<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Corey:</div><div><br></div><div>I think what you are proposing is a bad idea and false economy. </div><div><br></div><div>It is good practice to provide disconnecting and over-current protection devices to all discrete components in any system. This applies to power systems as well as signaling systems. This provides capability to isolate sub-systems for troubleshooting and temporary operation in case of partial failures. The cost of a small sub-panel is a minimal, necessary part of this type of installation.</div><div><br></div><div>Now that we have seen that very few cases support the math needed to comply with code, further discussion seems purely academic.</div><div><br></div><div>William Miller</div><div><br>Miller Solar</div><div><br>On Jun 30, 2014, at 11:50 AM, Brian Teitelbaum <<a href="mailto:bteitelbaum@aeesolar.com">bteitelbaum@aeesolar.com</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><meta name="Generator" content="Microsoft Word 14 (filtered medium)"><style><!--
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--></style><div class="WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Corey,</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The wire ampacity has to be sized for the OCPD, as this is potentially a bidirectional wire in a fault. While the inverter is current limited, the grid it’s connected to is only limited by the Service Main, and that 50A OCPD, which would exceed the ampacity of #10 wire.</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Brian Teitelbaum</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">AEE Solar</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> RE-wrenches [mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b>Corey Shalanski<br>
<b>Sent:</b> Monday, June 30, 2014 11:38 AM<br><b>To:</b> <a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a><br><b>Subject:</b> Re: [RE-wrenches] Combining Multiple Inverters</span></p>
<p class="MsoNormal"> </p><div><p class="MsoNormal">Thank you to all who responded to this thread - particularly Jason/Dave/Jay for pointing out the maximum OCPD requirements.</p><div><p class="MsoNormal"> </p></div><div>
<p class="MsoNormal">Getting back to my original question.. I would like to use Dave's "extremely small subset" example of two SB5s operating at 277V. In this case, if we were to parallel the output of each inverter onto a 50A OCPD (#6 wire), could we downsize the wire to #10 from the split going back to each individual inverter? or would we be better served (required?) to run #6 all the way back to each unit? Since we are dealing with current-limited devices I would tend to think we can downsize but wanted to get Wrenches' feedback on this.</p>
</div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">--</p></div><div><p class="MsoNormal">Corey Shalanski</p></div><div><p class="MsoNormal">Joule Energy</p></div><div><p class="MsoNormal">New Orleans, LA</p>
<div><p class="MsoNormal"><img id="_x0000_i1025" src="https://mailfoogae.appspot.com/t?sender=aY3NoYWxhbnNraUBqb3VsZS1lbmVyZ3kuY29t&type=zerocontent&guid=4bec5788-9903-4ff4-8f92-031ee1997a9c"><span style="font-size:7.5pt;font-family:"Euphemia","sans-serif";color:white">ᐧ</span></p>
</div><div><p class="MsoNormal" style="margin-bottom:12.0pt"> </p><div><p class="MsoNormal">On Fri, Jun 27, 2014 at 12:41 PM, <<a href="mailto:re-wrenches-request@lists.re-wrenches.org" target="_blank">re-wrenches-request@lists.re-wrenches.org</a>> wrote:</p>
<p class="MsoNormal"><br>Message: 5<br>Date: Fri, 27 Jun 2014 11:32:02 -0400<br>From: Dave Click <<a href="mailto:daveclick@fsec.ucf.edu">daveclick@fsec.ucf.edu</a>><br>To: <a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a><br>
Subject: Re: [RE-wrenches] Combining Multiple Inverters<br>Message-ID: <<a href="mailto:53AD8E72.4080009@fsec.ucf.edu">53AD8E72.4080009@fsec.ucf.edu</a>><br>Content-Type: text/plain; format=flowed; charset=ISO-8859-1<br>
<br>This is an interesting conversation, but I'm not sure it's going to<br>really impact anything.<br><br>When an inverter is listed, it is tested with some "maximum output<br>overcurrent protection" as part of its rating per UL 1741. Typically<br>
inverter manufacturers set this to be just above the inverter's max<br>current + 25%. As you know, many inverters can work at more than one<br>voltage, so for the SB5s their max current ratings at 277/240/208V are<br>
18/20.8/24A, respectively. The max overcurrent protection is 50A. This<br>figure often appears in the manual but not in the data sheet. For SMA,<br>it's in the manuals. For some manufacturers, it's only available from<br>
tech support.<br><br>For the Sunny Boy line, the only way you could have more than one<br>inverter on a shared OCPD is if you have two SB5s operating at 277V<br>(18.1A rated current each, so 2x18.1x1.25 < 50A). The SB6, SB7, and SB8<br>
all have currents too high to make this work, as they share the 50A max<br>OCPD. The SB3/3.8/4 have a max OCPD of 30A, which is too low to<br>double-up since each SB3 requires an OCPD of at least 20A. The TLs don't<br>
work either, as the max for any unit is too low. I don't see it in the<br>SMA manual, but I know that in other manuals I've seen a manufacturer<br>requirement for a dedicated OCPD. The only inverters I know of that have<br>
a max OCPD rating far beyond their rated current are micro-inverters.<br><br>As for the shared disconnect, since at least the 2005, 690.15 has noted,<br>"A single disconnecting means in accordance with 690.17 shall be<br>
permitted for the combined ac output of one or more inverters or ac<br>modules in an interactive system." That being said, the NEC requires ac<br>modules and micro-inverters to have ac disconnects (connectors,<br>typically) per 690.6 and 690.15(A). 690.15 notes that an inverter be<br>
able to be disconnected from all sources, but if doubling up these SB5s<br>you could argue that this shared disconnect accomplishes that via the<br>anti-islanding protection... so I agree now that this is a grey area.<br>
<br>Anyway, it comes down to whether it's worth worrying about this for what<br>is an extremely small subset of compatible inverter configurations, when<br>you can just do something like install a $50 Eaton BR24L70RP (70A bus,<br>
240V, 4 spaces) with two 30A breakers and be on your way.<br><br>DKC</p></div></div></div></div></div>
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