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<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial>Wrenches all,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial>I 100% second Bill B's comment Correct that... I 200% second
it. It should be the law.... <EM>"Don't begin to troubleshoot a faulted PV
circuit without a reliable DC clamp meter."</EM></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial>The <STRONG>MOST DANGEROUS</STRONG> <STRONG>PV
system</STRONG> is a wounded PV system. This includes danger to persons and
property. Safely and efficiently troubleshooting a faulted PV circuit requires a
voltmeter AND an ammeter. And PPE. And adequate knowledge and understanding of
operational and non-operational characteristics of PV
systems.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial>The simple reason for this is that, when one or more circuit
conductors are faulted to a short condition, the voltage between the faulted
elements is zero. Relying on just a voltage reading to determine whether or not
to open a circuit under this condition will result in an arc. The amount of
energy in that arc will depend on the amount of available sunlight and the
amount of PV that is feeding into it. The amount of potential hazard will
correspond to these factors as well.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial><SPAN class=914032115-06042010><FONT color=#0000ff size=2
face=Arial>Using a clamp style ammeter will allow you to understand where and
how much current is flowing in a circuit before you decide to open it.
</FONT></SPAN>It is one thing to know you have a 45 amp load in a circuit with a
potential of ~450V because you clamp it before you break it. </FONT></SPAN><SPAN
class=914032115-06042010><FONT color=#0000ff size=2 face=Arial>With this
knowledge you can assess the situation. You can do something to mitigate or
remove the potential hazards... Cover the array, open a disconnect somewhere,
put your PPE on and go for it, select a different location to open the
circuit, use insulated cable cutters, wait 'til dark.... You have
choices.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=914032115-06042010><FONT color=#0000ff
size=2 face=Arial>It is quite another to be surprised by the resulting arc in
tight quarters because you measured the voltage and figured it was a dead
circuit! </FONT></SPAN><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>When you react to the startlement (word?) by dropping
your screwdriver and yanking your hand back... Assuming you don't receive a
shock, flash injury, or fall off the roof in the process, of
course.... The result just may be that the now-dislodged conductor is
arcing and zapping and spitting. Now you're gonna have to
stick something back into that box to deal with it. In the meantime, a
number of possible things can happen, most of which are not favorable....
Melting insulation and conductor material are the most common. The degree (not
just a pun) of damage and remaining hazard will be determined by the amount of
sunshine and amount of PV feeding into the
arc.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>The <STRONG>MOST DANGEROUS single point on the DC side
of a PV system</STRONG> is ANYPLACE on the Inverter side of a fuse(s). This
is a simple function of the assinine "1.56 ISC minimum fuse" rule in the
NEC. The source cannot create enough current to blow the fuse(s). If you have a
fault between a combiner and the inverter, you WILL have current flowing into
the fault as long as the sun is up! If you are relying on just a voltmeter in a
central-inverter plant, you could very well be in for a 15-20kW surprise, or
greater!</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>The combination of shi##y wire, sloppy conduit
installation, and crappy wire-pulling methods have resulted in too many DC
feeder faults to count. It boggles my mind every time I hear of yet another guy
nearly joining the dead because he touched or opened up a connection somewhere
in a faulted circuit without de-energizing it. Time and time again I hear that
they tested it for voltage and it was "dead". Sometimes they even opened up the
service disconnect at the string combiner, "just to make sure".
</SPAN></FONT></FONT></FONT><FONT face=Arial><FONT size=2><FONT
color=#0000ff><SPAN class=914032115-06042010>Time and again it's a "journeyman
electrician". </SPAN></FONT></FONT></FONT><FONT face=Arial><FONT size=2><FONT
color=#0000ff><SPAN class=914032115-06042010>I like it best when it's the
same card-carrying jackass who "built" the
thing.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT><FONT face=Arial><FONT
size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>I consider THWN-2 to be on the list of shi##y
wire types for DC, by the way. </SPAN></FONT></FONT></FONT><FONT
face=Arial><FONT size=2><FONT color=#0000ff><SPAN class=914032115-06042010>I'm
an XHHW-2 guy, personally. Why would anybody select an insulation that is easy
to nick/slice/tear when you can have a super-tough insulation for a couple
pennies more? Why would anybody select an insulation that only has about 5% of
the dielectric resistance of one that is a couple pennies more? Why? Oh, I
know... It's that race to the bottom on BOS costs...
</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>Which leads to the next step in stupidity... Designing
and building LARGE PV plants without sufficient DC SERVICE disconnects... This
is what's going on out there.... PV plants with 500kW Central-inverters being
installed without string-combiner disconnects. Without any DC service
disconnects. </SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT><FONT face=Arial><FONT
size=2><FONT color=#0000ff><SPAN class=914032115-06042010>The NEC considers the
fuseholder in the combiner &/or the connector on the module to be a
"disconnect" and does not require a "service disconnect" in the circuit. So
these smart-ass engineers and project developers are out there building
this shi#. Some of these projects are being built by PV module manufacturers
masquerading as developers. <EM>"Vertically integrated..."</EM>
</SPAN></FONT></FONT></FONT><FONT face=Arial><FONT size=2><FONT
color=#0000ff><SPAN class=914032115-06042010>Others are being designed &
built by formerly respected integrators who have either sold out or lost
their conscience altogether. The trend is to build them to sell to PPA
companies who ostensibly own and "operate" them.
