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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Troy,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Overcurrent device size is matched to the conductor size. The inverse time constant nature of an overcurrent device can typically handle the surge currents as long as conductor sizing has truly been done correctly for the conductor. Circuit breakers are preferred to fuses because they can be reset. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>There has been volumes written on this issue. The constant current at lowest battery voltage should be used, plus the ac ripple content on the battery circuit. This is usually a much larger conductor than your average designer will plan for. The best thing is to look at Midnight, Outback, and Schneider and see what size overcurrent devices they require for their products. That will give you a good clue as to how to size the conductor and overcurrent device.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Bill.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><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-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Troy Harvey<br><b>Sent:</b> Friday, April 05, 2013 3:38 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> [RE-wrenches] Fuse sizing in battery circuits<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>I've got a question about battery string fusing. Typically we size the wire from the batteries to the inverter based on continuous rating procedures (max power/efficiency)*125%. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>However a 6kW inverter, can peak at 12kW for 5-10 seconds, doubling the source current. That is no big deal for the wire, because it is a short time frame... little heat will be generated. However, in fusing the sub-strings, you need to account for that peak surge current so you don't blow fuses all the time. But if you put a 500-1000 amp fuse on a 4/0 wire, above the max surge draw of the inverter, the wire will be under-protected for its ampacity rating. Any thoughts on the catch-22?<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:8.5pt'>thanks,<br><br>Troy Harvey<br>---------------------<br>Principal Engineer<br>Heliocentric<br>801-453-9434<br><a href="mailto:taharvey@heliocentric.org">taharvey@heliocentric.org</a></span><o:p></o:p></p></div></div></div></body></html>