A slug is not capable of producing power on its own, it uses power from another source. Think of a slug as a way to add extra traction motors to a locomotive. A slug is nothing more than a big block of weight on top of a set of powered trucks, all the electricity to power a slug comes from the mother unit. A slug has no prime motor, and no generator.
[en.wikipedia.org])
The rotary plow F7B’s on the other hand were the exact opposite of a slug. They had a prime motor and a generator, but often the traction motors were removed, as all the power produced by them goes to the rotary. This was/is the case with the BN rotary’s and their F units, I don’t know of the SP rotary F units still had working traction motors or not. I tend to think they don’t, because I have never seen a picture or video of one moving by itself, always pushed or pulled by a locomotive.
Matt F
Moscow ID