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<DIV dir=ltr align=left><SPAN class=218293818-21112008><FONT face=Tahoma
color=#000080 size=2>In 2008, we have had to replace our standard Sq. D HU361RB
used since our beginnings, with the Sq. D H361RB (U stands for
unfused). Was there some sort of code change NEC or CBC maybe that
made most jurisdictions in So Cal suddenly start requiring fused DC
disconnects? Typically, we fill the fused Sq. D. box with 15A 5"
fuses.</FONT></SPAN></DIV>
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<DIV><SPAN
style="FONT-SIZE: 10pt; COLOR: rgb(51,51,153); FONT-FAMILY: Tahoma"><SPAN
class=218293818-21112008><FONT color=#000080>Peter
D.</FONT></SPAN></SPAN></SPAN></DIV></DIV></DIV></DIV><BR>
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<FONT face=Tahoma size=2><B>From:</B> 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> Friday, November 21, 2008 9:43 AM<BR><B>To:</B>
RE-wrenches<BR><B>Subject:</B> Re: [RE-wrenches] DC Rating of
Disconnects<BR></FONT><BR></DIV>
<DIV></DIV>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>
<BLOCKQUOTE class=cite cite="" type="cite"><FONT face=arial color=#0000ff
size=2>
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</FONT><FONT face=tahoma size=2><B>From:</B> Peter Parrish [<A
href="mailto:peter.parrish@calsolareng.com"
eudora="autourl">mailto:peter.parrish@calsolareng.com</A>] <BR><B>Sent:</B>
Friday, November 21, 2008 9:10 AM<BR><B>To:</B> 'RE-wrenches'<BR><B>Cc:</B>
'Peter Parrish'<BR><B>Subject:</B> DC Rating of Disconnects<BR></FONT><FONT
face=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></FONT><BR><FONT face=arial
color=#000080 size=2>Peter T. Parrish,
President</FONT></BLOCKQUOTE></BODY></HTML>