I read an item in an old book here about a short-lived 5-wire DC system (Yes, five-wire!) which was installed in part of London for lighting in the 1880s.

Each house was connected to just two wires and ran with 100V lamps. The article doesn't mention which wire (if any) was grounded, but I would guess the middle one of the five. Even so, I wonder how many people got taken by surprise by one side of their 100V supplies being at 200V above ground.

An interesting historical curiosity, nonetheless.