Kirk, Well, the NEC just refers to the sum of the "ampere ratings" of the overcurrent devices, which doesn't leave much wiggle room for adjusting an 800A "rated" breaker downward. I would check with your inspector ahead of time if you want to try this approach.
-Hans From: [email protected] [mailto:[email protected]] On Behalf Of Kirk Herander Sent: Friday, March 30, 2012 12:44 PM To: RE-wrenches Subject: [RE-wrenches] dial-down breakers and buss rating Hello, Here's one I haven't come across before. I am about to start a 110kw system. This is a 480/277 three phase ac output. The calcs tell me I need a 200 amp breaker(after rounding up from the actual breaker calc of 180.5 amps) feeding a 800 amp panelboard which is also fed by a 800 amp utility main breaker. Following the 120% rule no more than 960 amps can be put on the buss. But the source input will be 1000 amps from grid and pv combined. However, the 800 amp breaker can be current-limited down lower (in this case at least to 760 amps) by a manual dial with calibration markings on its face. So I would think a reasonable AHJ would accept this as code-compliant. The only other alternative is to replace the main with a 700 amp (no fixed-amperage breaker is made between 700 and 800 amps), which for load reasons the owner doesn't want to do. Thanks for your comments. A pesky inspector might say "what's to prevent some yahoo from turning the breaker back up to 800 amps once I leave", for instance. 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
