Y primary closed Delta banks we use a floating ground, I have seen the same banks built at other utility's with all 3 pots grounded down, but have also saw on same system 1 of the pots in the bank opened up ( fuse blown ) bad pot animal whatever and with the pots grounded down it become an open delta with 2 overloaded pots, until there is another problem or someone from the power company sees it, it stays that way, now on some Delta banks we will hang a 4th cutout to temporarily ground down the floating neutral due to Ferroresence, but that's a whole different story.