i am planning a remodel of a restaurant with the following service; in the 400 amp fused disconnect there are (3) fuses, (2) 4/0 thhn conductors, (1) #1 thhn conductor. i get 240 volts between the enclosure box and "A" LEG, and leg "C". i get 120 volt between the enclosure box and leg "B" (CENTER). we have (3) 3-phase roof ac units at 60 amp each. all other loads are single phase 120/240 volt. what do i have? 3 wire open delta? corner grounded 3 wire delta? the small center wire concerns me a lot. the electrical plan checker here in houston is saying that i must have (4) wires for a 3 phase service. the previous tenant (subway) was in this building for about (15) years without any electrical issues with more equipment than we want to use. we were not planning to touch any 3 phase stuff. i do not know if the service pole has (2) or (3) transformers. this service pole is serving other service drops for other buildings, so there are many transformers on the pole. there is nothing 208 volt i could find. does that rule out wye? how would i tell that i had a 3 wire ungrounded delta 3 phase for sure? are where special calculations like 87% if (2) transformers are used open delta ?