I really want to see the insides of those buildings.
... what part of the "switchover" process is this? That is to say ...
... I get that you have to cut to switch over but ... what would come next? Does the new system get spliced in? Is it already wired - pending just the cut? (Thus the speed with which it is done) ...
the old system can't be isolated like that so they have to physically cut the wires to it before they electrically connect the new system, which is the switch throw at the end of the cutover.
There's a fully functional system deployed in Seattle as a Museum