I will be replacing 4 fuse boxes in a 3 unit residential building with 60 amp CB panels. A central boiler provides the heat and the hot water tank is gas. The property is served 120/249 volts from an underground utility system through a 1 ½ inch conduit.
When the utility undergrounded the area several years ago they installed a 480Y/277 volt 3 phase distribution system. They also installed 120/240 volt transformers in their vaults to pick up the existing 120/240 volt services. The utility requires that any new or rewired services be 480 volts so that they can eventually remove the 120/240 volt transformers. The utility proposed that I install a concrete pad in my back yard and they would install a 480/120/240 volt transformer on the pad. I would pull code sized conductors from the transformer to the new switchgear. Unfortunately I do not have room for the transformer because of mandated parking spaces. I requested a 100 amp 480 volt single phase service and my request was granted. The utility will disconnect the existing 120/240 volt service in their vault and reconnect it at 480/277 volt after I have installed the meter base on the existing 1 ½ inch conduit riser. The available fault current is 33,000. My plan is to install a 50 KVA 480/120/240 volt dry type transformer in the basement of the building.
The equipment layout will be:
Utility – Meter – 100 amp safety switch – transformer – 200 amp main lug panel with 4-60 amp 2 pole breakers – 4- 60 amp main lug panels.
Cabling will be: 3#2 CU THHN from the meter base to the safety switch and from the safety switch to the transformer. 2-3/0 and 1-2/0 CU THHN from the transformer to the 200 amp panel, and 3#6 CU THHN from the 200 amp panel to each 60 amp panel.
Grounding: The 100 amp safety switch is the grounding point. 1#6 BC from 2 ground rods, the water and gas pipes, the transformer and each 60 amp panel. 1#4 BC from the 200 amp panel to the safety switch.
If any of you guys would care to make comments it would be much appreciated.
