Currently working on a project where there is 1 large building with 2 separate incomming power feeds (1 at each building end) derived from an exterior distribution panel. The exterior distribution panel uses the 6-disconnect rule right off the utility transformer; 2 feeds to the building in question and 4 feeds to other buildings. There is no emergency generator which is what we are designing for the 1 large building only. There will be a life-safety transfer switch and an optional/standby transfer switch. Regarding the emergency side, there will be a normal/emergency panel for exit signs and an emergency only panel for emergency lights. My question, is how can I have 1 emergency transfer switch but monitor 2 separate feeds to the building or do I need 2 separate emergency transfer switches? If 1 switch, obviously the normal power will come from either feed A or B which means the opposite building half will have 2 power sources in it for the the exit signs; the normal source and the other source serving the exit signs. Then, if only 1 building half looses power, the opposite half that still has power will have both normal lights on and emergency lights on. I can't find anything in the NEC article 700 or 702 regarding this. If it helps, 1 feed is 800A 208 3-phase and the other is 200A 208 3-phase. I assume grounding is all bonded properly in accordance with buildings with multiple feeds. Thanks.
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