[RandyM]

Look at the wye configuration. What are your voltage to ground? It will be the same on all three (L1, L2, L3) what point is common to all lines?

On the Delta, could be corner ground or a 120/240 3 phase system.

On checking delta before closing. Must be lineman connecting pole pots or large individual transformers in a vault . Everything I have worked on is already connected. (3 Phase dry transformers)
This would verify if a winding was reversed before closing and starting a 4 of July fireworks show.

I was trying to get you to think about it some before handing you an answer.

 

[RandyM]

I was doing this on my phone. The pictures are the size of a postage stamp.
After I view a picture they disappear the next time I open the thread, just a gray box.
A Wye Delta setup is not that common in my opnion unless it may be used to feed A 240 volt machine from 208.

I did the opposite and fed a 3 phase 120/ 208 panel for a machine from 240 delta. Also 240 delta to 277/480 for another. Custom built by Square D, in the book but not on the shelf.

Back to your Delta. The drawing does not show a neutral, so it is ungrounded.
IF it was a 120/240 delta then there would be a connection by the letter 'B' for the neutral. The high leg would be above it.

IF the wye was an output then the neutral is in the center.

IF its for the input then NO neutral, just the 3 input lines.

 

[RandyM]

That is a symbol for the coil.