Hi Rebekah,
You make a good point and I definitely agree with your logic, but does current on an inverter output circuit act any differently than current on a branch, feeder, etc, covered under 220? I've used this code section to round down in the past and to date it's been accepted. It has never been questioned though either :/ As far as when to round up or down, it's a really good question. I almost always round to the more conservative value, after the calculations are complete, except when it will add significant cost to the project and the Code seems to allow us to round down and the AHJ deems it acceptable. Just another gray area in the Code that keeps life exciting! Think I need to get out more... Garrison ________________________________ From: RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org> on behalf of Rebekah Hren <rebekah.h...@gmail.com> Sent: Thursday, September 1, 2016 9:31:23 AM To: RE-wrenches Subject: Re: [RE-wrenches] SMA Tripower Woah way to pull out an awesome NEC reference Garrison! I'm not totally convinced it applies though, since Article 220 is specifically for branch circuits, feeders and service load calcs. The circuit in question here is defined by 690.1(b) as an inverter output circuit, the OCPD has to be sized per 690.9(B), and 90.3 says that Chapter 6 as a special condition modifies Ch 1-4. I've tried for a few years to figure out good rules for significant digits in relation to PV conductor calcs, and it seems really hard to apply any rules consistently or well, when we are dealing with temp coefficients likes .0031. If you apply common significant digit rules to maximum system voltage calcs, you seem to end up back at STC VOC... Which makes me hesitant to round up or down for ampacity or voltage calcs (especially since I was a liberal arts major in college). It's a very interesting Code question! On Thu, Sep 1, 2016 at 7:38 AM, Garrison Riegel <garri...@solarserviceinc.com<mailto:garri...@solarserviceinc.com>> wrote: Hi Brian, Can we not invoke Art. 220.5(B) Fractions of an Ampere to round down to a 30A OCPD in this case? I suppose that .1 could be pretty significant when combining many of these inverters. Garrison Riegel Solar Service Inc On Aug 31, 2016, at 11:24 PM, Brian Mehalic <br...@solarenergy.org<mailto:br...@solarenergy.org>> wrote: Hey Wrenches- Just a heads up on the SMA Tripower - I like the inverter, but you gotta read the install manual! Spec sheet says 24 A continuous output current for the 20 kW Tripower. Install manual (and tech support) says 24.1. That extra .1 A takes you from a 30 A to a 35 A breaker. Of course you should follow the install manual not the specs. But what about the label on the side of the inverter? Well I've seen more than a handful that are labeled with a flat-out 24 Aac output current. What's an installer or inspector to do besides hope mfg's can get their numbers in order? Upon closer examination, most of the STPs are 0.1 A higher than their spec sheet per the install manual - it doesn't really make a difference on the 12 or 15 kW models - just the 20 where you have to go up 1 standard OCPD size. Pretty sure there's lots of 20 kW units out there backfeeding a 30 A breaker. Hmmmmm.... Brian Mehalic NABCEP Certified Solar PV Installation Professional™ R031508-59 520.204.6639 Solar Energy International http://www.solarenergy.org SEI Professional Services http://www.seisolarpros.com _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org> _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org> -- Tel: 336.266.8800 NABCEP Certified Solar PV Installation Professional™ 091209-85 NC Licensed Electrical Contractor
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