Every section that is connected to a reactor is powered, up to at least 14 tiles radius, but you have to add a power thing on the wall every now and then (forgot how it was called, but it's the thing you place on the wall and get in the connectors and switches library).
See, that's important information, there. Nice of them to tell me that the super reactor that puts out a gajillion units of power can only push it out five tiles (if people are getting a radius of 14, I want to know what they're doing) before something else unexplained needs to be done. I'm all for "figure it out, guys", when the figuring out makes some kind of sense, but it's not really intuitive that the vault reactor will need a booster every three feet. :behave
--Jonah