Data can’t shut down the electrical arc. The only option is to interrupt the flow with a non-conductive material—but the only non-conductive material they have is Data’s body. He can shield his positronic brain from the surge of the arc, and then Riker can remove Data’s cranial unit and bring it to engineering. So, yeah, Riker gets to carry Data’s head to engineering, because THEY SAVED DATA’S BRAIN!!!!!