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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>Yes we have T-corrected the Voc. One of
the nice things we have going for us in the LA area, is the moderating
influence of the ocean. 90% + of our systems never see record cold temperatures
below 14 def F.</span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>You are correct about the Vdc rising upon
disconnection (from Vmp to Voc) and DC arcs being a different beast than AC arcs.
It is perhaps this latter reason which so few medium duty discos have a DC
rating.</span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'> </span></font></p>
<div>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Peter T. Parrish, Ph.D., President<br>
California Solar Engineering, Inc.<br>
820 Cynthia Ave., Los Angeles, CA 90065<br>
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885<br>
CA Lic. 854779, NABCEP Cert. 031806-26<br>
peter.parrish@calsolareng.com</span></font><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'> </span></font></p>
</div>
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face="Times New Roman"><span style='font-size:12.0pt'>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>William Miller<br>
<b><span style='font-weight:bold'>Sent:</span></b> Friday, November 21, 2008
9:43 AM<br>
<b><span style='font-weight:bold'>To:</span></b> RE-wrenches<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [RE-wrenches] DC
Rating of Disconnects</span></font></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> </span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Peter:<br>
<br>
I am resending, the first version inexplicably deleted some text:<br>
<br>
An arc is created in the process of disconnecting any current under load.
DC circuits have an enhanced ability to sustain that arc. PV circuits
exacerbate this problem as a short or load is disconnected because they can
sustain a short but the voltage rises drastically as a circuit is disconnected.<br>
<br>
This all justifies the added expense of a DC rated disconnect. We use the
Square D HU361 without hesitation. There are few alternatives available
and none with any significant cost savings. In selecting a disconnect, a
design-build contractor must use the highest Voc possible. Make sure you are
entering the 690.7 table with the record low temperature for the location.<br>
<br>
If we used a disconnect without the correct rating we would open ourselves to
unacceptable liability exposure and, worse yet, would not experience that
pleasant feeling one gets when you know you've done the job right.<br>
<br>
William Miller<br>
<br>
<br>
At 09:11 AM 11/21/2008, you wrote:<br>
<br>
</span></font></p>
<p class=MsoNormal><font size=3 face=Arial><span style='font-size:12.0pt;
font-family:Arial'> <br>
<br>
</span></font><br>
<font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Peter T. Parrish, Ph.D., President<br>
California Solar Engineering, Inc.<br>
820 Cynthia Ave., Los Angeles, CA 90065<br>
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885<br>
CA Lic. 854779, NABCEP Cert. 031806-26<br>
peter.parrish@calsolareng.com</span></font><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'> </span></font></p>
<div class=MsoNormal align=center style='text-align:center'><font size=2
color=blue face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:blue'>
<hr size=2 width="100%" align=center>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Peter Parrish [<a
href="mailto:peter.parrish@calsolareng.com" eudora=autourl>mailto:peter.parrish@calsolareng.com</a>]
<br>
<b><span style='font-weight:bold'>Sent:</span></b> Friday, November 21, 2008
9:10 AM<br>
<b><span style='font-weight:bold'>To:</span></b> 'RE-wrenches'<br>
<b><span style='font-weight:bold'>Cc:</span></b> 'Peter Parrish'<br>
<b><span style='font-weight:bold'>Subject:</span></b> DC Rating of Disconnects<br>
</span></font><font face=Arial><span style='font-family:Arial'> <br>
I am looking into using the PV Powered PVP2000 inverter for some small, low
voltage designs. The string Voc will be around 200 Vdc, worst case.<br>
<br>
Since the PVP2000 doesnt come with a DC disconnect, I am wondered what
other wrenches who install the PVP2000 have been doing about this. I hate to
spend $150 on a 600 V AC/DC disco such as the SD HU361RB to provide the means
of disconnection. I believe that the 240 V AC discos such as the SD DU221RB
have no DC rating.<br>
<br>
>From an academic point of view, I wonder why the smaller discos are not dual
rated, since we all know that the real-time voltage difference in a 240 V AC
system can be 41% greater than 240 V.<br>
<br>
In any event, any Code-compliant solutions would be greatly appreciated.<br>
<br>
- Peter<br>
</span></font><br>
<font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Peter T. Parrish, President</span></font></p>
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