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<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial>OK, this subject has come up before and this is a gray area in
the Code. What is the definition of "the output of the
inverters."</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial>I have sucessfully argued that the output of the inverters is
the last point in the circuit where the circuit is free of premise load
circuits. In this case it would be the 40A breaker connecting the dedicated PV
load center to the busbar of the main panel.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial>So...it is between you and you inspector. Tell him you are
going to put a label on the subpanel that says something to the effect of
"Dedicated inverter output accumulation subpanel. Add no additional
circuits."</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial>I think this is a much better interpretation and method
that preserves a clean and functional load side connection topology. I
think most reasonable inspectors would agree as well.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial>Good Luck.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375493620-29092011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN lang=en-us><FONT size=2 face=Arial>Mark
Frye</FONT></SPAN> <BR><SPAN lang=en-us><FONT size=2 face=Arial>Berkeley Solar
Electric Systems</FONT></SPAN> <BR><SPAN lang=en-us><FONT size=2 face=Arial>303
Redbud Way</FONT></SPAN> <BR><SPAN lang=en-us><FONT size=2 face=Arial>Nevada
City, CA 95959</FONT></SPAN> <BR><SPAN lang=en-us><FONT size=2
face=Arial>(530) 401-8024</FONT></SPAN> <BR><SPAN lang=en-us></SPAN><A
href="http://www.berkeleysolar.com/"><SPAN lang=en-us><U><FONT color=#0000ff
size=2 face=Arial>www.berkeleysolar.com</FONT></U></SPAN></A><SPAN
lang=en-us><FONT size=2 face=Arial> </FONT></SPAN> </DIV>
<DIV> </DIV><BR>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <B>On Behalf Of </B>Jason
Szumlanski<BR><B>Sent:</B> Thursday, September 29, 2011 1:33 PM<BR><B>To:</B>
RE-wrenches<BR><B>Subject:</B> Re: [RE-wrenches] Adding on to existing PV
System<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=WordSection1>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">I understand what you are saying
about the 40A breaker, but according to 690.64(B)(2), “…with panelboards
connected in series, the rating of the <B>*first*</B> overcurrent device
connected <B>*directly*</B> to the output of the inverters shall be used in the
calculations for <B>*all*</B> busbars and conductors.” The way I have seen that
interpreted is that the main distribution panel needs to be rated to support
120% of the two inverter circuits plus the main breaker, regardless of the fact
that there is a 40A backfeed breaker in the main panel.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">200+30+15 > 200 x
1.2<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">I know it doesn’t make much
sense, but that’s the way it’s been interpreted around here. It stands to reason
that this applies only to the PV subpanel busbar and the conductors between the
panels, and that the calculation for those should be:<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">(30 + 15 + 40) / 1.2 = 70.83A
required ampacity<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">…and the calculation for the
main distribution panel should be:<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">(200 + 40) / 1.2 = 200A required
ampacity<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">… but that’s not what I am being
told.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<DIV>
<P class=MsoNormal><SPAN style="COLOR: #1f497d; FONT-SIZE: 12pt">Jason
Szumlanski<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Fafco
Solar<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="COLOR: #1f497d"><o:p> </o:p></SPAN></P></DIV>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<DIV>
<DIV
style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; PADDING-BOTTOM: 0in; PADDING-LEFT: 0in; PADDING-RIGHT: 0in; BORDER-TOP: #b5c4df 1pt solid; BORDER-RIGHT: medium none; PADDING-TOP: 3pt">
<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>Mark
Frye<BR><B>Sent:</B> Thursday, September 29, 2011 4:19 PM<BR><B>To:</B>
'RE-wrenches'<BR><B>Subject:</B> Re: [RE-wrenches] Adding on to existing PV
System<o:p></o:p></SPAN></P></DIV></DIV>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: blue; FONT-SIZE: 10pt">Jason:</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"> <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: blue; FONT-SIZE: 10pt">SB 5000
= 21A @ 240V, 21A x 1.25 = 26.3A needs 30A breaker</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: blue; FONT-SIZE: 10pt">M215 =
0.9 A @ 240V, 0.9A x 9 = 8.1 A, 8.1 x 1.25 = 10.1A needs 15A breaker. (Or that
rounded to 10A and use a 10A breaker)?</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"> <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: blue; FONT-SIZE: 10pt">26.3A +
10.1A = 36.4 A needs 40A breaker</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"> <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: blue; FONT-SIZE: 10pt">So, get
a new 100A main lug subpanel. Connect it to a 40A breaker in the existing main
panel. Move the existing 30A breaker into the new subpanel and install the new
15A breaker into the same.</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"><BR></SPAN><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 10pt">Mark Frye</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt">
<BR></SPAN><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 10pt">Berkeley Solar
