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<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=453300802-01042011>Sigh...</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=453300802-01042011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=453300802-01042011>After talking with Generac today I went ahead and
ordered the ~$1,200 worth of 400A fused disconnect to put upstream of their 400A
ATS to protect it from the 480A of combined main breaker/PV back feed breaker
that I want to install. Of course their literature says that with a 600A circuit
breaker installed on the line side, the switch will withstand a hard short on
the load side just fine. But let us not even think about letting 480A run
through it for a few hours ever other blue moon. (Well that's what I get for
saying we should look more at overload than short circuit conditions in these PV
systems.)</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=453300802-01042011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=453300802-01042011>Still it's not like the my customer has been
plagued for the last 13 years with nuisance tripping of the existing 400A main
breaker because they tend to plug in one too many hair dryers....but...future
load expansion and uncontrolled recpticals loads...they can be a problem, so
better safe than sorry.</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><SPAN class=453300802-01042011><FONT color=#0000ff size=2 face=Arial>So now
I see, I have to do what I have to do if I want to be even half as good an
electrican as my NABCEP certification says I am.</FONT></SPAN></DIV>
<DIV><SPAN class=453300802-01042011></SPAN> <BR><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>Mark
Frye<BR><B>Sent:</B> Sunday, March 27, 2011 8:38 AM<BR><B>To:</B>
'RE-wrenches'<BR><B>Subject:</B> Re: [RE-wrenches] Generator and
Enphase<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>Larry,</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>There are alot of ways to skin that
cat.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>Here is what I am doing on my job.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>I have a 400A main disconnect with a feeder running
directly to a 400 ATS then to a 400A main lug dedicated load center under the
switch. All conductors are double - 250 mcm.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>I am going to tap the feeder on the line side, inside
the ATS cabinet, using a ten foot feeder tap of #3 running to a new 100A breaker
enclosure with an 80A breaker. From there I will go to a new 150A main lug load
center with 95A worth of PV backfeed breakers.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>I really am enjoying this one because it brings up so
many interesting Code quandaries.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>In my mind I am extending the premise wiring and
interconnecting at the new load center which is on the line side of the ATS.
Some folks might take issue with this, arguing that the "PV" circuit begins at
the tap in the ATS and as such is not at a dedicated OCPD. Some folks have
argued that feeder tap rules themselve do not apply to PV circuits. In any case,
the new 150A load center is not dedicated solely to backfeeding the PV, there
are other loads connected there. This is why I see it as an extension of the
premise wiring and as the point of interconnect of the PV
circuit.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>Interestingly enough, in order to follow NEC 2008, I
will have to place the PV backfeed breakers at the bottom of the new 150A load
center.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>But here is where it gets interesting. Taking the ATS
out of the picture for a moment, the existing 400A main lug load center is now
feed with through the main lug with a total of 480A of supply breakers. This
complies with NEC 2008 vis-a-vis the 120% allowance for conductors and busbars.
In this case it does sort of make it seem silly to go through the trouble of
putting the backfeed breakers on the bottom of the 150A load center. Especially
when thinking back, the whole idea of putting the breaker at the bottom of the
load center was that you could then have PV backfeed equal to the full rating of
load center busbar. Funny how things work out.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=546440715-27032011>Anyway, the real question comes up when we bring the
ATS back into the picture. The 400A ATS will see the same 480A of supply
breakers as the conductors and busbar of the 400A load center. Here is where I
am taking leap of faith that the AHJ will agree with me that the same 120%
allowance given to the conductors and load center will be given to ATS
itself.</SPAN></FONT></DIV>
<DIV><BR><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></BODY></HTML>