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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>William,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I’m not sure what the struggle is about here. If you have a
combiner box, you should always have a disconnect nearby to service the fuses.
The 2011 NEC will require such a disconnect. It is a no-brainer on a ground
mounted system. A roof-mounted residential system of 4 strings or less should
bring the strings off the roof, assuming less than a 100-foot run. That way you
would not need a rooftop disconnect—no backhoe problems here unless the backhoe
really gets reckless ;-). <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>With the 2011 NEC requirement, integrated disconnects with
combiners will become common.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Bill.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>William
Miller<br>
<b>Sent:</b> Sunday, December 20, 2009 12:29 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] DC disconnect placement<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Dick:<br>
<br>
We are gong to install HU361 disconnects at the PV. Touch-safe fuse holders are
one way to apply disconnecting means rated at 600 VDC to a Sola Deck
device. Fusing at an array and GFDI at an inverter do not de-energize PV
feeders. Combiner fuses, if required, protect only adjacent arrays.
They will not open if a feeder is violated. In my humble opinion, this is
one of the serious, unrecognized hazards of the PV industry.<br>
<br>
Burial tape is always a good idea, but it is only effective if the backhoe is
taking shallow scoops. I don't believe it is required so it does not
always get installed. Most of our run is already in the ground without
tape.<br>
<br>
If a PV array were present, I would hope an operator would be more cautious,
but without surface marking, it is difficult to be cautious over an unknown
distance. If I was digging near an array, I would examine the perimeter
of the array looking for a disconnect and/or a telephone number for the
installer.<br>
<br>
Never thought about dumping fill over arcing leads. I'm not sure this is
SOP.<br>
<br>
Each scenario is different, but I like working on de-energized leads and it is
standard in other electrical trades to require that it be possible to do
so. Without disconnecting means, how is this accomplished? I like
avoiding the expense of disconnecting means as much as anyone else, but I do
want to leave a legacy of safe installs.<br>
<br>
Lastly, a 1Kw array at 550 VDC is just as lethal as a 100KW array at 550VDC.<br>
<br>
This conundrum is new on my radar and I'm still working this out in my own
mind. It was brought up by a recent post regarding PV feeders through an
adjacent building and also this job with conduit-finding back hoes. I
think the issue is warrants discussion. Thanks for participating. I
enjoy your view point and the camaraderie of this list.<br>
<br>
<br>
William Miller<br>
<br>
<br>
At 11:34 AM 12/20/2009, you wrote:<br>
<br>
<o:p></o:p></p>
<p class=MsoNormal>William,<br>
<br>
Not sure I understand how buried PV runs protected by touchsafe fuses in<br>
combiner boxes at the array and GFCI protection at the inverters constitute a<br>
fire hazard.<br>
That's not saying I disagree with your disconnect here. I don't. If it was a
1kW<br>
system, would you still install one? I would not.<br>
<br>
Would not a deeper trench with properly located burial tape have been a good<br>
call? If the array was installed and visible, maybe the excavation operator<br>
would have thought to ask about underground utilities. <br>
They should have anyway. Would not common sense imply the operator would drop a<br>
bucket of fill on any sign of arcing. Would they know to look for a disconnect<br>
at the array in any case?<br>
<br>
Common sense can be slippery.<br>
<br>
Dick <br>
Solarwind Electric<br>
<br>
<br>
<br>
<br>
<br>
--- You wrote:<br>
Friends:<br>
<br>
I am embarking on a 10 Kw ground mount grid-tie installation. The client <br>
prepared for this installation some time ago by stubbing a PVC conduit <br>
underground towards the future location of the PV array. Prior to <br>
beginning this job, an excavation contractor intercepted the empty conduit <br>
with a backhoe.<br>
<br>
No harm was done because this conduit was empty. Had this conduit been <br>
filled with PV feeders, it would have been very necessary to be able to <br>
disconnect the PV arrays, both for safety and to prevent a brush fire in <br>
our very dry climate.<br>
<br>
The inverters will be located in a pump house about 130 feet from the PV <br>
arrays. I would not normally put disconnects at the array and they are
not <br>
required. This scenario, however, has caused me to reconsider. The
design <br>
now calls for a disconnect at each row of modules. I feel that it would <br>
not be prudent to delete this important safety item.<br>
<br>
I wish there were a better selection of compact, low profile disconnects <br>
suitable for a roof-top installation. I have put external handle <br>
disconnects on roof but they look terrible. I may specify touch-safe fuse
<br>
holders inside of a Sola Deck for future comp roof jobs. I am not sure <br>
what we will do with tile roofs.<br>
<br>
It seems to me that every source of power should have a means of <br>
disconnection as close to the source as possible. This is just common
sense.<br>
<br>
William Miller<o:p></o:p></p>
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