<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Why should the Code be practical :-)?</div><div><br></div><div>In a plain vanilla electrical system everything downstream of a breaker can be sized assuming that the breaker will protect things. There is only one source of energy, and the breaker is the gatekeeper which limits how much energy can get through. When you add a backfed solar breaker, however, you are introducing a second source of energy. Typically in a panel the sum of all the load breakers is greater than the rating of the bus bars, so you can't rely on the load breakers to protect the busing and the conductors. To keep things in check, the Code limits the total of all sources.</div><div><br></div><div>With the load center you have, the bus bars in the top section are not protected by anything other than the short-circuit capacity of the utility transformer. The idea is that the load breakers--all labeled as a service disconnect--provide a limit to the maximum current. You wouldn't want to put six 100 A breakers in there, because then you could potentially draw 600 A and exceed the capacity of the bus bars. When you backfeed solar onto this bus you're not really adding any significant amount to the transformer fault current.</div><div><br></div><div>So maybe to more directly address your question, where you backfeed doesn't make any difference to the bus bars in the top section of your panel, but when you feed into the bottom section you have to worry about the rating of the bus bars down there.</div><div><br></div><div>Scott</div><br><div><div>On Nov 2, 2010, at 1:59 PM, Dana Brandt wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Thanks. That's really helpful. I think the Code Corner quote will help in dealing with the AHJ. <br><br>From a practical standpoint, though, I don't see why our PV input power should limited by the 690.64 (B) (2) calculation if there's a main breaker present, but if there's no main breaker we can feed in 100% of the bus rating. <br>
<br><i> "The basic restriction (which will be in the 2011 NEC) that would apply to this type of main service panel is that the sum of the overcurrent devices from the PV inverter(s) should not exceed the rating of the panel bus bar or the rating of the service entrance cables."</i><br clear="all">
<br>Is there something special in the busing on these main-lug-only panels that means we don't have to be so conservative or is it a matter of the code not really being consistent?<br><br>Thanks,<br><br>Dana<br><br>Dana Brandt<br>
Ecotech Energy Systems, LLC<br><a href="http://www.ecotechenergy.com/">www.ecotechenergy.com</a><br><a href="mailto:dana@ecotechenergy.com">dana@ecotechenergy.com</a><br>360.510.0433<br>
<br><br><div class="gmail_quote">On Mon, Nov 1, 2010 at 10:01 PM, Philip Boutelle <span dir="ltr"><<a href="mailto:philboutelle@gmail.com">philboutelle@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Dana,<div>I'll echo Scott's earlier comment: connecting to an empty 'main' breaker position that is on the top bus will be a supply-side connection. From Code Corner #126:<div><div><i><br></i></div><div><i>Some dwellings have main-lug-only panels. There is no </i></div>
<div><i>single main breaker feeding the panel, but up to six main </i></div><div><i>breakers are allowed. Empty breaker positions can be used </i></div><div><i>as supply-side connections. The basic restriction (which </i></div>
<div><i>will be in the 2011 NEC) that would apply to this type </i></div><div><i>of main service panel is that the sum of the overcurrent </i></div><div><i>devices from the PV inverter(s) should not exceed the </i></div>
<div><i>rating of the panel bus bar or the rating of the service </i></div><div><i>entrance cables.</i></div></div><div><br></div><div>-Phil Boutelle</div><div>Real Goods Solar</div><div><div></div><div class="h5"><div><br>
<br><div class="gmail_quote">
On Mon, Nov 1, 2010 at 6:55 PM, Dana Brandt <span dir="ltr"><<a href="mailto:dana@ecotechenergy.com" target="_blank">dana@ecotechenergy.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Hi everyone,<br>
<br>
I just noticed my last email didn't go through because I'd attached
pictures of the panel. If you're interested in the pics of the panel please contact
me off-list. <br>
<br>
Thanks
for the feedback. To clarify, the upper part of the bus is lug-fed
directly from the service meter - no overcurrent protection. I have this
same situation in two homes - one has a Bryant panel, not sure about
the other. <br>
<br>It seems possible connecting to the top bus could be considered a
supply side connection. It's done through a panel bus, though, which
seems like maybe it wouldn't qualify.<br><br>It's true that the 60A
breaker feeding the 100A bus fulfills the calculation requirements. However, the calculation has to
follow upstream to the bus supplying that 60A breaker, so again we have a
potential problem since there's no overcurrent protection for that bus.<br>
<br>So, it seems the real question is about that top bus. Can we consider a connection there a supply side tap? If not, who do we do the
690.64 (B) (2) calculation without a main breaker? <br><div><br>Thanks!<br clear="all"><br>Dana<br><br>Dana Brandt<br>Ecotech Energy Systems, LLC<br><a href="http://www.ecotechenergy.com/" target="_blank">www.ecotechenergy.com</a><br>
<a href="mailto:dana@ecotechenergy.com" target="_blank">dana@ecotechenergy.com</a><br>
360.510.0433<br>
<br><br></div><div class="gmail_quote"><div><div></div><div>On Thu, Oct 28, 2010 at 6:37 PM, Matt Lafferty <span dir="ltr"><<a href="mailto:gilligan06@gmail.com" target="_blank">gilligan06@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div><div></div><div>
<div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2">Hi Dana,</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2">"Sounds like" you have a lower-bus rated at 100A being fed by
a 60A breaker... Yes?</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2">If so, technically speaking but not necessarily the right
thing to do, you have a SWEET SETUP! In 690.64 terms, you are legally allowed
120A to feed that bus. Which converts to a maximum 60A PV interconnection
breaker located at the opposite end of the bus from the 60A supply breaker. This
is a panel configuration that I have wished was still made for many years.
