Ray, A 2% wire loss is the generally accepted metric for battery based systems with relatively low PV voltage input (<150Voc). It's just plain bad design to accept more than a 1% VD on higher voltage systems. PVs ain't THAT cheap. Best, Bob-O
On Apr 6, 2010, at 11:44 AM, R Ray Walters wrote: Once I have fulfilled NEC min. requirements, I use a spreadsheet to analyze the cost of larger wire vs. the cost of power lost. Going under 2% is usually not worth it, if copper prices are high, and PV cost is low enough (current market). Sizing for under 2% was good economics a few years back, when PV was high, and copper was low, though. For NEC 2011, I agree: while I readily welcome development of DC AFI, implementing code before the technology is ready, is a bad idea. But that may be the only way to get the technology in place..... Ray On Apr 6, 2010, at 11:15 AM, Kent Osterberg wrote: > Ray, > > Considering that we design PV wiring to be efficient with voltage (and power) > loss typically less than 2%, the wire size is nearly irrelevant to arcing > issues. Essentially all the energy available from the PV array can be > dissipated in the dc arc. And since the current is limited by the nature of > the IV curve, breakers alone usually won't clear the fault. The best > combiner breakers can do (if you have enough parallel circuits) is isolate > the fault to one string in the PV array. With one string being 1 or 2 kW in > many systems there is still the potential for a lot of heat. > > With the 2011 code just around the corner and no dc arc fault protection on > the horizon, it looks like our industry is again going to have a code > requirement that no one can fulfill. > > Kent Osterberg > Blue Mountain Solar, Inc. _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
