It's called an "Inside the Delta" connection. It takes advantage of the motor's being wired for possible Y-Delta operation and places the soft starter "inside" of the Delta connection of the motor windings. It has no benefit other than to reduce the cost / rating of the soft starter (to 58% of normal), but it has some key risk factors. The primary risk factor is understanding by field personnel, as you have demonstrated. Most people are NOT going to know intuitively what the heck is going on there. You were at least astute enough to ask, some people are not and would assume something that would get them in trouble. If, for instance, you were to change out the motor with one that has different connections, you can hook it up wrong and damage both the motor and the soft starter. The other risk is in a theoretical increased risk of shorting an SCR because of the fact that instead of phase-to-neutral voltages, you now have phase-to-phase across the SCRs and they are at increased PIV damage risk. I don't happen to subscribe to this theory as being an automatic problem because some RVSS manufacturers use higher PIV ratings as standard anyway, but it isn't a universal truth. Look at the specs for yours and if the PIV rating is 1500V or higher, no problem in that regard.