</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2">The downside is... It's probably older than me. With
really wimpy buses. And really bad options for replacement breakers. And is full
of 2-wire homerun circuits. </font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2">If it doesn't have a perfect-in-every-way bus, it's time for a
new panel. You also need to be able to buy <span><font color="#0000ff" face="Arial" size="2">real...
Modern.... And New UL Listed breakers. Those gray looking replacement breakers
in the home improvement store? They're NOT OK. In any
way.</font></span></font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span></span></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span>Wadsworth? FPE? Bulldog?
&...??? These panels are NOT OK for interconnection at this point. Time to
upgrade. Yes, really. </span></font></span><span><font color="#0000ff" face="Arial" size="2"><span>Zinsco? Depends.
Any panel with signs of arcing around the bus anywhere? Better have a damned
good explanation before I'd be tying in some PV. I know of a couple. Warped
breakers? Change it!</span></font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span></span></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span>I just got done doing a 90%
rewire on a friend's house and it tore my heart out sending the panel to the
recycler.<i> (This friend is into long-term thinking and sustainable
everything. I would have left it if I could and so would they.) </i><span><font color="#0000ff" face="Arial" size="2"><span>The bus was pristine. It is rumored that Al Capone used
to stay in this place when he was in the area. The panel was giant, with
lots of room. This panel had a coolness factor off the charts. But...
I</span></font></span></span></font></span><span><font color="#0000ff" face="Arial" size="2"><span><span><font color="#0000ff" face="Arial" size="2"><span> couldn't reliably get trustworthy breakers. And
it was my friend's house. Somebody I care about. I couldn't leave it in there. I
use the same judgement whether my customer is a friend or
not.</span></font></span></span></font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span><span><font color="#0000ff" face="Arial" size="2"><span></span></font></span></span></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span>If what
you have is a modern panel, share! I know I would personally
appreciate it if you were able to share mfr, model, pictures, etc. Whenever we
are upgrading/swapping/moving a service panel, we need to be installing
something that provides the best opportunity for interconnection of distributed
resources. We don't have those at this point. And we need them. A
split-distribution <i>(not just split-bus)</i> service panel is one way to
accomplish this. The trick is to limit the possible size of the breaker feeding
the "2nd" bus <i>(the lower bus in this case).</i> It's not rocket science.
</span></font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span></span></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span>I'd be happy to use and
publicize a product that a mainstream manufacturer came up with to deal with
this. How about you? </span></font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span></span></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span>$0.02001,</span></font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span></span></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span>Solar
Janitor</span></font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span></span></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Arial" size="2"><span>PS - Home rewiring for friends
only. I love doing it, but I do it for love. There ain't no amount of money that
makes me want to do it just for money!</span></font></span>
<hr>
<font face="Tahoma" size="2"><b>From:</b> <a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b>Dana
Brandt<br><b>Sent:</b> Thursday, October 28, 2010 5:19 PM<br><b>To:</b>
RE-wrenches<br><b>Subject:</b> [RE-wrenches] backfeeding "six disconnect"
panel<br></font><br></div><div><div></div><div>
<div></div>Hi everyone,<br><br>I'm working on two systems for homes that have
the old style breaker panels with no single main breaker. Instead, they have six
breakers in the upper part of the panel each labeled "main breaker," which
satisfies the six disconnect rule. The bus bar is split, with one of the six
upper breakers (60A) feeding a separate bus in the lower half of the panel. It
appears that the upper bus is rated for 200A, and the lower at 100A. The
sum of the main breakers does not exceed the 200A rating of the upper bus. There
are spare breaker slots on both the top and bottom buses. How do I deal with
690.64 (B) (2) when there's no main breaker? <br><br>Thanks!<br clear="all"><br>Dana<br><br>Dana Brandt<br>Ecotech Energy Systems, LLC<br><a href="http://www.ecotechenergy.com/" target="_blank">www.ecotechenergy.com</a><br>
<a href="mailto:dana@ecotechenergy.com" target="_blank">dana@ecotechenergy.com</a><br>360.510.0433<br>
<div></div>
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