Here's a weird one

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
We have 4 customers all within a couple miles of each other who are claiming that their PV systems are causing AFCI load breakers unrelated to the PV system in their houses to trip. One of the customers has told us that his breakers are tripping at night when the PV system is (obviously) not producing. What the installations have in common besides geographic proximity is that they are on the same utility, the same electrician wired all these homes, all the panels and breakers are Square D, and in all cases the PV is interconnected in the MDP while the breakers that are tripping are in subpanels. And of course we built all the PV systems.

The systems are arrays of Sunpower modules with microinverters using their proprietary powerline communication for monitoring. We have several hundred systems in the field built on this same basic design, and these four customers are the only ones reporting this problem, if there is a problem.

The obvious first thing to do was to turn off the PV systems for a couple of weeks and see if the breakers stop tripping; all four customers did that and reported that they had no trips during that time but that the trips started up again when they turned their PV systems back on. Is something in the powerline communication that could indicate to the AFCI breakers that there is an arc fault, even though it's on another breaker in another panel? If so, why is it only happening in only these particular systems out of the hundreds of the same ilk we have built?

I've got nothing. You?
 
Maybe some kind of switching being done by the power company in that area? Switching in alternate feed, capacitors or inductors.
 
Are the all on the same transformer. Years ago in Colorado they had trouble with the power company wave being irregular which would cause all the sq.d afci's to not function
 
Are there any AFCI breakers in the main panels? If AFCIs are also there but not tripping then that might provide some clue.
 
On the amateur radio boards, there are discussions of solar power systems generating RFI (heard by the radios), and also discussions of AFCI devices which are susceptible to RFI (tripped by the radios). Perhaps the same issues are in play here.
 
I’ve had trouble with Siemens combination AFCIs tripping when micro inverters are used. I think it’s the switching waveform. An arcing fault looks like a square wave (arc ignited above a certain voltage then extinguishes at current zero) and the typical “bunny ear” inverter current profile looks very similar. Beyond this it’s whatever magic microprocessor algorithm the AFCI is running as to whether it false triggers or not. I have heard the GE’s are less sensitive but have no proof.
 
Let’s see, same guy wired all four, hundreds of systems working without a hitch, no tripping when pv is off. Since they are miles apart, would not be the local poco transformer, don’t think it would be a substation or switching down the road. Something was done different in these installs, the question is what? Find the difference, and you will probably find the problem!
 
If the powerline coms is indeed causing the breakers to trip I don't think it matters that they are in subpanels. That noise is either gonna make them trip or not. It's line side of the arc-fault breakers regardless.

Have you tried turning off just the monitoring breaker and not the inverter breakers?

I'd blame the Square D breakers. Bad batch maybe. Or Square D 'updated' something. As you say, you have hundreds of other similar systems installed with no problems.
 
jaggedben said:
If the powerline coms is indeed causing the breakers to trip I don't think it matters that they are in subpanels. That noise is either gonna make them trip or not. It's line side of the arc-fault breakers regardless.

Have you tried turning off just the monitoring breaker and not the inverter breakers?

I'd blame the Square D breakers. Bad batch maybe. Or Square D 'updated' something. As you say, you have hundreds of other similar systems installed with no problems.
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I'd blame AFCI technology in general, too many phenomenon out there that can cause undesired trips.

Had one about a week to 10 days ago - Siemens dual function supplying dishwasher/disposer. Was tripping within a second or two after turning breaker on. Indicator said was tripping on AFCI function. Took switch and receptacle apart didn't change anything, didn't find anything wrong. Put back together and it held when trying again. Swapped it with another dual function in the panel and decided to see what happens next. So far no call back yet.
 
winnie said:
On the amateur radio boards, there are discussions of solar power systems generating RFI (heard by the radios), and also discussions of AFCI devices which are susceptible to RFI (tripped by the radios). Perhaps the same issues are in play here.
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This is highly likely.
 
hillbilly1 said:
Let’s see, same guy wired all four, hundreds of systems working without a hitch, no tripping when pv is off. Since they are miles apart, would not be the local poco transformer, don’t think it would be a substation or switching down the road. Something was done different in these installs, the question is what? Find the difference, and you will probably find the problem!
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Thank you, Captain Obvious! :)
 
hillbilly1 said:
Somebody locally with an illegal linear amp on their CB? Don’t hear much of those anymore, but a possibility.
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But why would turning off the breaker from the PV stop the nuisance tripping of unrelated AFCI breakers, if we can trust that our customers are giving us reliable information?
 
hillbilly1 said:
Somebody locally with an illegal linear amp on their CB? Don’t hear much of those anymore, but a possibility.
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ggunn said:
But why would turning off the breaker from the PV stop the nuisance tripping of unrelated AFCI breakers, if we can trust that our customers are giving us reliable information?
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Maybe the PV cabling was acting as an antenna and picking up the RF interference, and the breaker was effectively an antenna disconnect?
If so maybe a common-mode choke on the PV lines might help.
It's all speculation but that's all I can do from this end.
 
electrofelon said:
That is a concern of mine. If I had a dollar for every time a homeowner led me astray with inaccurate/false/assumed information......😠
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Don’t even have to be a homeowner, was on a call yesterday at a big box store, work order said pylon sign next to gas station was not working, and a pole light down at the end of the grocery side parking lot was out. Manager confirmed that was the issues. Pylon sign was working, but one of the three floods on it were out. Went down to the parking lot on the far side of the shopping center, pole light was out, but so was the monument sign at that entrance! Not even remotely close to the gas station! Sign circuit was in the same conduit, both circuits were tripped, but only one at a time would hold. Wires burnt up underground due to a lightning strike.
 
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