[RE-wrenches] Troubleshooting Stumper - Homerun Interference in Conduit/Inverter Turning Off/On Rapidly

[Matt Partymiller]

Wrenches,

One of our systems is having an issue I have not encountered before where
the inverter switches between nighttime mode and interconnection every few
seconds.  I am hoping for some technical wisdom from the community.

We have an array of 20 TrinaSmart modules in two strings of 10.  The array
is connected to a Solectria 3.8 kW inverter.  The conduit run is simple,
all four homerun wires (#10 PVwire) in 1" EMT down to the proximity of the
Solectria inverter where the conduit switches to 1" LFMC before entering
the inverter.  The run is about 20', straight down the side of the wall
before hitting the inverter.  A 600V jacketed communications wire was also
in the conduit but has since been removed and run separately.

Our inverter is starting up, running for a few seconds, giving a low
voltage error, briefly showing nighttime mode, then going into startup
mode again.  Solectria was gracious enough to send us a new inverter but
we have the exact same issue.  They tell us their error codes (266, 274)
indicate 0 volts.  The transition between low voltage error and startup is
almost instant.  Basically we have 20 seconds of start up, 5 seconds of
run, 5 seconds of error then repeat.  This is not a grid problem, the
identical system next door works fine.

In the process of troubleshooting, our technician pulled all four homerun
wires out of our conduit and meggered them.  They all tested fine so he
connected to the inverter.  The inverter worked fine.  The technician
verified grounding of the array and conduit, pulled new homeruns back
through the conduit, and reconnected to the inverter.  He had the same
error as before.

He connected each string separately to the inverter by removing the string
fuses.  Either string will operate fine independently.  With string one in
conduit and either homerun of string two in conduit (but not both) the
inverter operates fine.  With string two in conduit but string one outside
of conduit, the inverter does not operate.

I was certain the error had something to do with homerun roof wiring so I
went out with the technician and removed and checked pretty much every
module.  Everything appears fine, all connections solid, all homeruns have
been remade at least once at this point.  Now I am stumped and lack the
technical knowledge to diagnose the problem.  I would be extremely
grateful if an esteemed wrench can provide technical support/advice.

Thanks,

Matt




Matthew Partymiller
Solar Energy Solutions LLC
(877) 312-7456
matt at solar-energy-solutions.com