We are in the process of value engineering for a new office building that is running over budget. We are considering the option of running POCO primary voltage (12470V) to the electrical room on each of the four floors. The present plan calls for 480V service at 3000A, with step-downs to 120/208 on each floor for the receptacle loads (250KVA each). If we sent primary to each floor, we would need one 250KVA 120/208V transformer and one 350KVA 277/480V transformer on each floor, but we would eliminate the 2.5MVA service transformer (which we must pay the POCO for) and the 3000A bus duct. Is there a general guideline for when MV distribution becomes cost-effective, in terms of service capacity? Is 3000A too small to even consider upping the voltage, or might it be an option?
