arc when using the DC disconnect if the inverter is not under load – there should be no DC current to create this arc if the AC is disconnected. Please (safely) ensure that there is no DC current flowing when you are throwing this switch. It is preferable to disconnect the AC from the inverter, then the DC whenever possible.

      Reply »
  • avatar

    George

    06/06/2017 at 11:46 am

    What is required to reset an error code on a SB6000U, or do they just go away when the problem is fixed?

    Reply »
    • avatar

      Mike

      06/14/2017 at 1:59 pm

      George – it depends on the error. For DC voltage low or AC voltage and frequency out of range errors, the inverter will reconnect and produce power automatically once the value return to an acceptable range. There are some safety errors, such as a ground fault, that will require a manual reset. These faults signify that there is a safety-related issue with the system (whether on the array, the wiring, or the inverter) that must be fixed before the system is safe to go back into operation. The installation manuals of our inverters have a section entitled “Troubleshooting” that describe the error messages and codes along with a short description. If you cannot find this, or have further questions, please call the SMA Service Line at 1-877-697-6283.

      Reply »

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