Electrolysis Damage Story [RE-wrenches]

Sat May 14 12:22:42 PDT 2005

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Wrenches,
Thank you for the responses to my story about the electrolysis-damaged pole
(original post below). Last Monday we went back to the site, dismantled the
array and tracker (before it blew over), took photos, did some
investigating, and have a fairly clear plan of action.

Here's what we found: The array racking had been grounded to a rod with #8
bare copper. However, a bonding conductor had not been included with the 2/0
input conductors back to the DC buss in the BOS equipment, and the PV
negative conductor had not been bonded to ground at the array (the "separate
structue" approach). The ground wire was corroded to nothing at the points
between the pole and the ground rod where it entered and left the earth, and
there was green "slime" in a few spots where the wire had been.

It is our guess that the short at the 1/2" Romex connector that served as
strain relief for the PV+ input wires had been there for a long time,
perhaps since installation. We speculate (none of us are engineers, and we
haven't seen this before) that the ground conductor had carried some fault
current to ground for all that time, and eventually galvanic corrosion had
caused the wire to dissolve sacrificially. Once the ground wire no longer
carried any fault current, the steel pole had to carry it, and it began an
accelerated rusting from galvanic action.

When we looked down into the pole, we saw that the entire area below grade
was heavily blistered on the inside of the pipe, but it was fine above
grade. The outside of the pipe was also heavily blistered, and the ground
around the pipe was rust-colored.

If the array negative had been bonded to ground at the array, the direct
short and resultant power loss would have been easy to spot and correct. If
the system had an array GFCI (which wasn't available at that time), it would
have likewise tripped, and the fault could have been easily corrected. If
the array ground had been bonded to the BOS, a ground loop would have been
present, and it may or may not have been detected, but it would probaly have
prevented or greatly slowed the galvanic corrosion. (As it was, we also
discovered that no DC grounding conductor had been installed; the DC was
grounded only through the Power Panel backplate to the chassis ground lug in
the IBS, which was carried back to the utility main disconnect bond point
and lug by a #10 conductor. But at this point, that's a separate issue
needing correction.)

At this point, we plan to repair and use the existing pipe, using both
internal (a second 5" pipe, rebar, and welding) and external (built-up
concrete containing rebar drilled into the existing concrete base, bent and
welded to the pole). The clients are out of town for awile (birth of a
granddaughter) so the project is now on hold; stay tuned.

Allan at Positive Energy

----- Original Message ----- 
From: "Allan Sindelar" <allan at positiveenergysolar.com>

> Wrenches,
> A simple mistake can have major consequences.
>
> In 1997, in my first year of business, I designed and sold a SW4024-based
> grid-tied system for a new home. As I wasn't licensed at the time, another
> local electrical contractor with a history of doing solar installations
was
> separately contracted to pull the permit and do the installation. Upon
> completion, I corrected a few things I didn't like (battery cables
connected
> at one end of the bank, rather than diagonally, for example) and have
> supported the system and the customer in the years since. This is a good
> customer.
>
> The system has worked well, with only the Wattsun tracker and the E-Meter
> requiring repair or replacement. The client called recently about tracker
> malfunction, and today Mark (partner) went to the site to service it. What
> he found was battery voltage at the tracker ground, which he determined
was
> from a ground fault at the array. The galvanic action caused by the fault
> had rusted the 8-year-old 6" Sch 40 steel pole to the point that he could
> poke a screwdriver through the pole at the base, and was concerned about
the
> whole thing toppling over any minute.
>
> The cause of the ground fault was the use of two 1/2" Romex clamps for
> strain relief where the USE-2 array input conductors entered a steel 3R
> combiner box on the pole. Each of the two clamps held four #10 USE-2
> conductors and one bare #8 or #10 grounding electrode conductor. One of
the
> clamps had shorted one of the PV+ conductors to ground. I am guessing that
> it had been like this for a long time, maybe since installation, and I had
> never detected the fault during routine service calls. An array GFDI
wasn't
> installed or required (and I'm not sure anyone even made one at that
time).
>
> The customer is looking at repair options for the pole, including
outriggers
> with driven steel posts and welded braces, and a poured concrete cap over
> the base of the pole. We will head out soon to disassemble the array, to
> reduce wind sail and the chance that it will come down, and to buy some
time
>  for a good repair to be devised. We are also looking at setting a 5"
steel
> pole inside the 6", with cement slurry between the two.
>
> We haven't worked out a course of action yet. A couple of questions:
>
> We use SO connectors for USE wire, and use Romex clamps for jacketed wire
in
> indoor locations. Is the use of Romex clamps on USE wire in this
application
> legal per NEC? What Code section addresses this?
> If issues of liability and responsibility come up (and they probably will
> not) who's liable? The contractor who installed the system and pulled the
> permit? The inspector who signed off on the job? Us? How would you serve
the
> customer in this case? I supplied a one-year warranty on system design and
> component failures, and the installer gave the same against failures due
to
> incorrect installation.
>
> Has anyone ever repaired a rusted pole? Howdja doit, and did it work?
>
> Thanks for any good advice. I'll share your responses with the client.
>
> Allan at Positive Energy
>

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