According to Don Foreman :

[ ... ]

It has finally occurred to me that the neutral is what's causing the
confusion.

Nearly all three phase machines are three-terminal devices. There
may be a physical neutral in a Y-connected machine, but it's rarely
used. We agree that the neutrals would not be connected with
Y-connected idlers and loads. If they were delta-connected, there'd
be no neutrals to connect.

I've been wondering why nobody has considered the motors as
black-box devices, with only the three terminals leading to the outside
available for consideration.

Under those conditions, there is really no way to tell a Wye
from a Delta connected motor, if you allow that the windings could be
special to make them work from the same voltages.

And -- you could analyze the circuits from that basis (it is
commonly done when sufficient information about the internals is not
available, or when the details about the internals don't really *matter*
to the functionality.

Enjoy,
DoN.

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