[RE-wrenches] FM80 failures due to arc faults

Wed Jan 26 12:52:05 EST 2022

Aw shucks, Nick, thanks for the compliment.

I am not sure it is justified here because I have not experienced the
failure scenario you have with this system.  I must return the compliment
in that it appears your approach to troubleshooting has been very diligent.

Here are a few ideas off the top of my head, in no particular order:

·        If you think you are overworking the FM80s, ask yourself if the
failures might have occurred outside of peak sun hours.  If so, overdriving
is likely not the problem.  If you can't determine this, try shutting off
part of the PV input to each controller temporarily to see if the failures
abate.  It may be the input section of the FM80s is working hard and an arc
fault causes a spike to ripple through to the FM80 input, causing a failure
on the input, said failure I think being what you are experiencing..

·        I think the E-gauge might have some form of THD logging.  I could
be wrong here, but check it out and see if there is some load-induced
waveform distortion that might be contributory.

·        You could rent an AC power quality monitor to log potential AC
power issues.

·        It's a long time since I looked at data loggers, but could you log
the PV voltages to see if there are spikes on that side of the system?

·        If you think FM100s will solve the problem, don’t assume you need
to rewire the arrays or upgrade breakers.  If you drop in FM100s as direct
replacement for the FM80s you are still operating in the sub 150 VDC
realm.  I know this is an expensive repair, but if it seems justified it is
less expensive than a stress-induced heart attack..

·        Often times resolving an intermittent like this is a process of
trial and error.  Pulling a ground conductor on that long feeder is no
guaranteed fix, but sometimes you got try everything you can.

·        Someone else may have suggested this, but instead of pulling a
ground you could install an isolation transformer to reestablish the
grounding.  Some sound companies have these for rent.  United Rents shows
some models on their website.

Good luck.

William Miller

Miller Solar

17395 Oak Road, Atascadero, CA 93422

805-438-5600

www.millersolar.com

CA Lic. 773985

-----Original Message-----
From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of Nick A Lucchese
Sent: Tuesday, January 25, 2022 12:02 PM
To: rE-wrenches
Subject: [RE-wrenches] FM80 failures due to arc faults

Hello again Wrenches,

While the failed controller topic is fresh I want to ask opinions/advice on
arc faults. I know quite well that they can be mysterious so not sure I’ll
really get anywhere but here goes. This particular off grid system consists
of two Radians, 2 GSLC’s, FNDC, a 25.2 KW array and 6 FM80’s. 4.2 KW STC
into each controller which I now know is over their new recommended max
wattage after they changed the spec sheets on us a couple years ago without
renaming it an FM70. The system has been in for over 5 years now but from
the beginning I’ve had a large amount of failures with the FM80’s failing
and registering a dead short on the PV input side of the controller. Not
exclusive to any one of the six arrays and I’ve definitely gone through to
torque and tighten all of the connections. I’ve tried other controllers
throughout my troubleshooting and concluded it’s arc faults for a few
reasons. Mainly, as long as I have a Midnite Classic installed with the
other 5 FM80’s it will absorb the arc fault and just go to it’s temporary
state of displaying an arc fault and after I reset it everything starts
back up and operates normally. Survives the incident without failure unlike
the FM80 and at the same time protects all the other FM80’s. When the site
goes back to FM80’s exclusively the failures are inevitably more frequent.
I’ve also installed a Magnum PT100 for awhile to see if it would fail too
but it survived for over a year before I terminated that particular test.

Luckily, one of the times I was there when an FM80 failed so I was able to
see that it coincided with some fans (obviously on the AC side) that had
kicked on when I observed usage on his Egauge (system has Blue Ion 2.0’s
and HI's). I have also been able to determine it’s likely some fans because
the long durations without failures also coincide with long periods without
the fans although failures are still happening sometimes and he says he’s
changed up his fans. The Egauge has been a very useful tool for various
reasons but unfortunately I can’t pinpoint when the units fail since they
often go unnoticed until I am at the site or notice low PV production on
Opticsre. I just happen to get lucky the one time I was there to correlate
the exact moment with the fans.

One major detail that makes this site different is that after my initial
install work he had some other yahoos in to pull the feeders to power his
other subpanel some 1300’ feet away. Unfortunately they did so without
pulling an equipment ground along with the power conductors so the two
sides do not share a common ground. This is the most major deviation from
any of the other systems I’m responsible for and this is the only site I
have frequent high rates of unwarranted controller failures. I’m uncertain
if the failures are due to AC ripples/transients from the extremely long
run, lack of common ground or perhaps one particular appliance. My
preferred solution in the process of elimination is fixing the lack of
common ground by re-pulling all the conductors with an EGC but that would
not only be expensive but quite difficult as he just informed me the other
day that there are no pull boxes in between the two destinations. I wish I
could just walk away from any responsibility since their foolish decision
not to pull the EGC originally was not a mistake of mine but I really need
to help him resolve this since replacing the FM80’s so often is obviously
expensive as well as time consuming. Obviously it would be extremely
frustrating and defeating if he were to go to all the effort of pulling the
new ground and the failures still occur.

I thought about replacing the 6 FM80’s with 4 FM100’s but that would
require a profound amount of work by the time I change up the array strings
and OCPD’s plus I’d have to re-imagine placement due to the physical
differences. To avoid nuisance tripping, I already have the Midnite 100 amp
GFP assemblies in place and am adding two more Radians with GSLC’s so
feasibly would have the accommodations as far as space for OCPD’s are
concerned. We do plan on expanding his arrays soon so at some point I will
have to address this known snag of mixing FM80’s and 100’s in the same
system as recently discussed on the list. Thinking I might try this mix
approach on my own house for awhile but not rushing to deploy at any client
sites.

Any ideas? Suck it up and have him pull a ground 1300’ at today’s copper
prices? I’ve got Midnite SPD’s on all the arrays as well as the AC side but
perhaps there’s some other sort of additional surge suppressor or something
I can install to suppress arc faults originating on the AC side? WWWMD
(what would William Miller do)? Only half joking here, I often find myself
asking that when I encounter some sort of unusual solution required to
balance something out of the ordinary and William’s procedures have
impressed me for decades. No offense to the rest of you pro’s though, his
meticulous documentation and notes just appear levels beyond (especially
speaking for myself)!

Off to work, enjoy your day, Nick

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