Electric Systems</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt">
<BR></SPAN><SPAN style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 10pt">303
Redbud Way</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt">
<BR></SPAN><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 10pt">Nevada City, CA
95959</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt">
<BR></SPAN><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 10pt">(530)
401-8024</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"> <BR><A
href="http://www.berkeleysolar.com/"><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 10pt">www.berkeleysolar.com</SPAN></A></SPAN><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 10pt"> </SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt">
<o:p></o:p></SPAN></P>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"> <o:p></o:p></SPAN></P></DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"><o:p> </o:p></SPAN></P>
<DIV style="TEXT-ALIGN: center" class=MsoNormal align=center><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt">
<HR align=center SIZE=2 width="100%">
</SPAN></DIV>
<P style="MARGIN-BOTTOM: 12pt" 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>Jason
Szumlanski<BR><B>Sent:</B> Thursday, September 29, 2011 12:55 PM<BR><B>To:</B>
RE-wrenches<BR><B>Subject:</B> Re: [RE-wrenches] Adding on to existing PV
System</SPAN><SPAN
style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 12pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">That’s not a bad idea, except
that 690.64(B)(2) requires that the breaker directly connected to each
inverter(s) must be used for the calculation.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">I have an existing SB5000 with a
30A breaker and a new string of nine Enphase M215’s requiring a 15A breaker. If
you combine these in a 100A or higher rated subpanel with a 40A main breaker,
you still calculate the total current supplying the busbar in the main
distribution panel based on 200A + 30A + 15A = 245A (with 30A and 15A being the
overcurrent protection directly connected to the inverters). This exceeds the
120% rule by 5A. It also requires that the ampacity of the conductors between
the two panels be 85A / 1.2 = 70.83A (assuming a 40A backfeed breaker in the
main distribution panel). If your interpretation is different, please let me
know!<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">If my interpretation is correct,
I like the idea of just adding a fusible disconnect and using #10 conductors all
the way to the tap. That would be the most cost effective solution I believe,
and since there is no foreseeable further system rating increases, the advantage
of a subpanel is reduced.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Thanks for all the other
suggestions provided. Unfortunately I can’t put in smaller main breaker, and the
busbar in the main panel is definitely rated 200A.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<DIV>
<P class=MsoNormal><SPAN style="COLOR: #1f497d; FONT-SIZE: 12pt">Jason
Szumlanski<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Fafco
Solar<o:p></o:p></SPAN></P></DIV>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<DIV>
<DIV
style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; PADDING-BOTTOM: 0in; PADDING-LEFT: 0in; PADDING-RIGHT: 0in; BORDER-TOP: #b5c4df 1pt solid; BORDER-RIGHT: medium none; PADDING-TOP: 3pt">
<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>Glenn
Burt<BR><B>Sent:</B> Thursday, September 29, 2011 2:40 PM<BR><B>To:</B>
'RE-wrenches'<BR><B>Subject:</B> Re: [RE-wrenches] Adding on to existing PV
System<o:p></o:p></SPAN></P></DIV></DIV>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">How about feeding both systems
into an AC combining subpanel before feeding the main load
center?<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Often the calculations required
will allow you to do more backfeeding than the simple backfeeding a load center
with individual breakers.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">-Glenn<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<DIV>
<DIV
style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; PADDING-BOTTOM: 0in; PADDING-LEFT: 0in; PADDING-RIGHT: 0in; BORDER-TOP: #b5c4df 1pt solid; BORDER-RIGHT: medium none; PADDING-TOP: 3pt">
<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>Jason
Szumlanski<BR><B>Sent:</B> Thursday, September 29, 2011 11:49 AM<BR><B>To:</B>
RE-wrenches<BR><B>Subject:</B> [RE-wrenches] Adding on to existing PV
System<o:p></o:p></SPAN></P></DIV></DIV>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>We’ve been contracted to add on to an existing PV system in a
residence. The existing system has a 30A 2P Breaker on a 200A rated panel with a
200A main breaker. The new system would require a 15A breaker, which would
exceed the limit in NEC 690.64(B)(2).<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>The existing system has a fusible AC disconnect mounted next
to the meter. This was originally intended as the utility external disconnect.
The utility no longer requires a disconnect, but if we do a supply side
connection, we would need a fusible AC disconnect anyway for the new system. I
would collocate the new disconnect with the old.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Does anyone see any problem with doing a supply size
connection for the new system? Any labeling snags that I might need to
consider?<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 12pt">Jason
Szumlanski<o:p></o:p></SPAN></P>
<P class=MsoNormal>Fafco Solar<o:p></o:p></P></DIV></BODY></HTML>