</SPAN></FONT></FONT></FONT><FONT face=Arial><FONT size=2><FONT
color=#0000ff><SPAN class=914032115-06042010>These solar timebombs are
being built on both sides of the fence. Frosty ain't the only one with a solar
flamethrower!</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>All in the race to the bottom of the $/Watt pile that
they are now calling LCOE. Har Dee Har
Har! </SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>I hate to say this, but I hope somebody gets really
hurt out there, and soon. I hope it's the same smart-ass engineer (or
his boss) who thought it was alright to design this way after some field
technician walks away from it because it's dangerous.
</SPAN></FONT></FONT></FONT><FONT face=Arial><FONT size=2><FONT
color=#0000ff><SPAN class=914032115-06042010>And then I hope his family sues the
crap out of the company and companies involved with designing, supplying,
building, and owning it so they STOP DOING THIS SHI#! And then I hope he
takes his cooked carcass on the road doing safety awareness training so others
don't repeat these stupid, avoidable catastrophes! And then I hope these
cheap-ass developers go out to every site that doesn't have sufficient
disconnects and re-fits the systems with them to avoid further injuries and $$$$
settlements. </SPAN></FONT></FONT></FONT><FONT face=Arial><FONT size=2><FONT
color=#0000ff><SPAN class=914032115-06042010>What is the levelized cost of
energy for that system now, Mr. CFO?</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>Unfortunately it isn't likely to be that smart-ass
engineer. Or his boss. It is far more likely to be a Wrench. A Wrench without a
DC clamp and the knowledge that he needs one. A Wrench without the proper PPE
because he "tested it and it was dead" so, even if he had his gear on to "test
it", he took his gloves and face-shield off to work on it. A Wrench who doesn't
fully understand the operation of GFP circuits. A Wrench who doesn't understand
that not all faults are ground faults and the characteristics of a fault change
in terms of potential and magnitude with varying environmental conditions. A
Wrench that doesn't fully understand that power can be coming from both
directions. A Wrench who figures he doesn't have the time to completely isolate
a section of a circuit because there AIN'T NO REAL DISCONNECTS.
</SPAN></FONT></FONT></FONT><FONT face=Arial><FONT size=2><FONT
color=#0000ff><SPAN class=914032115-06042010>I hope it's not your
Wrench.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>As the size of the inverter grows, so does the hazard.
To a point. The idiotic 1.56 ISC rule only increases the
potential hazards. Central-inverter plants should not be
serviced by anybody who doesn't have an extremely comprehensive
understanding of these systems, and the tools and PPE to safely work on it. For
systems with inverter-integral re-combiners</SPAN></FONT></FONT></FONT><FONT
face=Arial><FONT size=2><FONT color=#0000ff><SPAN class=914032115-06042010>, the
most dangerous spot in these systems are the feeders between string
combiners and re-combiners. Anything between the output of a string combiner and
the input of a re-combiner. For systems with standalone re-combiners, a fault
between the re-combiner output and the line side of the
next disconnect is the most dangerous point, but certainly not the
only dangerous point. If either of these systems are built without
load-break disconnects at the string-combiner level, the cost to service goes
thru the roof. It either goes thru the roof to do it safely or it goes thru the
roof in terms of risk to do it not safely. Pick
one.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>There is an interesting dynamic between the potential
hazard on a faulted DC homerun feeder and the kW of the
inverter. The less re-combiner inputs you use, the greater the potential
hazard on faulted input feeders. Again, this is because of the UNSAFE
AND STUPID 1.56 ISC rule. In systems with a relatively low number of re-combiner
inputs, there are large portions of time when there isn't enough combined
amperage in the non-faulted feeders to blow the re-combiner fuse of the faulted
feeder. If your system only has 4 or 5 re-combiner inputs and it's
winter-time, it is quite likely that a faulted feeder is being fed from both
ends. <EM>(Commonly 100A fuses in the re-combiner with ~60A ISC feeding a
string-combiner)</EM> T</SPAN></FONT></FONT></FONT><FONT face=Arial><FONT
size=2><FONT color=#0000ff><SPAN class=914032115-06042010>hat feeder can be fed
from the re-combiner end, by anything up to about 105% of the fuse rating,
for pretty much ever without blowing the fuse. The more parrallel inputs there
are, the more likely there will be sufficient current generated by the other
feeders to blow the fuse. </SPAN></FONT></FONT></FONT><FONT face=Arial><FONT
size=2><FONT color=#0000ff><SPAN class=914032115-06042010>Since the vast
majority of systems out there don't have load-break disconnects at the
re-combiner inputs, the technician needs to be able to open disconnects at each
string combiner in order to isolate this feeder. But what about systems without
DC service disconnects? Repair at night?</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>My hope is that anybody on this list will refuse... Say
it with me now... <STRONG>R-E-F-U-S-E </STRONG>to install PV systems
without adequate disconnect provisions to isolate faulted feeders. And only
allow technicians with proper knowledge and equipment to work on a busted PV
system. "Journeyman electrician" does NOT automatically mean that person has the
proper knowledge to do it safely. Safely working on a faulted PV DC circuit
requires ALWAYS clamping the thing for starters. It might also mean "not
working" on it until the sun goes down. A technician with the proper knowledge
and equipment should be able to determine the proper course of
repair.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>In the case of the faulted lightning arrestor, it was
"only" a small circuit, but it got the guy's attention and apparently nobody got
hurt. The bigger these systems get, the bigger the potential hazard.
