You would only have a 6 lead motor if it was designed to be dual voltage, started Star-Delta, started Part Winding, or is 2 speed 2 winding. If it is not dual voltage or 2 speed, and is IEC* (where PW is not used on 6 lead motors as far as I know) then it is designed for Star-Delta. If your line voltage matches the nameplate nominal voltage, you cannot connect it in a manner that will apply too much voltage to it because the Delta connection will always be for the rated nameplate voltage. So the only way you could over excite it is if someone ignored the nameplate data. For example using a motor rated at 230V single voltage on the nameplate and connecting it in Delta to a 400V supply.
If you then connect it in Star and run it that way, the effective voltage across the windings is 58%, so peak (accelerating) torque is reduced to 33% (.58 squared) and if attempting to run a load larger than roughly 50% of rated, the slip [ignore][/ignore]will increase, it will draw too much current and overload. But if the motor is lightly loaded and never needs acceleration torque, i.e. a centrifugal pump or fan started with valves or dampers closed, then never needing to run at more that 50% flow, it might do this without anyone even knowing. I have seen this happen for years.
* I am assuming this is an IEC application because of your use of the term “Star Delta” instead of Wye Delta as we refer to it here.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
