I'm working on a story in which someone who is an experienced electrician debugs and/or fixes an electrical problem (which has knocked out power to most of the building) by doing something, a real-world thing based on his experience, that seems like magic to a less-experienced person watching. In the current draft I have him identifying the one live wire in a bunch of dead ones by feeling for the warmth and 60-cycle hum. Is this plausible? Can you suggest anything better? It would be best if it were something that you had actually done.