</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>To answer Tom's question about jumping around a fault:
Maybe, maybe not, depending on the nature of the fault (+/-, +/G, -/G) and the
location of the jumper relative the fault and the power source. Even if jumping
to ground eliminates the arcing when you are working with the terminal, you will
still have arcing when you land/un-land the jumper &/or remove the fault. If
the sun is shining and you have a DC fault, you will have arcing at some point
when you make/break the circuit. Hopefully it's safely contained and localized
to the contacts of a service disconnect!</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>Pray for Sun!</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010>Matt Lafferty</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=2><FONT color=#0000ff><SPAN
class=914032115-06042010></SPAN></FONT></FONT></FONT> </DIV>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> <B> </B>Bill Brooks<BR><B>Sent:</B>
Monday, April 05, 2010 8:12 PM<BR><B>To:</B> 'RE-wrenches'<BR><B>Subject:</B>
Re: [RE-wrenches] ground fault troubleshooting<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=Section1>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">Tom,<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">Your
dc clamp-on meter would have saved you from removing a conductor that had
current on it. It is likely a lightning event caused the LA602 to do its
job—thus the cracked case. The dc clamp-on meter would have shown the current
flowing into the SOV and on to ground.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">Bill.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
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<P class=MsoNormal><B><SPAN
style="FONT-FAMILY: 'Tahoma','sans-serif'; FONT-SIZE: 10pt">From:</SPAN></B><SPAN
style="FONT-FAMILY: 'Tahoma','sans-serif'; FONT-SIZE: 10pt">
re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <B>On Behalf Of </B>Tom
DeBates<BR><B>Sent:</B> Monday, April 05, 2010 7:04 PM<BR><B>To:</B>
re-wrenches@lists.re-wrenches.org<BR><B>Subject:</B> [RE-wrenches] ground fault
troubleshooting<o:p></o:p></SPAN></P></DIV>
<P class=MsoNormal><o:p> </o:p></P>
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<P class=MsoNormal>hello Wrenches,<BR> We recently had an
interesting (amusing?) experience that I thought might be worth sharing
and to get some feedback.<BR> I received a call from a fellow
contractor that had a ground fault in his PV system (Wattsun DA tracker,
24 Siemens (Shell?)110, 1 string, Sunny Boy 2500). The GF fuse in the
Sunny Boy had blown. Another installer and I went to his site to try to
determine what the cause was. fortunately the Ground Fault article by Paul
Mync had just been in Solar Pro and we used this as a template for
troubleshooting the problem. To make a long story short, we spent the
better part of a day troubleshooting and still could not solve the
problem. What seemed to be happening was that we were getting a different
ground fault current based upon how many modules we had eliminated for the
string and it seemed to be approximately proportional. <BR> A few
days later our friend was going to run through the procdedure again and
take better notes. Since I was not there, the details may be a bit
sketchy, but basically are as follows. As he reconnected the
positive(ungrounded) home-run at the module j-box, the lightning arrestor
(Delta LA602DC), proceeded to "go off like a Roman candle". As he pulled
the conductor off the terminal he got a nice arc between them. The obvious
thing to do was to eliminate the arrestor.... that solved the problem.
Upon further inspection, the arrestor had a crack in the case. Had the
arrestor had a slight fault (due to moisture) initially that lead to
leakage current based upon voltage applied and then finally
"fully-faulted"?<BR> At least two lessons here:<BR>1. When
troubleshooting a GF, always eliminate any accessories from the
system.<BR>2. When dealing with a faulted array never assume that opening
the grounded conductor will open the circuit. Just wondering...would a
jumper form grounded conductor to ground had prevented the acring he
experienced?<BR>thanks,<BR>tom<BR><BR>Tom DeBates<BR>Habi-Tek<BR>524
Summit St.<BR>Geneva,IL. 60134<BR>630-262-8193<BR>fax
630-262-1343<o:p></o:p></P></TD></TR></TBODY></TABLE>
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