Kirk, You're basically doing a feeder tap, which you'll find the rules for in NEC 240.21(B). The difference from the intent of this code is that your tap is working in reverse. It will supply current to the feeder rather than receive current from it. If your subpanel doesn't have a main breaker appropriately sized to protect the feeder wiring, then technically your 80A from PV and 200A from the service could add to 280A and overload the feeder wiring between the tap and the subpanel, as well as the subpanel bussing. If I was the AHJ, I would require a main breaker in the subpanel in addition to the conditions specified in 240.21(B). This is definitely one to check on with the AHJ ahead of time.
Regards, -Hans From: [email protected] [mailto:[email protected]] On Behalf Of Kirk Herander Sent: Tuesday, June 05, 2012 3:44 PM To: RE-wrenches Subject: [RE-wrenches] sub-panel supply-side tap Hello, Ideally I'd like to make a supply-side tap on a feeder to a sub-panel. And I mean tapping the feeder line-side of the sub-panels 200 amp breaker. This is due to the limitations of the sub-panels 200 amp buss. My PV system max output is 80 amps and therefore requires a 100 amp breaker. A no-go with the 200 amp buss. The 20% allowance won't work and I cannot downsize the 200 amp breaker to make it work due to panel loads. I would have to upgrade the panel to 400 amps. FYI this is 208/120 3 phase. I have done supply-side connections before but only on a buildings main service. Do all the same rules apply? What might be different I should take into consideration? Thanks. Kirk Herander VT Solar, LLC dba Vermont Solar Engineering NABCEPTM Certified installer Charter Member NYSERDA-eligible Installer VT RE Incentive Program Partner 802.863.1202 _______________________________________________ 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
