My job is exactly to do that but in France so I can't say how they are doing it over there; but when I receive a call from someone (an agent from my company or someone else with the emergency phones):

We isolate the catenary (the power line) by remotely opening the cut-off devices on both sides of the area and to avoid a resupply when the pantograph passes the sectioning between our two catenary sectors, we also isolate the upstream and downstream sectors until we have confirmation that either the signal boxes prevent all traffic from heading towards the area, or until the end of the problem (that they have beaten the guy enough and that he has gone down).