I am reviewing a design package that has a couple of these. I have not encountered them before. My guess is that the secondary is a delta with the center point of one coil (A-C, perhaps) being grounded. In that case, you cannot use a single-pole breaker to supply a 120 volt load, unless you limit yourself to using phases A or C. Is that right? Am I also right in understanding that if you used a single pole breaker on the B phase, the voltage to neutral would be 208V?