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With that logic, why bother with any smaller breakers in a load
center at all? We could just run the whole house on the 200 amp
main OCPD. Sure make installations easier. Actually though, there
is over a hundred years of evidence to show that over sizing
breakers and fuses leads to fires. 1000's of people have died. It's
why the National Fire Protection Association started printing the
NEC, and why they keep updating it. (we're on the 52nd edition)<br>
You're right, the difference between 200A and 240A is relatively
negligible, they're both unsafe. One could feed a short with 48 KW
and the other with 57.6 KW. In this case, I'm advocating for that
alleged #6 to be on its own 60 amp breaker, and fix the mess, not
add 40 amps to it. Ultimately though, it's not so much what we
think we could get away with, but proper application of the current
code as licensed electrical professionals.<br>
On my electric vehicles, I do all sorts of things that aren't code
compliant (vehicles are covered by the SAE), but no one's house is
going to burn down either. If you have points that you can back
with code references, that's what this list is all about. We're
always open to new views.<br>
<br>
Ray<br>
<br>
<blockquote
cite="mid:1324695636.86969.YahooMailNeo@web39305.mail.mud.yahoo.com"
type="cite">
<div style="color:#000; background-color:#fff; font-family:times
new roman, new york, times, serif;font-size:12pt">
<div>If there's evidence that shorts or ground faults commonly
develop with a resistance this high, causing sustained arcing,
and that the marginal difference in resistance in our example,
and in most system scenarios, makes a statistical difference,
I'm willing to concede the point. </div>
<div><br>
</div>
<div>Jeffrey Quackenbush</div>
<div><br>
</div>
<div style="font-size: 12pt; font-family: 'times new roman',
'new york', times, serif; ">
<div style="font-size: 12pt; font-family: 'times new roman',
'new york', times, serif; "> <font face="Arial" size="2">
<hr size="1"> <b><span style="font-weight:bold;">From:</span></b>
Ray Walters <a class="moz-txt-link-rfc2396E" href="mailto:ray@solarray.com"><ray@solarray.com></a><br>
<b><span style="font-weight: bold;">To:</span></b>
RE-wrenches <a class="moz-txt-link-rfc2396E" href="mailto:re-wrenches@lists.re-wrenches.org"><re-wrenches@lists.re-wrenches.org></a> <br>
<b><span style="font-weight: bold;">Sent:</span></b>
Friday, December 23, 2011 10:29 PM<br>
<b><span style="font-weight: bold;">Subject:</span></b>
[RE-wrenches] Fwd: Re: Landing into a sub-panel without a
main service panel, just a main switch<br>
</font> <br>
<div id="yiv2028186693">
<div> <br>
<br>
-------- Original Message --------
<table class="yiv2028186693moz-email-headers-table"
border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<th align="RIGHT" nowrap="nowrap"
valign="BASELINE">Subject: </th>
<td>Re: [RE-wrenches] Landing into a sub-panel
without a main service panel, just a main switch</td>
</tr>
<tr>
<th align="RIGHT" nowrap="nowrap"
valign="BASELINE">Date: </th>
<td>Fri, 23 Dec 2011 09:41:24 -0700</td>
</tr>
<tr>
<th align="RIGHT" nowrap="nowrap"
valign="BASELINE">From: </th>
<td>Ray Walters <a moz-do-not-send="true"
rel="nofollow"
class="yiv2028186693moz-txt-link-rfc2396E"
ymailto="mailto:ray@solarray.com"
target="_blank" href="mailto:ray@solarray.com"><ray@solarray.com></a></td>
</tr>
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<th align="RIGHT" nowrap="nowrap"
valign="BASELINE">To: </th>
<td>JRQ <a moz-do-not-send="true" rel="nofollow"
class="yiv2028186693moz-txt-link-rfc2396E"
ymailto="mailto:quackkcauq@yahoo.com"
target="_blank"
href="mailto:quackkcauq@yahoo.com"><quackkcauq@yahoo.com></a></td>
</tr>
</tbody>
</table>
<br>
<br>
HI Jeffrey;<br>
<br>
Electricity certainly can flow in both directions on a
conductor (unless they've installed huge diodes). If
there is a short circuit in the smallest conductor
feeding one of the subpanels (I'm guessing #6) The
short circuit would be fed by up to 260 amps without
tripping an OCPD anywhere. In this particular case
705.12 actually makes more sense than when just applied
to a bussbar. Tapping the solar into the load side
makes a dangerous situation even worse.<br>
You're right, it's not a problem if everything is
operating normally, but breakers don't do anything
normally either. It's when something bad happens (like
a rodent chewing through some wiring) that the breakers
and their ratings suddenly become the difference between
a power outage or a structure fire.<br>
Allan Sindelar taught me the importance of exactly
wording your permit to limit the scope of work and your
potential liability.<br>
In this case, I would replace the 200A main with a
larger load center (as I said before) and purposely word
the permit to not take responsibility for any
distribution wiring beyond the new load center. A line
side tap would do the same thing, but is the coward's
way out. If there is an electrical problem later, they
could still blame the new 10 KW PV system on the roof.
