Jason: SB 5000 = 21A @ 240V, 21A x 1.25 = 26.3A needs 30A breaker M215 = 0.9 A @ 240V, 0.9A x 9 = 8.1 A, 8.1 x 1.25 = 10.1A needs 15A breaker. (Or that rounded to 10A and use a 10A breaker)? 26.3A + 10.1A = 36.4 A needs 40A breaker So, get a new 100A main lug subpanel. Connect it to a 40A breaker in the existing main panel. Move the existing 30A breaker into the new subpanel and install the new 15A breaker into the same.
Mark Frye Berkeley Solar Electric Systems 303 Redbud Way Nevada City, CA 95959 (530) 401-8024 <http://www.berkeleysolar.com/> www.berkeleysolar.com _____ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jason Szumlanski Sent: Thursday, September 29, 2011 12:55 PM To: RE-wrenches Subject: Re: [RE-wrenches] Adding on to existing PV System That's not a bad idea, except that 690.64(B)(2) requires that the breaker directly connected to each inverter(s) must be used for the calculation. I have an existing SB5000 with a 30A breaker and a new string of nine Enphase M215's requiring a 15A breaker. If you combine these in a 100A or higher rated subpanel with a 40A main breaker, you still calculate the total current supplying the busbar in the main distribution panel based on 200A + 30A + 15A = 245A (with 30A and 15A being the overcurrent protection directly connected to the inverters). This exceeds the 120% rule by 5A. It also requires that the ampacity of the conductors between the two panels be 85A / 1.2 = 70.83A (assuming a 40A backfeed breaker in the main distribution panel). If your interpretation is different, please let me know! If my interpretation is correct, I like the idea of just adding a fusible disconnect and using #10 conductors all the way to the tap. That would be the most cost effective solution I believe, and since there is no foreseeable further system rating increases, the advantage of a subpanel is reduced. Thanks for all the other suggestions provided. Unfortunately I can't put in smaller main breaker, and the busbar in the main panel is definitely rated 200A. Jason Szumlanski Fafco Solar From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Glenn Burt Sent: Thursday, September 29, 2011 2:40 PM To: 'RE-wrenches' Subject: Re: [RE-wrenches] Adding on to existing PV System How about feeding both systems into an AC combining subpanel before feeding the main load center? Often the calculations required will allow you to do more backfeeding than the simple backfeeding a load center with individual breakers. -Glenn From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jason Szumlanski Sent: Thursday, September 29, 2011 11:49 AM To: RE-wrenches Subject: [RE-wrenches] Adding on to existing PV System We've been contracted to add on to an existing PV system in a residence. The existing system has a 30A 2P Breaker on a 200A rated panel with a 200A main breaker. The new system would require a 15A breaker, which would exceed the limit in NEC 690.64(B)(2). The existing system has a fusible AC disconnect mounted next to the meter. This was originally intended as the utility external disconnect. The utility no longer requires a disconnect, but if we do a supply side connection, we would need a fusible AC disconnect anyway for the new system. I would collocate the new disconnect with the old. Does anyone see any problem with doing a supply size connection for the new system? Any labeling snags that I might need to consider? Jason Szumlanski Fafco Solar
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