Everyones talking like the disconnects are existing or that someone else is providing them.
Generally I purchase all the disconnects for my projects so its my choice to install the neutral block or not.
If a black wire is passing through the disconnect,how do I know its a neutral? unless I open take the panel cover off or look inside the transformer and see where it goes.
Especially if its #4 or larger and the conductor is black. Of course I would expect it to be, but since it isnt termated in the disconnet, and more than likely not phase taped as it passes through the disconnect, it could just as well be an Isolated Ground wire coming from a ground lug in the Transformer and you would not be taking readings from a true neutral at all.