User blog comment:The Milkman/Everybody Shut Up./@comment-1341687-20120423035921/@comment-1221773-20120424001608

The Crucible isn't powered by the Citadel, it uses the Citadel like a giant antenna to amplify its energy so that it can distributed across the entire mass relay network. Per Vendetta, the Crucible originally didn't involve the Citadel at all, but at some point a previous generation realized that the Crucible's energy output was insufficient and incorporated the Citadel into the designs because it was the nerve center of the mass relays.