Matt Novak of Paleofuture sent me this great photo of an early 20th century trade school electricity class. According to the Library of Congress, there's no specific date associated with this shot, although I'd guess early 1920s, which was when electricity installation really started to take off in a meaningful way. There are a lot of apartments in Minneapolis that still have those tacked-to-the-ceiling conduits.
Also interesting, this photo comes to us from the Bain News Service, one of the first news photography agencies, which started distributing photos to subscribing newspapers in 1898. The LOC has the Bain archives now, and you can check them out on Flickr.
Thanks, Matt! We miss you up here in the Frozen North.