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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>William,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>I have been following this back-and-forth
thread and need you to please explain one thing:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>Your 140A point makes perfect sense (from
the point of 690.64 in requiring that the busbar to which both utility and PV
feeds are connected. No question there. But you write: “</span></font>It
is my understanding that if one is going to install a load side tape, the back
feed calculations need to work for every link of the distribution system
upstream to the meter.” It seems to me that there’s still no way to
exceed main disconnect current rating. <o:p></o:p></p>
<ol style='margin-top:0in' start=1 type=1>
<li class=MsoNormal style='mso-list:l0 level1 lfo1'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>100A utility (using
100A subpanel main) + 40A PV tied into subpanel busbar = 140A, which is OK
if the subpanel busbar is rated at least 125A (residential) or 150A
(commercial).<o:p></o:p></span></font></li>
<li class=MsoNormal style='color:black;mso-list:l0 level1 lfo1'><font size=3
color=black face="Times New Roman"><span style='font-size:12.0pt;
color:windowtext'>100A + 40A tapped into subpanel ahead of 100A main
breaker:</span></font><o:p></o:p></li>
<ol style='margin-top:0in' start=1 type=a>
<li class=MsoNormal style='mso-list:l0 level2 lfo1'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>maximum current
passing through 100A main breaker = 100A. Adding 40A of PV only reduces
amount through conductors from main AC panel to 60A.<o:p></o:p></span></font></li>
<li class=MsoNormal style='color:black;mso-list:l0 level2 lfo1'><font size=3
color=black face="Times New Roman"><span style='font-size:12.0pt;
color:windowtext'>no AC load in daytime = 40A of current back to main AC
load center</span></font><o:p></o:p></li>
<li class=MsoNormal style='color:black;mso-list:l0 level2 lfo1'><font size=3
color=black face="Times New Roman"><span style='font-size:12.0pt;
color:windowtext'>some subpanel loads in daytime reduces 2.b. above</span></font><o:p></o:p></li>
</ol>
<li class=MsoNormal style='mso-list:l0 level1 lfo1'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>At the main panel,
maximum current flow through breaker feeding subpanel is 100A, as any PV reduces
load at breaker. However, main panel must itself meet 690.64, as it’s
still possible to feed 40A of PV (daytime with no subpanel load) into main
panel. So same busbar requirements apply in the main panel as in the
subpanel. But that’s all. The subpanel feeders don’t need to
be upsized.<o:p></o:p></span></font></li>
</ol>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>What am I missing here, please?</span></font><font color=black><span
style='color:black'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>Allan Sindelar<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Times New Roman"><span
style='font-size:10.0pt;color:black'><a
href="mailto:Allan@positiveenergysolar.com">Allan@positiveenergysolar.com</a></span></font><font
color=black><span style='color:black'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Times New Roman"><span
style='font-size:10.0pt;color:black'>NABCEP Certified Photovoltaic Installer</span></font><font
color=black><span style='color:black'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Times New Roman"><span
style='font-size:10.0pt;color:black'>EE98J Journeyman Electrician</span></font><font
color=black><span style='color:black'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>Positive Energy, Inc.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>3201 Calle Marie<o:p></o:p></span></font></p>
<p class=MsoNormal><st1:place w:st="on"><st1:City w:st="on"><font size=3
color=black face="Times New Roman"><span style='font-size:12.0pt;color:black'>Santa
Fe</span></font></st1:City><font color=black><span style='color:black'>, <st1:State
w:st="on">New Mexico</st1:State> <st1:PostalCode w:st="on">87507</st1:PostalCode></span></font></st1:place><font
color=black><span style='color:black'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>505 424-1112<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'><a
href="http://www.positiveenergysolar.com">www.positiveenergysolar.com</a></span></font><o:p></o:p></p>
</div>
<div>
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face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</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'>
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> Saturday, August 01, 2009
6:11 PM<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]
down-sizing main breaker</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Dick:<br>
<br>
Your logic is correct but incomplete. Consider it like this: The
buss bars in the service panel can handle 100 amps (they are rated for that
amount). The main breaker feeds 100 amps into that buss, maximizing it's
capabilities. If you feed an additional 40 amps into that buss bar, you
have the potential of exceeding the ampacity of that buss assembly. If no
other loads are fed from that buss bar, there is no over current
scenarios. Say, however, someone puts more breakers on that buss bar and
draws 140 amps from them. 100 amps comes in from the utility, 40 amps
comes in from the PV and the buss is overloaded.<br>
<br>
This is the scenario for which 690.64(B) was written. This will occur
only if the overload amperage is not drawn from a space on the buss bar between
the utility feeder and the PV feeder. If, however, the PV feeder breaker
and the utility feeder are both on one end of the buss and the load is on the
other end, then the loads are additive on the buss assembly.<br>
<br>
Some want the code passage re-written to say that if the feeder is on one end
of the bus assembly and the PV is on the other, there is no possibility of an
overdraw on the buss bar and the installation is legal. This has not
happened yet.<br>
<br>
William<br>
<br>
<br>
<br>
<br>
At 03:47 PM 8/1/2009, you wrote:<br>
<br>
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>William,<br>
<br>
I don't know if I've solved Brian's dilemma yet either. But, with regard to
your<br>
example below, if the 100 amp meter main is accepting 20 amps, or even all of<br>
the 50 amps of PV, that would mean that the house, at that moment, presented no<br>
load at all, and that all the PV would be backfeeding the grid, turning the<br>
meter backwards. That, of course, would mean the main 100 amp breaker is only<br>
handling 50 amps, well below its rating. Likewise the feeder from the house<br>
would only be carrying the 50 amps from the PV, instead of anything near
it's100<br>
amp rating. The code can be perverse, but it's my understanding that the point<br>
of 690.64(B) is to ensure none of the distribution components are exposed to<br>
overcurrent, not to arbitrarily throw numbers around.<br>
<br>
I was just kidding about offering you those 200 amp Milbank breakers. I've got<br>
to figure out how to list them on Ebay.<br>
<br>
Dick<br>
<br>
--- You wrote:<br>
Dick:<br>
<br>
I don't believe you have solved Brian's dilemma yet. It is my <br>
understanding that if one is going to install a load side tape, the back <br>
feed calculations need to work for every link of the distribution system <br>
upstream to the meter. In the scenario you suggest, that will not be the <br>
case. The 100 amp meter main on Brian's project will still accept
only 20 <br>
amps of PV AC feed, still not satisfying his requirements.<br>
--- end of quote ---<br>
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<p></x-sigsep><u><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><x-sigsep>Please note new e-mail address and domain:<br>
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</span></font></u>William Miller <br>
Miller Solar<br>
Voice :805-438-5600 Fax: 805-438-4607<x-tab> </x-tab><br>
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<a href="http://millersolar.com/" eudora=autourl>http://millersolar.com<br>
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