I've got an assisted living facility which is classified as residential. Their are five 200A panels servicing the facility. Everything is single phase 120/240 VAC. Why would the previous electricians have requested that the utility transformer be a delta with a 208 VAC high leg? My line of thinking is that now I have a high leg that if I really wanted to take advantage of it then I would have to purchase 3 phase panels and pull additional wire and for what benefit. Not to mention the unused spaces in the panel that I would have liked to use for 120VAC circuits but cant because they would be 208VAC. Why wouldn't you get a 120/240 VAC 3 phase wye transformer?