Everything up to the panelbd will be replaced (the entire service). There is no question on the line side.
I assume (I am going over to look at it tomorrow) that only the 3 phase loads are connected to the middle bus (in this case maybe a rooftop unit - it is retail). So when it becomes 208V the middle phase will be un-balanced. In addition - the panelbd is currently the service entrance. That will no longer be the case after the change (there will be a line side main disconnect). So the neutral needs to be separated (I'm thinking out-loud). Any other considerations?
