There is nothing wrong with connecting 1PH 240 loads from A-B or B-C. As stated above the breaker must be rated at straight 240V. As far as balancing the transformers I don’t think one load, unless it is very large, is going to be a problem. When balancing loads from a delta bank you can do one of two things with 1PH 240 loads. You could put them all on A-C and size the 1PH transformer accordingly. (This transformer is already larger. A lot of these loads would make it huge!) Or you can count the total KVA as three phase load and balance them accordingly. Closed delta banks are sized as follows. Take 67% of the entire 1PH load and add it to 33% of the entire 3PH load. This gives you the size of the mid tap transformer. The two power transformers are found by taking 33% of the total single and three phase loads.
