Ryan, Agreed that the line side tap does not necessitate any change in the size of the main... we got off track a bit there. Thanks for straightening that out.
The initial question from Nick was whether he could _avoid_ a line side tap or service upgrade. He wants an exception to install load side PV source breakers larger than 20% of the main by showing that the sum of the residential load calc and the PV source does not exceed 120% of the bus rating. I don't see how this could be accepted by the AHJ since 690.64(B)(2) speaks only of the amp ratings of source overcurrent devices and does not allow an exception based on actual loads. When adding loads to a service, it is common practice (when in doubt) to perform a load calc to show that the service rating isn't being exceeded... Perhaps Nick heard from someone who was trying to creatively apply that practice to size a PV source. Since the 120% limit is a frequent problem, I think if there was a legal workaround as easy as showing a load calc, we would all be aware of it by now. -Hans -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Ryan LeBlanc Sent: Wednesday, March 31, 2010 4:29 PM To: [email protected] Subject: Re: [RE-wrenches] Supply Side Tap Overcurrent Protection Steven, A Line Side Tap, by nature, allows us 100% of the Service Entrance Conductor Ampacity. This typically ~equals Main Breaker rating, but is regardless of the Main Breaker rating or size of Loads, it's about the conductor. NEC recognizes that our systems produce power, not draw it, so downsizing the Main would have no effect on the size of a Line Side Tap. Corrected PV output is considered continuous, so if you have 100Amps worth of conductor, 100A worth of Loads (Coming), and 100A of Solar (Going), we're still considered square on that service conductor. Doesn't matter what the draw is in the panel, the remainder of energy goes out the meter. If you downsize the main, you are just missing out on that much load capacity. Downsizing Main breakers only assists Load Side connections, obviously by increasing the Main Panel to Main Switch ratio for 120% Rule math. Check out: Solar Pro SP2.4 Article "Can We Land: Means and Methods of Utility Interconnection." (LeBlanc/Yates) Available Free online at SolarPro's website. Ryan J. LeBlanc NABCEPT Certified Solar PV Installer Santa Rosa, CA Cell: 707.591.1950 Direct: 707.536.9839 [email protected] http://www.NaturalEnergyWorks.com Today's Topics: 1. Re: Supply Side Tap Overcurrent Protection (Steven Lawrence) ---------------------------------------------------------------------- Why can't you do a line side tap and downsize the main breaker? Use a 60A main disconnect for the line side tap, and use a 60A main breaker for the service panel. That's similar to what I did except I downsized the 200A main to a 150A. This also allowed a manual interlock kit in the main service panel that can be fed from the backup load panel. Steven Lawrence ______________________________________________________ Date: Wed, 31 Mar 2010 08:13:10 -0700 (PDT) From: Nick Soleil <[email protected]> To: RE-wrenches <[email protected]> Subject: Re: [RE-wrenches] Supply Side Tap Overcurrent Protection Message-ID: <[email protected]> Content-Type: text/plain; charset="us-ascii" Downsize the main breaker? I would if I could, but the customer only has 100 Amps now, and the solar is fed with two breakers, a 30A and a 40A. So to be under 120Amps, I would have to size the main to 50 Amps, which may be problematic. I can also do the line side tap, but had heard that a load analysis may be accepted instead. The loads of the house will never use more than 100 Amps. I am wondering if any codes or white papers detail that option. Nick Soleil Project Manager Advanced Alternative Energy Solutions, LLC PO Box 657 Petaluma, CA 94953 Cell: 707-321-2937 Office: 707-789-9537 Fax: 707-769-9037 _______________________________________________ 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 _______________________________________________ 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
