Two of those electricians are real-life brothers Jeff and Jack Silk, who were both fairly prolific British bit players and stunt performers who specialized in motorcycle stunts.
You've seen Guy Standeven in something because the man was in everything.

My guess is that detail is from a letter Ranger wrote to Lordmany Titanic survivors were still alive at the time it was published and the book/film is largely based off survivors' letters that they wrote to him when he decided to contact them for the purpose of writing the book, as you probably know. Or perhaps it's from another private latter Ranger wrote to a friend or relative, as I can't imagine it would be the kind of detail he would bother mentioning at the official British government inquiry back in 1912.

It's been quite a while since I posted the original question. Since that time, I came across this paragraph in Walter Lord's book staring me in the face:
Far below, Greaser Thomas Ranger began turning off some 45 electric fans used in the engine room, and he thought about the ones he had to repair tomorrow. Electrician Alfred White, working on the dynamos, brewed some coffee at his post.
I'm guessing the scene in the movie is based on that. But I don't know what Walter Lord's source is; I love his book, but unfortunately it's not well annotated.

Since none of the engineering officers or electricians survived, there is no way of knowing whether this actually happened or not. It's therefore historically permissible for the filmmakers to have included it.