A delta breaker was designed to allow a three phase circuit to be fed from a single phase panel. These breakers are no longer manufactured (I believe Square D stopped making them 30 years ago). They were used where the service was a 240/120 3Phase 4Wire and only one three phase load was being served.
408.36(C)has nothing to do currently built equipment, it should probably be retired just like rosettas were a few cycles back.