Whether its making some electrical improvements or
reroofing, I always try to make things better when I add
a PV system. <br>
<br>
Ray<br>
<br>
On 12/22/2011 8:05 PM, JRQ wrote:
<blockquote type="cite">
<div style="color: rgb(0, 0, 0); background-color:
rgb(255, 255, 255); font-size: 12pt; font-family:
'times new roman', 'new york', times, serif; ">
<div>The flow of electricity isn't two-way traffic
along a conductor. If there are no loads on the
conductor between the main system disconnect and
the main breaker of a subpanel, in this scenario,
there can only be up to 200 A coming from the
utility OR up to 60 A coming from the solar system
backfed through the subpanel. , logically it
follows that the sum of the OCPDs supplying that
conductor and the main disconnect is 200 A <i>or</i> 60
A, but not 260 A.</div>
<div><br>
</div>
<div>Furthermore, the alternate interpretation
misunderstands the rule in this context.</div>
<div><br>
</div>
<div>Jeffrey Quackenbush</div>
<div><br>
</div>
<div><br>
</div>
<div style="font-size: 12pt; font-family: times,
serif; ">
<div style="font-size: 12pt; font-family: times,
serif; "> <font face="Arial" size="2">
<hr size="1"> <b><span
style="font-weight:bold;">From:</span></b>
Ray Walters <a moz-do-not-send="true"
rel="nofollow"
class="yiv2028186693moz-txt-link-rfc2396E"
ymailto="mailto:ray@solarray.com"
target="_blank"
href="mailto:ray@solarray.com"><ray@solarray.com></a><br>
<b><span style="font-weight:bold;">To:</span></b>
JRQ <a moz-do-not-send="true" rel="nofollow"
class="yiv2028186693moz-txt-link-rfc2396E"
ymailto="mailto:quackkcauq@yahoo.com"
target="_blank"
href="mailto:quackkcauq@yahoo.com"><quackkcauq@yahoo.com></a>;
RE-wrenches <a moz-do-not-send="true"
rel="nofollow"
class="yiv2028186693moz-txt-link-rfc2396E"
ymailto="mailto:re-wrenches@lists.re-wrenches.org"
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<br>
<b><span style="font-weight:bold;">Sent:</span></b>
Friday, December 23, 2011 4:45 AM<br>
<b><span style="font-weight:bold;">Subject:</span></b>
Re: [RE-wrenches] Landing into a sub-panel
without a main service panel, just a main
switch<br>
</font> <br>
<div id="yiv2028186693">
<div> I'm not a huge fan of this 120% rule
myself, but if you're going to apply it
properly, it applies to all of the
conductors, buss bar, cables, etc. between
the main disco to all of the sub panels.
This rule is not limited just to a load
center buss(read 705.12D2), it applies to
all the conductors, and clearly says the sum
of breakers feeding in (200 + 40) can't
exceed 120% of the rating of any of the
conductors between the main and the subpanel
main breakers. <br>
This is an interesting situation, where
apparently the original electrical work took
liberal advantage of the tap rules in
240.21. 705.12, however, doesn't have any
exemptions that include the tap rules, so
actually it would be applied to the smallest
conductor. If any of the conductors between
the 200 amp main and sub panels is less than
200 amp rating, you're off to a bad start. <br>
<br>
Here's how I would fix it: Charge extra to
put in a new 250 amp rated load center, with
a 200 amp main breaker, feed all the
subpanels with breakers properly sized for
the various conductors, and then leave
yourself a nice 60 amp breaker on the far
end of the buss for your 10 KW PV system.
It's not a service upgrade (you're still at
200 amps), you've made the house much safer,
and you've fixed your PV intertie issues as
well. Besides being PV installers, we ARE
electricians, and we should be fixing bogus
wiring when it also benefits the PV
install. Then all of us could sleep better.<br>
<br>
Ray<br>
</div>
</div>
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